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SYNTHESIS OF THIOARSENATE COMPOUNDS FROM THE REACTIONS OF
MAIN-GROUP, TRANSITION AND RARE-EARTH METALS IN ALKALI
POLYTHIOARSENATE FLUXES
By

Ratnasabapathy Gurunathan Iyer

A DISSERTATION
Submitted to
Michigan State University
In partial fulfillment of the requirements
For the degree of
DOCTOR OF PHILOSOPHY
Department of Chemistry

2004

 

 

 

ABSTRACT
SYNTHESIS OF THIOARSENATE COMPOUNDS FROM THE REACTIONS OF
MAIN-GROUP, TRANSITION AND RARE-EARTH METALS IN ALKALI
POLYTHIOARSENATE FLUXES
By

Ratnasabapathy Gurunathan Iyer

The use of alkali metal polychalcophosphate fluxes as media for synthesizing Group 15
chalcogenides has resulted in the discovery of a large number of new compounds that
feature an astonishing variety of structures and chalcophosphate anion building blocks. It
was therefore appropriate to question how the corresponding chalcoarsenate fluxes would
behave under similar conditions. Though P and As belong to the same group, there seems
to be a considerable divide in their reactivity in a chalcogen environment. Thus P mostly
exists in the +4 and +5 oxidation state, whereas As usually exhibits the +3 and the +5
oxidation states with the former being predominant. Therefore, we expected the
chalcoarsenate anion, Astyn', to be different from the chalcophosphate anions formed
under similar conditions. An interesting structural aspect of As is the tendency to
stereochemically express its lone pair of electrons. Another interesting property of arsenic
chalcogenides is the propensity to form glasses. We therefore set out on a systematic
investigation of main-group, transition and rare-earth metals in alkali polythioarsenate
fluxes.

In this dissertation, the syntheses, structures, and properties of the various compounds

that we obtained during the course of this research are described. The reaction of the

 

 

 

 

main-group metals Sn, Pb, In, and Bi resulted in the isolation of compounds containing
molecular anions such as CszsnA5289, A6111AS3SI3 (A = K, Rb, Cs) and AgBiAS4Sm (A =
K, Rb), the one-dimensional compounds NaSnAsS4, ASnAsSs (A = K, Rb) and
A4PbAsZSs (A = Rb, Cs), the two-dimensional compounds A28flASzS6 (A = K, Rb, T1)
and APbAsS4 (A = Rb, Cs). The transition metals Mn, Cd, Cu, Ag and Au, gave
A3MI12AS4S|6 (A = K, Rb, Cs), RbngzAs4818, CsloCuzAs4Sw, CszCuAsss and
CszAgAsss, which contain molecular anions, and the one-dimensional compound
CszAuAsS4. Finally, we sought to study the reactivity of Eu with Ag and Cu as the
counter—cations. This resulted in the formation of the three-dimensional compounds
AgEuAsS4 and Eu3Aszsg. These compounds feature thioarsenate building blocks such as
the pyramidal AsS33', AsS43‘, and AsS53' and the tetrahedral AsS43' and AsSs3' anions.
CszsnAszsg, RbZSnAS286 and leSflAsteé exhibit reversible glass to crystal transition.
These compounds melt on heating; however, upon cooling, they do not recrystallize and
form glasses. The glasses convert to the crystalline form on heating.

Our results suggest that the polythioarsenate fluxes are as interesting and promising as

the chalcophosphate fluxes and provide foundation for further exploratory studies.

 

 

 

 

—T ‘ —_ -. wax—HTE-W-r

ACKNOWLEDGMENTS

Five years and I still don’t know if I have learnt much of chemistry but I do know that I
here today due to the support and encouragement of a few people. My advisor, Professor
Mercouri G. Kanatzidis, is instrumental in much of what I know today about research and
scientific thinking. His patient guidance and passion for chemistry have left an indelible
mark in me. I surely hope that I can one day make him proud of me.

I have no words of gratitude for my parents and my brother who stood by me through all
times, thick and thin. It is the result of their hard work, perseverance, love and

understanding that I have now reached this position. Another person with whom I share a

 

very special relationship and who has helped me wade through the difficult-waters of my
fifth year is Nan. I cannot thank her enough for being the most kind, caring and accepting
friend a person could ask for. In the same breath, I would also like to thank my friends
Malini and Pops for being there for me whenever I needed them. I could not have
survived graduate school had it not been for my awesome friends at MSU particularly,
Abhi, Mahesh, Manish, Chetan, Misra, Padmesh and Vijaygopal. My stay at MSU was
made great in no mean part by the past and present group members of the Kanatzidis lab,
particularly Jim, Jen, Kasthuri, Pantelis, Theodora and Oleg.

I have been fortunate enough to interact with the professors in the Chemistry Department
who I consider to be some of the best minds in business. I am extremely grateful to
Professor Aaron Odom for serving on my committee as the second reader and for writing
recommendation letters for me. I would also like to thank Professors Merling Bruening
and Piotr Piecuch for being on my committee. Lastly I would like to thank the National

Science Foundation for fimding my research.

 

iv

—-. ¥ _ .

TABLE OF CONTENTS

LIST OF TABLES .......................................................................................................... x
LIST OF FIGURES ....................................................................................................... xv
LIST OF ABBREVIATIONS ....................................................................................... xxi

CHAPTER 1 AN INTRODUCTION TO THE POLYTHIOARSENATE FLUX
METHOD FOR THE SYNTHESIS OF COMPLEX METAL THIOARSENATE

 

COMPOUNDS 1
A. INTRODUCTION ........................................................................................................ 1
B. SOLVENTOTHERMAL PATHWAY ................................................................................ 2
C. THE MOLTEN FLUX METHOD ................................................................................... 6

C. I The Polychalcogenide Flux ............................................................................... 6

C.2 The Polychalcophosphate Flux .......................................................................... 7

C3 The Polythioarsenate Flux .............................................................................. 11

C.3-1 The formation of a polythioarsenate flux .................................................. 12
C.3-2 Spectroscopic investigations in arsenic

“and phosphorus chalcogenide glasses ................................................................. 14

D. CONCLUSION ......................................................................................................... 19

CHAPTER 2 REACTIVITY OF Sn IN ALKALI POLYTHIOARSENATE
F LUXES: SYNTHESIS AND CHARACTERIZATION OF NaSnASS4, ASnAsSs (A

 

= K, Rb), Azsmzss (A = K, Rb) AND CstnASpJ; 27
A. INTRODUCTION ...................................................................................................... 29
B. EXPERIMENTAL SECTION ........................................................................................ 30

3.1 Reagents .......................................................................................................... 30
B. 2 Physical Measurements ................................................................................... 31
Powder X—ray Diffraction .................................................................................. 31
Energy Dispersive Spectroscopy ........................................................................ 31
Diffuse Reflectance Spectroscopy ...................................................................... 31
Infrared and Raman Spectroscopy ...................................................................... 31
Differential Thermal Analysis ............................................................................ 32
3.3 Synthesis ......................................................................................................... 32
NaSnAsS4 .......................................................................................................... 32
KSnAsSs ........................................................................................................... 32
RbSnAsSs .......................................................................................................... 33
AzsnA8285 ......................................................................................................... 33
CSzSflASng ....................................................................................................... 33

B. 4 X-ray DifiPaction Analysis ............................................................................... 34
C. RESULTS AND DISCUSSION ..................................................................................... 43

C. 1 Synthesis ......................................................................................................... 43

C. 2 Structure description of NaSnAsS4 ................................................................... 44
C3 Structure description of RbSnAsS5 ................................................................... 45
C4 Structure description of Rb 2SnAszS6 ................................................................ 48
CS Structure description of Cs 2SnAs2S9 ................................................................ 49
C6 Thermal Analysis ............................................................................................ 57
C. 7 Optical Spectroscopy ...................................................................................... 63
D. CONCLUSION ......................................................................................................... 64

CHAPTER3 SYNTHESIS, CHARACTERIZATION OF THE LAYERED

 

COMPOUNDS Tl;SnAszQ5 (Q = S, Se) 69
A. INTRODUCTION ...................................................................................................... 70
B. EXPERIMENTAL SECTION ........................................................................................ 71

B. 1 Reagents .......................................................................................................... 71
8.2 Physical Measurements ................................................................................... 72
Powder X-ray Diffraction .................................................................................. 72
Energy Dispersive Spectroscopy ........................................................................ 72
Diffuse Reflectance Spectroscopy ...................................................................... 72
Differential Thermal Analysis ............................................................................ 72
Band Structure Calculations ............................................................................... 73

3.3 Synthesis ......................................................................................................... 73
lesnA8286 ........................................................................................................ 73
leSflASzSCs .................. - ..................................................................................... 74

B. 4 X -ray Crystallography ..................................................................................... 74
C. RESULTS AND DISCUSSION ..................................................................................... 75
CI Synthesis ......................................................................................................... 75
C.2 Structure description of TI zSnAszQ6 (Q = S, Se) ............................................. 75
C3 Diflerential Thermal Analysis and Phase Change Properties .......................... 77
C. 4 Optical Spectroscopy ...................................................................................... 78
C. 5 Band structure calculations ............................................................................. 85
D. CONCLUSION ......................................................................................................... 86

CHAPTER 4 CHEMISTRY OF Pb IN ALKALI THIOARSENATE FLUXES:
ISOLATION AND CHARACTERIZATION OF APbAsS4 (A = Rb, Cs) AND

 

A4PbASst (A = Rb, Cs) 97
A. INTRODUCTION ...................................................................................................... 98
B. EXPERIMENTAL SECTION ........................................................................................ 99

3.1 Reagents .......................................................................................................... 99
3.2 Physical Measurements ................................................................................... 99
Energy Dispersive Spectroscopy ........................................................................ 99
Powder X-ray Diffraction .................................................................................. 99
Differential Thermal Analysis ............................................................................ 99
Diffuse Reflectance Spectra ............................................................................. 100

vi

Single Crystal UV/V is Spectra ......................................................................... 100

Far-Inflated Spectra ......................................................................................... 100

B. 3 Synthesis ....................................................................................................... 100
RbeASS4 ........................................................................................................ 100
Rb4PbASst ..................................................................................................... 1 01
CstAsS4 ........................................................................................................ 101
CS4PbASst ...................................................................................................... 101

B. 4 Single Crystal Difi'action .............................................................................. 101
C. RESULTS AND DISCUSSION ................................................................................... 107
C. 1 Synthesis ....................................................................................................... 107
C.2 Structure description of APbAsS4 .................................................................. 108
C3 Structure description of A4PbAs zSg ................................................................ 114
C4 Pb Series ....................................................................................................... 118
C5 Thermal Analysis .......................................................................................... 119
C. 6 Optical Spectroscopy .................................................................................... 1 19
D. CONCLUSION ....................................................................................................... 123

CHAPTERS SYNTHESIS AND CHARACTERIZATION OF TWO NEW
EUROPIUM THIOARSENATES FEATURING THE TETRAHEDRAL AsS43'

 

LIGAND: AgEuAsS4 AND EU3A82$3 - - - _- -- 126
A. INTRODUCTION .................................................................................................... 127
B. EXPERIMENTAL SECTION ...................................................................................... 127

B. 1 Reagents ........................................................................................................ 129
3.2 Physical Measurements ................................................................................. 129
Powder X-ray Diffraction ................................................................................ 129
Energy Dispersive Spectroscopy ...................................................................... 129
Diffuse Reflectance Spectroscopy .................................................................... 130
Differential Thermal Analysis .......................................................................... 130
Magnetic Susceptibility Measurements ............................................................ 130

B. 3 Synthesis ....................................................................................................... 131
AgEuAsS4 ....................................................................................................... 131
EU3ASst ......................................................................................................... I 3 I

B. 4 X- ray Crystallography .................................................................................. 131
C. RESULTS AND DISCUSSION ................................................................................... 136
C. 1 Synthesis ....................................................................................................... 136
C2 Structure description of AgEuAsS4 ................................................................ 136
C3 Structure description of Eu 3AszS8 .................................................................. 143
C. 4 Magnetism .................................................................................................... 144
CS Difluse Reflectance Spectroscopy and Thermal Analysis ............................... 144
D. CONCLUDING REMARKS ....................................................................................... 145

vii

CHAPTER6 CHEMISTRY OF TRIVALENT MAIN GROUP METALS:
DISCOVERY OF A,InAs3s,3 (A = K, Rb, Cs), A3BiAszsg (A = Rb, Cs) AND

AgBIAS-tsm (A = K, Rb) FROM ALKALI POLYTHIOARSENATE FLUXES ...... 156
A. INTRODUCTION .................................................................................................... 157
B. EXPERIMENTAL SECTION ...................................................................................... 159

B. 1 Reagents ........................................................................................................ 159
B. 2 Physical Measurements ................................................................................. 15 9
Powder X-ray Diffraction ................................................................................ 159
Energy Dispersive Spectroscopy ...................................................................... 159
Diffuse Reflectance Spectroscopy .................................................................... 160
Infrared Spectroscopy ...................................................................................... 160
B. 3 Synthesis ....................................................................................................... 160
Kalil/563813 ...................................................................................................... 1 60
Rb5InAS3 S 13 ..................................................................................................... 161
CsalnA33813 ..................................................................................................... 161
Rb3BiASzSg ...................................................................................................... 1 61
CS3BIA8283 ...................................................................................................... l 61
K9BIAS4S 15 ...................................................................................................... I 62
RbgBIAS4S 15 .................................................................................................... 162
B4 Single Crystal X-ray Crystallography ............................................................ 162
C. RESULTS AND DISCUSSION ................................................................................... 183
C. 1 Synthesis ....................................................................................................... 183
C.2 Structure description of A61nAs 3S 1 3 ............................................................... 184
C3 Structure description of A 3BlAS)Sg ................................................................. 185
C. 4 Structure description of A 9BiAs4Sl6 ............................................................... 187
C. 5 Spectroscopy ................................................................................................. 198
D. CONCLUSION ....................................................................................................... 199

CHAPTER7 [Mn2(AsS4)4] 8' AND [Cd2(AsS4)2(AsSS)z]8‘: DISCRETE CLUSTERS
WITH HIGH NEGATIVE CHARGE FROM ALKALI POLYTHIOARSENATE

 

FLUXES 206
A. INTRODUCTION .................................................................................................... 207
B. EXPERIMENTAL SECTION ...................................................................................... 208

3.1 Reagents ........................................................................................................ 208
3.2 Physical Measurements ................................................................................. 208
Powder X-ray Diffraction ................................................................................ 208
Energy Dispersive Spectroscopy ...................................................................... 209
UVVis/nearIR and Infrared Spectroscopy ........................................................ 209
Magnetic Susceptibility Measurements ............................................................ 209
Differential Thermal Analysis .......................................................................... 209
B. 3 Synthesis ....................................................................................................... 210
K3[MD2(ASS4)4] ............................................................................................... 210
Rbs [Mn2(AsS4)4] ............................................................................................. 210
Css[Mn2(AsS4)4] .............................................................................................. 21 1

viii

 

 

Rbs[Cd2(ASS4)2(ASSs)2] ................................................................................... 21 1

8.4 Single Crystal X-ray Crystallography ............................................................ 211
C. RESULTS AND DISCUSSION ................................................................................... 212
CI Synthesis ....................................................................................................... 212
C.2 Structure description of K8[Mn2(AsS4)4 ] ........................................................ 223
C3 Structure description of Rb3[ Cd2(AsS4) 2(AsS5) 2 ] ............................................ 230
C. 4 Spectroscopy ................................................................................................. 232
CS Magnetism .................................................................................................... 233
D. CONCLUDING REMARKS ............................. 237

CHAPTERS CsloCuzAs4Sm, CszMAsSS (M = Cu, Ag) AND CszAuAsS4: LOW
DIMENSIONAL COINAGE METAL COMPOUNDS FROM CESIUM

 

 

THIOARSENATE FLUXES 240
A. INTRODUCTION .................................................................................................... 241
B. EXPERIMENTAL SECTION ...................................................................................... 242

3.1 Reagents ........................................................................................................ 242
3.2 Physical Measurements ................................................................................. 242
Powder X-ray Diffraction ................................................................................ 242
Energy Dispersive Spectroscopy ...................................................................... 242
Diffuse Reflectance Spectroscopy .................................................................... 243
Infrared Spectroscopy ...................................................................................... 243
Differential Thermal Analysis .......................................................................... 243
3.3 Synthesis ....................................................................................................... 244
CSloCU2AS4S 19 ................................................................................................. 244
CSzCLIASSs ...................................................................................................... 244
CSzAgA885 ...................................................................................................... 244
CSzAuASS4 ...................................................................................................... 245
3.4 Single Crystal X-ray Crystallography ............................................................ 245
C. RESULTS AND DISCUSSION ................................................................................... 254
CI Synthesis ....................................................................................................... 254
C.2 Structure description of Cs 10C uzAs4S 19 .......................................................... 255
C3 Structure description of Cs zMAsS 5 ................................................................ 261
C4 Structure description of Cs 2A uAsS4 ............................................................... 262
C. 5 Spectroscopy ................................................................................................. 268
C. 6 Dijfirential Thermal Analysis ....................................................................... 271
D. CONCLUDING REMARKS ....................................................................................... 273

APPENDIX 277
SYNTHESIS AND STRUCTURE OF Cs4As2Sw ................................................................ 277
SYNTHESIS AND STRUCTURE OF TlssnloSb16se43 ....................................................... 286
SYNTHESIS AND STRUCTURE OF A3CCASzSg (A = Rb, Cs) .......................................... 298

ix

CHAPTER 1

LIST OF TABLES

TABLE 1A. Reaction conditions leading to the different chalcophosphate ligands ....... 9

TABLE 18. Structures of various reported chalcophosphate ligands ............................ 9
TABLE 2. Thiophosphate ligands observed in the glassy and crystalline compounds
belonging to the system (Ag;S)x(PZSS)1.x for different values of x. ......... 17
CHAPTER 2
TABLE 1. Crystallographic data for NaSnAsS4, RbSnAsSs, Rb28nA3286, CSzSIlASzSg
and CSzSflASzSeg .................................................................................... 36
TABLE 2. Fractional Atomic Coordinates and Isotropic Displacement Parameters (A2
x 103) for NaSnAsS4, RbSnAsSs, RbZSnAszsé, CSZSnAS259 and
CSzSflASzSCg .......................................................................................... 37
TABLE 3. Anisotropic displacement parameters* (A2 x 103) for NaSnAsS4,
RbSflASSs, szsnAS255, CSle’lASzSg and CSzSflASzSCg. ........................ 40
TABLE 4. Selected bond distances for NaSnAsS4, RbSnAsSs, Rb28nASZS6 and
CSzSflASzSg ............................................................................................ 50
TABLE 5. Selected bond angles for NaSnAsS4, RbSnAsSs, RbZSnAszSg and
CSzSflASzSg ............................................................................................ 52
TABLE 6. Band gaps for I-V .................................................................................. 65
TABLE 7. Far IR and Raman bands of I, III, IV and V ........................................... 65
CHAPTER 3
TABLE 1. Crystallographic refinement details of lesnA5236, TIZSnAS2$e6 ............ 80
TABLE 2. Fractional Atomic Coordinates and Equivalent Isotropic Displacement

Factors (A2 x 103) for Tl;SnAsz86 and TIZSnAszseé. .............................. 81

TABLE 3.

TABLE 4.

TABLE 5.

CHAPTER 4

TABLE 1.

TABLE 2.

TABLE 3.

TABLE 4.

TABLE 5.

CHAPTERS

TABLE 1.

TABLE 2.

TABLE 3.

TABLE 4.

TABLE 5.

CHAPTER 6

TABLE 1.

Anisotropic displacement parameters“ (A2 x 103) for TIZSnAszss and

lesnAszse6. .......................................................................................... 82
Selected bond distances (A) for lesnA3286 and TIZSHASZSC6. ............... 84
Selected bond angles (deg) for Tl;SnASZS(, and TIZSnAszSe6 .................. 84

Crystallographic data for RbeAsS4, CstASS4, Rb4PbAszsg and

CS4PbASzSg .......................................................................................... 102
Fractional atomic coordinates and isotropic displacement parameters (A92
x 10"3) for RbeAsS4, CstAsS4, Rb4PbAszsg and Cs4PbAszsg .......... 103
Anisotropic displacement parameters“ (A2 x 103) for RbeAsS4,
CSPbASS4, Rb4PbASst and CS4PbAS4Ss. ............................................. 105
Selected bond distances for RbeAsS4, CstAsS4, Rb4PbA5283 and
CS4PbASzSg .......................................................................................... 1 10
Selected bond angles for RbeAsS4, CSPbAsS4, Rb4 PbA5283 and
CS4PbASst .......................................................................................... I 12
Crystallographic refinement data for AgEuAsS4 and Eu3A5283 ............. 133
Fractional atomic coordinates and equivalent isotropic displacement
parameters (A2 x 103) for AgEuAsS4 and EU3AS233. ............................. 134
Anisotropic displacement parameters“ (A2 x 103 ) for AgEuAsS4 and
EleSst. ............................................................................................. 135
Selected bond distances for AgEuAsS4 and EU3ASZSg. .......................... 138
Selected bond angles for AsEuAsS4 and EU3A8283 ............................... 139

Crystallographic refinement details for K61nAS3S. 3, RbglnAs381 3 and
(38611119183313 .......................................................................................... 164

Xi

TABLE 2. Crystallographic refinement details for Rb3BiA52S3 and CS3BiASzSg.... 165
TABLE 3. Crystallographic refinement details for KgBiAs4S.6 and RbgBiAs4SI6... 166

TABLE 4. Fractional atomic coordinates and equivalent isotropic displacement
parameters (A2 x 103) for K61IlAS3SI3, Rb6InAs3SI3 and CsalnAs3813.... 167

TABLE 5. Fractional atomic coordinates and equivalent isotropic displacement
parameters (A2 x 103) for Rb3BiASzSg and CS3BiASzS8 ......................... 171

TABLE 6. Fractional atomic coordinates and equivalent isotropic displacement
parameters (A2 x 103) for K9BiAs4816 and Rb9BiAs4S|6 ....................... 173

TABLE 7. Anisotropic displacement parameters“ (A2 x 103) for K61HAS3SI3,
RbsInAS3sl3 and CSaIl’lAS3Sl3 ............................................................... 175

TABLE 8. Anisotropic displacement parameters“ (A2 x 103) for Rb3BiAszSg and
CS3BIASst .......................................................................................... 179

TABLE 9. Anisotropic displacement parameters“ (A2 x 103) for K9BiAs4S16 and
Rb9B1A54Sm ......................................................................................... 181

TABLE 10. Selected bond lengths for CS6InAS3813, CS3BiASzSg and RbgBiAs4816 .. 192
TABLE 11. Selected bond angles for (38611115153313, CS3BiA5283 and RbgBiAs4816... 195

CHAPTER 7

TABLE 1. Crystallographic refinement details of K3MI12AS4815, RbsanAS4816,
CSganAS4815 and RbngzAS4Slg ......................................................... 214

TABLE 2. Fractional Atomic Coordinates and Isotropic Displacement Parameters (A2
X 103) for KganAs4Sw RbsanAS4S16, CSsanAS4Sm and RbngzAS4Sls.
............................................................................................................ 215

TABLE 3. Anisotropic displacement parameters* (A2 X 103) for K3 anAs4SI6
RbsMflzAS4Sl6, CSganAS4S l6 and RbngzAS4Sls. ................................ 219

TABLE 4. Selected bond distances for K3MI'12AS4316, and RbngzAS4Sls. ............. 226
TABLE 5. Selected bond angles for KganAs4S16, and RbngzAs4Sm. ................. 228

xii

CHAPTER 8

TABLEl. Crystallographic data and refinement details for CsloCuzAs4819,
CszCuAsss, CszAgAsSS, and CszAuAsS4 ............................................. 247

TABLE 2. Fractional Atomic Coordinates and Isotropic Displacement Parameters (A2
x 103) for CsloCuzAs4819, CszCuAsSS, CSzAgAsss, and CszAuAsS4 ..... 248

TABLE 3. Anisotropic displacement parameters" (A2 x 103) for CsloCuzAs4819,
CszCuAsss, CszAgAsss, and CszAuAsS4 ............................................. 251

TABLE 4. Selected bond distances for CsloCuzAs4Sm, CSZCuAsSS and CSzAuASS4.
............................................................................................................ 258

TABLE 5. Selected bond angles for CsmCuzAs4819, CszCuAsss and CszAuAsS4. .266

TABLE 6. Comparison of IR frequencies of CszCuAsss, CszAgAsss and CSzAuASS4.

............................................................................................................ 268
APPENDIX

TABLE A-l. Crystallographic refinement details for CS4AS2810. ............................... 278
TABLE A-2. Fractional Atomic Coordinates and Isotropic Displacement Parameters (A2
x 103) for Cs4Aszsm. ............................................................................................... 279
TABLE A-3. Anisotropic displacement parameters* (A2 X 103) for Cs4Aszsm. .......... 281
TABLE A-4. Selected bond distances for CS4ASleo. ................................................. 283
TABLE A-5. Selected bond angles for Cs4Aszslo. ..................................................... 284
TABLE A-6. Crystallographic refinement details for Tlgsn103b168648. ....................... 288

TABLE A-7. Fractional Atomic Coordinates and Isotropic Displacement Parameters
(A2 x 103) for TlgSnloSbmSe“. ................................................................................ 289

TABLE A-8. Anisotropic displacement paraemeters“ (A2 x 103) for TlgSnmemSe43. 291

TABLE A-9. Selected bond distances for TlgSnloSb15Se43. ........................................ 293

xiii

TABLE A-lO. Selected bond angles for TlgSnloSb168e4g. ........................................... 294
TABLE A-l 1. Crystallographic refinement details for Rb3CeA52Sg and CS3CCAS233. 299

TABLE A-12. Fractional Atomic Coordinates and Isotropic Displacement Parameters

(A2 x 103) for Rb3CeASZSg and CS3CeAszsg. ........................................................... 300
TABLE A-13. Anisotropic Displacement Parameters (A2 x 103) for Rb3CeA5283 and

CS3C€ASzSg ......................................................................................................... 302
TABLE A-14. Selected bond distances for Rb3CeA5283 and C53CeAszsg .................. 304
TABLE A-15. Selected bond angles for Rb3CeAszsg and CS3CCASzSg. ...................... 306

xiv

LIST OF FIGURES

CHAPTER 1

FIGURE l.a) Unit cell of (Ph4P)2Hg2As4Sg looking down the a- axis with the organic
cations removed. b) Single constituent chain of the structure consisting of the
tetramer (AS489)6' coordinating to trigonal planar Hg. ................................... 4

FIGURE 23) Unit cell of RbAngs3Se6 down the b-axis showing the three dimensional
framework of the compound. b) Coordination of the cyclic (AS3Sea)3’ ligand
and short range Ag-Ag interactions ............................................................... 5

CHAPTER 2

FIGURE l.a) View of the unit cell of NaSnAsS4 down c-axis. b) Single chain of
NaSnAsS4. .................................................................................................. 46

FIGURE 2.3) Unit cell of RbSnAsSs showing chains running along the a-axis. b)
Coordination environment of the Rb+ cation. ............................................... 47

FIGURE 3.a) Layers of Rb2$nA5286 parallel to the ab plane and stacked perpendicular to
the c- axis. b) A single layer showing octahedral Sn bound by pyramidal ASS3
ligands. c) Coordination environment of Rb ................................................ 55

FIGURE 4.a) The unit cell of CszsnAszsg showing the two cyrstallographically unique
clusters. b) The individual clusters with one showing a disorder in the
disulfide linkage. ......................................................................................... 56

FIGURE 5.Differential Thermal Analysis of a) NaSnASS4 b) RbSnAsSs c) Rb2SnA5286
d) CSle‘lASzS9 ............................................................................................. 58

FIGURE 6.0ptical absorption spectra of a) NaSnAsS4 b) RbSnAsSs c) RbZSnAszss and
d) Cs;SnA3289. Energy gaps are caculated as 2.17 eV, 2.07 eV, 1.68 eV and
1.98 eV respectively. ................................................................................... 59

FIGURE 7.a) Comparison of the powder patterns of pristine, glassy and re-crystallized

CSzSflASzSg shows that the glass-crystal transition is reversible. b) Optical
Spectrum of the glassy CszsnAszsg shows an absorption onset at 1.98 eV. .. 60

FIGURE 8.Far Infrared spectra of a) NaSnAsS4 b) RbSnAsSs c) szSnAszsg and d)
CSzSflASzSg ................................................................................................. 61

XV

FIGURE 9.Raman Spectra of a) NaSnAsS4 b) RbSnAsSs c) szsnAszs¢5 and d)
CSle’lASzSg. ................................................................................................ 62

CHAPTER 3

FIGURE 1.a) Unit cell of Tl;SnAszQ6 looking down the b-axis. The As lone pair is
oriented towards the T1 cations between the layers. b) A single layer showing
an octahedral Sn coordinated by 6 AsQ33' anions. c) The irregular seven
coordination pocket of T1 created by 6 O atoms and an As atom. ................. 83

FIGURE 2.Differential Thermal Analysis of (I) T12SnA5286 showing a melting point of
490 °C and a recrystallization point of 424 °C and (II) TIZSHA82866 showing
that the compound melts at 350 °C but does not crystallize on cooling.
Crystallization occurs on heating the compound at 297 °C. ......................... 87

FIGURE 3.Comparison of the powder patterns of the pristine, glassy and recrystallized
forms of T12SnASZSe6 Shows that the compound switches reversibly between
crystalline and glassy states upon heating. ................................................... 88

FIGURE 4.0ptical absorption spectra of a) lesnA5286 showing, a steep absorption edge
at 1.68 eV corresponding to its dark red color b) TIZSnAszse6 with a energy
gap of 1.08 eV c) the glassy form of Tl;SnAszSe6 Shows a red shift compared
to the crystalline form and absorbs at 0.85 eV. ............................................ 89

FIGURE 5.a) Band structure plot for leSflAsteé shows that the band gap is an indirect
gap with an approximate energy of 0.6 eV arising from a transition from a
general point in the region AH to the point A of the Brillouin zone. b) The
Brillouin zone for a trigonal system. ............................................................ 90

FIGURE 6.a) Density of states for T1 5 and p orbitals showing that the S electrons are
below the Fermi level and interact weakly with As p orbitals. b) Density of
states for As 5 and p orbitals Showing that the AS 8 electrons lie much below
the Fermi level. ........................................................................................... 91

FIGURE 7.a) Density of states for Se 8 and p orbitals Showing that the p orbitals form
the energy levels closest to the Fermi level in the valence band. B) Density of
states for Sn 3 and p orbitals showing that Sn orbitals contribute mainly tO the
conduction band. ......................................................................................... 92

FIGURE 8.Total density of states for leSnAszseg. ...................................................... 93

xvi

CHAPTER 4

FIGURE l.a) Unit cell down the a- axis for APbASS4 b) A single[PbASS4]“' layer c)
Trigonal prismatic geometry of Pb (1) Coordination of (ASS4)3' ................. 109

FIGURE 2.a) Unit cell of Rb4PbAS283 b) Distorted dodecahedral environment around Pb
c) Coordination of (ASS4)3' (1) Coordination of K+ cations ......................... 115

FIGURE 3.a) Unit cell of CS4PbASzSg along the a- axis b) View of the unit cell along the
ac- plane, CS atoms have been omitted for clarity c) Coordination geometry

around Pb (1) Coordination of (AsS4)3' e) Coordination environments of Cs+
.................................................................................................................. 116

FIGURE 4.a) DTA of RbeAsS4 showing a melting point at 435°C and recrystallization
point at 397°C. b) DTA of CS4PbASzSg showing that it melts at around 543°C
and recrystallizes at 524°C. ....................................................................... 120

FIGURE 5.a) Single crystal UV-Vis spectrum of RbeAsS4 showing a Sharp absorption
at 2.53 eV. Diffuse reflectance spectra of b) CstAsS4 c) Rb4PbASzSg d)
CS4PbASzSg ............................................................................................... 121

FIGURE 6.Far-IR Spectra of a) RbeAsS4 b) Rb4PbASZSs c) CstAsS4 d) Cs4PbAszsg
................................................................................................................................ 122

CHAPTER 5

FIGURE la) The red rectangular rods of AgEuAsS4 b) Unit cell of AgEuAsS4 viewed
down the c- axis. c) Unit cell of LiEuPSe4 looking down the c-axis showing
that it is isostructural to AgEuAsS4. The two structures differ in the positions
of the univalent cations (Li+ and Ag). ...................................................... 141

FIGURE 2.a) AgS4 and A584 tetrahedra fuse to form layers parallel to the bc- plane.
These tetrahedra point in the same direction implying lack of center of
symmetry. b) Extended coordination sphere of Eu showing that it is
coordinated by 6 AsS4 ligands in a bicapped trigonal prismatic geometry. c)
The distorted tetrahedral environment around Ag d) Coordination Sphere of
an ASS4 ligand ........................................................................................... 142

FIGURE 3.a) Unit cell of EU3AS283 viewed down the c- axis showing the hexagonal

arrangement of Eu atoms around the staggered ASS4 tetrahedra b) Unit cell
view of Pb3P2$3 down the diagonal. .......................................................... 146

xvii

FIGURE 4.a) Unit cell View of Eu3Aszsg down the 110 direction. b) Unit cell view of
Pb3PZSs down the 110 direction. The figure shows that the two compounds
are structurally different. ........................................................................... 147

FIGURE 4.a) Unit cell view down the a- axis Shows the repeating unit of four AsS4
tetrahedra. The pairs of tetrahedra labelled m and n are staggered 17° with
respect to each other. The second tetrahedron of m and the first tetrahedron of
n are staggered 60° with respect to each other. b) Extended coordination
sphere of Eu c) Coordination of the A884 ligand. ....................................... 148

FIGURE 5.Plots of the inverse magnetic susceptibility and magnetic susceptibility of a)
AgEuAsS4 showing a pm of 7.2 BM b) Eu3Aszsg showing a pm of 12.53 BM.
.................................................................................................................. 149

FIGURE 6.0ptical absorption spectrum of EU3A82Ss shows that it absorbs strongly at 1.9
eV corresponding to its red color. .............................................................. 150

FIGURE 7.DTA plot of Eu3Aszsg showing two melting and two recrystallization points.
The powder pattern of the residue after DTA indicated that the compound
decomposes on heating. ............................................................................. 150

CHAPTER 6

FIGURE 1.The two co-crystallized anions in the CS61nAS3813 lattice, [In(AsS4)2(As85)](*
and [In(Ass.)(Asss)2]‘r ............................................................................. 189

FIGURE 2.a) The unit cell of C83BiAS283 looking down the b- axis b) A single chain
showing the orientation of the 6s2 lone pair and coordination geometry around
Bi .............................................................................................................. 190

FIGURE 3.a) View down the b- axis of RbgBiAs4816. b) A single cluster anion,
[Bi(AsS4)4]9' showing the octahedral geometry of Bi. The split site is due to
the stereochemically active lone pair on Bi. ............................................... 191

FIGURE 4.0ptical absorption Spectra of a) (38611115183313 b) C53BiAszS3 and c)
RbgBiAs4Sm showing sharp absorption with onsets at 2.64 eV, 2.34 eV
and 1.98 eV corresponding to their light-yellow, golden-yellow and red colors
.................................................................................................................. 200

FIGURE 5.Far-IR spectra of a) CsalnA83813, the peak at 469 cm'1 is due to S-S
stretching b) RbgBiAs4S16, the peaks above 400 cm'1 are due to As-S
stretching. ................................................................................................. 201

xviii

 

CHAPTER 7

FIGURE 1.The molecular anion [Mn2(AsS4)4]8'. The black circles are Mn, the white
circles are S and the grey circles are AS. .................................................... 225

FIGURE 2.Coordination environments of the five cyrstallographically unique K+ ion 225

FIGURE 3.a) The molecular [Cd2(AsS4)2(ASS5)2]8’ anion. b) The co-crystallized
[Cd2(AsS4)4]8' anion. ................................................................................. 231

FIGURE 4.a) Optical absorption spectra of CSg[MIIz(ASS4)4] and Rb3[Mn2(AsS4)4]
showing energy gaps at 2.26 and 2.33eV respectively. b) Optical absorption
spectra of Rb3[Cd2(AsS4)2(Asss)2] with an onset at 2.67eV. ...................... 234

FIGURE 5.a) Far IR spectrum of K3[M112(ASS4)4] b) Far IR spectrum of
Rbg[Cd2(AsS4)2(As85)2]. The peak at 468 cm'l is attributed to S-S stretching.
.................................................................................................................. 235

FIGURE 6.a) Plot of inverse molar susceptibility against temperature for
Kg[Mn2(AsS4)4] showing a nearly Curie—Weiss behavior till 20K. b) Plot of
molar susceptibility against temperature from 0-50K. The susceptibility
reaches a maximum at 6K. ........................................................................ 236

CHAPTER 8

FIGURE l.a) The unit cell oszloCuzAs4819 b) The unit cell showing a clear view of the
two co-crystallized anions CuzAs38157' and 1518343-. CS+ ions have been
removed for clarity. b) The Cu2(ASS5)37' and the AsS43' anions .................. 257

FIGURE 2.a) The unit cell of CszCuAsss. b) The single tetrameric cluster anion
[Cu4(As85)4]8‘ c) The [I-lg4(PSe4)4(Se2)2]8’ cluster ...................................... 263

FIGURE 3.Schematic representation of the transformation of [Hg4(Se2)(PSe4)4]8' cluster
to [Cu4(As85)4]8' cluster. The dotted lines indicate the breaking of the Se-Se
bond in the former cluster followed by the formation of the diselenide bond in
the thioarsenate ligand in the latter compound. .......................................... 264

FIGURE 4.a) The unit cell of CszAuAsS4 looking down the c- axis. b) A single chain of
1,,[AuAsS4]2' running along the c- axis. ..................................................... 265

FIGURE 5.Diffuse reflectance spectra of a) CszCuAsss Showing a Sharp absorption at
2.10 eV b) CszAgAsSS showing an absorption at 2.41 eV. The molecular
nature of these clusters implies that the absorption is HOMO-LUMO

xix

transition. c) CszAuAsS4 displays a steep slope at 2.54 eV corresponding to
its bright yellow color ................................................................................ 269

FIGURE 6.Far- IR spectra of a) CszCuAsss, b) CszAgAsss and c) CszAuAsS4. The peak
at 470 cm'1 for II and 488 cm'1 for 111 are due to S-S asymmetric stretching.
The peaks between 400 and 450 cm’1 are due to As-S stretching ................ 270

FIGURE 7.Differential Thermal Analysis of CszAuAsS4 showing a melting point at
~470°C and an exothermic crystallization peak at 430°C. The powder pattern
of the product after the DTA matched the one before indicating a congruently
melting compound ..................................................................................... 272

APPENDIX

FIGURE A-1.Unit cell of Cs4Assz down the b-axis. Cs atoms have been removed for
clarity. The figure shows two crystallographically distinct Assz‘l' anions.285

FIGURE A-2.a) Unit cell view down the b-axis of TlgSnloSwae“ showing the two
different kinds of layers constituting the cell. b) The (Sn58b28e14)2' layer c)
The (Sb68e10)2' layer. The large light gray circles are Tl, small dark gray
circles are Sb, black circles are Sn and open circles are Se ......................... 295

FIGURE A-3.a) Differential Thermal Analysis of TlgsnmemSe“ showing a melting
point of 433°C and a recrystallization point of 372°C. The peaks labeled m
and n are due to minor impurities. b) The diffuse reflectance spectrum
showing a narrow band gap of 0.64 eV ...................................................... 296

FIGURE A-4.A plot of the Seebeck coefficient of TlgSnloSb16Se4g against temperature
shows that it is a n-type semiconductor with a room temperature value of -
400 uV/K. ................................................................................................. 297

FIGURE A-5.a) Unit cell of Rb3CCASzSg looking down the b-axis. The large light gray
circles are Rb, the small dark gray circles are As, the black circles are Ce and
the open circles are S. b) The [CeAszsgI chain showing the bicapped trigonal
prismatic Ce coordinated by two different kinds of AsS43' ligands ............. 308

XX

DTA
EDS
SEM

SQUID

LIST OF ABBREVIATIONS
Differential Thermal Analysis
Energy Dispersive Spectroscopy
Scanning Electron Microscope

Superconducting Quantum Interference Device

xxi

Chapter 1
An Introduction to the Polythioarsenate Flux Method for the Synthesis of Complex

Metal Thioarsenate Compounds

A. Introduction

Thioarsenates belong to the vast class of naturally occuring minerals called sulfosalts.
These minerals exhibit an astounding variety of structures and some have recently been
Shown to have interesting optical properties.1 For example, Ag3A583 and Ag3ASSe3 are
well known for their non-linear optical properties.2 Pb7A59820 and PbgASgSzo have been
reported to exhibit strong piezoelectricity.3 T13 ASS4 has shown promise as a
photoacoustic material.4 The sulfosalts can be denoted by the formula MASxSy or
MM'ASxSy, where M and M' are metals. In the case of the naturally occuring minerals, M
and M' are both soft metals like Pb, Tl, Ag, Hg etc. Some examples are TngA33.S.5,5
TleAS589,6 TleAs3S6,7 TngAsS3,8 T12Sb6As4S16,9 AngAsS3,‘° Cu6Hg3As4Su,”
PbASZS4,12 PbgASBSzg,l3 Pb5A59S13 etc.l4 Therefore the bonding in these minerals is
primarily covalent. It is possible to substitute one of the metals by an alkali or alkaline
earth metal leading to ionic bonding in the lattice and subsequently a different structure.
The large class of arsenic sulfosalts mainly arises from the strong tendency of As“ to
stereochemically express its lone pair. Another advantage of this expression is that the
resulting compounds may be non-centrosymmetric. The structural variety found in
naturally occurring sulfosalts, is a major driving force in the quest to further explore

synthetic multinary chalcoarsenates.

Conventionally, solid state materials were made by the ceramic route which involved
heating the reactants to a high temperature (>600°C). High temperatures were required
because solid state reactions are usually diffusion limited and in order for the reactants to
diffuse sufficiently they have to be melted. Under such conditions the resulting products
tend to be the thermodynamically stable simple binary or ternary phases with building
blocks usually limited to the atoms themselves. In order to avoid these thermodynamic
phases and pursue more complex ones, it was necessary to overcome the diffusion control
barrier. Low temperature techniques such as the solventothermal method15 and the molten
flux method16 sought to present mild conditions in which complex building blocks such
as chains and rings remain intact for incorporation into the final structure. The advent of

these methods gave a big fillip to synthetic inorganic solid state chemistry.

B. Solventothermal Pathway

Over the last decade, numerous ternary and quaternary chalcoarsenate compounds have
been reported.” 17 These compounds, like their natural counterparts, have shown
astounding structural diversity. Most of these compounds have been prepared by
solventothermal techniques that tend to mimic the conditions in which sulfosalts were
made in the earth's crust (i.e. hydrothermally). The structural variation found in the
chalcoarsenates made by this method derives from the condensation ability of AsQ33' to
form novel anionic units. Scheme 1 depicts the condensation reactions of the ASQ33'

anion:

AsQ33‘ + AsQ33' ——> ASZQ54'
ASQ33- + ASzQ54-——> AS3Q75-

ASQ33'+ AS3Q75-——> AS4Q96'
2.
AS3Q75-—-—>- S AS3Q63-

2-
AS4Q96_;S——> AS4Q34'

Scheme 1

Each of these ligands differs in its mode of coordination to the metal leading to isolation
of different structures. In these reactions, the cation not only serves to counterbalance the
negative charge but also acts as a structure-directing agent. The complexity of the
chalcoarsenate ligands and their elaborate bonding modes can be observed in the
compounds (Ph4P)2Hg;>,As48918 and RbAngS3sefi.19

(Ph4P)2Hg2AS489 was obtained by reacting HgClz, K3ASS3 and Ph4PBr in 0.3 mL water at
130°C for a week. In this compound, trigonal planar Hg is coordinated by [AS489]6'
ligands to form chains running along the a-axis, see Figure la. The [AS489]6' ligand is
formed by the corner sharing of 4 [ASS3]3' units as shown in Figure 1b.

RbAngS3SC6 was synthesized by heating RbCl, AgBF4 and L13ASSC3 in methanol at
130°C for 2h. This compound features a very complicated three-dimensional framework

formed by distorted trigonal planar Ag+ cations and [AS3Se6]3' rings. The AS3866 ring

 

   

   
 

 

 

O"
,.

 

Figure 1. a) Unit cell of (Ph4P)2Hg2As489 looking down the a-axis with the organic
cations removed. b) Single constituent chain of the structure consisting of the tetramer
(AS489)6' coordinating to trigonal planar Hg.

 

Figure 2. a) Unit cell of RbAg2A33Se6 down the b-axis Showing the three dimensional
framework of the compound. b) Coordination of the cyclic (AS3Se6)3' ligand and short
range Ag-Ag interactions.

consists of 3 As atoms bridged by 3 Se atoms in a chair conformation. The [A33Se6]3’ ring
can be formally obtained by the condensation of 3 [AsS3]3' anions followed by a ring
closure reaction and elimination of Sez'. Figure 2a shows the three-dimensional
framework of the compound. The extended coordination of Ag and AS3366 is shown in
Figure 2b.

There are several other chalcoarsenates that have been made solvothermally and that
Showcase the remarkable structural diversity of these compounds. Some of them include
[(n-Bu)4N]2MoAszSe10,20 featuring the molecular anion [Mo(AsSe5)2]2' consisting of an
octahedral Mo coordinated by two pyramidal ASSe53' ligands; KCU2ASS321 consists of a
complex layered structure formed by tetrahedral Cu bound by pyramidal ASS33' units; the
molecule (Ph4P)4[Pd-;As10822]22 presents two kinds of thioarsenate anions viz., As2554'
and AS3865' that bind to the Pd atoms through S and As; (Ph4P)2PI(AS385)223 is molecular

cage compound with an octahedral Pt4+ bound by cyclic AS3SS3’ ligands.

C. The Molten Flux Method

CI The Polychalcogenide Flux

The application of the alkali polychalcogenide flux to synthesize new compounds has
contributed to an exponential increase in the number of ternary and quaternary
chalcogenides.24 This method is also called the reactive flux method because it supplies
the chalcogenide for incorporation into the final product. The flux acts like a solvent and

allows for better diffusion of the reactants. However unlike the solventothermal method,

where the temperature range is limited due to solvent loss, the flux method readily allows

 

for a wide variation in the temperature (ZOO-700°C). The flux also acts as a mineralizer

and helps in crystal growth. The polychalcogenide flux is formed in the reaction:
A2Q + XQ ———> A2(Q'Q'Q')x

In this reaction, A is an alkali, alkaline earth metal or even an organic cation.25 Q is the
chalcogen S, Se or Te. As shown in the reaction, an alkali chalcogenide reacts with
excess of chalcogen to form polychalcogenide chains of different lengths. The length of
the chain is a function of the amount of alkali chalcogenide (also known as the flux
basicity) present. The greater the flux basicity the Shorter are the chains. In other words,
the more the amount of A2Q, the more the basicity of the flux and less the number of Q-Q
bonds. At lower concentrations of AzQ, there will be more Q-Q bonds and the flux will
have a greater oxidizing power. The inner chalcogen atoms of the chain have a formal
oxidation state of 0. Therefore, they can oxidize the metals present. In this process, they
get reduced thereby breaking the chain. The metal ion is then coordinated by the sz'
fragments present. The other superb feature of this method is that it can be applied to any
metal, thereby allowing us to study trends in the periodic table. Using this method, a
plethora of compounds containing various metal ions have been prepared like C53Ti3Te11,

CszSnSm, KzHg384, CSBISz etc.26

C2 The Polychalcophosphate Flux
The idea of using a polychalcophosphate flux basically involved the additional bonding

possibilities that a group 15 element would Offer. For example,

 

Scheme 2

This idea led to the discovery of KBiPZS7.27 Since then, we and others have advanced this
field to include numerous new quaternary chalcophosphate phases that display novel
Pny ligands in various binding modes and structures of different dimensionalities.28

The polychalcophosphate flux is more basic than a polychalcogenide flux and is
generated by the fusion of AzQ, P2Q5 and excess Q. A more appropriate description of
this flux would be a polychalcogenide flux in which various Pny"' anions are solubilized.
The nature of the chalcophosphate ligand usually depends on the basicity of the flux and
there is now a fair understanding of the conditions that promote a certain kind of
chalcophosphate ligand. Table 1a gives a list of chalcophosphate ligands and the
synthetic conditions that give rise to them. Each of these ligands exhibits different modes
of connectivity to the metal giving rise to solid state compounds having molecular,
chains, layers or framework structures. Chalcophosphate ligands other than those
mentioned in the table such as P2S62" 34 P2872” 35 P28e32" 36 etc have also been reported.

The structures of these ligands are shown in Table 1b.

Table la. Reaction conditions leading to the different chalcophosphate ligands

 

Reactant ratio

AzsefM/stes/Se

Chalcophosphate anion

PxSeyn°

 

1-2/1/1-3/10

 

3-4/1/1.5-2/10

PSe43', PSe53', P236114- (P5330

 

 

2/1/2-3/10

 

PZSe74', PZSe94'(P5+)31

 

 

AzsfM/sts/ S

PxSyn-

 

2-4/1/1.5-3/4-12

PS4}, P2374} P2394- (P5+)32

 

 

2/1/3/4

 

 

Table lb. Structures of various reported chalcophosphate ligands

 

Pny ligands

Structure

 

3- 30a, 328
PQ4

Q\ ‘gx Q
P..-“
Q/ \Q

 

4-29.33
P2Q6 '

 

 

Q74», ,te‘fQ
Q P —- P 3 Q
Q/ \Q

 

 

4- 31, 32b
P2Q7

 

 

 

 

 

 

 

 

 

 

 

 

 

 

P2Q94-31,32c Q\ gossQ Q32" Q
/P Q3": P
\ / / \
Q Q Q Q
SB \ SC Se Se
\\ /
P2 8684- 30c \ 389° ’59,...” /
/P\ /P\
Se Se Se Se
Se , Se
PSes3' 30b \ 39$
/P\
Se Se Se
S S, S
P2862- 34 \ “55$ ‘94.," /
s S
S
S— S
- S e‘ ’4 S
P2872 35 \ s? ’6” /
S S
Se — Se
stesz- 36

 

 

10

 

C3 The Polythioarsenate Flux

Given the considerable success in using a polychalcophosphate flux, it was inevitable that
the question of what happens in a polychalcoarsenate flux should arise. A few ternary and
quaternary chalcoarsenate compounds have been made via direct combination of the
elements.37 It is surprising that even though literature is abound with the structural
diversity shown by chalcoarsenate compounds, there were almost no attempts to prepare
chalcoarsenates by the flux method. We therefore became interested in such an
investigation. There seems to be a considerable divide in the electronegativities of P and
As. Thus while P exists in the +4 or +5 oxidation state in its compounds, this cannot be
the case for As which does not Show the +4 state. The most favored oxidation states of
As are +3 and +5. This implies that the chalcoarsenate ligands would be quite different
from the corresponding chalcophosphate ligands and so would the resulting compounds
that are formed by these ligands. The only ligand that is common to both P and As is the
PnQ43' anion with the pnictogen in the +5 oxidation state.

We also expect the chalcoarsenate fluxes to yield ligands that are not Simple
condensation products of the A5833 ' ligand. Since these fluxes have solubilized
polychalcogenide anions along with ASnyn' anions, we can expect compounds with
chalcoarsenate ligands that contain Q-Q bonds.

We therefore began a systematic investigation of the reactivity of main group, transition
and rare earth metals in alkali polythioarsenate fluxes. The remainder of the chapter deals
with the details of the flux and a summary of the compounds we have obtained during the

course of this research.

11

C.3-1 The formation of a polythioarsenate flux

Conceptually, the alkali polythioarsenate flux can be generated by an insitu reaction of
A28, A5283 and excess of S, in a manner similar to the polychalcophosphate flux. This
reaction leads to the formation of various ASxSy“' anions along with 822' anions. The
metal that is present in the flux is oxidized by both ASxSyn' and 822' anions. The resulting
metal ion is then coordinated by the thioarsenate ligands present in the solution according
to its coordination preferences. Since the flux is oxidizing, frequently we observe the
metal in its highest possible oxidation state. There is usually an excess of sulfur in the
flux, because it helps lower its melting point and if needed acts as an electron acceptor.
The excess of sulfur can also get incorporated into the structure in the form of polysulfide
ligands. The structure therefore presents an interesting mix of thioarsenate and
polysulfide ligands.

The high basicity of the fluxes generally implies that AsxSyn' ligands of high charge are
isolated. The basicity of the flux is also affected by the kind and amount of alkali sulfide
used. Generally, the greater the amount of A28, the greater the flux basicity and greater is
the likelihood of obtaining highly charged thioarsenate ligands. This high basicity also
leads to the formation of molecular phases. As we go from Nags to C528, the basicity of
the flux increases. This increases the probability of incorporating the alkali metal in the
final structure. Thus it has generally proved difficult to form compounds with Na and Li.
Another governing principle for dimensionality of the observed structures is the counter-
ion effect.38 The counter-ion effect explains that the dimensionality of the structure is

inversely proportional to the size of the counter ion. Thus the possibility of obtaining a 3-

12

D framework is highest for Li/Na, and molecular phases will most probably be obtained
with Cs.

The general method of setting up an alkali thioarsenate flux reaction is as follows:

The starting materials, alkali sulfide (A28), the metal, AS283 and excess of S are weighed
in a glove box and loaded into a fused-silica tube. The tube is then flame sealed under
vacuum (~10'4 Torr). This tube is put in a computer-controlled furnace and heated
according to a desired temperature profile. After cooling, usually well-formed crystals are
visible inside tube, embedded in a matrix. Isolation of these crystals is done by opening
the tube in N, N-dimethyl formamide, which has been previously degassed by bubbling
N2 through it. The excess of flux gets dissolved away in this solvent. After the flux is
washed Off (this can be observed when the solution loses all its color and usually takes
about 8-10 h), the crystals are washed with ether and dried. Ofcourse, this method
assumes that the product is insoluble in the solvent. If the product dissolves in DMF, then
we need to use another solvent, but usually it is possible to find atleast one solvent in
which the product is stable. If this fails then a manual extraction of the crystals should be
attempted.

At this point, it is important to consider the As-S speciation in the flux. The flux can be
considered to be a liquid glass with different kinds of As-S units present. Two questions
arise from this consideration: 1) What are the different units present in the melt? 2)
Which one gets incorporated in the final product? Spectroscopic investigations done on
arsenic and phosphorus chalcogenide glassy systems can provide us with some clues to

answer the above questions. This will be the topic of the next section.

13

C.3-2 Spectroscopic investigations in arsenic and phosphorus chalcogenide glasses.

Raman spectroscopic studies done on arsenic chalcogenide glasses have shed some light
on the kind of As-Q units present in the glass. Though these studies were done to
understand asymmetries in local bonding sites of the arsenic chalcogenide glass, it is still
constructive to our purpose. According to one Raman study39 done on ASxSeloo-x glass
system, it was found that all the glasses consist of a band at 227cm’l corresponding to
pyramidal AsSe3 units. As the content of the Se was increased in the glass, the ASSe3
peak overlapped with a peak due to -Se-Se-Se- chains. At very high concentrations of Se,
a strong band at 252cm‘l appeared which showed the presence of 863 rings. As the As
content was increased, the AsSe3 band became weaker with simultaneous increase in the
intensity of peaks due to AS4Se3 and AS48e4 cage units formed in the glass. The As rich
glass also Showed a narrow Raman band at 280 cm'1 corresponding to Se-Se bridges that
link AsSe33' units and/or AS4Se3/As48e4 cages. This configuration of the glass can be

empirically represented as follows:

Se

3..
/ l \8e
8e Se

Se

As Se
/ ' \8 / \Se
e
Se

As

AS/Ts’i

 

Scheme 3

l4

It is quite possible that the thioarsenate flux has ASSx units similar to the ones seen in the
glassy systems. In addition, internal redox equilibria between the different thioarsenate

anions might also be taking place as shown below:
As
\ / S ____> AS
8 ‘ "”—
S 5

In a Raman investigation conducted on Asx8100-x glasses,40 it was found that for x <25%,
the glasses contained 83 rings indicated by the characteristic peaks at 155, 234 and 474
cm". When x = 40%, the Raman spectrum shows a Single broad peak at 343 cm],
corresponding to the pyramidal A583 units. There are also very weak peaks due to As-AS
and 8-8 bonds. However at x >40%, there are distinct peaks due to As-As bond
formation. The authors also conducted differential scanning calorimetn'c experiments on
these glasses. They found that for x <25%, the glasses consist of two phases: one whose
glass transition temperature depends on the concentration of As and another that has a
fixed composition of ~AS285. Based on the Raman spectrum, it has been proposed that
the structure of the glassy AS285 consists of tetrahedral A584 units that are linked
polymerically or pyramidal A583 units linked by S-S chains or an equilibrium between
these two possibilities.

High temperature liquid state 77Se NMR performed on ASXSel.x glassy melts41 have also

shed some light on the type of AsSe units present in the liquid. It was found that the

15

average chemical shift showed a linear dependence on the amount of As in the range 0< x
<40%. This shift corresponds to the progressive dismantling of Se-Se-Se chains to form
As-Se-Se and As-Se-As fragments as the amount of As is increased. The chemical shift
remains constant at x >40% indicating a chemically ordered network consisting of
pyramidal AsSe3 units. Since the 77Se peak remains constant at higher concentrations of
As, this can only mean that addition of As leads to As-As bonds. 75AS NQR
measurements on arsenic sulfide glasses with As >40 at%, have proved the existence of
As-As bonds.44

In chalcophosphate systems, 31P NMR has contributed advantageously to understand
short-range order in different glassy systems like P-S, P-Se, Ag2S-P285, Li2S-P285 etc.42
In the P-S glassy system, it was reported that up to about 12 at% of P, the glass consisted
of PS4 units connected by S-S chains. However as the phosphorous content is increased,
there is a marked decrease in the glass transition temperatures, implying that the structure
Of the glass does not contain as many bonds. The chemical shifts observed in the NMR of
these glasses at high concentration of phosphorous point to the formation of clusters of
the type P48x (x = 3, 4, 5, 7, 9, 10). This behavior is very similar to arsenic chalcogenide
glasses, which show a tendency to form AS4Q4/AS4Q3 cages at high concentrations of
arsenic.

31P NMR of ternary Ag2S-P285 system42 has revealed some interesting facts about the
different thiophosphate units found in the glass and the corresponding crystalline
compound obtained through annealing of the glass. Shown below is a table (Table 2) of
thiophosphate units observed in glassy and crystalline (Ag2S),((P285)1.x compounds for

different values of x. As seen, the tendency to form dimeric P2862' groups does not exist

16

in the glass. Instead it seems that the sulfur atoms of the PS4
chains. We can infer from this table that the Short range order in these glasses is unique

and some of these Species may not stable in the crystalline forms of the same

composition.

Table 2. Thiophosphate ligands Observed in the glassy and crystalline compounds

belonging to the system (Ag2S),,(P285)1.x for different values of x.

3' groups form polymeric

 

 

 

Glass Crystal x
S>P/S S\P/S\ /S 0.5
\
S\ /S S\P/S 5\ P/S S\ /S S\P/S\P/S 06
P
\S/P\S/ \S/PS \ \S/ \S/ s/ \S/ \S
S\F/S Sxp/S S\P/\S S\/: S:>_P_/_S.§ 0.67

s/P\s/s

 

 

 

 

 

17

 

From the standpoint of a thioarsenate flux, the above discussion tells us that a) the flux
consists of different structural units like A583, Sn chains, AS484 molecular cages, which
are probably in dynamic equilibrium. These units may or may not be linked with each
other. b) It is quite possible that the structural units that finally get incorporated in the
compound may not necessarily be the ones observed in the melt.

A very pertinent question to the flux methodology is the role of the metals present and
how they affect the structural units. We can attempt to Obtain some answers by observing
how does the introduction of a metal in an arsenic chalcogenide glass change its
structure.

Refractive index measurements on thin films of Tl-AS-S glasses,4 3 75As NQR
measurements on Cu-As—S and Cu—As-Se systems44 and IR absorption measurements on
Ag2S-AS2S3-Agl glasses“ have shown that the introduction of a metal leads to the
breaking of the AS-S bond and formation of the M-8 bond. There are also homopolar A5-
A5 and 8—8 bonds formed as a result. Since most of the M-8 bonds have a different
degree of covalency compared to AS-S bonds, the covalent glassy network of the pure
arsenic chalcogenide glass is modified. The addition of these metals also leads to the
formation of additional structural units such as Ag3AsS3, AgAsS2, TlAsS2, Tl3AsS3 etc.
We can infer from the above studies that the presence of two kinds of metals in our
reactions will significantly alter the makeup of the thioarsenate melt and the final

outcome will depend on the amount ratio of the metal to the thioarsenate composition.

18

D. Conclusion
The large family of natural sulfosalts and the synthetically obtained metal
chalcoarsenates are evidences of the exciting structural chemistry observed in these
compounds. Chalcophosphate compounds have been successfully prepared using molten
polychalcphosphate fluxes. In fact, since the advent of these fluxes the number of
chalcophosphate compounds has more than doubled. However Similar efforts, though
logical, are lacking in the area of chalcoarsenate fluxes. In a sulfur environment, the
chemistry of arsenic is mainly dominated by the AS3+/AS5+ couple as compared to the
PM/P5+ couple observed for phosphorus. Thus we can expect that there will be a
difference in the reactivities of the two fluxes. Even for the well-studied chalcophosphate
flux there are some issues that need answering. These are concerned with the kind of
ligand observed for a particular flux ratio and the influence of the metal on the isolation
Of a certain kind Of ligand. NMR and Raman spectroscopic investigations on glassy P-Q
and ternary Ag2S-P285 systems have shown what kind of chalcophosphate units are
present in the local structures of these glasses and what units are observed when these
glasses crystallize. However there has been no study of high temperature flux melts to
prove that they have units Similar to the short range order observed in the above
mentioned glasses. Insitu experiments in the future can hope to clarify this situation.
Thioarsenate systems face the same issues mentioned above, even more 50. Based
on Raman and NMR studies of arsenic chalcogenide glasses, we can possibly predict that
under sulfur rich conditions, we will observe A583 pyramidal ligands along with S-S

linkages. In sulfur poor conditions, in other words when the flux basicity is high, we

19

should probably expect compounds that contain ASxSy cages and a tendency to form
molecular phases. Ofcourse, these predictions can only be used as guidelines and we
hope to observe a wide structural variety depending on different flux conditions and the
type of metal used. Compared to the polychalcophophate fluxes, the thioarsenate flux is
still in its infancy and extensive studies are warranted.

During the course of this Ph.D. dissertation, a number of quaternary thioarsenates were
discovered. These compounds will be presented in Chapters 2-8 and the Appendix.
Chapter 2 describes the synthesis, structural and physical characterization of four new tin
thioarsenates, NaSnAsS4, RbSnAsSs, Rb2SnA5286 and CS2SnAS289. These compounds
feature the pyramidal A5833} A5843' and A5853' ligands. The latter two are derived from
the A5833’ anion by the substitution of one and two 8 atoms by disulfide units,
respectively. CS2SnAS289 is an interesting compound that crystallizes in a non-
centrosymmetric space group and exhibits reversible crystal - glass transition.

The compounds obtained from a flux can give us ideas to make useful materials.
Rb2SnA5286 crystallizes in the trigonal space group R3 and consists of SnAS2$5 layers.
’We reasoned that if we could substitute Rb with T1, then we should obtain a better
semiconductor material due to the tendency of T1 to form covalent bonds compared to
Rb. Chapter 3 describes the synthesis of Tl2SnA52S6 and Tl2SnAS2Se6. During our
attempts to prepare Tl2Sn8b28e6, we obtained a new layered compound, TlgSnme16Se43.
This compound is discussed in the Appendix.

Chapter 4 presents the compounds Obtained from the investigation of Pb in Rb and Cs
thioarsenate fluxes. The compounds APbAsS4 and A4PbAS283 prepared from these fluxes

are isostructural or very Similar to their thiophosphate counterparts. Since Eu reactivity is

20

similar to Pb in chalcophosphate systems, we decided to forgo the reaction of Eu in
thioarsenate fluxes. Instead, we decided to study the reaction of Ag, Cu/Eu/AS2S3/S
which yielded us the framework compound AgEuAsS4 and a surprising ternary
compound Eu3AS283 with a unique structure. These compounds are discussed in Chapter
5. Chapter 6 deals with A6InAS3813, A3BiAS283 and A9BiAs4816. A6InAS3813 and
A9BiAs4816 contain molecular anions [In(AsS4)2(A585)]6' and [Bi(AsS4)4]9' respectively.
The reactions of transition metals Cd and Mn resulted in the molecular phases
AgMnAs4816 and Ang2As4813. The latter compound displays a rare octahedral Cd
geometry. This is the subject of Chapter 7. Chapter 8 talks about the reaction of coinage

metals Cu, Ag and Au in cesium thioarsenate fluxes.

21

References

1)

2)

3)

4)

5)

6)

7)

8)

9)

a) Feichtner, J. D.; Roland, G. W. App]. Optics 1972, II, 993. b) Dittn'ch, H; Konrad,
H. Institute of Physics Conference Series, 1998, 152 (Ternary and Multinary
Compounds), 293. c) Gottlieb, M.; Roland, G. W. Proceedings of the Society of
Photo-Optical Instrumentation Engineers, 1979, 214 (Acousto-Opt. Bulk Wave
Devices), 88.

a) Ye, N.; Chen, Q.; Wu, B.; Chen, C. J. Appl. Phy. 1998, 84, 555. b) Kityk, I. V.;
Kasperczyk, J.; Plucinski, K. J. Optic. Soc. Am. B: Optic. Phys. 1999, 16, 1719

a) Le Bihan, M. Th. Bull. Soc. Franc, Mineral. Crist. 1962, 85, 15. b) Marumo, F.;
Nowacki, W. Z. Kristallogr. 1967, 124, 409.

a) Roland, G. W.; Gottlieb, M.; Feichtner, J. D. Appl. Phy. Lett. 1972, 21, 52. b)
Goutzolis, A. P.; Davies, D. K.; Gottlieb, M. Optics Commun. 1986, 5 7, 93.

Engel, P.; Nowacki, W.; Balic-Zunic, T.; Scavnicar, 8. Z. Kristallogr. 1982, 161, 159.

Takeuchi, Y.; Ghose, 8.; Nowacki, W. Z. Kristallogr. 1965, 121, 321.

Balic-Zunic, T.; Engel, P. Z. Kristallogr. 1983, I 65, 261.

Brown, K. L.; Dickson, F. W. Z. Kristallogr. 1976, 144, 367.

Engel, P.; Gostojic, M.; Nowacki, W. Z Kristallogr. 1983, 165, 209.

10) Wuensch, B. J.; Nowacki, W. Z. Kristallogr. 1967, 125, 459.

11)Kaplunnik, L. N.; Pobedimskaya, E. A.; Belov, N. V. Dokl. Akad. Nauk. 1980, 251,

96.

12) Iitaka, Y.; Nowacki, W. Acta Cryst. 1961, 14, 1291.

22

 

13) Le Bihan, M. T. Acta Cryst. 1961, 14, 1211.

14) Le Bihan, M. T. Acta Cryst. 1961, 14, 1210.

15)a) Wachhold, M.; Sheldrick, W. S. Coord. Chem. Rev. 1998, 176, 211. b) Drake, G.
W.; Kolis, J. W. Coord. Chem. Rev. 1994, 13 7, 131. c) Wachhold, M.; Kanatzidis, M.
G. Inorg. Chem. 1999, 38, 3863. d) Hanko, J.; Chou, J. H.; Kanatzidis, M. G. Inorg.
Chem. 1998, 37, 1670.

16) a) Sutorik, A. C.; Kanatzidis, M. G. Prog. Inorg. Chem. 1995, 43, 151. b) Keane, P.
M.; Lu, Y. J.; Ibers, J. A. Acc. Chem. Res. 1991, 24, 223. c) Zhang, X.; Kanatzidis,
M. G. J. Am. Chem. Soc. 1994, 116, 1890. d) Chan, B. C.; Hulvey, Z.; Abney, K.;
Dorhout, P. K. Inorg. Chem. 2004, 43, 2453. e) Gieck, C.; Derstroff, V.; Block, T.;
Felser, C.; Regelsky, G.; Jepsen, O.; Ksenofontov, V.; Gutlich, P.; Eckert, H.;
Tremel, W. Chem. Eur. J. 2004, 10, 382.

17)a) Schimek, G. L.; Kolis, J. W. Acta Cryst. 1997, C53, 991. b) Pertlik, F. J. Solid
State Chem. 1994, 112, 170. c) Chou, J. H.; Hanko, J. A.; Kanatzidis, M. G. Inorg.
Chem. 1997, 36, 4. d) Kanatzidis, M. G.; Chou, J. H. J. Solid State Chem. 1996, 127,
186. e) Martin, T. M.; Wood, P. T.; Schimek, G. L.; Pennington, W. T.; Kolis, J. W.
Inorg. Chem. 1995, 34, 4385.

18) Chou, J. H.; Kanatzidis, M. G. Chem. Mater. 1995, 7, 5.

19) Wachhold, M.; Kanatzidis, M. G. Inorg. Chem. 1999, 38, 4178.

20) O'Neal, 8. C.; Pennington, W. T.; Kolis, J. W. J. Am. Chem. Soc. 1991, 113, 710.

21)Jerome, J. E.; Wood, P. T.; Pennington, W. T.; Kolis, J. W. Inorg. Chem. 1994, 33,
1733.

22) Hanko, J. A.; Chou, J. H.; Kanatzidis, M. G. Inorg. Chem. 1998, 3 7, 1670.

23) Chou, J. H.; Kanatzidis, M. G. Inorg. Chem. 1994, 33, 5372.

23

24) a) Kanatzidis, M. G. Chem. Mater. 1990, 2, 353. b) Sunshine, 8. A.; Kang, D.; Ibers,
J. A. J. Am. Chem. Soc. 1987, 109, 6202. c) Liao, J. H.; Kanatzidis, M. G. Chem.
Mater. 1993, 5, 1561. d) Rumpf, C.; Nather, C.; Bensch, W. Inorg. Chem. 1999, 38,
4612. e) Marking, G. A.; Evain, M.; Petricek, V.; Kanatzidis, M. G. J. Solid State
Chem. 1998, 141, 17. f) Li, J.; Liszewski, Y. Y.; MacAdams, L. A. Chem. Mater.
1996, 8, 598. g) Palchik, 0.; Iyer, R. G.; Liao, J. H.; Kanatzidis, M. G. Inorg. Chem.
2003, 42, 5052.

25) Dhingra, 8.; Kanatzidis, M. G. Science 1992, 258, 1769.

26) a) Pell, M. A.; Ibers, J. A. Chem. Mater. 1996, 8, 1386. b) Liao, J. H.; Varotsis, C.;
Kanatzidis, M. G. Inorg. Chem. 1993, 32, 2453. c) Axtell, E. A.; Park, Y.;
Chondroudis, K.; Kanatzidis, M. G. J. Am. Chem. Soc. 1998, 120, 124. d) McCarthy,
T. J.; Ngeyi, S. P.; Liao, J. H.; DeGroot, D. C.; Hogan, T.; Kannewurf, C. R.;
Kanatzidis, M. G. Chem. Mater. 1993, 5, 331.

27) McCarthy, T. J .; Kanatzidis, M. G. Chem. Mater. 1993, 5, 1061.

28) a) Kanatzidis, M. G. Curr. Opin. Solid State Mater. Sci. 1997, 2, 139. b) Schleid, T.;
Hartenbach, 1.; Komm, T. Z. Anorg. Allg. Chem. 2002, 628, 7. c) Gieck, C.; Tremel,
W. Chem. Eur. J. 2002, 8, 2980. d) Aitken, J. A.; Chondroudis, K.; Young, V. G.;
Kanatzidis, M. G. Inorg. Chem. 2000, 39, 1525.

29)Aitken, J. A.; Evain, M.; Iordanidis, L.; Kanatzidis, M. G. Inorg. Chem. 2002, 41,
180.

30) a) Aitken, J. A.; Marking, G. A.; Evain, M.; Iordanidis, L.; Kanatzidis, M. G. J. Solid
State Chem. 2000, I53, 158. b) Chondroudis, K.; Kanatzidis, M. G. J. Solid State
Chem. 1998, 136, 79. c) Chondroudis, K.; Hanko, J. A.; Kanatzidis, M. G. Inorg.
Chem. 1997, 36, 2623.

31) Chondroudis, K.; Kanatzidis, M. G. Inorg. Chem. 1995, 34, 5401.

32)a) Aitken, J. A.; Kanatzidis, M. G. Inorg. Chem. 2001, 40, 2938. b) Hess, R. E;
Gordon, P. L.; Tait, C. D.; Abney, K. D.; Dorhout, P. K. J. Am. Chem. Soc. 2002,
124, 1327. c) Bree, R.; Grenouilleau, P.; Evain, M.; Rouxel, J. Rev. Chem. Miner.
1983, 20, 283.

24

33) McCarthy, T. J.; Kanatzidis, M. G. J. Alloys de5. 1996, 236, 70.

34) Gieck, C.; Rocker, F.; Ksenofontov, V.; Gutlich, P.; Tremel, W. Angew. Chem. Int.
Ed. Engl. 2001, 40, 908.

35) Jandali, M. Z.; Eulenberger, G.; Hahn, H. Z. Anorg. Allg. Chemie, 1985, 530, 144.

36) Zhao, J.; Pennington, W. T.; Kolis, J. W. J. Chem. Soc, Chem. Commun. 1992, 265.

37) a) Bogget, D. M.; Gibson, A. F. Phys. Lett. 1968, 28, 33. b) Seung, D. Y.; Gravereau,
P.; Trut, L.; Levasseur, A. Acta Cryst. 1998, C54, 900. c) Gostojic, M.; Edenharter,
A.; Nowacki, W.; Engel, P. Z. Kristallogr. 1982, 158, 43.

38) Kim, K. W.; Kanatzidis, M. G. J. Am. Chem. Soc. 1998, 120, 8124.

39) Kovanda, V.; Vlcek, M.; Jain, H. J. Non-Cryst. Solids 2003, 326-327, 88.

40) Wagner, T.; Kasap, S. O.; Vlcek, M.; Sklenar, A.; Stronski, A. J. Mater. Sci. 1998,
227-230, 752.

41)Rosenhahn, C.; Hayes, 8. E.; Rosenhahn, B.; Eckert, H. J. Non-Cryst. Solids 2001,
284, 1.

42)a) Mutolo, P. F.; Witschas, M.; Regelsky, G.; Guenne, J. S. auf der; Eckert, H. J.
Non-Cryst. Solids 1999, 256-25 7, 63. b) Zhang, 2.; Kennedy, J. H.; Eckert, H. J. Am.
Chem. Soc. 1992, 114, 5775. c) Eckert, H.; Zhang, 2.; Kennedy, J. H. Chem. Mater.
1990, 2, 273.

43)Petkov, K.; Todorov, R.; Kozhuharova, D.; Tichy, L.; Cemoskova, E.; Ewen, P. J. S.
J. Mater. Sci. 2004, 39, 961.

44) Saleh, Z. M.; Williams, G. A.; Taylor, P. C. Phys. Rev. 1989, B40, 10557.

25

45)Jun, L.; Videau, J. J.; Reau, J. M.; Tanguy, B.; Portier, J.; Hagenmuller, P. .1. Non-
Cryst. Solids 1989, 111, 43.

26

Chapter 2
Reactivity of Sn in Alkali Polythioarsenate Fluxes: Synthesis and Characterization
of NaSnAsS4, ASnAsSs (A = K, Rb), A28nA5286 (A = K, Rb), and CS2SnA52Q9 (Q = 8,

Se)

Abstract

Six new quaternary tin thioarsenates have been prepared by heating 8n in alkali
polythioarsenate fluxes at intermediate temperatures. The one-dimensional NaSnAsS4 (I)
crystallizes in Pnnm with cell parameters a = 11.859(4) A, b = 7.318(2) A and c =
7.508(2) A. It consists of centrosymmetric [Sn2(AsS3)2] centers linked together by II2—S to
form a chain. A variation of this chain is observed in KSnAsSs (II), Pbam with a =
8.1369(2) A, b = 13.784(4) A and c = 7.428(2) A) and RbSnAsSs (III), P21/c with a =
7.373(4) A, b = 15.694(8) A, c = 7.486(4) A and B = 102.61(14)°. Both 11 and III contain
chains made up of [Sn(ASS4)2] cores linked by 11.2-8. The B-[ASS4]3' ligand featured in
these chains is derived from the pyramidal [A583]3' ion by substituting a terminal sulfur
atom with a disulfide unit. A2SnAS286 (IV) is layered and crystallizes in P-3 with a =
6.717(5) A, c = 7.204(8) A for A= K and a = 6.7358(18) A, c = 7.454(3) A for A = Rb.
The layers consist of edge sharing [SnSe] octahedra and [A583] pyramids charged
balanced by K or Rb ions. C52SnAS2Q9 (V) is molecular: s. g Pmc21, a = 7.386(3) A, b =
14.614(5) A, c = 14.417(5) A for Q = S and s.g P21, a = 7.175(5) A, b = 17.555(l2) A, c
= 7.663(5) A, B = 115.857(11)° for Q = Se. The molecule consists of Sn coordinated by

B-[ASQ4]3' and [ASQ5]3' ligands. The [AsQ5]3' ligand is obtained by substitution of two

27

terminal Q atoms in [ASQ3] with disulfide arms. Compounds I-V are semiconductors

with optical bandgaps of 2.17, 2.11, 2.07, 1.89 and 1.98 eV respectively.

28

A. Introduction

In view of the considerable body of information now available on polychalcophosphate
fluxes,l it is timely to ask how the corresponding polychalcoarsenate fluxes perform as
synthetic tools and what type of phases are likely to form. Because P and A5 are members
of the same group in the periodic table, one might expect simple analogues both in
composition and structure. However, there seems to be a significant divide at the P-As
boundary in terms of chemical and electronic behavior in these two elements. For
example, whereas the most stable oxidation states of P as evidenced by the frequency of
the [P2Q6]4' 2 and [PQ4]3‘ 3 (Q = 8, Se) anions in known phases are +4 and +5, this is not
likely to be the case for AS because of the greater stability of the +3 state and the extreme
rarity of the +4 state. The corresponding ethane-like unit [AS2Q6]4' (ubiquitous in P
chemistry) does not exist; however, other anions such as [AS2Q5]4', [ASQ3]3' are known
and might form in the melt. 4’ 5 Conversely, in P chemistry, these species are unknown or
are extremely rare. The only species common in both elements are the classical
tetrahedral [PQ4]3' and [AsQ4]3' 6 anions with P and As in the +5 oxidation state.
Therefore, we anticipate a sharp contrast between [Asty]z' and [Pny]z’ chemistry. The
number of naturally occurring thioarsenates is quite large, and this diversity is a harbinger
of what could be expected in synthetically based systems. Structures with [As(III)Qx]3’ (x
= 3, 4, 5) units are expected to have unique structural chemistry because of the strong
tendency of As3+ lone pair to be stereochemically expressed. To date, the solventothermal
technique7 has been the primary means for the formation of ternary or quaternary

chalcoarsenate phases. We expect the structures obtained from a flux to be quite different

29

 

from that Obtained by the solution route. We therefore set forth on a systematic study of
the reactivity of different metals in these fluxes.

Tin has proven to be an extremely versatile metal for use in the flux method. The
reactions of Sn in polychalcogenide fluxes have yielded compounds like A2Sn489 (A = K,
Rb, CS)8, OI,B—Rb28n283, K28n285, CS28n286, C528n8149. In a polychalcophosphate flux,
compounds such as Rb3Sn(PSes)(P28e6)'°, Rb4 Sn2Ag4(P2Se(,)3l 1, K5 Sn(PSe5)312,
Rb68n28e4(PSe5)2'2, K.;8n2P6825l3 have been isolated. All these compounds feature Sn in
an octahedral or tetrahedral or a W-trigonal bipyramidal geometry bound by
chalcophosphate anions. Our studies with Sn in AASXSy ( A = alkali metal) fluxes have
proven to be very rewarding and yielded us with six new quaternary phases, NaSnAsS4,
(K, Rb)SnAsSs, (K, Rb)2SnA52S(, and CS2SnAS289. Each of these compounds features an
octahedral, diamagnetic 8n“ ion bound to a thioarsenate [AS3+SX]3' (x = 3,4,5) ligand.

The structures and physical properties of these compounds are discussed here.

B. Experimental Section

8.1 Reagents

All manipulations were done in a nitrogen-filled dri-vac glove box. Reagents: Sn (99.999
%; Cerac, Milwaukee, WI), A5283 (99.9 %; Strem Chemicals, Newburyport, MA), A5
(99.9%; Aldrich Chemical Co, Milwaukee, WI), S (99.9 %; Strem Chemicals,
Newburyport, MA). MN—dimethylformamide (Spectrum Chemicals, AC8 reagent grade);
diethyl ether (CCI, ACS grade). Na28, K28, Rb28 and C528 were prepared by dissolving
the alkali metal in liquid NH3 and reacting it with a stoichiometric amount of sulfur

according to a modified literature procedure. 14

3O

8.2 Physical Measurements

Powder X-ray Dijfiaction

X-ray powder diffraction patterns were recorded on a CPS 120 IN EL diffractometer (Cu
K01 radiation) operating at 40kV/20mA and equipped with a position sensitive detector
and a flat sample geometry.

Energy Dispersive Spectroscopy

Semiquantitative microprobe analyses on the compounds were done with a JEOL J SM-
35C scanning electron microscope equipped with a Tracor Northern Energy Dispersive
Spectroscopy detector. Elemental compositions were obtained from an average of three
readings. Acquisition times were 305 or 455 per reading.

Difluse Reflectance Spectroscopy

Solid state diffuse reflectance Spectra were measured using a Shimadzu UV-3101 PC
double-beam, double-monochromator spectrophotometer. BaSO4 was used as reference.
Finely ground sample was spread on a sample holder preloaded with the reference.
Energy gap was determined from a plot of absorbance vs energy by converting
reflectance to absorbance using the Kubelka-Munk function. '5

Infrared and Raman Spectroscopy

Far IR spectra of the compounds were recorded as CsI pellets on a Nicolet 740 FT-IR
spectrometer with a TSG/PE detector and silicon beam splitter. Raman Spectra were
recorded on a Bio-rad FT- Raman spectrometer equipped with a Germanium detector and

using 633nm radiation from a HeNe laser for excitation with a 4cm’l resolution.

31

 

mu; :4.» 3--

Differential Thermal Analysis

The thermal behavior of the compounds was investigated by differential thermal analysis
using a Shimadzu DTA-50 thermal analyzer. Typically a sample (~20 mg) of ground
crystalline material was sealed in a Silica ampule under vacuum. A Similar ampoule of
equal mass filled with A1203 was sealed and placed on the reference side of the detector.
The sample was heated to the desired temperature at 10°C/min, and after 1-3 min it was
cooled at a rate of -10°C/min to 50°C. Residues of the DTA experiments were examined
by X—ray powder diffraction. Reproducibility of the results was checked by running

multiple heating/cooling cycles.

B.3 Synthesis

NaSnAsS4 (I): A pure synthesis of I was achieved by heating a mixture of Na2S (0.07g,
0.9mmol), 8n (0.108g, 0.9mmol), AS (0.136g, 1.8mmol), 8 (0.288g, 9mmol) in the ratio
1/1/2/10 at 500°C. The reactants were held at this temperature for 3 d and then cooled to
250°C at the rate Of 3°C/h followed by rapid cooling to room temperature. Isolation of
the product using degassed N, N—dimethylforrnamide and diethyl ether afforded orange
needles in almost 70% yield. The crystals are stable in air and water. Energy Dispersive
Spectroscopic analysis on several crystals gave an average composition of
NaI.oSnI.oASI.oS4.1-

KSnAsS; (II): KSnA585 was synthesized by reacting K28, Sn, AS283 and S in the ratio
1/1/1/10. The reactants were soaked at 500°C for 60h, followed by cooling to 250°C at

5°C/h and then fast cooled to room temperature. Golden-brown rectangular crystals were

32

 

o"..--

Obtained as the product after washing the excess of flux. Electron microprobe analysis on
these crystals gave a composition of KLOSHLOASLOSSJ. Yield > 85%

RbSnAsS; (III): RbSnAsSs was obtained as dark red rod-like crystals by fusing
Rb28/8n/A52S3/S in a 1/1/1/10 ratio using the same procedure mentioned above with a
yield of ~60%. EDS measurement gave an average reading of Rb1,18n1,oAsl_085,4.

A 2SnAS2S6 (IV): K2SnAS2S6 was obtained by combining a 4/1/3/10 mixture of K28, Sn,
AS283 and 8 at 500°C for 60h. For Rb2SnAS286, Rb2S, Sn, As and S were mixed
stoichiometrically in a 1/1/2/5 ratio and isothermed at 500°C for 72h. Both phases were
isolated as dark red hexagonal crystals. EDS analysis indicated K2_08n1,oAsl,986.o and
Rb2_18n3.oAS2,085,9. The crystals are air stable and insoluble in common solvents like
water and acetone. Both compounds were obtained in pure phase with yields greater than
80%.

CS2SnAs2Q9 (V): Red plates of CS28nA5289 were initially obtained from a reaction of
2/1/1/10 ratio Of C528/8n/AS2S3/S at 500°C. The product also contained yellow plates of a
ternary phase CS4ASleo (see Appendix). A pure synthesis for V was achieved by a direct
combination of C528, Sn, As and S in the ratio 1:1:2:8 at 550°C. The product is insoluble
in water, acetone and alcohol but soluble in DMF after exposure of more than a day.
Elemental analysis using EDS gave an average composition of CSz_1Sl’l1_oASL9Sg_5.
CS28nAS2Se9 was obtained as black plate-like crystals in pure form from a reaction of the
stoichiometric amounts of C52Se/Sn/AS/8e at 500°C. The product was stable in air and

water.

33

3.4 X-ray Diffraction Analysis

The homogeneity of compounds I-V were ascertained by comparing the experimental
powder diffraction patterns to their theoretical patterns calculated from their single
crystal structures.

The single crystal diffraction data on these compounds were collected on a SMART
platform diffractometer equipped with a 1K CCD area detector using graphite
monochromatized Mo K01 (A = 0.71073 A) radiation at room temperature. The crystals
were mounted on glass fiber tips. The data were acquired using the SMART software and
integrated using the SAINT program. An empirical absorption correction was done using
SADABS and all refinements were done using the SHELXTL16 package of
crystallographic programs.

The structural refinement of I, II, III and IV was straightforward with final R1/wR2
values of 0.0203/0.0429, 0.0314/0.0785, 0.0296/0.0729 and 0.0209/0.0462 respectively.
In the case of C52SnAS289 (V), systematic absences indicated the orthorhombic Pmc21
space group. After anisotropic refinement of all atom positions, there was one high-
intensity peak remaining in the electron density map. This peak (assigned as 813) was
observed between the disulfide ion in the [AsS(S2)2]3' fragment and was 1.04 A and 1.15
A away from atoms 811 and 812, respectively. A disordered model was considered and
structure refinement led to 80% occupancy for 811 and 812 and 40% occupancy of 813
' which resulted in a drop in the R values from R1 = 0.0499, wR2 = 0.1369 to R1 =
0.0399, wR2 = 0.1068. However, the structure refinement result considering the
disordered disulfide ions did not give any reasonable structural models. It is not clear

why the disulfide ion in one cluster anion shows an unusual disorder. A possible

34

supercell structure was sought, however zone photos with long exposure times (5 min)
gave no evidence for supercell reflections. The structure of C528nA528e9 was refined in
the space group P2,. NO disorder was observed in this compound. Crystallographic
details for I-V are listed in Table 1. Fractional atomic coordinates and isotropic
displacement parameters are given in Table 2. Anisotropic displacement parameters are

given in Table 3.

35

Table 1. Crystallographic data for NaSnAsS4, RbSnAsSs, Rb2SnA5286, C52SnAS289 and

CS2SnA528e9
empirical
formula

fw

space group
a, A

b, A

c, A

01, deg

B, deg

7. deg

V, A 3

Z

pcaica, g/cm3
11. m"

T, K

A, A

Total reflections

Total unique
R(int)
No. of

parameters

Goodnes of fit on

F2
Refinement
method

R1 a

wR2b

NaSnAsS4

344.84
Pnnm
11.859(4)
7.318(2)
7.508(2)
90

90

90
651.6(4)
4

3.515
10.174
293(2)
0.71073
6080
859
0.0389
39

1.030

0.0203
0.0429

RbSIlASS 5

439.38
P21/c
7.373(4)
15.694(8)
7.486(4)
90
102.61(14)
90
845.3(8)
4

3.453
13.766
293(2)
0.71073
4615
1956
0.0313

73

1.015

szSnA8286

631.83
P-3
6.7358(18)
6.7358(18)
7.454(3)
90

90

120
292.89(16)
2

3.582
17.051
293(2)
0.71073
2898

480
0.0292

19

1.12l

CSzSIlASzSg

822.89
Pmc21
7.386(3)
14.614(5)
14.417(5)
90

90

90
1556.2(9)
4

3.512
11.643
293(2)
0.71073
9626
3730
0.0635
158

1.062

Full-matrix least-squares on F2

0.0296
0.0729

0.0209
0.0462

0.0399
0.1068

“ RI = 2 “For Ian/21m. ” wR2 = {2 [W(Foz-Fc2)zl/EIW(F02)2]}”2

36

CSzSflASzSCg

1244.99
P2,
7.175(5)
17.555(12)
7.663(5)
90
115.857(1 1)
90
868.5(11)
2

4.761
11.643
293(2)
0.71073
6787

3670
0.1449
129

0.802

0.0739
0.1442

Table 2. Fractional Atomic Coordinates and Isotropic Displacement Parameters (A2 x

103) for NaSnAsS4, RbSnAsSs, Rb28nA5286, CS2SnAS289 and Cs28nAS28e9.

 

 

Atom x y z Ueqa
NaSnAsS4
Sn 0.5 0.5 0.2646(1) 16(1)
Na 0.1635(2) 0.6003(3) 0 32(1)
As 0.3433(1) 0.1945(1) 0 18(1)
5(1) 0.4414(1) 0.7221(1) 0.5 18(1)
5(2) 0.5330(1) 0.2601(2) 0 18(1)
5(3) 0.3028(1) 0.3802(1) 0.2328(1) 18(1)
RbSnAsSs
8n 0.2309(1) 0.5062(1) 0.4958(1) 20(1)
As 0.5203(1) 0.2095(1) 1.1383(1) 25(1)
Rb 0.0501(1) 0.3396(1) 0.9878(1) 40(1)
8(1) 0.0596(2) 0.5093(1) 0.7417(2) 23(1)
5(2) 0.4479(2) 0.4981(1) 0.2533(2) 22(1)
5(3) 0.2682(2) 0.3445(1) 0.4580(2) 28(1)
5(4) 0.2464(2) 0.6681(1) 0.4811(2) 28(1)
5(5) 0.5511(2) 0.1132(1) 1.3734(2) 30(1)
Rb28nAs286
8n 0 0 0 12(1)
As 0.3333 0.6667 0.068(1) 15(1)

37

0...... ._~ ,

Rb

5n(1)
Sn(2)
C5(1)
CS(2)
C5(3)
Cs(4)
As(1)
As(2)
As(3)
As(4)
5(1)
5(2)
5(3)
5(4)
5(5)
5(6)
8(7A)
5(8)
5(9)

8(10)

0.1945(2)

0.3333

0.5

0.5

0.5

0.5
0.5

0.5

0.5

0
0.2795(4)
0.2224(3)
0
0.5454(8)
0
0.2527(3)

-0.2446(3)

0.336(2)

0.6667

CSzSflASzSg

0.1783(1)
0.6543(1)
0.4917(1)
-0.0645(1)
0.1417(1)
0.2935(1)
0.4507(1)
0.2542(1)
0.1616(1)
0.2901(1)
0.2790(2)
0.0608(2)
0.4830(2)
0.2760(2)
0.6712(2)
0.1247(2)
0.1409(4)
0.8307(2)
0.6557(2)

0.5335(2)

0.2204(1)

-0.3927(1)

0.4739(1)
0.4425(1)
0.4793(1)
0.1801(1)
0.9851(1)
-0.3878(1)
0.2995(1)
0.1495(1)
0.7103(1)
0.2771(1)
0.6158(2)
0.3395(3)
0.4481(2)
0.3812(2)
0.5794(2)
0.0584(3)
0.2252(3)
0.4238(3)
0.3243(2)

0.2525(2)

38

22(1)

27(1)

27(1)
27(1)
45(1)
46(1)
50(1)
41(1)
36(1)
41(1)
51(1)
58(1)
34(1)
40(1)
30(1)
48(1)
39(1)
51(1)
49(2)
46(1)
42(1)

43(1)

5(11)
5(12)

8(13)

Cs(l)
Cs(2)
Sn

As(1)
As(2)
86(1)
5e(2)
56(3)
Se(4)
Se(5)
Se(6)
8e(7)
56(8)

86(9)

0.2428(6)
0.2523(6)

0.3046(11)

1.3085(6)
1.0817(6)
0.6805(6)
1.1824(10)
0.6419(9)
0.8129(9)
0.8021(9)
0.2953(9)
1.0360(10)
1.2869(10)
1.3746(10)
0.7591(13)
0.5688(9)

0.5917(10)

0.0819(3)
0.0867(3)

0.0878(6)

CSzSHASzSeg

0.4374(3)
0.2044(3)
0.3322(3)
0.6429(4)
0.5495(4)
0.3942(4)
0.4544(4)
0.3814(5)
0.2470(5)
0.5080(4)
0.6454(4)
0.5233(5)
0.2070(4)

0.2737(4)

0.5322(2)
0.6724(3)

0.5970(6)

0.2439(6)
0.5131(6)
0.1 170(6)

0.0570(9)

-0.01573(9)

0.2374(9)

0.7519(8)

0.2163(10)

0.0017(9)

0.6990(12)

0.4103(9)

0.1839(10)

0.0172(9)

0.5285(9)

62(1)
67(1)

59(2)

82(2)
79(1)
60(1)
68(2)
66(2)
73(2)
65(2)
79(2)
73(2)
85(2)
73(2)
88(2)
66(2)

72(2)

 

a Ueq is defined as one third of the trace of the orthogonalized Uij tensor.

39

Table 3. Anisotropic displacement parameters“ (A2 x 103) for NaSnAsS4, RbSnAsSs,

szSI‘lASzSe, CSzSflASzSg and CSzSflASzSCg.

 

 

U11 U22 U33 U23 U13 U12
NaSnAsS4
Sn(l) 16(1) 19(1) 11(1) 0 0 -2(1)
Na(1) 39(1) 31(1) 25(1) 0 0 12(1)
As(1) 22(1) 16(1) 15(1) 0 0 -2(1)
5(1) 21(1) 17(1) 14(1) 0 0 2(1)
5(2) 20(1) 18(1) 17(1) 0 0 2(1)
5(3) 17(1) 22(1) 15(1) -2 1 -2(1)
RbSnAsSs
5n(1) 17(1) 20(1) 23(1) -1(1) 3(1) 0(1)
As(1) 27(1) 17(1) 29(1) -2(1) 1(1) 0(1)
Rb(1) 56(1) 25(1) 37(1) 1(1) 4(1) 9(1)
5(1) 22(1) 28(1) 19(1) -1(1) 2(1) 0(1)
5(2) 23(1) 20(1) 21(1) -3(1) 3(1) 0(1)
5(3) 26(1) 19(1) 34(1) —2(1) -4(1) -1(1)
5(4) 27(1) 20(1) 38(1) -6(1) 8(1) 1(1)
5(5) 41(1) 26(1) 21(1) -3(1) 3(1) 0(1)
Rb28nA586
5n(1) 9(1) 9(1) 16(1) 0 0 5(1)
As(1) 15(1) 15(1) 14(1) 0 0 7(1)

S(1)
Rb(1)

5n(1)
Sn(2)
Cs(l)
Cs(2)
Cs(3)
Cs(4)
As(1)
As(2)
As(3)
As(4)
5(1)
5(2)
5(3)
S(4)
5(5)
5(6)
8(7A)
5(8)
5(9)

5(10)

30(1)

31(1)

27(1)
28(1)
35(1)
49(1)
60(1)
35(1)
42(1)
54(1)

66(1)

1 12(2)

46(2)
51(2)
36(1)
51(1)
38(1)
72(2)
77(6)
63(2)
40(1)

41(1)

11(1)

31(1)

22(1)
23(1)
33(1)
40(1)
48(1)
44(1)
28(1)
33(1)
46(1)
33(1)
27(1)
24(1)
20(1)
34(1)
38(1)
22(2)
39(2)
23(2)
43(1)

39(1)

19(1)

19(1)

CSzSflASzSg

31(1)
31(1)
68(1)
48(1)
42(1)
44(1)
38(1)
35(1)
41(1)
30(1)
29(1)
45(2)
35(1)
58(1)
40(1)
59(2)
32(2)
52(2)
43(1)

50(1)

41

-2

0

-1(1)
2(1)
-2(1)
-6(1)
-10(1)
-1(1)
-3(1)
7(1)
16(1)
2(1)
-1(1)
-9(1)
2(1)
-3(1)
-2(1)
6(2)
-10(2)
7(1)
0(1)
-3(1)

6(1)
15(1)

5(11) 69(2) 75(3) 42(2) -1(2) 3 -42
5(12) 76(3) 81(3) 45(2) 22(2) 0 -34
C528nA52Se9
Cs(l) 65(2) 96(4) 77(3) -4(3) 21(2) 8(3)
Cs(2) 63(2) 94(4) 69(3) 3(3) 20(2) -6(2)
Sn 51(2) 63(3) 58(2) 1(2) 17(2) 1(2)
As(1) 70(4) 64(5) 65(4) -12(4) 26(3) 0(4)
As(2) 69(4) 65(5) 62(4) 0(3) 25(3) 4(3)
56(1) 63(4) 91(6) 55(4) 6(4) 16(3) 9(4)
8e(2) 60(3) 72(6) 68(4) 0(4) 33(3) -1(4)
86(3) 45(4) 100(7) 80(5) 6(4) 16(3) 0(4)
86(4) 53(4) 91(6) 66(4) -4(4) 17(3) 5(3)
36(5) 58(4) 79(6) 112(6) 9(5) 31(4) 0(4)
86(6) 74(4) 81(6) 63(4) 9(4) 30(3) -4(4)
Se(7) 121(6) 72(6) 66(4) 3(4) 35(4) -7(4)
8e(8) 76(4) 59(5) 70(4) 5(4) 38(4) -7(4)
Se(9) 82(5) 70(5) 63(4) -5(4) 31(4) 9(4)

* The anisotropic displacement factor exponent takes the form:

~27t2[h2a*2UH + k2b*2U22 + lzc*2U33 + 2hka*b*U12 + 2k1b*c*U23 + 2h1a*c*U13]

42

C. Results and Discussion

C.l Synthesis

The syntheses and crystallization of I-V were carried out in A2AsxSy fluxes that were
generated by an in situ reaction of A28, AS283 and 8. These fluxes act as reaction media
allowing for easy diffusion of reactants and also as oxidizing agents. They are termed as
reactive fluxes because they are an essential part of the reaction outcome. The different
[Asx8y]"' anions that are generated in these fluxes bind to the metal based on its preferred
coordination geometry and oxidation charge to give structurally variant compounds.
NaSnA584 was synthesized from a ratio of 1:122:10 ofNa2828n2AS:8 in almost pure form.
Increasing the amount of Na2S, thereby increasing the flux basicity leads to the formation
of Na8n82 and 8n82 exclusively. However reducing the amount of sulfur from 10
equivalents to 5 equivalents, but keeping the ratios of the metals intact gives a
stoichiometric mixture of NaSnA584 (68% based on 8n) and NaA582. Since both the
phases have a needle morphology and are orange in color, it is difficult to separate them.
The use of A5283 instead of As leads to the formation of ternary NaASS2 and NaSnS2 but
no quaternary phases were found. The one-dimensional ASnA585 (A = K, Rb) phase,
which features the B-[ASS4]3' ligand, forms from a flux ratio 1:121:10 of A28:8n:A5283:8.
Increasing the flux basicity leads to the formation of A2SnA5286 and A3A584 in the case
of K. In the case of Rb, the addition of Rb28 usually led to the formation of glasses and
Rb3A584.

Using C528, we obtained the molecular CS2SnAS289, consisting of B-[ASS4]3' and [A585]3'
ligands, from a CS4A82315 flux. This flux also gave a ternary phase, Cs4A52810 (Appendix,

Page 270). Any change in the flux basicity led to the formation of glassy products. A pure

43

 

 

quantitative synthesis of this compound was achieved by a direct combination of the
reactants. We attempted to use a mixed rubidium-cesium thioarsenate flux with the hope
that we might be able to obtain the clusters that are connected together to form chains.
But these reactions gave red glasses as products. Attempts to prepare CsSnAsSs and

Cs28nA5285 also failed, giving glasses as products.

C.2 Structure description of NaSnAsS4 (I)

NaSnAsS4 crystallizes in the orthorhombic space group Pnnm, Figure l. The structure of
I is made up of [Sn(AsS3)]2 dimers which are linked together by bidentate 8 atoms to
form chains running along the c-axis. These chains are separated by charge balancing Na+
ions. The [Sn(AsS3)]2 core is formed by the coordination of Sn with the pyramidal
[A583]3' ion. Each A583 ligand utilizes all three of its sulfiIr atoms to bind to two 8n
atoms. One sulfur atom forms a bridge between the two 8n atoms within the dimeric unit,
while the other two sulfur atoms each bind to one tin to complete the core. These cores
are then sewed together by two 112-8 atoms to form the chain. 8n is in a distorted
octahedral Site with 8n - 8 bond distances varying from 2.4997(9) to 2.6802(10) A. S-Sn-
8 bond angles range from 80.6(3)° to 172.18(3)°. The 8n - Sn distance within the core is
3.973 A. The Na+ cation is surrounded by six sulfur atoms with Na—S bond lengths
between 2.8948(18) to 3.034(3) A. The average A5-8 bond distance is normal at
2.2772(11) A. Tables 4 and 5 give selected bond lengths and bond angles for compounds
I, III, IV and V.

The structure of NaSnAsS4 is reminiscent of the one dimensional K3Cr2(P84)3l7 that

features [Cr(PS4)]2 centers that are stitched together by [P84]3' tetrahedra. A similar

comparison can be made with the chains of KTiP8e5.'8 This compound contains
[Ti(PSe4)]2 units that are connected by uz-Se atoms on either side to form a chain. Ti8e6
octahedra share edges with two [P8e4]3' tetrahedra, each employing 3 8e atoms to bridge

the two Ti atoms while one 8e remains non-bonding.

C.3 Structure description of RbSnAsSs (III)

The structures of II and III are similar; therefore, we will discuss the structural details of
111 here. The structure of III was solved in the monoclinic space group P21/c. This
structure is one-dimensional and similar to the structure of I. It is composed of chains,
running down the c-axis, consisting of centrosymmetric [Sn(AsS2(S2)]2 dimeric cores
linked together by two 112- bridging 82' ions, Figure 2. The major difference between the
structIIres of I and III is the type of thioarsenate ligand. In the case of III, this ligand is a
pyramidal B-[ASS4]3' ligand which is a derivative of the [A583]3'ligand in I. It is obtained
by substituting one terminal 8 atom in [A583] by a disulfide arm. In these cores, two
[ASS2(S2)]3' ligands bridge two octahedral tin atoms employing three sulfur atoms each,
of which one of the sulfur atoms is the terminal sulfur atom of the disulfide unit.

The adjacent chains are separated by hepta-coordinated Rb+ ions with Rb-S distances
varying from 3.2468(18) to 3.710(2) A. 8n is coordinated by six 8 atoms at distances of
2.4503(9) to 2.6831(17) A. (Table 3) The 8-8 distance is normal at 2.0415(19) A. Sn4+ is
distorted with S-Sn-S bond angles ranging from 84.65° to 174.18°. The Sn-Sn distances
within the dimeric unit and between the dimeric units are 3.959 A and 3.425 A
respectively; Table 4. As-S distances range from 2.2024(17) A to 2.2924(16) A with S-

As-S angles between 98.36(6)° and 105.45(7)°.

45

 

 

 

 

 

Figure l. a) View of the unit cell of NaSnAsS4 down c-axis. b) Single chain of
NaSnAsS4.

46

 

b)

 

Figure 2. a) Unit cell of RbSnAsSs showing chains running along the a-axis. b)
Coordination environment of the Rb+ cation.

47

KSnAsSs (I I) crystallizes in the orthorhombic space group Pbam. The lowering of
symmetry going to Rb can be attributed to the bigger size of Rb, which does not allow the
chains to pack as efficiently as in the potassium analog. This is also observed in the
cation coordination environment. The K ion sits in a regular six-coordinate trigonal
prismatic geometry whereas the Rb sits in an irregular seven-coordinate site, Figure 2.

NaSnAsS4 and RbSnAsSs have very similar chain structures. The major difference comes
from the type of the thioarsenate ligand present in these two compounds. In the case of
RbSnAsSs, there is more 8 present in the flux as compared to NaSnA584. Therefore the
A5833' anion can take another 8 atom to form A5843' thereby releasing the strain on the

8n4+ ion upon coordination.

C.4 Structure description of Rb28nA5285 (IV): Rb28nA5286 is a layered material that
crystallizes in the trigonal space group P-3. The layers are made up of edge sharing Sn86
octahedra and [A583] pyramids. This compound is isostructural to the mineral emigillite,
T128nA5286.19 It was synthesized from a direct combination of Rb28/Sn/A5/S mixture in
the ratio 1/1/2/5. It could not be made from any other ratio Of the starting materials.
Attempts to obtain the compound by using A5283 instead of As ended up yielding glassy
products. Figure 3a shows the unit cell of Rb2SnA5286 down the a-axis. The anionic
[Sn(AsS3)2]n2"' lie perpendicular to the c-axis. Two rows of Rb+ cations sit between
adjacent anionic sheets. The structure belongs to the Ti82 structure type with 8n
occupying the position of Ti and A583 taking up the 8 position. Octahedral Sn86 and
pyramidal [A583] units alternate forming eight membered -8-Sn—S-As-S-8n-8-As- rings

that have a chair like conformation. These rings share As-S-Sn edges with each other to

48

form the condensed rings running along the ab-plane forming the two—dimensional
network. Each [A583]3' unit binds to 3 8n atoms, while each 8n is bonded to 6 [A583]3'
anions, Figure 3b. The [A583]3' pyramids lie in such a way that the lone pair on the As
points towards the Rb+ ions between the layers, Figure 3c.

Sn—S bond distances are equal at 2.564(10) A. As-S bond distance is 2.2458(10) A. The
closest interlayer distance is 4.4609 A and the closest Sn-Sn distance within the layer and
between the layers is 6.736 A and 7.454 A. S-Sn-S bond angles are 83.33(3)° and
96.67(3)°. 8-As—8 angles are equal at 96.66(4)°. (Tables 3 and 4) The layers are separated
by ten-coordinate Rb+ ions with Rb-S bond lengths from 3.43 80(13) A to 3.720(14) A.
The Rb sits between a hexagonal plane created by 6 8 atoms and a trigonal plane created
by 38 atoms. In addition, Rb+ Shows a significant bonding interaction at a distance of
3.4385 A with the lone pair on As. (Figure 3c) The structure has also been encountered in
A2Mn(Te83)220 (A = Rb, Cs). In these compounds the Sn is substituted by Mn, which is

octahedrally bound by pyramidal [Te83]2' units.

C.5 Structure description of C528nA5289 (V): The structure of V was solved in the
noncentrosymmetric space group Pmc21. The structure is built up of molecular complex
anions {Sn[AsS2(82)][A58(S2)2])2' separated by Cs+ cations. Figure 4 shows the unit cell
and a single cluster anion. The 8n4+ ion is in a distorted octahedral environment
coordinated by two pyramidal-shaped tridentate ligands, [ASS2(82)]3' and [A58(82)2]3‘
forming a cage-like structure. The Sn-S bond lengths range from 2.510(4) A to 2.589(5)

A for 8n] and 2.504(4) A to 2.592(5) A for 8n2.

49

Table 4. Selected bond distances for NaSnASS4, Rb8nAsSs, Rb28nA5286 and C528nA5289

Sn(1)- 5(1)
5n(1) - 5(3)
5n(1) - 5(2)

Na(1) - 5(3)

Sn(l) - 5(1)
Sn(l) - 5(1)
5n(1) - 5(4)
Sn(1)- 5(3)
Sn(1)- 5(2)
Sn(1)- 5(2)
As(1) - 5(4)
As(1) - 5(3)

3(2) - S(5)

Sn(1)- 5(1)
As(1) - 5(1)

Rb(1)- 5(1)

NaSnAsS4
2 x 2.4997(9)
2 x 2.5088(10)
2 x 2.6802(10)
4 x 2.8949(19)
RbSnAsSs
2.4503(15)
2.4790(16)
2.5465(19)
2.5754(18)
2.6714(16)
2.6831(17)
2.2024(17)
2.2130(16)
2.0415( 19)
Rb28nAS286
6 x 2.5640(10)
3 x 2.2458(10)
3 x 3.4380(13)

CSzSflASzSg

8n(1)- 5(11) 2 x 2.510(3)

As(1) - 5(3)
As(1) - 5(2)
Na(1) - 5(1)

Na(1) - 5(1)

As(1) - 5(5)
Rb(1) - 5(1)
Rb(1) - 5(1)
Rb(1) - 5(3)
Rb(1) - 5(4)
Rb(1) - 5(3)
Rb(1) - 5(5)

Rb(1) - 5(1)

Rb(1) - 5(1)

Rb(1) - 5(1)

Rb(1) - As(1)

Cs(1)- 5(5)

50

2 x 2.2655(10)
2.3006(14)
2.937(2)

3.034(3)

2.2924(16)
3.2468(18)
3.3308(17)
3.338(2)
3.5071(19)
3.537(18)
3.666(3)

3.710(2)

3 x 3.4737(14)
3 x 3.7720(14)

3.4345(15)

2 x 3.628(3)

Sn(1)- 5(1)
Sn(l) - 5(4)

5n(1) - 5(2)

5n(1) - 5(13)

Sn(2) - 5(3)
Sn(2) - 5(9)
Sn(2) — 5(5)
Sn(2) - 5(8)

As(1) - 5(3)

As(1) - 8(10)

As(2) - 5(5)
As(2) - 5(6)

As(3) - 5(1)

As(3) - 5(12)

As(3) - 5(13)

As(4) - 5(4)
As(4) - 5(7)
5(2) - 5(7)

5(6) - 8(8)

Cs(3) - As(3)

Cs(4) - 8(12)

Cs(4) - 5(1)

Cs(4) - 8(11)

2.520(3)

2 x 2.545(2)
2.589(4)

2 x 2.641(8)
2.504(3)

2 x 2.528(3)
2 x 2.579(3)
2.592(4)
2.194(4)

2 x 2.278(3)
2 x 2.216(3)
2.304(4)
2.190(3)

2 x 2.201(4)
2 x 2.432(8)
2 x 2.224(3)
2.328(5)
2.049(7)
2.046(6)
3.972(2)

2 x 3.655(5)
2 x 3.6995(13)

2 x 3.756(5)

Cs(1) - 5(1)
Cs(1) - 5(3)
Cs(1) — 5(9)

Cs(1) - 5(4)

Cs(1) - 5(10)

3.679(3)
2 x 3.7225(13)
2 x 3.752(3)
2 x 3.820(3)

2 x 3.825(3)

Cs(1) - As(4) 4.145(2)

Cs(2) - 5(11)
Cs(2) - 5(12)

Cs(2) - As(2)

Cs(2) - 5(2)
Cs(2) - 5(8)
Cs(2) - 5(7)
Cs(2) - 5(4)
Cs(3) - 5(7)
Cs(3) - 5(2)
Cs(3) - 5(5)

Cs(3) - 5(8)

Cs(3) - 8(11)

Cs(3) - 5(6)
Cs(4) - 5(3)

Cs(4)-8(9)

2 x 3.557(4)
2 x 3.589(4)
3.7038(18)

2 x 3.7043(13)
2 3.732(4)

2 x 3.792(6)

2 x 3.820(3)

2 x 3.478(5)
3.628(4)

2 x 3.678(3)

2 x 3.8185(16)
2 x 3.841(5)

2 x 3.8492(17)
3.643(3)

2 x 3.658(3)

Cs(4) - 5(10) 2 x 3.707(3)

Cs(4) - 5(13) 3.762(8)

51

 

 

Table 5. Selected bond angles for NaSnA584, RbSnAsSs, Rb28nA5286 and C528nA5289

NaSnA584

5(1)- Sn(l)- 5(1) 9001(4) 5(1)- Sn(1)- 5(3) 2x95.71(3)

5(1) - Sn(l) - 5(3) 2 x 9202(3) 5(3) - Sn(l) - 5(3) 169.07(4)

5(1) - Sn(1)- 5(2) 2 x 9330(3) 5(1) - 5n(1) - 5(2) 2 x 172.18(3)

5(3) - 8n(1)- 5(2) 2 x 8060(3) 5(3) - Sn(1)- 5(2) 2 x 9126(3)

5(2) - 8n(1)- 5(2) 8432(4) 5(3) - As(1) - 5(3) 100.97(5)

5(3) - As(1) - 5(2) 9472(3) 5(3) - As(1) - 5(2) 9472(3)
RbSnAsS5

5(1) - Sn(1)- 5(1) 9196(6) 5(1) - Sn(l) - 5(4) 9278(4)

5(1) - 5n(1) - 5(4) 9612(4) 5(1) - Sn(1)- 5(3) 100.73(4)

5(1) - 5n(1) - 5(3) 8546(4) 5(1) - Sn(l) - 5(2) 9343(6)

5(4) - 5n(1) - 5(3) 166.35(5) 5(1) - 5n(1) - 5(2) 174.18(4)

5(4) - 5n(1) - 5(2) 8882(4) 5(3) - Sn(l) - 5(2) 7754(4)

5(1) - 5n(1) - 5(2) 8973(6) 5(1) — Sn(1)- 5(2) 172.76(4)

5(4) - 8n(1)- 5(2) 9083(4) 5(3) — Sn(1)- 5(2) 8731(4)

5(2) - 5n(1) - 5(2) 8465(6) 5(4) - As(1) - 5(3) 105.45(7)

5(4) - As(1) - 5(5) 9932(6) 5(3) - As(1) - 5(5) 98.36(6)
Rb28nA5286

5(1)- 8n(1)-8(1) 6x83.33(3) 8(1)-Sn(1)- 5(1) 3 x 180.0

5(1)- Sn(1)- 5(1) 6x96.67(3) 8(1)-As(1)- 5(1) 3 x96.66(4)

52

5(11) - Sn(l) - 5(11') 98.4(2)

5(4) - 8n(1)- 5(4')
5(1) - 5n(1) - 5(2)
5(3) - Sn(2) - 5(9)
5(5) - Sn(2) - 5(5')
5(3) - Sn(2) - 5(8)
5(3) - As(1) - 500’)
5(5) - As(2) - 5(6)
5(1) — As(3) - 5(12)

8(4) - As(4) - 8(7)

79.56(15)
174.20(12)
91.70(8)
79.14(12)
175.87(12)
100.13(9)
98.28(10)
103.57(13)

103.64(16)

C528nA5289
5(1) - 5n(1) - 5(11)
5(2) - Sn(l) - 5(4)
5(11) - Sn(l) - 5(4)
5(9) - Sn(2) - 5(9')
5(5) - Sn(2) - 5(8)

5(5) - Sn(2) - 5(9)

93.2(10)
8879(9)
167.17(12)
9520(13)
8911(9)

170.19(9)

5(10) - As(1) - 5(10') 104.95(15)

5(5) - As(2) - 5(5')

95.72(13)

5(12) - As(3) - 5(12') 112.4(3)

8(4) - As(4) - 8(4')

53

9414(14)

There are four crystallographically unique Cs+ cations surrounded by eleven 8 atoms in
the range of 3.628(3) A -3.825(3) A for C51, 3.557(4) A - 3.820(3) A for CS2, 3.478(5) A
-3.972(2) A for C53, and 3.643(3) A -3.756(5) A for CS4. Weak interactions, Similar to
the one observed in IV between Rb)r and A5, are observed for C51, C52 and CS3 with
A54, A52 and A53, respectively at distances of 4.145 A, 3.703 A and 3.976 A. The
average 8-8 distance is normal at 2.0475 A. The structure of the double cage—like
[8nA5289]2' cluster anion is reminiscent of those in the centrosymmetric compounds [(n-

Bu)4N]2[MAS2Se10]21 (M=Mo, W), which also have two [ASSe(8e2)2]3' ligands.

The structure of C52SnA528e9 is Similar to C528nA5289 and consists Of the same structural
motif, {8n[A58e2(8e2)][AsSe(8e2)2]2' anions. This compound crystallizes in the
monoclinic space group P2).

An important feature Of the flux method is the freedom it allows the metal to choose its
own ligands for lattice construction. In this context, an issue that deserves comment is the
composition of the cluster anion, [8nA5289]2', which contains both [A585]3' and [A584]3'
instead of only one type of ligand. A speculative explanation of this behavior can be
based on electronic and steric considerations of the ligands involved. [A585]3' being more
electron donating than [A584]3', because of the additional chalcogen atom, coupled with
its ability to form a larger cage, might be preferred by the electrophilic 8n4+ ion.
Coordination to this ligand reduces the electron density requirement of the central metal

atom and allows for the relatively less electron-rich and less bulky [A584]3’ to bind.

54

 

 

 

 

Figure 3. a) Layers of Rb28nA5286 parallel to the ab plane and stacked perpendicular to
the c- axis. b) A single layer showing octahedral 8n bound by pyramidal A583 ligands. c)
Coordination environment of Rb

55

 

Figure 4. a) The unit cell of C52SnA5289 Showing the two cyrstallographically unique
clusters. b) The individual clusters with one showing a disorder in the disulfide linkage.

56

 

 

C.6 Thermal Analysis

Differential thermal analyses (DTA) were performed on pure samples of all the
compounds to ascertain their thermal behavior. In each case, the compound was checked
for decomposition at the end of two heating cycles by taking its powder X-ray diffraction
pattern. NaSnA584 (I) melts at 488°C and on cooling shows a recrystallization peak at
375°C, Figure 5a. The powder pattern of the compound taken after the DTA indicated
that the compound had decomposed to NaA582 and 8n82. RbSnAsSs (I I) Shows an
endothermic (melting) peak at 380°C. On cooling, however, no recrystallization is
observed implying glass formation. When this glass is heated again, an exothermic peak
is observed at 320°C which is followed by melting at 372°C, Figure 5b. The powder
pattern of the product after cooling showed that the compound had decomposed to a
glassy matrix along with 8n82. The DTA of Rb28nA5286 (IV) shows a melting point of
482°C and recrystallization at 365°C. As seen in Figure 5c, the recrystallization is partial.
A slower heating rate allowed complete recrystallization of the compound. A powder
pattern taken after the DTA matched the one before, indicating congruent melting. The
DTA of V, Figure 5d, showed that it melted at 351°C but no recrystallization was
observed on cooling implying the formation of a glassy phase. The glass crystallizes on
heating at 268°C. Comparison of the powder patterns of the pristine compound, the
glassy phase and recrystallized phase indicate that the glass-crystal transformation is

reversible, Figure 7a.

57

 

 

exo ——>
exo ——>

0

11V

 

6)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

b)
l I l l l l l L l l
100 200 300 400 500 600 700 100 200 300 400 500 600 700
Temperature, °C Temperature, 0C
I ’
5 268
8 if
> i
:5.
c) d)
1 L l L l 1 1 1 1
100 200 300 400 500 600 700 100 200 300 400 500 600 700
Temperature, 0C Temperature, 0C

Figure 5. Differential Thermal Analysis of a) NaSnAsS4 b) RbSnAsSs c) Rb2SnAS286 d)
CSzSflASzSg

58

 

 

   
 

 

 

 

 

 

 
 

 

 

 

 

 

 

 

 

 

 

a) b)
3 S
.S a
E" ‘5
a 4
Eg=2.17 eV Eg=2.07 eV
0 2 3 4 0 2' 3 4
Energy, eV Energy, eV
c) d)
{3 0?
E E
E .‘2‘
{3, '8
Eg = 1.68 eV
1 2 3 4
Energy, eV Energy, eV

 

 

Figure 6. Optical absorption spectra of a) NaSnAsS4 b) RbSnAsSs c) Rb28nA5286 and d)
C528nA5289. Energy gaps are caculated as 2.17 eV, 2.07 eV, 1.68 eV and 1.98 eV

respectively.

59

 

 

 

 

pristine

recrystallized

 

 

Intensity (arbitrary units)

 

 

 

 

10 20 30 40 50 60

 

 

 

 

 

b)
a
E
r:
.2
E“
.8
:6
E8 = 1.98 eV
0 1 2 3 4 5
Energy, eV

Figure 7. a) Comparison of the powder patterns of pristine, glassy and re-crystallized
C528nA5289 shows that the glass-crystal transition is reversible. b) Optical spectrum of
the glassy Cs2SnA5289 Shows an absorption onset at 1.98 eV.

60

 

 

 

 

   

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

S S
9 3‘3
E E
F i
1.. I"
287
a) b)

l l l l l l l l l l I
150 200 250 300 350 400 450 500 150 200 250 300 350 400 450 500

wavenumbers (cm'l) wavenumbers (cm")
8 411 3
5 .5:
s, a
r:
a E

263

279
350
c) d)
l I l l l L l l l l l l

150 200 250 300 350 400 450 500 150 200 250 300 350 400 450 500

wavenumbers (cm'l) wavenumbers (0111.1)

Figure 8. Far Infrared spectra of a) NaSnA584 b) RbSnAsSs c) Rb28nA5286 and d)
CSzSflASzSg

61

 

 

 

324

a) 253 283 b)

Intensity
Intensity

   

 

 

 

 

L l l l J l l I l l M l

150 200 250 300 350 400 450 500 150 200 250 300 350 400 450 500
wavenumbers (cm'l)

 

 

-1
wavenumbers (cm )

 

 

342 c) 293 d)

 

 

 

 

 

 

 

 

 

 

.E‘
g 324 a
c: 8
8 c:
G u—n
"‘ 386 99
407 478
l 1 1 l J l J l l 1
150 200 250 300 350 400 450 500 150 200 250 300 350 400 450 500

-1 wavenumbers (cm’l)
wavenumbers (cm )

Figure 9. Raman Spectra of a) NaSnAsS4 b) RbSnAsSs c) Rb28nAs286 and d)
CSzSIlASzSg.

62

C.7 Optical Spectroscopy

The energy gaps in these compounds were estimated by recording their diffuse
reflectance spectra. As seen in Figure6, these compounds are semiconductors with band
gaps ranging from 1.68eV for szSIlASzS6 to 2.17eV for NaSnAsS4. For C52SnA5289,
this energy gap arises from localized levels and therefore can be considered as a HOMO-
LUMO transition. The glassy form of V also shows an absorption onset at 1.98 eV,
Figure 7b. The absence of the typical red shift in the absorption edge, as is typically
observed in the glassy forms of compounds with extended solid state structures,22 also
supports the notion that the electronic properties of V are intracluster in nature. In
extended systems with a well-developed band structure, the crystal to glass conversion
produces a red-shift because of the large number of defect-induced midgap states
generated in the glass. The discrete molecular nature of C528nA5289 does not generate
such states and the glass structure probably represents a disordered arrangement of
[SnA5289]2’ anions and Cs+ cations. Table 6 gives the band gaps for all these compounds.

Table 7 gives the peaks observed in the IR and Raman spectra of compounds I, III, IV
and V. The IR spectra for the above compounds are shown in Figure 8. Based on
previous reports,23 the vibrations between 420 cm'1 and 300 cm’1 can be assigned to As-S
stretching vibrations. Below 300 cm'l, the peaks can be attributed to either Sn-S
stretching or As-S bending modes. The Raman spectra are shown in Figure 9.
Assignments similar to the IR spectra can be made here. RbSnAsSs and C528nA5289
Show peaks at 494 and 478, respectively. These peaks are diagnostic of 8-8 stretching

vibrations.24

63

D. Conclusion

The synthesis, structural characterization and optical properties of six new quaternary
alkali metal tin thioarsenates have been presented. The dimensionality of these
compounds ranges from molecules to layers. This is the first time that the ligands,
[A584]3' and [A583]3' have been observed in the flux methodology. NaSnAsS4, K8nA585
and RbSnAsSs are one-dimensional materials that might give anionic chains when
exfoliated in polar solvents. C528nA5289 crystallizes in the non-centrosymmetric space
group Pmc21 and needs to be investigated for its non-linear Optical behavior. It also
displays a reversible glass to crystal transition, a requisite condition for energy storage
systems. The compounds presented here have no known thiophosphate analogs indicating

that these fluxes have a promising potential that needs to be exploited.

64

Table 6. Band gaps for I-V
Compound

NaSnAsS4

KSnAsSs

RbSnAsS3

K28nA5286

Rb2SnA5286

CSzSflASzSo

Band gap (eV)

2.17

2.11

2.07

1.89

1.68

1.98

Table 7. Far IR and Raman bands of I, III, IV and V

Compound

NaSnAsS4

RbSnAsS 5

szSI‘lASzS6

CSzSflASzSg

Far-IR(cm'1)

415, 365, 342, 318, 300,
279, 254, 244, 236, 203,
181

458, 418, 382, 371, 351,
326, 287, 254, 247, 228,
208,203,176
411,350,263
458, 391, 376, 360, 328,
313, 279, 228, 203, 192,

186

65

Raman (cm!)
157, 174, 201, 246, 275,

292, 324, 364

165, 183, 253, 283, 317,

328, 336, 382, 494

324,342,407
162, 173, 206, 222, 263,
284, 298, 313, 386, 399,

478

References

1. a) Kanatzidis, M. G. Curr. Opin. Solid State Mater. Sci. 1997, 2, 139. b) McCarthy,
T. J.; Kanatzidis, M. G. Inorg. Chem. 1995, 34, 1257. c) Gauthier, G.; Jobic, 8.; Brec,
R.; Rouxel, J. Inorg. Chem. 1998, 37 (10), 2332. (1) Chen, J. H.; Dorhout, P. K.;
Ostenson, J. E. Inorg. Chem. 1996, 35, 5627.

2. a) McCarthy, T. J.; Hogan, T.; Kannewurf, C. R.; Kanatzidis, M. G. Chem. Mater.
1994, 6, 1072. b) Hanko, J. A.; Sayettat, J.; Jobic, 8.; Brec, R.; Kanatzidis, M. G.
Chem. Mater. 1998, 10, 3040.

3. a) Chondroudis, K.; McCarthy, T. J.; Kanatzidis, M. G. Inorg. Chem. 1996, 35, 840.
b) Evenson, C. R.; Dorhout, P. K. Inorg. Chem. 2001, 40 (12), 2884.

4. a) Wachhold, M.; Kanatzidis, M. G. Inorg. Chem. 1999, 38 (17), 3863. b) Gostojic,
M.; Edenharter, A.; Nowacki, W.; Engel, P. Z. Kristallogr. 1982, 158, 43.

5. a) Jerome, J. E.; Wood, P. T.; Pennington, W. T.; Kolis, J. W. Inorg. Chem. 1994, 33,
1733. b) Chou, J.-H.; Kanatzidis, M. G. J. Solid State Chem. 1996, 123, 115.

6. a) Aitken J. A.; Kanatzidis, M. G. Inorg. Chem. 2001, 40, 2938. b) Chondroudis, K.;
McCarthy, T.J.; Kanatzidis, M. G. Inorg. Chem.1996, 35, 840. c) Loken, 8.; Tremel,
W. Eur. J. Inorg. Chem. 1998, 35, 283.

7. a) Wachhold, M.; Sheldrick, W. 8. Z. Naturforsch., B 1997, 52, 169. b) Wachhold,
M.; Sheldrick, W. 8. Z. Naturforsch., B 1996, 51, 32. c) Chou, J.-H.; Hanko, J. A.;
Kanatzidis, M. G. Inorg. Chem. 1997, 36, 4. d) Wachhold, M.; Kanatzidis, M. G.
Inorg. Chem. 1999, 38, 4178. e) Hanko, J. A.; Chou, J.-H.; Kanatzidis, M. G. Inorg.
Chem. 1998, 3 7, 1670. D Chou, J.-H.; Kanatzidis, M. G. Inorg. Chem. 1994, 33,
1001. g) Chou, J.-H.; Kanatzidis, M. G. Inorg. Chem. 1994, 33, 5372.

8. Marking, G. A.; Evain, M.; Petricek, V.; Kanatzidis, M. G. J. Solid State Chem. 1998,
141, 17.

9. Liao, J. -H.; Varotsis, C.; Kanatzidis, M. G. Inorg. Chem. 1993, 32, 2453.

66

 

 

 

10. Chondroudis, K.; Kanatzidis, M. G. J. Solid State Chem. 1998, 136, 79.

ll. Chondroudis, K.; Kanatzidis, M. G. Inorg. Chem. 1998, 37, 2848.

12. Chondroudis, K.; Kanatzidis, M. G. J. Chem. Soc, Chem. Commun. 1996, 1371.

13. Derstroff, V.; Tremel, W.; Regelsky, G.; Eckert, H. Solid State Sci. 2002, 4, 731.

l4.Feher, F. In Handbuch der Praparativen Anorganischen Chemie; Brauer 0., Ed.;
Ferdinand Enke: Stuttgart, Germany, 1954; vol. 1, pp 280-281.

15.a) Wendlandt, W. W.; Hecht, H. G. Reflectance Spectroscopy; Interscience: New
York, 1966. b) Kotum, G. Reflectance Spectroscopy; Springer-Verlag, New York,
1969. c) Tandon, 8. P.; Gupta, J. P. Phys. Status Solidi 1970, 38, 363.

16.SMART, SAINT, SHELXT L: Data Collection and Processing Software for the
SMART-CCD system; Siemens Analytical X-ray Instruments Inc., 1997.

17. Coste, 8.; Kopnin, E.; Evain, M; Jobic, 8.; Payen, C.; Brec, R. J. Solid State Chem.
2001, 162, 195.

18. Chondroudis, K.; Kanatzidis, M. G. Inorg. Chem. 1995, 34, 5401.

19.Graeser, 8.; Wulf, R.; Edenharter, A. Schweizerische Mineralog Petrogr. Mitteil.
1992, 72, 293.

20. Zhang, X.; Kanatzidis, M. G. Inorg. Chem. 1994, 33, 1238.

21. O'Neal, 8. C.; Pennington, W.T.; Kolis, J. W. Inorg. Chem. 1992, 31, 888.

22. a) Dhingra, 8.; Kanatzidis, M. G. Science 1992, 258, 1769. b) Marking, G. A.; Hanko,
J. A.; Kanatzidis, M. G. Chem. Mater. 1998, 10, 1191.

67

23. a) Bastow, T. J.; Whitfield, H. J. J. Chem. Soc., Dalton Trans. 1973, 1739. b) Billes,
F.; Mitsa, V.; Mateleshko, N.; Fejsa, I. J. Mo]. Struct. 1999, 513, 109. c) Nakamoto,
K. Infrared and Raman Spectra of Inorganic and Coordination Compounds, 5th ed.;
John Wiley and Sons: New York, 1997. d) Siebert, H. Z. Anorg. Allg. Chem. 1954,
225, 275.

24. a) Jaroudi, O. E.; Picquenard, E.; Demortier, A.; Lelieur, J. P.; Corset. J. Inorg. Chem.
1999, 38, 2394. b) Jaroudi, O. E.; Picquenard, E.; Gobeltz, N.; Demortier, A.; Corset.
J. Inorg. Chem. 1999, 38, 2917. c) Janz, G. J.; Coutts, J. W.; Downey, J. R.; Roduner,
E. Inorg. Chem. 1976, 15, 1755.

68

 

 

Chapter 3

Synthesis, Characterization of the layered compounds T128nA52Q6 (Q = 8, 8e)

Abstract

The reaction of Sn in potassium and rubidium thioarsenate fluxes gave the trigonal
compound K(Rb)2SnA5286, which consists of [SnA5286]2' layers with the alkali cations
lying between the layers. Given the high symmetry of this compound, we reasoned that if
we could substitute the alkali cations with T1 and S with Se, we would be able to obtain
better semiconductor that might possibly have some interesting thermoelectric properties.
We were successful in discovering leSDASzS6 (I) and Tl2SnAS28e6 (II) which crystallize
in the space group P-3 with a = 6.706(4) A, c = 7.187(6) A for I and a = 6.996(3) A, c =
7.232(4) A for 11. These compounds are semiconductors with band gaps of 1.68 eV for I
and 1.08 eV for 11, corresponding to their dark red and black colors respectively. II, on
melting followed by cooling forms a glass, which has a band gap of 0.87 eV. This glass

can be crystallized back on heating.

69

 

A. Introduction

The ultimate goal in solid state chemistry is the ability to predict and prepare materials
with pre-designed structures and properties. This requires that we have a good
understanding of different structure types. Therefore it is important that new structures be
discovered. In the case of multinary chalcogenides, this purpose is served by the hugely
successful alkali metal polychalcogenidel and polychalcophosphate flux methods.2 These
fluxes allow reactions to be done at lower temperatures and reduce or eliminate
thermodynamic control over the reaction pathway. Under such conditions molecular
building blocks rather than atoms are available for bonding. These building blocks can
show a variety of binding modes resulting in different structural assemblies. Recently we
began investigating the reactivity of main group and transition metals in alkali
polythioarsenate fluxes.3 The driving force for this investigation was the dissimilar redox
behavior of the As3+/As5+ couple in a sulfur environment compared to the PM/P5+ couple.
We anticipate the structures of thioarsenate compounds to be quite different from those
observed in chalc0phosphate chemistry. We therefore set forth on a systematic study of
the reactivity of different metals in these fluxes.

We chose 8n because of our success with this metal in polychalcogenide and
polychalcophosphate fluxes.4 The reactions of Sn in AAsxSy (A = K, Rb, Cs) fluxes gave
the one-dimensional compounds NaSnAsS4 and ASnA583 (A = K, Rb), the layered
compounds A28nAS286 (A = K, Rb) and the molecular C52SnAS289, which features
discrete molecules.3

The layered phase, A28nA52S6, crystallizes in the trigonal space group P-3. The band gap

of K28nA5286 is 1.89 eV. Because of the highly symmetrical crystal structure of this

70

 

phase, we became interested in them as possible semiconductors. If Tl could be
substituted for the alkali metal, there will be a lowering of the band gap because of the
tendency of T1 to act in a more covalent fashion compared to the alkali metals. Additional
reduction in the band gap can be achieved by substituting 8e for 8. Compounds with low
band gaps and high symmetry are desirable for thermoelectric applications.5 Another
useful class of thallium thioarsenate materials which has gained considerable interest is
the glassy system T128-AS283, where T1 is used as a modifier to modify the glassy A5283
network and hence change its properties.6 Thin films of Tl-As-S glasses have shown
potential as high-resolution photoresist. Most of the known thallium thioarsenates are
minerals. These minerals include TleA5389,7 TngAsS3,8 Tl2Sb6As4816,9 TngA5386,lo
TlA5383,” T12SnA5286,” T12MnA5285,” T1,As5.,,14 TleAs386,‘ 5 T13Ass3,16 and
TlA582.” Some of these minerals like T12MnAS285, TleA53S6, T13A584, T13A583 and
TlA582 have been synthesized in the laboratory. Here we present the synthesis and
characterization of T128nA52Q6 (Q = 8, 8e), which are the synthetic equivalents of the
mineral emigillite (T128nA5286).12 A highlight of T128nA528e6 is its ability to form glass
on melting. During our attempts to make the analogous Tl2Sn8b28e6, we discovered a
new phase TlgSn108b168e43 that has an interesting layered structure. The structure of this

compound is discussed in the appendix.

B. Experimental Section
B.l Reagents
All manipulations were done in a nitrogen-filled dri-vac glove box. Reagents: Tl, 8n

(99.999 %; Cerac, Milwaukee, WI); A5 (99.9%; Aldrich Chemical Co, Milwaukee, WI);

71

8 (99.9 %; Strem Chemicals, Newburyport, MA); Se (99.999 %; Noranda Advanced
Materials, Quebec, Canada); N,N-dimethylformamide (Spectrum Chemicals, AC8

reagent grade); diethyl ether (CCI, AC8 grade).

Caution: T hallium and its compounds are extremely toxic and proper precautions need to

be taken when handling these compounds.

B.2 Physical Measurements

Powder X -ray Dijfiaction

X-ray powder diffraction patterns were recorded on a CPS 120 INEL diffractometer (Cu
K01 radiation) operating at 40kV/20mA and equipped with a position sensitive detector
with a flat sample geometry.

Energy Dispersive Spectroscopy

Semiquantitative microprobe analyses on the compounds were done with a JEOL 6400V
scanning electron microscope equipped with a Noran Vantage Energy Dispersive
Spectroscopy detector.

Difluse Reflectance Spectroscopy

Solid state diffuse reflectance spectra were measured using a Shimadzu UV-3101 PC
double-beam, double-monochromator Spectrophotometer. BaSO4 was used as reference.
Band gaps were computed according to a procedure described elsewhere.18

Difl'erential Thermal Analysis

The thermal behavior of the compounds was investigated by differential thermal analysis

with a Shimadzu DTA-50 thermal analyzer. Typically ~ 20mg of the sample was sealed

72

in fused-silica tube. An equal amount of a reference material, A1203, was also sealed in
another tube. The sample and the reference were then heated/cooled at the rate of
10°C/min. Melting and recrystallization events result in a difference in the temperatures
of the sample and the reference, which is recorded. Congruent melting of the compound
was analyzed by recording powder patterns before and after the DTA experiment.
Reproducibility of the result was checked by running multiple heating/cooling cycles.
Band structure calculations

Band structure calculations were performed on Tl2SnA528e6 using the self-consistent,
full-potential linearized augmented plane wave method (LAPW)19 within density
functional theory (DFT) with a generalized gradient approximation (GGA) for the

l.20 Scalar

exchange and correlation potential within the Perdew—Burke-Ernzerhof mode
relativistivic corrections were added and spin-orbit interactions (801) were incorporated
using a second variational procedure.21 The calculations were performed with the
WIEN97 program.22 Self-consistent iterations were performed with 24 k points in the
reduced Brillouin zone with a cutoff between valence and core states of -6.0 Ry;

convergence was assumed when the total energy difference between cycles was within

0.0001 Ry.

B.3 Synthesis

Tl2SnA52S6 (I): Tl2SnA52S6 was prepared by reacting stoichiometric amounts of T1, Sn,
As and S at 500°C. The reactants were loaded in a fused-silica tube in a nitrogen
atmosphere and the tube sealed under vacuum. The tube was then heated to 500°C in 10h,

held at that temperature for 60h and cooled down to 250°C at the rate of 5°C/h followed

73

by rapid cooling to room temperature. The product consisted of homogeneous red plates.
The average composition, as determined by EDS analysis using a scanning electron
microscope on several red plates, was "Tl2SnAS2386". The powder pattern of the product
was compared to the pattern simulated on the basis of single crystal structure and
revealed an almost pure phase, the minor impurity being T128n83.

Tl28nAszSe6 (II): T128nA528e6 was made by a direct combination of the elements using a
slightly different heating profile from above. The reactants were sealed in an evacuated
silica tube, heated to 600°C and maintained there for 4 days. On cooling the tube to
200°C at the rate of 5°C/h followed by rapid cooling to room temperature, shiny black
plate like crystals of the targeted phase were obtained. Energy dispersive spectroscopy
gave an average composition of "Tl28nA51_78e3,9". The powder pattern of the compound
matched the simulated powder pattern based on the crystal structure revealing a pure

phase with a 100% yield.

B.4 X-ray Crystallography

Single crystal diffraction data for the title phases were collected on a Bruker SMART
Platform CCD diffractometer, operating at 50kV/40mA and employing graphite
monochromatized Mo K01 radiation. A full sphere of data was collected with scan widths
of 0.3 in (o and an exposure time of at least 455 per frame. The SMART program was
used to extract reflections and obtain an initial cell. The program SAINT was used to
integrate data using the orientation matrix obtained from SMART. An empirical
absorption correction was done using SADABS. All refinements were carried out using

the SHELXTL package of crystallographic programs. Intensity statistics and systematic

74

absence conditions pointed to the trigonal space group P-3 for I and II.23 The structure
solution was straightforward and all atoms were found in two least squares cycles. After
complete anisotropic refinement of all the atoms, the final R1/wR2 values were
4.92/11.84 for I and 4.14/ 10.19 for 11. Table 1 lists the crystallographic refinement data
for the two compounds. Fractional atomic coordinates and equivalent isotropic
displacement parameters are listed in Table 2. Anisotropic displacement parameters are

given in Table 3.

C. Results and Discussion

C.l Synthesis

Tl2SnAS286 was achieved by the fusion of T1, 8n, As and S in the ratio 2/1/2/6 at 500°C
for 60h. A similar heating profile failed to produce pure Tl2SnA52See. Instead, along with
the required phase, we always formed Tl2SnSe3 as a byproduct. Pure synthesis of
Tl2SnA52Se6 was realized by heating the elements at 600°C for 4 days. We also attempted
to prepare T12 SnA52Te6, T12 SnSb286, T12 8n8b28e6 and T128n8b2Te6, however the

reactions yielded inhomogeneous products along with Tl2SnQ3 (Q = 8, 8e, Te).

C.2 Structure description of Tl2SnA52Q6 (Q = 8, 8e)

T128nAS2Q6 (Q = 8, Se) is isostructural to K2SnAS286 and consists of layers formed by
edge sharing 8nQ5 octahedra and AsQ3 pyramids. Another compound that has the same
structure as Tl2SnA52Q6 is C52Mn(Te83)2.24 The Tl+ cations act as spacers and lie
between the layers, Figure 1. Each layer is made up of an octahedral 8n“ ion which is

coordinated by six different [AsQ3]3’ ligands, each utilizing one of its terminal Q atoms.

75

Thus an eight-membered ring of alternating -Q-Sn—Q-As-Q-8n—Q-As- is formed. The
orientation of the AsQ3 ligands are such that apex of the pyramid, where the As is
located, points towards the T1 between the layers. This leads to significant Tl-As
interactions through the lone pair of electrons on A5. A5 a result, Tl-As distance is
comparable to Tl-Q distances.

Sn has a slightly distorted octahedral geometry with 6 equivalent Sn-Q bond distance of
2.564(5) A for 8 and 2.6873(15) A for Se, see Table 4. The equatorial and axial Q-Sn—Q
bond angles are exactly 180°, while the Q-Sn—Q bond angles between equatorial and axial
atoms are 82.77(15)° and 97.23(15)° for S and 82.83(5)° and 97.17(5)° for Se, see Table
5. As-Q distance is 2.256(5) A for S and 2.3854(17) A for Se. The AsQ3 pyramid is
distorted from the ideal with Q-As-Q bond angle of 97.03(18)° for S and 96.58(7)° for
Se. Tl sits in a irregular seven coordinate pocket and is bonded to 3 8e atoms at distances
of 3.2856(18) A, 3 Se atoms at 3.422(2) A and one As atom at a distance of 3.287(3) A.
The corresponding Tl-S and Tl-As distances are 3.274 A, 3.395 A and 3.277(4) A
respectively. The distance between two adjacent layers is 4.341 A for Tl2SnA5285 and
4.287 A for Tl2SnAS2Se6.

Comparison of isostructural Rb28nAS286 and Tl2SnAS286 can give us important clues as
to the role of Tl+ in the structure. Does it act as an inert counter-cation or is it involved in
bonding? Since T1 and Rb have almost the same ionic radii, one would expect the cell
parameters to be almost identical.25 The cell volume of Tl2SnA5286 is nearly 4.4%
smaller than Rb28nAS2S6. Also the interlayer distance in Rb2SnAS286 is longer at 4.4609
A. This implies that there exist stronger forces of attraction between Tl+ and the AsQ3

anions as compared to Rb. Some more understanding of these bonding forces can come

76

from comparison with other Tl-As-Q compounds. In Tl2MnA5285,l3 the Tl-S distances
range from 2.933(5) to 3.531(8) A. Similarly, Tl-As distance in this compound is
3.580(1) A. The shortest Tl-S distance in Tl2Au4S326 is 2.978(1) A and as observed from
the density of states plot, there is a strong interaction between the T1 5 and S p orbitals.
The density of states plot and the band structure plots of TlTa8327 indicate there is very
little Tl-S contribution. The Tl-S bond lengths in this compound are in the range 3.128(3)
to 3.331(3) A. Another interesting set of compounds are the thallium polysulfides,
(Ph4P)2Tl2(84)2 and Ko_(,3T11_3285.28 Tl-S bond lengths in the former are significantly
shorter with a mean distance of 2.926 A whereas in the latter it is 3.316 A. The average
Tl-S distance is 3.334 A in Tl2SnA5286 and the average Tl-Se distance is 3.354 A in
Tl2SnAS2Se6. From the above discussion we can interpret that the Tl-Q interactions in the
title compounds, though stronger than A2SnA5286 (A = K, Rb), are predominantly ionic.
A better idea of the extent of involvement in bonding of TI- based orbitals can be

obtained from band-structure calculations.

C.3 Differential Thermal Analysis and Phase Change Properties

The differential thermal analysis of Tl2SnAS286, Figure 2, shows a melting point of about
490°C and recrystallization point around 424°C. The powder pattern taken after the DTA
matches with the one taken before the experiment indicating a congruent melting
compound. The thermal behavior of Tl2SnA528e6 showed a reversible crystal -glass
transition. On heating, the compound melts at 350°C, however on cooling does not
crystallize. Crystallization occurs on heating the sample in a second cycle at 297°C. The

X-ray powder diffraction pattern of the compound after cooling from 325°C matches very

77

well with the parent pattern indicating a congruently melting compound, Figure 3.
Interestingly, the compound Rb28nA5286 also shows partial glass formation on heating
while C52SnA5289 shows a complete and reversible glass-crystal transformation. It is
therefore possible that Tl2SnA52S6 may also form a glass if we quench it in ice-cold water
from a molten state. Such compounds are potentially interesting candidates for use in
memory storage devices29 and further studies need to be done in this direction.

It is probably not surprising that these compounds form glasses readily. Structural studies
on AS283 glasses have shown that the local structure in these glasses is dominated by
A5833' units.3O Given that the above mentioned compounds contain the same anions, they
are perhaps predisposed to form glassy structures. It is also possible that the glassy and
the crystalline forms do not have a large thermodynamic disparity since they can be

converted reversibly.

C.4 Optical Spectroscopy

The diffused reflectance spectra of I, II and the glassy form of II are shown in Figure 4.
As seen in the figure, I shows a steep absorption starting at 1.68 eV. This corresponds to
its dark red color. K28nA52S6 Shows a band gap of 1.89 eV, which indicates that the Tl+
ions interact with the layers through bonding interactions that are only slightly stronger
than those of the alkali metals. II shows a steep absorption edge at 1.08 eV. The glassy
form of II absorbs at 0.84 eV. This is expected because in glasses the large number of
defects create significant midgap states and "band-tailing" in the electronic structure.”
This leads to a red shift in the band gap. The change in the band gap results in a sharp

difference in the reflection coefficient or conductivity between the amorphous and

78

crystalline states and is the principle on which memory storage devices like Ge28b2Te5
work.32 In this context, T128nA528e6 is a promising compound.

We also performed thermoelectric power measurements on the crystalline and glassy
forms of T128nA52Se5. While we could not measure the thermoelectric power of the
crystalline form due to its very high electrical resistivity, the Seebeck coefficient of the

glassy form was very small, ~0.5 uV/K at room temperature.

79

 

 

 

Table 1. Crystallographic refinement details of Tl2SnA52S6, Tl2SnAS2Se6.

Formula
Space Group
a, A

b, A

c, A

01, deg

B. deg

11. deg

Z, V

D, mg/m3
Temp, K

A, A

H, mm'
F (000)
0",“, deg

1

Total reflections

Total unique reflections
No. of parameters
Refinement method
Final R indices(I>25(I))

R indices (all data)

Goodness of fit on F2

Tl2SnAS286
P-3

6.706 (4)
6.706 (4)
7.187 (6)
90

90

120

1, 279.9(3)
5.159

293
0.71073
37.846
374

28.26
2648

453

18

Tl2SnA52Se6
P-3

6.996 (3)
6.996 (3)
7.232 (4)
90

90

120

1, 306.5 (3)
6.236

293
0.71073
51.354

482

28.15

2283

484

18

F ull-matrix least-squares on F 2

R11 = 0.0492, wR2b =
0.1184

R1 = 0.0890, wR2 =
0.1293

1.085

R1= 0.0414, wR2
0.1019
R1= 0.0579, wR2
0.1126
1.060

“ RI = 2 IIFol- IFcll/ZIFol- ” wR2 = {2 [w(Foz-F.2)2]/ZIW(F02)2]}”2

80

Table 2. Fractional Atomic Coordinates and Equivalent Isotropic Displacement Factors

(A2 x 103) for Tl2SnA52S6 and Tl2SnAS28e6.

 

 

Atom x y z Ueqa
Tl2SnAS2S6

5n(1) 0 0 0 14(1)

T1(1) 0.3333 0.6667 0.3829(2) 29(1)

As(1) 0.3333 0.6667 0.0730(4) 16(1)

5(1) 0.2070(8) 0.3339(7) 0.2305(7) 23(1)
T128nAS2Se6

Sn(l) 0 0 0 16(1)

T1(1) 0.3333 0.3333 0.6180(1) 45(1)

As(1) 0.3333 0.3333 -1.0726(3) 19(1)

Se(1) 0.2204(2) 0.1 126(2) 0.2398(2) 27(1)

 

a Ueq is defined as one third of the trace of the orthogonalized Uij tensor

81

Table 3. Anisotropic displacement parameters“ (A2 x 103) for Tl2SnA52S6 and

 

 

Tl2SnA528e6.
U11 U22 U33 U23 U13 U12
Tl2SnA5286
Sn(l) 11(1) 11(1) 19(2) 0 0 6(1)
T1(1) 32(1) 32(1) 24(1) 0 0 16(1)
As(1) 13(1) 13(1) 23(2) 0 0 6(1)
5(1) 31(3) 9(2) 22(2) 1(2) -1(2) 4(2)
Tl2SnA52Se6
Sn(l) 13(1) 13(1) 22(1) 0 0 6(1)
T1(1) 55(1) 55(1) 24(1) 0 0 27(1)
As(1) 20(1) 20(1) 17(1) 0 0 10(1)
Se(1) 37(1) 33(1) 26(1) 6(1) 10(1) 28(1)

* The anisotropic displacement factor exponent takes the form:

~271:2[h2a*2Un + k2b*2U22 + 120*2U33 ‘1' 2hka*b*U12 + 2klb*C*U23 '1' 2hla*c*U13]

82

b)

 

Figure l. a) Unit cell of T128nA52Q6 looking down the b-aXis. The A5 lone pair is
oriented towards the T1 cations between the layers. b) A single layer showing an
octahedral 8n coordinated by 6 AsQ33' anions. c) The irregular seven coordination
pocket of T1 created by 6 Q atoms and an A5 atom.

83

Table 4. Selected bond distances (A) for T128flASzS6 and Tl2SnAS2Se6.

Tl(1)-Q(1)

T1(1)-As(1)
SH(1)-Q(1)
AS(1)-Q(1)

Tl2SnAS286
3 x 3.274(2)
3 x 3.395(2)
3.277(4)

6 x 2.564(5)

3 x 2.256(5)

T 1281113182866

3 x 3.2856(18)

3 x 3.422(2)

3.287(3)

6 x 2.6873(15)

3 x 2.3854(17)

Table 5. Selected bond angles (deg) for Tl2SnA5286 and Tl2SnA52Se6.

Tl2SnAS286
S(1)-Sn(1)-S(l)
S(1)-Sn(1)-S(1)
S(1)-8n(1)-8(1)

8(1)-As(1)-8(1)

3 x 180.0
6 x 82.77(15)
6 x 97.23(15)

3 x 97.03(18)

Tl2SnAS2Se6

8e(l)-Sn(1)-8e(1)
8e(1)-8n(1)-8e(1)
Se(1)-8n(1)-Se(1)

Se(1)-As(1)-Se(l)

84

3 x 180.0
6 x 82.83(5)
6 x 97.17(5)

3 x 96.58(7)

C. 5 Band structure calculations

We performed band structure calculations to get a better understanding of the type of gap
present in this material and the orbital character and nature of the conduction and valence
bands near the gap. Figure 5 shows the band structure plot of Tl2SnAS2Se6. As can be
seen, the minimum in the conduction band occurs at point A of the Brillouin zone while
the maximum in the valence band occurs at general points in the region between H and T
and T and L. There is another maximum between A and H which is very close to the
above two maxima. Given the almost vertical nature of the diffuse reflectance spectrum
of the compound, it seems more likely the band gap transition involves the maxirna in the
AH region and the point A in the conduction band giving rise to an indirect gap of about
0.6 eV. Because they are ground state calculations, usually the LAPW method tends to
understimate energy gaps in semiconductors and therefore this value can be qualitatively
acceptable. Figures 8 shows the total density of states plot while Figures 6 and 7 plot the
contribution of the s and p orbitals of T1, Sn, AS and 8e to the total density of states. As
can be seen from Figure 6a, there is some interaction of the T1 65 orbital with As p- and
8e p- orbitals. However these interactions are relatively weak. Figure 6b shows that the
As 5 electrons lie much below the Fermi level (~ -10 eV) and therefore are unavailable
for bonding. Figures 7a and 7b reveal that the top energy levels of the valence bands are
constructed mainly from Se based p- orbitals whereas the conduction band closest to the
Fermi level is constructed from Sn based 5- orbitals and Se based p- orbitals (see peak at
~0.5 eV) with the main contribution coming from 8n 5- orbitals. We can therefore
attribute the absorption spectrum of the compound to charge-transfer transition from 8e

to 8n.

85

D. Conclusion

leSflASzQ5 was predicted and obtained based on the synthesis of A2SnA5286 (A = K, Rb)
from a polythioarsenate flux. It was expected that the tendency of T1 to form covalent
bonds would lead to lowering of the bandgap as compared to A28nA5286 and better
semiconducting properties. Tl-Q interactions, though stronger, are mainly ionic in nature.
Tl2SnA52Se6 shows a crystal to glass transition. It is possible that Tl2SnA5286 may also
exhibit this property at faster quenching rates. Further studies are needed to probe the
phase change properties of these compounds as well as to determine conditions under

which Tl2SnA52Te6, Tl2SnSb2Q6 (Q = 8, 8e, Te) may be isolated.

86

 

424 I

LII
O
I
exo —>

DJ
O
T

490

 

E
l
4— endo

 

 

_2 1 1 I, 1 1 1
0 100 200 300 400 500 600 700

T,°C

 

 

 

o
"O
c:
Q)
1

1 1 1 1 l 1 1
0 100 200 300 400 500 600 700 800

T, 0C

 

 

 

Figure 2. Differential Thermal Analysis of (I) Tl2SnA5286 showing a melting point of
490 °C and a recrystallization point of 424 °C and (II) Tl2SnA52Se6 showing that the
compound melts at 350 °C but does not crystallize on cooling. Crystallization occurs on
heating the compound at 297 °C.

87

 

 

 

   

 

 

A . 1 4— glass
.5 l *
§
,5 pristine
“g recrystallized
d.)
W
L l I I l
10 20 3O 40 50 60
2 theta

Figure 3. Comparison of the powder patterns of the pristine, glassy and recrystallized
forms of Tl2SnAs2Se6 shows that the compound switches reversibly between crystalline
and glassy states upon heating.

88

 

 

 

 

 

 

 

 

A
A Q
m :5
\ v
8 g
D
o 5
a s
'8 .8
m m
.D
N
0 0

 

Energy, eV

 

 

 

 

 

C)
iv?
3
d)
O
5
+3
8
.0
(6
E8 = 0.85 eV
I L l l l
0 1 2 3 4 5
Energy, eV

Figure 4. Optical absorption spectra of a) T128nA5286 showing a steep absorption edge at
1.68 eV corresponding to its dark red color b) T128nA528e6 with a energy gap of 1.08 eV
0) the glassy form of Tl2SnA52Se6 shows a red shift compared to the crystalline form and
absorbs at 0.85 eV.

89

 

 

 

 

 

 

 

 

-10:

2.0.E\'~\:/

g/\C“\\, r"\.
ALGA/V “vv‘
\f 1..

J

-20:

 

 

 

 

 

 

b\<<§?\31 '
x

 

1?)
\\

 

1))

 

Figure 5. a) Band structure plot for Tl2SnA52Se6 shows that the band gap is an indirect
gap with an approximate energy of 0.6 eV arising from a transition from a general point
in the region AH to the point A of the Brillouin zone. b) The Brillouin zone for a trigonal
system.

90

1.5

DOS

0.5

1.5

DOS

0.5

Figure 6. a) Density of states for T1 5 and p orbitals showing that the S electrons are
below the Fermi level and interact weakly with As p orbitals. b) Density of states for As 5

 

 

 

 

 

 

 

 

 

 

1 partial 005: TH p _.
_ partlal DOS: T" s .....
iii
“ ‘;::L,(‘1:‘"E 13.31.10,: 1:.
:10 14 A; - J.;. ‘k ' 0A . ,,\..:‘ on"
Energy [eV]
17 partial D'Os: A81 p __'_
5 partial DOS: Asi s .....
-1o : 0 e 1 .
Energy [eV]

and p orbitals showing that the As 5 electrons lie much below the Fermi level.

91

 

 

2 , . ' .
rtlal DOS: Sei
F13301211 DOS: 891 g .....
1.5 . _ .
8 1 _
o

   

 

 

 

 

 

   

 

  

 

 

 

0.5 . 1 , ,
it - .‘ ,
Energy [eV]
b
) 2 7 . l iD'OS s '
rta : n1 ....
Bgnlal DOS: Sn1 g .....
1.5 . g g .
w
8 ‘ ' .
0.5 . 25;:
l 3 :;
0 5 n. A ‘A' .-.c

0 - ... .. .5
Energy [eV]

Figure 7. a) Density of states for 8e 5 and p orbitals showing that the p orbitals form the
energy levels closest to the Fermi level in the valence band. B) Density of states for 8n 5
and p orbitals showing that Sn orbitals contribute mainly to the conduction band.

92

35

30-

25

15.

10-

 

020 -

 

 

 

 

'totai DOS __'_

 

 

6
Energy [eV]

Figure 8. Total density of states for T128nAs28e6.

93

mi-

10

 

References

1. (a) Sutorik, A. C.; Kanatzidis, M. G. Prog. Inorg. Chem, 1995, 43, 151. b)
Kanatzidis, M. G. Chem. Mater. 1990, 2, 353.

2. Kanatzidis, M. G. Curr. Opin. Solid State Mater. Sci. 1997, 2, 139.

3. a) Iyer, R. G.; Kanatzidis, M. G. Inorg. Chem. 2002, 41, 3605. b) Iyer, R. G.; Do, J.;
Kanatzidis, M. G. Inorg. Chem. 2003, 42, 1475.

4. a) Marking, G. A.; Kanatzidis, M. G. Chem. Mater. 1995, 7, 1915. b) Chondroudis,
K.; Kanatzidis, M. G. J. Chem. Soc, Chem. Commun. 1996, 1371.

5. Hsu, K. F.; L00, 8.; Guo, F.; Chen, W.; Dyck, J. 8.; Uher, C.; Hogan, T.;
Polychroniadis, E. K.; Kanatzidis, M. G. Science 2004, 303, 818.

6. a) Petkov, K.; Todorov, R.; Kozhuharova, D.; Tichy, L.; Cemoskova, E.; Ewen, P. J.
8 J. Mater. Sci. 2004, 39, 961. b) Lippens, P. E.; Idrissi, -R. M. A.; Olivier, -F. J.;
Jurnas, J. C. J. Alloys Compd. 2000, 298, 47.

7. Takeuchi, Y.; Ghose, 8.; Nowacki, W. Z. Kristallogr. 1965, 121, 321.

8. Brown, K. L.; Dickson, F. W. Z. Kristallogr. 1976, 144, 367.

9. Engel, P.; Gostojic, M.; Nowacki, W. Z. Kristallogr. 1983, I65, 209.

10. Engel, P.; Nowacki, W.; Balic, -Z. T.; Scavnicar, 8. Z. Kristallogr. 1982, 161, 159.

ll. Pasava, J .; Pertlik, F .; Stumpfl, E. G.; Zemann, J. Mineral. Mag. 1989, 53, 531.

12.Grae5er, 8.; Wulf, R.; Edenharter, A. Schweizerische Mineralog Petrogr. Mitteil.
1992, 72, 293.

94

13.

14.

15.

16.

l7.

18.

19.

20.

21.

22.

23.

24.

25.

26.

27.

Gostojic, M.; Edenharter, A.; Nowacki, W.; Engel, P. Z. Kristallogr. 1982, 158, 43.
Engel, P.; Nowacki, W. Croat. Chem. Acta 1984, 57, 499.

Balic -Zunic, T.; Engel, P. Z Kristallogr. 1983, 165, 261.

Yang, Z. -M.; Pertlik, F. J. Alloys Compd. 1994, 216, 155.

Balic-Zunic, T.; Makovicky, E.; Moelo, Y. Neues Jb. Miner. Abh. 1995, 168, 213.
McCarthy, T.J.; Tanzer, T. A.; Kanatzidis, M. G. J. Am. Chem. Soc. 1995, 117, 1294.

a) Hohenberg, H.; Kohn, W.; Phys. Rev. 1964, 136, B864. b) Kohn, W.; Sham, L.
Phys. Rev. 1965, 140, A1133.

Perdew, J. P.; Burke, K.; Ernzerhof, M. Phys. Rev. Lett.l996, 77, 3865.
Koelling, D. D.; Harmon, B. J. Phys. Chem. 1980, 136, 147.

Blaha, P.; Schwartz, K.; Luitz, J.WIEN97, a full potential linearized augmented plane
wave package for calculating crystal properties, Karlhienz Schwartz, Tech.
Universitat Wien, Austria, 1999.

SMART 5.054, SAINT 6.36, SHELH L 5.1: Bruker- Axs Inc., Madison, WI 1997.
Zhang, X.; Kanatzidis, M. G. Inorg. Chem. 1994, 33, 1238.

Shannon, R. D. Acta Cryst. 1976, A32, 751.

Loken, 8.; Felser, C.; Tremel, W. Chem. Commun. 1998, 1603.

Teske, C. L.; Bensch, W. Z. Anorg. Allg. Chem. 2002 628, 1511.

95

 

28. Dhingra, 8.; Kanatzidis, M. G. Inorg. Chem. 1993, 32, 2298.

29. a) Kyratsi, T.; Chrissafis, K.; Wachter, J .; Paraskevopoulos, K. M.; Kanatzidis, M. G.
Adv. Mater. 2003, 15, 1428. b) Breshears, J. D.; Kanatzidis, M. G. J. Am. Chem. Soc.
2000, 122, 7839. c) Marking, G. A.; Hanko, J. A.; Kanatzidis, M. G. Chem. Mater.
1998, 10,1191.

30. a) Idrissi, -R. M. A.; Durand, J. -M.; Bonnet, B.; Hafid, L.; Olivier, -F. J.; Jumas, J. C.
J. Alloys Compd 1996, 239, 8. b) Koudelka, L.; Pisarcik, M.; Blinov, L. N.; Gutenev,
M. S. J. Non-Cryst. Solids 1991, 134, 86.

31. Drabold, D. A.; Fedders, P. A.; Klemm, 8.; Sankey, O. F. Phys. Rev. Lett. 1991, 67,
2179.

32. a) Kolobov, A. V.; Tominaga, J. J. Mater. Sci. -Mater. El. 2003, 14, 677. b) Lowrey,
T. A.; Hudgens, 8. J.; Czubatyj, W.; Dennison, C. H.; Kostyley, S. A.; Wicker, G. C.
Mater. Res. Soc. Symp. Proc. 2004, 101.

96

Chapter 4
Chemistry of Pb in Alkali Thioarsenate Fluxes: Isolation and Characterization of

APbAss. (A = Rb, Cs) and A4PbAs283 (A = Rb, Cs)

Abstract

The reaction of Pb in AASxSy fluxes (A = Rb, Cs) yielded four new compounds.
APbAsSa crystallizes as yellow plates in ana with a= 17.360(5) A, b = 6.7925(18) A, c
= 6.6090(17) A for A = Rb and a= 18.170(9) A, b = 6.890(4) A, c = 6.486(3) A for A =
C5. This compound consists of trigonal biprismatic Pb coordinated by tetrahedral (A584)3'
ligands to form two-dimensional [Pb(ASS4)]“' layers which are separated by the alkali
cations. Rb4PbA52Sg crystallizes in Ibam with a = 18.754(9) A, b = 9.142(4) A and c =
10.143(5) A. This compound is made up of [Pb(AsS4)2] motifs that are connected
together to form chains running along the c- axis. CS4PbAS283 has a similar one-
dimensional structure as the Rb compound and crystallizes in the monoclinic space group
C2/c with a = 13.994(5) A, b = 19.106(6) A, c = 9.423(3) A, B = 131.414(4)°.
Rb4PbA5283 and C54 PbA5283 form as yellow chunks. All the compounds are
semiconductors with bandgap ranging from 2.26 eV to 2.58 eV. The compounds are air

stable and insoluble in water and DMF.

97

A. Introduction

Lead arsenosulfide minerals form a considerable subclass of the sulfosalt family.1 These
minerals have an extensive structural variation arising due to the stereochemically active
lone pairs on both As and Pb. Some of these compounds like Pb7A598202 and Pb3A538203
exhibit strong piezoelectric effect. The structural variety found in natural lead
thioarsenates promotes the need to explore synthetic analogs. The use of polythioarsenate
fluxes is well suited to synthesize new alkali lead thioarsenates. In these fluxes, different
kinds of [AsxSy]“' anions are generated from an in-situ fusion of A28, AS283 and 8. These
anions coordinate to the metal ion present, according to its coordination preference, to
give compounds with varying dimensionalities. Before the advent of the flux method,
thioarsenates have been prepared mainly by solventothermal techniques.4

We started investigating the reactivity of different metals in polythioarsenate fluxes with
an aim to compare the results with the well-documented chalcophosphate flux.5 We
expect the thioarsenate flux to behave differently from the chalcophosphate flux mainly
due to the different oxidation states exhibited by P (+4 and +5) and As (+3 and +5) in
their compounds. This is observed in the reaction of Sn in thioarsenate fluxes where we
observe thioarsenate ligands based on the pyramidal (A583)3' anion.6 In the case of tin
thiophosphates, the thiophosphate ligands are derived from the (PS4)3' anion.7 The
reaction of Pb in polychalcophosphate fluxes has yielded the phases APbPQas, A4PbP2Q3
(Q = 8, 8e)8, Na1_5Pbo,75P8e49, 01- and B- Nast3(P84)4'°. Each of these compounds
consists of Pb coordinated by the tetrahedral (PQ4)3' ligand to form l-D 2-D or 3-D

compounds.

98

-‘_ v. I . v,‘_ '_‘fi_

Here we present the synthesis, structure and physical characterization of APbA584 and
A4PbAS283 (A = Rb, CS). RbanAs283 is isostructural to its thiophosphate counterpart
whereas APbA584 represents a centrosymmetric version of APbPSa. All the compounds

are air and water stable.

B. Experimental Section

B] Reagents

The chemicals used in this work were as follows: Pb powder (Spectrum, Gardena, CA),
AS283 (99.9%; Strem Chemicals, Newburyport, MA), 8 (99.9%; Strem Chemicals,
Newburyport, MA), N, N-dimethylformamide (Spectrum Chemicals, AC8 reagent
grade), diethyl ether (CCI, AC8 grade). K28, Rb28 and C528 were made by reacting
stoichiometric amounts of the elements in liquid ammonia following a modified literature

procedure. I '

B.2 Physical Measurements

Energy Dispersive Spectroscopy was performed on a JEOL ISM-35C Scanning Electron
Microscope equipped with a Tracor Northern Energy Dispersive Spectroscopy Detector.
Acquisition time per reading was 305. The composition of the compound was determined
as an average of several readings on atleast 3 crystals.

Powder X-ray Dififaction patterns were obtained on a CPS INEL 120 diffractometer with
graphite monochromatized Cu K01 radiation, operating at 40kV and 20mA.

Differential Thermal Analysis was performed using a Shimadzu DTA-50 thermal

analyzer. The reproducibility of the thermal behavior of the compounds was monitored

99

by running two heating/cooling cycles. To check for congruent melting, powder X-ray
diffraction patterns taken after the DTA cycle were compared to the ones recorded before
the DTA.

Diffuse Reflectance Spectra were recorded using a Shimadzu UV-3101 PC double-beam,
double-monochromator spectrometer. Energy gaps were extracted from a plot of
absorbance vs energy.

Single Crystal UV/Vis Spectra were obtained at room temperature on single crystals using
a Hitachi U-6000 microscopic FT spectrophotometer with an Olympus BH-2
metallurgical microscope over a range of 380-900 nm.

Far-Infiared Spectra were obtained in the 600-1000m’l range (4cm’l resolution) on a
Nicolet 740 F T-IR spectrophotometer with a TSG/PE detector and silicon beam splitter.
Samples were prepared by grinding the compounds with CsI and pressing the mixtures

into translucent pellets.

B.3 Synthesis

RbeAsS4: In a N2 filled glove box, Rb28 (0.061 g, 0.3mmol), Pb (0.062g, 0.3mmol),
A5283 (0.074g, 0.3mmol) and 8 (0.096g, 3mmol) were loaded in a fused silica tube. The
tube was sealed under vacuum and put in computer controlled furnace. The furnace was
ramped up to 500°C and held there for 60h. It was then slow cooled at the rate of 5°C/h
to 250°C and then rapidly cooled to room temperature. Isolation of the product with N2-
bubbled N, N-dimethylformamide, revealed yellow transparent crystals and a small
amount of black crystals. EDS analysis on several of the yellow crystals gave an average

composition of Rb12PbAsHS43. The black crystals were identified as PbS. The yield of

100

the product was about 60% based on Pb and product purity based on powder X-ray
diffraction pattern was ~ 95%.

RbanAs283: An optimum synthesis with a yield of ~65% for Rb4PbA5283 was obtained
by reacting a mixture of Rb28, Pb, A5283 and 8 in the ratio 3.5/1/1.5/4 using the heating
profile as above. The product consisted of golden brown crystals of average composition
Rb4,4PbA51.987,9 and light yellow crystals of Rb3AsS4.

CstA584: This compound is obtained as the majority product (>95% phase purity) from
a reaction of C528, Pb, AS283 and 8 in the ratio 2/1/1/8. The reactants were heated to
600°C and held there for 4 days. The reaction mixture was then cooled to 200°C at the
rate of 5°C/h and then fast cooled to room temperature. The product on isolation revealed
almost pure yellow transparent crystals, some colorless and black crystals. Elemental
analysis on several of the yellow crystals gave an average composition of
C51_3Pb),oA51,oS4,3. The colorless crystals were C53A584 and the black crystals were Pb8.
The yield of the reaction was ~ 60%.

Cs4PbA52Sg: A reaction of C528, Pb, A5283 and 8 in the ratio 3/1/1/10 using the above
heating profile afforded mostly CS4PbA5283, with a small amount of CS3ASS4, in nearly

70% yield. The EDS analysis gave a composition of CS4,3PbAS2,483.

B.4 Single Crystal Diffraction

Single crystal X-ray diffraction data on the compounds were collected at room
temperature on a SMART platform diffractometer with a 1K CCD area detector using
monochromatized Mo K01 (A = 0.71073 A) radiation. Reflection data were recorded using

the SMART software. Data integration was done with SAINT and an empirical

101

Table 1. Crystallographic data for RbeAsSa, CstAsSa, Rb4PbA5283 and CS4PDASzSg

empirical formula
fw

space group

a, A

b, A

c, A

01, deg

B. deg
Y. deg
V, A 3
Z

peaiea, g/cm3
14 mm‘1
T, K

A, A
Total reflections
Total unique

R(int)

No. of parameters
Goodnes of fit on F2
Refinement method
R1a

wR2b

RbeAsS4
495.82
ana
17.360(5)
6.7925(18)
6.6090(17)
90

90

90
779.3(4)

4

4.226
33.027
293(2)
0.71073
7279

1020
0.0672

40

l .063

0.0348
0.0809

“R1=>:iiF.i-iF.ii/21F.I.”wR2={21w(F.2-Fffl/2[w(F.2)Zl1”2

102

CstAsSa Rb4PbA5283 Cs4PbA5283
543.26 955.39 1145.15
ana Ibam C2/c
18.170(9) 18.754(9) 13.994(5)
6.890(4) 9.142(4) 19. 106(6)
6.486(3) 10.143(5) 9.423(3)
90 90 90
90 90 131.414(4)
90 90 90
812.0(7) 1739.1(14) 1889.4(10)
4 4 4
4.444 3.649 4.026
30.162 25.530 20.857
293(2) 293(2) 293(2)
0.71073 0.71073 0.71073
7440 8368 9574
1045 1 130 2325
0.0354 0.0431 0.0343
41 43 72
1.128 1.080 1.135

F ull-matrix least-squares on F 2
0.0327 0.0279 0.0300
0.0702 0.0668 0.0676

Table 2. Fractional atomic coordinates and isotropic displacement parameters (A02 x

1003) for RbeAsSa, CstAsSa, Rb4PbA8283 and Cs4PbAs283

 

 

Atom x y z Ueqa
RbeA584
Pb(1) -0.0204(1) 0.2500 0.7862(1) 38(1)
As(1) -0.0952(1) 0.2500 1.2837(2) 20(1)
Rb(1) 0.2120(1) 0.2500 0.5009(3) 46(1)
8(1) -0.1661(2) 0.2500 0.5512(5) 31(1)
8(2) 0.1 179(2) 0.0047(3) 0.9012(4) 30(1)
8(3) 0.0262(2) 0.2500 0.3619(6) 46(1)
CstAsS4
Pb(l) 0.0165(1) 0.2500 0.2095(1) 41(1)
As(1) 0.0941(1) 0.2500 -0.2855(2) 21(1)
Cs(1) 0.2911(1) 0.2500 -0.0405(2) 50(1)
8(1) 0.1585(1) 0.2500 0.4373(4) 28(1)
8(2) -0.1158(1) 0.0031(3) 0.1000(3) 31(1)
8(3) -0.0224(2) 0.2500 -0.3580(5) 60(1)
Rb4PbAS2Ss
Pb(1) 0 -1.0000 0.2500 39(1)
As(1) -0.1274(1) —0.7954(1) 0 18(1)
Rb(1) -0.0836(1) -0.3754(1) 0 32(1)

103

Rb(2)
5(1)
5(2)

8(3)

Pb(1)
Cs(1)
Cs(2)

Cs(3)

Cs(33)

As(1)
5(1)
5(2)
5(3)

S(4)

0.241 1(1) 0
-0.2396(1) -0.7504(2)
-0.0774(1) -O.7047(2)
-0.1045(1) -1.0276(2)
CS4PbASzSg

0.5000 -0.2362(1)
0.2389(1) -0.l619(1)
0.5000 0.0020(1)
0.5000 -0.4709(9)
0.5000 -0.4862(7)
0.2580(1) -0.1262(1)
0.2494(2) 0.0168(1)
0.4246(2) -0. 1746(1)
0.4126(2) -0.3221(1)
0.2776(2) -0. 1438(1)

0.2500
0
0.1720(1)

0

0.2500
0.1 102(1)
0.2500
0.2500
0.2500
0.2914(1)
0.2534(3)
0.0350(2)
0.3866(3)

0.4995(3)

45(1)
31(1)
36(1)

41(1)

32(1)
30(1)
35(1)
34(1)
34(1)
17(1)
28(1)
27(1)
33(1)

33(1)

 

a Ueq is defined as one third of the trace of the orthogonalized Uij tensor

104

A
51

rt."

13

Si:

Table 3. Anisotropic displacement parameters* (A2 x 103) for RbeAsSa, CstAsSa,

Rb4PbASst and CS4PbAS4Sg.

 

 

U11 U22 U33 U23 U13 U12
RbeAss4
Pb(1) 30(1) 59(1) 24(1) 0 0(1) 0
As(1) 22(1) 17(1) 22(1) 0 1(1) 0
Rb(1) 29(1) 31(1) 77(1) 0 12(1) 0
5(1) 27(2) 34(2) 30(2) 0 10(2) 0
5(2) 38(1) 17(1) 36(1) -5(1) -4(1) 1(1)
5(3) 20(2) 88(4) 32(2) 0 5(2) 0
CstAsS4
Pb(1) 29(1) 70(1) 24(1) 0 1(1) 0
As(1) 20(1) 22(1) 21(1) 0 2(1) 0
Cs(1) 27(1) 31(1) 92(1) 0 -15(1) 0
5(1) 23(1) 33(1) 27(1) 0 6(1) 0
5(2) 39(1) 22(1) 33(1) 5(1) -3(1) -4(1)
5(3) 16(1) 132(4) 31(2) 0 2(1) 0
Rb4PbAs283
Pb(1) 37(1) 39(1) 42(1) 0 0 0
As(1) 17(1) 16(1) 22(1) 0 0 0(1)

Rb(1) 38(1)

Rb(2) 63(1)

5(1)
5(2)

8(3)

Pb(1)
Cs(1)
Cs(2)

Cs(3)

19(1)
50(1)

27(1)

34(1)
33(1)
24(1)

24(1)

Cs(33) 24(1)

As(1) 17(1)

5(1)
5(2)
S(3)

S(4)

"‘ The anisotropic displacement factor exponent takes the form:

-27l32[1'12a*2U11 + k2b*2U22 + 120*2U33 '1' 2hka*b*U12 '1' 2klb*c*U23 '1' 21113*C*U|3]

30(1)
19(1)
20(1)

49(1)

24(1)
42(1)
36(1)
37(1)

18(1)

28(1)
34(1)
45(1)
45(4)
45(4)
19(1)
23(1)
36(1)
44(1)

36(1)

34(1)
30(1)
39(1)
22(1)

78(2)

CS4PbASzSg

41(1)
28(1)
33(1)
26(1)
26(1)
17(1)
32(1)
22(1)
31(1)

30(1)

106

-7(1)

-3(1)

0(1)
3(1)
6(1)
-4(1)

7(1)

28(1)
22(1)
18(1)
13(1)
13(1)
12(1)
20(1)
11(1)
16(1)

33(1)

5(1)

10(1)
-6(1)

3(1)

1(1)
-3(1)
6(1)

-8(1)
13(1)

absorption correction was applied using SADABS. The structures were solved by direct
methods using the SHELXTL package of programs.12 Based on the intensity statistics,
centrosymmetric spacegroups were assigned to all the four compounds. RbeA584 and
CstA584 were refined in ana with final R1/wR2 values of 0.0348/0.0809 and
0.0327/0.0702 respectively. RbanA5283 was refined in the orthorhombic spacegroup
Ibam with R1/wR2 = 0.0279/0.0668 while Cs4PbA5283 was refined as monoclinic C2/c
with R1/wR2 = 0.0300/0.0676. Table 1 lists crystal refinement details and Table 2 lists
the fractional atomic coordinates and isotropic displacement parameters for all the
compounds. Anisotropic displacement factors are listed in Table 3. Selected bond

distances and angles are given in Tables 4 and 5 respectively.

C. Results and Discussion

C.1 Synthesis

RbeAsS4 and CstAsSa were both synthesized initially from a 1/1/1/10 ratio of
A28/Pb/AS2S3/S. For RbeAsSa, this flux composition proved to be optimum for
maximum yield of the compound. CstAsS4 could be obtained in a better yield and
purity from a composition of 2/1/1/8 of C528/Pb/AS283/8 at 600°C. In both the fluxes,
increasing the basicity by adding A28 gave products consisting of APbA584 and
A4PbA5283. The amount of A4PbA5283 increased as the amount of A28 was increased.
RbanA5283 was initially obtained from a composition of 4/1/1/10 of Rb28/Pb/AS2S3/S.
This reaction also gave PbS and Rb3ASS4. A better synthesis was achieved by heating a
mixture with formal composition Rb7PbA53812. This gave Rb4PbASzSg as well-formed,

irregular golden-yellow crystals along with light yellow crystals of Rb3A584. Cs4PbA5283

107

-———v.-->—r

was obtained as irregular yellow crystals, along with some C53A584, from a flux
composition of C56A52816.

We also performed reactions with Pb in KAsxSy flux. These reactions resulted in the
formation Of a 3-D compound KPbA584 and the molecular K4PbAS283. However the
structures of these compounds could not be refined satisfactorily. Repeated attempts to
obtain good quality crystals and better data were unsuccessful. The crystal details of these

two compounds along with their structures are shown in Appendix B.

C.2 Structure description of APbA584

Since RbeAsSa and CstAsS4 are isostructural, we will discuss the structure of
RbeAsS4. The structure of this compound consists of [PbA584]"' layers stacked along
the a-axis and parallel to the bc- plane, Figure la. Each layer consists of a trigonal
prismatic Pb coordinated by tetrahedral (A584)3' ligands, Figure 1b. A better
understanding of the bonding can be seen in Figure 10. As shown in this figure, Pb is
coordinated by four (A584)3' ligands. Two of these ligands are bidentate and use two of
its sulfur atoms to link to the metal, the other two are monodentate and use one sulfur to
link to the metal thus forming the trigonal prismatic geometry around Pb. Each (A584)3'
ligand uses all its sulfur atoms to bind 4 Pb atoms. It uses two sulfur atoms to bind to one
Pb in a bidentate fashion. The other two sulfur atoms bridge three Pb atoms. In other
words, the (A584)3' tetrahedron uses one edge and two corners to bind to 4 Pb, Figure 1d.
Pb-S bond distances range from 2.918(4) to 3.182(1) A while AS-S bond lengths are in
the range 2.154(3) to 2.169(4) A. Rb sits in a 8 coordinate site generated by 8 atoms at

distances ranging from 3.355(4) to 3.639(4) A. There is a weak Rb-As interaction at

108

 

Figure 1. a) Unit cell down the a- axis for APbA584 b) A single[PbA584]“' layer c)
Trigonal prismatic geometry of Pb (1) Coordination of (A584)3'

109

Table 4. Selected bond distances for RbeAsSa, CstAsS4, RbanA5283 and C54PbA5283

Pb(1) - 5(3)
Pb(1) - 5(1)
Pb(1) - 5(2)
Pb(1) - 5(2)
As(1) - 5(2)

As(1) - 5(3)

Pb(1) - 5(3)
Pb(1) — 5(1)
Pb(1) - 5(2)
Pb(1) - 5(2)
As(1) - 5(1)

As(1) - 8(2)

Pb(1) - 5(2)
Pb(1) - 5(3)
As(1) - 5(1)

As(1) - 5(2)

2.918(4)
2.968(4)

2 x 3.020(3)
2 x 3.182(1)
3 x 2.154(3)

2.169(4)

2.893(4)
2.972(3)
2 x 3.030(2)
2 x 3.213(1)
2.145(3)

2 x 2.155(2)

4 x 3.1656(19)
4 x 3.2144(17)
2.143(2)

2 x2.1478(15)

RbeASS4

CstAsS4

Rb4PbASst

110

Rb(1) - 5(3)
Rb(1) - 5(2)
Rb(1) - 5(1)
Rb(1) - 5(2)

Rb(1) - 5(1)

Rb(1) - As(1)

As(1) - 5(3)
Cs(1) - 5(2)
Cs(1) - 5(2)
Cs(1) - 5(3)

Cs(1) - 5(1)

Cs(1) - As(1)

Rb(1) - 5(2)
Rb(1) - 5(1)
Rb(1) - 5(2)

Rb(2) - 5(1)

3.355(4)
2 x 3.484(3)

2 x 3.5057(13)
2 x 3.528(3)
3.639(4)

3.839(2)

2.168(3)
2 x 3.730(3)

2 x 3.652(3)
3.451(4)

2 x 3.5675(18)

3.918(2)

2 x 3.481(2)
3.508(3)
2 x 3.563(2)

2 x 3.4115(18)

-_‘ ...-

As(1) - 5(3)
Rb(1) - 5(3)

Rb(1) - 5(2)

Pb(1) - 5(4)
Pb(1) - 5(2)
Pb(1) - 5(3)
As(1) - 5(1)
As(1) - 5(3)
As(1) - 5(2)
As(1) - 5(4)
Cs(1)-8(4)
Cs(1)-8(3)
Cs(1)-8(1)
Cs(1)-8(2)

Cs(1)-8(2)

2.166(2)
3.204(3)

2 x 3.409(2)

2 x 2.940(2)
2 x 3.0710(18)
2 x 3.220(2)
2.1519(19)
2.1554(19)
2.1616(17)
2.1778(19)
3.363(2)
3.558(2)
3.639(2)
3.6490(19)

3.658(2)

CS4PbASzSg

Rb(2) - 5(1)
Rb(2) - 5(3)

Rb(2) - As(1)

Cs(1)-8(3)
Cs(1)-8(3)
Cs(1)-8(2)
Cs(2) - 5(4)
Cs(2) - 5(1)
Cs(2) - 5(1)
Cs(3) - Cs(33)
Cs(3) - 5(1)
Cs(3) - 5(1)
Cs(3) - 5(4)

Cs(3) - As(1)

2 x 3.4353(17)
2 x 3.614(2)

2 x 3.8040(13)

3.699(2)
3.657(2)
3.654(2)

2 x 3.647(2)
2 x 3.545(2)
2 x 3.547(2)
0.293(1)

2 x 3.577(5)
2 x 3.583(2)
2 x 3.652(11)

2 x 3.809(9)

‘

Table 5. Selected bond angles for RbeAsS4, CstAsS4, Rb4PbASzSg and C54PbA5283

5(3) - Pb(1) - 5(1)
5(3) - Pb(1) - 5(2)
5(1) - Pb(1) - 5(2)

5(2) - Pb(1) - 5(2)

5(3) - Pb(1) - 5(1)
5(3) - Pb(1) - 5(2)
5(1) - Pb(1) - 5(2)

5(2) - Pb(1) - 5(2)

5(2) - Pb(1) - 5(2)
5(2) — Pb(1) - 5(2)
5(2) - Pb(1) - 5(2)
5(3) - Pb(1) - 5(3)
5(3) - Pb(1) - 5(3)
5(3) - Pb(1) - 5(3)

5(2) - Pb(1) — 5(3)

74.51(10)
2 x 9124(8)
2 x 144.02(5)

66.98(10)

7434(8)
2 x 9190(7)
2 x l43.62(4)

6831(8)

125.414(1)
151.054(1)
62.964(l)
170.997(1)
104.875(1)
75.855(1)

90.886(1)

RbeA584

CstA584

Rb4PbASzSg

112

5(2) - As(1) - 5(2)
5(2) - As(1) - 5(1)
5(2) - As(1) - 5(3)

5(1) - As(1) - 5(3)

5(1) - As(1) - 5(2)
5(2) - As(1) - 5(2)
5(1) - As(1) - 5(3)

8(2) - As(1) - 8(3)

5(2) - Pb(1) — 5(3)
5(2) - Pb(1) - 5(3)
5(2) - Pb(1) - 5(3)
5(1) - As(1) - 5(2)
5(2) - As(1) - 5(2)
5(1) - As(1) — 5(3)

5(2) - As(1) - 5(3)

106.82(15)
2 x 111.14(10)
2 x 108.27(10)

111.04(16)

2 x 111.58(8)
108.01(12)
110.52(13)

2 x 107.48(8)

6582(5)
81.411(1)
122.93(2)
2 x 110.77(6)
108.63(9)
1 1256(8)

2 x 106.96(6)

5(4) - Pb(1) - 5(4)
5(4) - Pb(1) - 5(2)
5(4) - Pb(1) - 5(2)
5(2) - Pb(1) - 5(2)

5(1) - As(1) - 5(3)

106.27(9)
2 x 6973(5)
2 x 8349(5)
134.93(7)

109.64(8)

C54PbA5283

113

5(1) - As(1) - 5(2)
5(3) - As(1) — 5(2)
5(1) - As(1) - 5(4)
5(3) - As(1) - 5(4)

5(2) - As(1) - 5(4)

110.79(7)
1 1036(8)
1 1256(7)
108.58(8)

104.80(8)

3.839(2) A. The two AsS4 tetrahedra are slightly distorted with S-As-S angles between
106.82(15)° and 111.14(10)°. S-Pb-S angles vary from 65.86(1)° to 144.02(5)°.

APbAsS4 crystallizes in the CstPSe48a structure type. This structure type is also found
in AEuPS48b (A = Rb, Cs). Distortions of this structure type are seen in the compounds
APbPS48b (A = Rb, Cs) which crystallize in the non-centrosymmetric space group
P212121. These compounds differ from APbAsS4 with respect to the binding mode of the
(PS4)3' ligand. In APbPS4, each Pb is still coordinated by 4 (PS4)3' ligands. However
each of the (PS4)3' unit uses two edges and one corner to ligate to 4 Pb atoms. Another
compound CsSmGeS413 shows a striking similarity to this structure type. This compound
crystallizes in P212121 and consists of a monocapped trigonal prismatic Sm3+ coordinated

by 4 (GeS4)4' tetrahedra. Each (GeS4)4' uses three edges and one comer to 4 Sm3+ ions.

C.3 Structure description of A4PbAsz83

Rb4PbAszsg crystallizes in the orthorhombic space group Ibam. The structure is
composed of 1-D chains running parallel to the c- axis, Figure 2a. Each chain is made up
of eight coordinate Pb ligated by 4 tetrahedral (AsS4)3' units. This gives rise to a distorted
dodecahedral geometry for Pb, Figure 2b. Each (AsS4)3' anion employs three of its sulfur
atoms to bridge to two adjacent Pb atoms while the remaining sulfur remains non-
bonding, Figure 2c.

There are four Pb-S distances at 3.1656(19) A and four distances at 3.2144(17) A. As-S
distances vary between 2.143(2) to 2.166(2) A. There are two Rb ions, one coordinated
by sulfur atoms in a bicapped trigonal prismatic geometry and the other in an irregular

six-coordinate site with average Rb-S distances of 3.45(1) A and 3.49(1) A, Figure 2d.

114

“-1;—

 

 

 

Figure 2. a) Unit cell of Rb4PbAszsg b) Distorted dodecahedral environment around Pb
c) Coordination of (A884)3' (1) Coordination of K+ cations

115

 

 

 

    

 

 

Figure 3. a) Unit cell of Cs4PbAszsg along the a- axis b) View of the unit cell along the
ac- plane, Cs atoms have been omitted for clarity c) Coordination geometry around Pb d)
Coordination of (AsS4)3' e) Coordination environments of Cs+

116

There is also a weak interaction of one of the Rb ions with As at a distance of 3.8040(13)
A. S-As-S bond angles of 110.77(6)° and 106.96(6)° are close to tetrahedral angles. S-Pb-
S angles range from 62.964(1)° to 170.997(1)°. The Pb-S bond distances are longer than
those found APbAsS4 however the other distances and angles are similar.

The structure of Cs4PbAszsg is similar to the Rb compound. There is a lowering of the
symmetry going from Rb to Cs owing to the bigger size of the Cs+ ion which does not
allow better packing of the chains. The chains run along the ac- direction and the Pb
atoms have a kink-like arrangement along this chain, Figure 3a and 3b. The Pb-Pb
distance in the chain is 5.275 A compared to 5.072 A for the Rb compound. The other
significant difference comes from the coordination environment of Pb. In CS4PbASst, Pb
has a trigonal prismatic geometry similar to that found in APbAsS4, Figure 3c. Each
(AsS4)3' anion uses one edge and one corner to bridge two Pb atoms while the fourth
sulfur atoms remains non-bonding, Figure 3d. Figure 3e shows bonding geometry of the
three crystallographically unique Cs cations.

Rb4PbASst is isostructural to A4PbP283 (A= K, Rb, Cs). Cs4PbAszsg represents a
distorted version of this structure type. A closely related structure is observed in the one-
dimensional compounds K3LaPZSe3”, K3PuP28315, A3REP28eg (A = Rb, Cs; RE = Ce,
Gd).16 In these compounds, the rare-earth metal is in a bicapped trigonal prismatic
environment coordinated by 4 tetrahedral (PQ4)3' anions in a bidentate manner. The rare-

earth metals are arranged in a kink-like fashion along the chain, akin to Cs4PbAszsg.

117

C.4 Pb Series

Based on the Pb compounds we have obtained so far, it is possible to envision a series of
Pb compounds belonging to the general formula (A3AsS4),,(Pb3Aszsg)lm where the first
compound of the series is Pb3A5283 (m = 1, n= 0), Scheme 1. By adding one equivalent
of A3AsS4, we can obtain the compound APbAsS4 (m = 1, n = 1). For m= 1, n= 2, we
should get the compound A4PbAszsg, further addition of A3AsS4 should give
A7PbA53Su. We can think of this series as a gradual dismantling of the 3-D framework of
Pb3A5283 to give the 2-D APbAsS4, the 1-D A4PbASzSg and A7PbA53Sn which is
probably molecular. A similar series has been postulated for lead chalcophosphate

compounds.8

 

 

 

 

 

 

 

 

A ASS
3 4 p 3 APbAsS4
A
3 A3ASS4 3 Pb3ASzSg
4 11313.384 V
Pb3ASzSg > 3 A4PbASzSg
1
3 A3ASS4
7 A AsS V
3 4 p 3 A7PbAS3312

Scheme 1. Flow chart showing the different members belonging to the series

(A 3ASS4)n(P b3ASzSg)m

118

C.5 Thermal Analysis

The thermal behavior of RbeAsS4 and Cs4PbAsz83 were monitored by DTA. RbeAsS4
melts at 435°C and recrystallizes at 397°C, Figure 4a. The powder pattern of the
compound after DTA contained peaks belonging to the parent compound along with
some PbS and Rb4PbAszsg. Cs4PbASZSs melts at 547°C and recrytallizes at 524°C. As
seen in Figure 4b, the melting point shifts to 540°C on the second heating cycle. The
powder pattern after DTA matched the one before indicating no decomposition of the

compound.

C.6 Optical Spectroscopy

Since RbeAsS4 was obtained as yellow transparent plates, suitable crystals could be
picked up for single-crystal band gap measurements. Figure 5a shows that RbeAsS4 is a
semiconductor with a sharp absorption at 2.53 eV. This value corresponds well to its
yellow color. The band gaps of Rb4PbASzSg, CstAsS4 and Cs4PbAszsg were determined
by diffuse reflectance spectroscopy. These compounds absorb at 2.26 eV (figure SC), 2.42
eV (figure 5b) and 2.58 eV (figure 5d) respectively. As a general rule, for the same
structure, the band gap should decrease as we go down a group. This is observed in the
case of RbeAsS4 and CstAsS4. Like wise Rb4PbP2$3 has a higher band gap (2.68 eV)

compared to Rb4PbASst.

119

 

I». I
i o
><
. 0
435
i a
397 g
" W‘ l

 

 

 

l l l l l l

0 100 200 300 400 500 600 700
Tfk:

 

 

 

 

 

l l l l l l

o 100 200 300 400 500 600 700
13°c:

 

Figure 4. a) DTA of RbeAsS4 showing a melting point at 435°C and recrystallization

point at 397°C. b) DTA of Cs4PbAszsg showing that it melts at around 543°C and
recrystallizes at 524°C.

120

 

 

 

 

 

 

 

 

 

 

   

 

 

a) b)
6*
° a
E s
'53 .5
7; E”
,3 133 = 2.53 eV g
g
B
(U
1 l 1 L 1 1 1 l I " l 1
1.6 1.8 2 2.2 2.4 2.6 2.8 3 0 l 2 3 4
Energy, eV Energy, eV
c) d)
a ’1?
3. Eg = 2.26 eV 3 E, = 2.58 eV
= s
.g 1?}
5* a
43 a
1 1 1 1 l I l l
0 l 2 3 4 5 l 2 3 4
Energy, eV Energy, eV

 

 

 

 

 

 

 

 

Figure 5. a) Single crystal UV-Vis spectrum of RbeAsS4 showing a sharp absorption at
2.53 eV. Diffuse reflectance spectra of b) CstAsS4 c) Rb4PbA5283 d) Cs4PbA5283

121

 

Transmittance

 

 

 

l 1 1 l 1 1
150 200 250 300 350 400 450 500
wavelength (cm-l)

 

 

 

Transmittance

419

 

 

l l l 1 l 1

150 200 250 300 350 400 450 500
wavelength (cm'l)

 

 

b)

167

221
207

Transmittance

 

1

429

 

l 1 l L l

 

150 200 250 300 350 400 450 500

wavelength (cm'l)

 

d)

163
183

Transmittance

220

 

l

425

 

1 1 l l l

 

150 200 250 300 350 400 450 500

wavelength (cm!)

Figure 6. Far-IR spectra of a) RbeAsS4 b) Rb4PbAszSg c) CstAsS4 d) CS4PbASst

122

The Far-IR spectra of APbAsS4 and A4PbAszsg are shown in Figure 6. As seen in the
figure, the spectra compare very well to each other. There are three strong peaks in the
range 380-440 cm], which can be attributed to As-S stretching. The peaks in the 160-250
cm'1 range belong to either Pb-S or As-S vibrations. The simplicity of these spectra point
to the very symmetrical coordination environments of As and Pb. Similar vibrational

energies are observed for APbPS4 and A4PbP283.

D. Conclusion

The reaction of Pb in thioarsenate fluxes formed compounds that are isostructural to their
thiophosphate counterparts. This similarity has its foundation on the type of ligand that is
formed in both these fluxes. The formation of the tetrahedral (PnS4)3' (Pn = P, As) ligand
can be explained on the basis of the ease of oxidation of the metal. Since Pb is easily
oxidized to Pb“, the flux can further oxidize As ( or P) to Ass+ (or P“). The As(P)5+ ion
forms the well known tetrahedral (PnS4)3' ligand which then coordinates to Pb”. The
other significant observation that can be made here is the prediction of a series of Pb
compounds. Usually predicting the outcome of a solid state reaction is very difficult.
Varying the flux basicity in our system allowed us to isolate two members of the series
(A3AsS4)n(Pb3Aszsg)m whereby we can now predict the composition of the other

members and try to target their synthesis.

123

References

1. Gmelin Handbook of Inorganic and Organometallic Chemistry, 8th Edition2TYPIX-
Standardized Date and Crystal Chemical Characterization of Inorganic Structure
Types, Vol. 1, Springer-Verlang Berlin, 1993.

2. Le Bihan, M.-T. Bull. Soc. Franc. Miner. Crist. 1962, LXXXV, 15.
3. Marumo, F.; Nowachi, W. Z. Kristallogr. 1967, 124, 409.

4. a) Sheldrick, W. S.; Wachhold, M. Angew. Chem. Int. Ed. Engl. 1997, 36, 206. b)
Jerome, J. E.; Wood, T. P.; Pennington, W. T.; Kolis, J. W. Inorg. Chem. 1994, 33,
1733. c) Hanko, J. A.; Chou, J. H.; Kanatzidis, M. G. Inorg. Chem. 1998, 3 7, 1670. d)
Chou, J. H.; Kanatzidis, M. G. Chem. Mater. 1995, 7, 5.

5. a) McCarthy, T. J.; Kanatzidis, M. G. Chem. Commun. 1994, 1089. b) McCarthy, T.
J .; Kanatzidis, M. G. Chem. Mater. 1993, 5, 1061. c) Chondroudis, K.; Kanatzidis, M.
G. J. Solid State Chem. 1998, 136, 79. d) Kanatzidis, M. G. Curr. Opin. Solid State
Mater. Sci. 1997, 2, 139.

6. a) Iyer, R. G.; Kanatzidis, M. G. Inorg. Chem. 2002, 41, 3605. b) Iyer, R. G.; Do, J .;
Kanatzidis, M. G. Inorg. Chem. 2003, 42, 1475.

7. Derstroff, V.; Tremel, W.; Regelsky, G.; Eckert, H. Solid State Sci. 2002, 4, 731.

8. a) APbPSe4 and A4PbP28e3: Chondroudis, K.; McCarthy, T. J.; Kanatzidis, M. G.
Inorg. Chem. 1996, 35, 840.
b) APbPS4 and A4Pbstg: Aitken, J. A.; Kanatzidis, M. G. Unpublished results.

9. Aitken, J. A.; Marking, G. A.; Evain, M.; Iordanidis, L.; Kanatzidis, M. G. J. Solid
State Chem. 2000, 153, 158.

10. Aitken, J. A.; Kanatzidis, M. G. Inorg. Chem. 2001, 40, 2938.

124

11. a) Feher, F. In Handbuch der Pra'parativen Anorganischen Chemie; Brauer G., Ed.;
Ferdinand Enke: Stuttgart, Germany, 1954; vol. 1, pp 280-281. b) Liao, J. -H.;
Varotsis, C.; Kanatzidis, M. G. Inorg. Chem. 1993, 32, 2453.

12.SMART, SAINT (Version 6.45), SHELXTL (Version 5.1): Data Collection and
Processing Software for the SMART-CCD system; Siemens Analytical Instruments
Inc., 1998.

13. Bucher, C. K.; ku, S. J. Inorg. Chem. 1994, 33, 5831.

14. Evenson, C. R.; Dorhout, P. K. Inorg. Chem. 2001, 40, 2875.

15. Hess, R. R; Gordon, P. L.; Tait, D. C.; Abney, K. D.; Dorhout, P. K. J. Am. Chem.
Soc. 2002, 124, 1327.

16. Chondroudis, K.; Kanatzidis, M. G. Inorg. Chem. 1998, 37, 3792.

125

Chapter 5
Synthesis and Characterization of Two New Europium Thioarsenates Featuring the

Tetrahedral AsS43' Ligand: AgEuAsS4 and Eu3Aszsg

Abstract

AgEuAsS4 (I) was obtained from a direct combination of Ag, Eu, As and S at 650°C. It
crystallizes in the orthorhombic space group Ama2 with a = 10.198(4) A, b = 10.084(4)
A, c = 6.479(3) A. The structure consists of tetrahedral AsS43' anions coordinating to Ag+
ions in a distorted tetrahedral geometry and Eu2+ ions in a bicapped trigonal prismatic
geometry to form a complex 3-D framework. Eu3A3283 (I I) crystallizes in the
rhombohedral space group R-3c with a = 9.254(3) A, c = 27.698(l2) A, y = 120°. It is
prepared by heating Eu, As and S in the required ratio at 650°C. This compound presents
a new structure type consisting of 8 coordinate Eu2+ and tetrahedral AsS43‘ ligands. The
magnetic susceptibility measurements on these compounds confirm that the Eu ions have

a +2 charge. Both compounds are stable in air and water over extended periods.

126

A. Introduction

Rare-earth chalcogenides are a subject of extensive investigation since the past decade.
These compounds exhibit a rich structural chemistry arising from the variable
coordination environment, ranging from 6-coordinate to 9-coordinate, of the rare-earth
ions. Some of these compounds include LiEuGeS4l, EugsmSezoz, EuzCuS33, KzEuTSes,
KEuTS4 (T = Si, Ge)4, CePS45, Ce28i356, EuSe27, EuzGeS48, AEuPSe4 (A = K, Li)9,
K4EuP2Qg, KEuPQ4 (Q = s, Se)1°' ”, NaCeP28e6, €61,33P23e6, AgCesteé,
Cu0,4Ce1_2PZSe612, RbgCeP4Se16'3, BaLaBi2Q6 (Q = 8, Se)”, A3REPZSe3 and A2REP28e7
(RE = Ce, Gd; A = Rb, Cs)”, Aszpzseé‘é, BaGdCuSe3”, BaLnMQ3'8, KzCuzCeS419,
KzAg3CeTe420, KCuCeTe42', Ca4(RE)zln4Q1322, CsCuCeS323, KLnMQ424, ALnQ4 (A = K,
Rb; Ln = Ce, Tb; Q = Se, Te), NaLnS325, ALn3Teg (A = K, Rb, Cs; Ln = Ce, Nd)“,
Cuo_66EuTe227, CS3PI‘5(PS4)628, AYbZnQ329, LazCuS430, KszCu489 etc.31 A recent review
by Ibers et a1. details the exquisite structural variety of transition metal-rare-earth
chalcogenides.32 These compounds can exhibit many interesting properties. For example,
EuSe27 exhibits meta-magnetic transition. CezsiSS, Ce6Si4817 and Ce4Si38126 are
potentially important as pigment materials. EuzGeS48 displays ferroelectric behavior
while EuzCuS33 consists of En in mixed valent states. KCuCeTe42' and KCUzEUTC427
consist of square Te nets, which show superstructure modulations arising from charge
density waves in the Te nets. Rare-earth sulfides have shown promise as optical and
electronic materials.” Incorporation of rare-earth cations led to increased thermal
stability in oxygen-atmosphere.22 Yet another important area where rare-earth cations
have found application are the lanthanide containing non-oxide glasses.34 These glasses

are potentially useful as fiber lasers and optical amplifiers.

127

The use of the solid state reactive flux technique for the synthesis of new materials at low
to intermediate temperatures35 has contributed immensely to the advancement of this
class of materials. Recently we started exploring the reactivity of different main group,
transition and rare earth metals in alkali metal thioarsenate fluxes.36 We undertook such
an endeavor in order to compare the behavior of the thioarsenate fluxes vis-a-vis the
thiophosphate fluxes. We were successfirl in isolating ASnAsSs, AzsnASZS6, A61nA53813,
APbAsS4, A4PbASzSg, A3MI’12AS4816 and AngzAs4813. The structures range from
molecular anions to layers. The reaction of Ce in Rb and Cs thioarsenate fluxes gave the
one-dimensional compound A3CeA5283 (see Appendix), which is isostructural to its
thiophosphate counterpart. The reactions of Eu in thiophosphate fluxes yield AEuPS4,
A4E11P233 (A = K, Rb, Cs)37 which are similar or isostructural to their Pb counterparts.
Since Pb and En have a similar chemistry, we realized that the reaction of En in
thioarsenate fluxes may yield compounds similar to APbAsS4 and A.;PbAszSg. We
therefore decided to study the reaction of Eu with Ag and Cu as the counter cation instead
of the alkali metals.

Ag and Cu have ionic radii similar to the alkali metals, K and Na, however their
interactions with chalcogens are covalent compared to the ionic bonding shown by the
alkali metals. In addition, Ag and Cu prefer low coordination environments and belong to
the d10 class of cations, which are known to exhibit interesting dm-dlo homoatomic
interactions.38 They are also known for their anomalous high atomic displacement
parameters attributed to anharmonic thermal vibrations.39 There are a very few synthetic
quaternary sulfides that contain both a coinage metal and As. These are K2AuAsS440,

KAngsS4“, CszAgAsS442, KAg3AszS543, [Fe(NH3)6]AgAsS444, (NI-I4)Ag2AsS445,

128

(NH4)Ag2A53S(5, (NH4)5Ag16(AsS4)746, (enH2)AgASS447, KCuzASS3 and KCu4AsS4.48
Copper or silver containing europium sulfides are even fewer such as KCuEu28649,
EuzCusg.3 and EuCuzMS4 (M = Ge, Sn).50 In view of this paucity, Eu3Aszsg and
AgEuASS4 represent welcome additions to this class of compounds. AgEuAsS4 is
isostructural to LiEuPSe4 whereas Eu3ASZSg presents a new structure type. The structures

and physical properties of these two compounds are discussed.

B. Experimental Section

B.l Reagents

The following reagents were used as obtained: Eu (metal chunk, 99.9%, Chinese Rare
Earth Information Center, Inner Mongolia, China), Ag (99.999% purity, Liberty coins,
Lansing, MI), AS283 (99.9 %; Strem Chemicals, Newburyport, MA), As (99.9%; Aldrich

Chemical Co, Milwaukee, WI), S (99.9 %; Strem Chemicals, Newburyport, MA).

B.2 Physical Measurements

Powder X-ray Difiraction

X-ray powder diffraction patterns were recorded on a CPS 120 INEL diffractometer (Cu
Ka radiation) operating at 40kV/20mA and equipped with a position sensitive detector
and a flat sample geometry.

Energy Dispersive Spectroscopy

Semiquantitative microprobe analyses on the compounds were done with a JEOL JSM-

6400V scanning electron microscope equipped with a Tracor Noran Energy Dispersive

129

Spectroscopy detector. Elemental compositions were obtained from an average of three
readings. Acquisition times were 303 or 453 per reading.

Diffuse Reflectance Spectroscopy

Solid state diffuse reflectance spectra were measured using a Shimadzu UV-3101 PC
double-beam, double-monochromator spectrophotometer. BaSO4 was used as reference.
Finely ground sample was Spread on a sample holder preloaded with the reference.
Energy gap was determined from a plot of absorbance vs energy by converting
reflectance to absorbance using the Kubelka-Munk function.51

Diflerential Thermal Analysis

The thermal behavior of the compounds was investigated by differential thermal analysis
using a Shimadzu DTA-50 thermal analyzer. Typically a sample (~20 mg) of ground
crystalline material was sealed in a silica ampule under vacuum. A Similar ampoule of
equal mass filled with A1203 was sealed and placed on the reference side of the detector.
The sample was heated to the desired temperature at 10°C/min, and afier 1-3 min it was
cooled at a rate of -10°C/min to 50°C. Residues of the DTA experiments were examined
by X-ray powder diffraction. Reproducibility of the results was checked by running
multiple heating/ cooling cycles.

Magnetic Susceptibility Measurements

Magnetization measurements as a function of applied magnetic field and temperature
were made on a MPMS Quantum Design SQUID susceptometer in the temperature range
of 2 to 300 K and magnetic fields of 0 to i55 kG. The samples consisted of about 70 -
80mg of each compound. For AgEuAsS4, the crystals were picked under the microscope

to eliminate any impurities in the sample.

130

B.3 Synthesis

AgEuAsS4 (I): AgEuAsS4 was synthesized by reacting a mixture consisting of Ag
(0.032g, 0.3mmol), Eu (0.045g, 0.3mmol), A3283 (0.074g, 0.3mmol) and S (0.038g,
1.2mmol). The starting materials were loaded in a fused-silica tube in a nitrogen-filled
dry glove box. The tube was then evacuated (<104 Torr) and sealed. The sealed tube was
put in a computer-controlled furnace and heated to 650°C. It was maintained at this
temperature for 60h. The tube was then cooled at the rate of 5°C/h to room temperature.
The product consisted of ruby-red rectangular rods (Figure 1), dark-red chunks and
yellow glass. The rectangular crystals constituted ~30% of the product. Semiquantitative
microprobe analysis using energy dispersive spectroscopy on the red rods gave an
average composition of "Ag._4Eu1.4A385,5". The average composition of the dark-red
chunks was "EuHAsSM" while the yellow glass had a composition of "A586". The
powder pattern of the product revealed that the dark red chunks were Eu3Aszsg.

Eu3AszSg (II): Eu3Aszsg was prepared by combining Eu (0.091g, 0.6mmol), AS (0.03g,
0.4mmol) and S (0.051g, 1.6mmol) at 650°C following the same procedure as described
above. The compound forms as ruby-red chunks with an average composition, as

determined by EDS, Of "EU34A82S72".

8.4 X-ray Crystallography

Single crystal data for AgEuAsS4 and EU3ASZSg were collected on Bruker SMART CCD
diffractometer with Mo KOL radiation. A full sphere of data was collected for both the
compounds. For AgEuAsS4, a rectangular rod with dimensions of 1.2 x 0.6 x0.7 mm3 was

mounted on a goniometer head and a full Sphere of data was collected using the SMART

131

software. An empirical absorption correction was applied using SADABS. The structure
was solved by direct methods using the SHELXTL packager"2 Systematic absences and
E2-1 statistics indicated a non-centrosymmetric Space group. The two choices were
Cch, and Ama2. Based on the combined figure of merit (CF OM) value, the space group
Cmc21 was chosen. However a suitable structural refinement could not be obtained.
Hence the space group Ama2 was chosen and after an initial round of refinement, one Ag,
one Eu, one AS and three S atoms were found. The thermal displacement parameter for
Ag was found to be very high and it occupied a position just slightly off the mirror plane
(1/4,y,z). Hence its occupancy was allowed to refine freely. This reduced its site
occupancy factor to 50% and generated a symmetry equivalent site 0.556 A away.
Anisotropic refinement of all the atoms gave a final R1/wR2 value of 4.69/ 12.71. We
suspected merohedral twinning of the crystal due to the fact that a and b are very close to
each other. Analysis of the structure using the program JANA200053 found no rotational
twinning.

For Eu3A52Sg, a red crystal chunk was mounted on a goniometer head and a full sphere of
data was collected. The space group R-3c was chosen based on intensity statistics and
systematic absences. The structure solution was straight-forward and after anisotropic
refinement of all the atoms, the final R1/wR2 value was 2.3 8/5.80.

The relevant crystallographic data for I and II are presented in Table 1. Table 2 gives the
coordinates of the atoms along with their isotropic displacement values. Anisotropic

displacement parameters are listed in Table 3.

132

Table 1. Crystallographic refinement data for AgEuASS4 and Eu3Aszsg.

Formula
Space Group
a, A

b, A

c, A

v, deg

Z, V

D, mg/m3
Temp, K

A, A

ll, mm'
F(000)
0m, deg

Total reflections

Total unique reflections
No. of parameters
Refinement method
Final R indices(I>28(I))
R indices (all data)
Absolute structure
parameter

Goodness of fit on F2

AgEuASS4
Ama2
10.198 (4)
10.084 (4)
6.479 (3)
9O

2, 666.3 (5)
4.615

293
0.71073
18.314
828

28.23
2388

776

44

R1= 0.0513, wR2 = 0.1271

009(4)

1.064

Eu3Aszsg
R-3c
9.254(3)
9.254(3)
27.698 (12)
120

3, 2054.2 (13)
4.182

293
0.71073
19.540
2298

28.15

1834

541

21

Full-matrix least-squares on F 2
R1: = 0.0469, wR2b = 0.1217 R1= 0.0238, wR2 = 0.0580

R1= 0.0272, wR2 = 0.0598

1.088

“ RI = 2 IIFol- IF.|l/ZIF.|. ” wR2 = {2 1w(F.2-F.2)21/21w(F.2)21}”2

133

(A2 x 103) for AgEuAsS4 and Eu3A5283.

Table 2. Fractional atomic coordinates and equivalent isotropic displacement parameters

 

 

Atom x y z Ueqal
AgEuASS4
Eu(l) 0.5000 0 0.9494(3) 18(1)
As(1) 0.7500 -0.2864(2) 0.9705(3) 12(1)
Ag( 1) 0.2770(20) 0.161 1(3) 1.5051(4) 106(6)
S(1) 0.5757(3) 0.2165(3) 1.2796(6) 20(1)
8(2) 0.7500 0.0604(4) 0.7034(8) 18(1)
3(3) 0.2500 0.0993(4) 1.1424(7) 14(1)
Eu3Aszsg
Eu(1) 0.3456(1) 0.0122(1) 0.0833 18(1)
As(1) 0 0 0.1595(1) 16(1)
8(1) 0 0 0.0806(1) 19(1)
8(2) 0.7035(1) 0.1330(1) 0.0182(1) 20(1)

 

134

a Ueq is defined as one third of the trace of the orthogonalized Uij tensor.

Table 3. Anisotropic displacement parameters“ (A2 x 103) for AgEuAsS4 and EU3ASZSg.

Eu(1)
As(1)
As(1)
S(1)
8(2)

8(3)

Eu(l)
As(1)
S(1)
S(3)

* The anisotropic displacement factor exponent takes the form:

-21t2[h2a*2U11 '1' 1(2b*2U22 + 120*2U33 '1' 2hka*b*U12 '1' 2k1b*C*U23 '1' 2hla*c*U13]

 

 

U11 U22 U33 U23 U13 U12
AgEuAsS4
14(1) 16(1) 24(1) 0 0 3(1)
12(1) 12(1) 14(1) 1(1) 0 0
257(19) 45(2) 16(1) -1(1) -34(5) -37(5)
16(2) 20(2) 25(2) -4(1) -9(1) 3(1)
14(2) 18(2) 21(3) 6(2) 0 0
15(2) 12(2) 16(2) 2(2) 0 0
Eu3Aszsg
21(1) 21(1) 15(1) 1(1) -1(1) 11(1)
17(1) 17(1) 13(1) 0 0 9(1)
21(1) 21(1) 13(1) 0 0 11(1)
23(1) 18(1) 20(1) 0(1) -6(1) 10(1)

135

C. Results and Discussion

C.1 Synthesis

The synthesis of AgEuAsS4 was achieved by combining Ag, Eu, AS283 and S in the ratio
2/1/1/4. This ratio gave the best yield for the compound. Even a direct combination of the
reactants failed to give a pure product as the product was contaminated with Ell3ASzSg.
Other ratios of the starting materials were attempted, but the reactions produced almost
always a mixture of the title compound, AgAsS2 and Eu3AS283. We made numerous
attempts to make CuEuAsS4 but always ended up with Cu3AsS4, Eu2CuS3 and Eu3AS283.
Eu3AS283 was a surprise find from the reaction of Cu, Eu, AS283 and S in the ratio
1/1/1/4. A pure synthesis of this compound was possible by combining Eu, As and S in a
3/2/8 ratio at 650°C. Both AgEuASS4 and EU3A8233 are valence precise compounds and
possess Eu in +2, Ag in +1, As in +5 and S in -2 oxidation states.

We also attempted reactions of Ag/Cu, AS2S3/As and S with Ce and Yb. For both the

metals, the reactions only gave Ce2S3, YbS or glassy products.

C.2 Structure description of AgEuAsS4

Figure 1b shows the unit cell of AgEuAsS4 looking down the c-axis. As seen in the
figure, columns of edge Sharing AgS4 and A884 tetrahedra are arranged parallel to the b -
axis. Adjacent columns are staggered with respect to each other. These columns are held
together by EuSs bicapped trigonal prisms to form the three dimensional network. The
edge sharing AgS4 and A884 tetrahedra form layers parallel to the bc- plane, Figure 2a.
The layers are made up of fused 12- member rings. These layers form channels down the

a -axis within which the Eu atoms reside. Also figure 2a shows that all the AgS4 and ASS4

136

tetrahedra point in the same direction showing the lack of a center of symmetry. Figure
2b shows the extended coordination of Eu. As can be seen, each Eu atom Shares two
edges and four comers with 6 ASS4 ligands. Each ASS4 ligand binds to 6 Eu atoms by
utilizing all its S atoms, Figure 2d. All the four S atoms connect to two Eu and one Ag
atom. Three of these S atoms do so in an edge-comer Sharing fashion while one S atom is
purely comer sharing. AgS4 tetrahedron is highly distorted with three short Ag-S bonds at
2.447(5) A, 2.592(7) A and 2.633(12) A and one long Ag-S bond at 2.985(14) A, Figure
2c. Similar distortions in the AgS4 tetrahedra are also observed in CS2AgAsS421 and
Fe(NH3)(5AgAsS4.23 The bond angles in the AgS4 tetrahedron range from 78.2(2)° to
146.4(7)°, Table 5. AS-S bond lengths are normal at 2.160(5) and 2.165(3) A. There are 8
Eu-S distances between 3.011(3) and 3.160(4) A, Table 4. Similar Eu-S distances are
observed in K4EuP283 and KEuPS4. The Eu—Eu distance is 5.993 A, too long for electron
exchange interactions to occur.

This compound is isostructural to LiEuPSe4, Figure 1c.9 Comparison of Figures 1b and
1c shows that there are two important differences between this structure and AgEuAsS4.
i) There is no disorder in the LiEuPSe4 structure and ii) In LiEuPSe4, Li and En sit in the
4a crystallographic Site whereas in AgEuAsS4, Ag (8c) and En (4a) occupy different
crystallographic sites. The other difference comes from the physical stability of the two
compounds. LiEuPSe4 is extremely air-sensitive whereas AgEuAsS4 is very stable in air.
In view of the fact that these compounds are non-centrosymmetric and can be potentially

useful NLO materials, the air-stability of AgEuAsS4 is an advantage.

137

Eu(1) - S(3)
Eu(1) - S(2)
Eu(1) - S(1)
Eu(1) - S(1)
As(1) - S(2)

As(1) - S(1)

Eu(1) - S(2)
Eu(1) - S(2)
Eu(1) - S(2)

Eu(l)- S(1)

Table 4. Selected bond distances for AgEuAsS4 and Eu3AS283.

2.191(4)

Ag(1) - Ag(1) 056(4)

AgEuAsS4
2 x 3.011(3) As(1) - S(3)
2 x 3.068(3)
2 x 3.153(4) Ag(1) - S(3)
2 x 3.160(4) Ag(l) - S(2)
2.160(5) Ag(l) - S(1)
2 x2.165(3) Ag(1)- S(1)
Eu3AS2Sg
2 x 2.9549(13) Eu(l) - S(2)
3.0519(16) As(1) - S(2)
3.0522(16) As(1) - S(1)
2 x 3.1438(10)

138

2.447(5)
2.592(6)
2.633(12)

2.985(14)

2 x 3.4309(14)
3 x 2.1630(12)

2.187(2)

Table 5. Selected bond angles for AsEuASS4 and Eu3AS2Sg

S(3) - 1511(1) - S(3)
S(3) - Eu(1) - S(2)
S(3) - Eu(1) - S(2)
S(2) - 1311(1) - S(2)
S(3) - 1311(1) - S(1)
S(3) - Eu(1) - S(1)
S(2) - 1311(1) - S(1)
S(2) - Eu(1) - S(1)
S(1) - 1311(1) - S(1)
S(3) - Eu(1) - S(1)
S(3) - 1311(1) - S(1)
S(2) - Eu(1) - S(1)

S(3) -Ag(1)- S(1)

S(3) - 1311(1) - S(3)
S(3) - Eu(1) - S(3)
S(3) - Eu(l) - S(3)
S(3) - 1511(1) - S(3)
S(3) - Eu(1) - S(1)

S(3) - 1311(1) - S(1)

130.93(17)
2 x 65.05(10)
2 x 148.58(12)
117.40(17)

2 x 75.00(10)
2 x 72.26(10)
2 x 9066(12)
2 x 133.92(9)
9453(15)

2 x 68.69(10)
2 x 130.75(9)
2 x 78.20(11)

126.8(2)

109.59(5)
2 x 126.52(3)
2 x 7520(3)
145.73(4)

2 x 141.28(4)

2 x 8004(3)

AgEuASS4

S(2) - Eu(1) - S(1)
S(1) - 1311(1) - S(1)
S(1) - Eu(1) - S(1)
S(1) - Eu(1) - S(1)
S(2) - As(1) - S(1)
S(1) - As(1) - S(1)
S(2) - As(1) - S(3)
S(1) - As(1) - S(3)
S(3) - Ag(1) - S(2)
S(3) -Ag(1) - S(1)
S(2) - Ag(1) - S(1)
S(2) - A811) - S(1)

S(1)--1‘\1°-.~(1)- S(1)

131131915283

S(3) - Eu(1) - S(3)
S(3) - Eu(l) - S(3)
S(3) - 1311(1) - S(3)
S(3) - Eu(1) - S(3)
S(1) - Eu(1) - S(3)

S(1) - 1311(1) - S(3)

139

2 x 80.95(10)
2 x143.42(12)
2 x 7071(6)
139.24(15)

2 x114.13(13)
110.3(2)
105.1(2)

2 x106.19(12)
104.2(2)
146.4(7)
97.5(3)
8926(2)

78.2(2)

2 x 6692(4)
2 x 6937(4)
2 x 144.54(3)
2 x 6427(4)
2 x 8323(2)

2 x l42.93(3)

S(3) - 1311(1) - S(1) 2 x 9211(3) S(3) - Eu(l) - S(3) 9957(4)
S(3) - 1311(1) - S(1) 2 x 6968(4) S(3) - As(1) - S(3) 3 x 10997(3)

S(1)-Eu(1)-S(1) 116.446(10) S(3)-As(1)-S(1) 3x108.97(3)

140

3)

 

b) Eu

 

 

 

 

 

Figure l. a) The red rectangular rods of AgEuAsS4 b) Unit cell of AgEuAsS4 viewed
down the c- axis. c) Unit cell of LiEuPSe4 looking down the c-axis showing that it is
isostructural to AgEuAsS4. The two structures differ in the positions of the univalent
cations (Li+ and Ag).

141

 

 

 

 

Figure 2. a) AgS4 and A384 tetrahedra fuse to form layers parallel to the bc- plane.
These tetrahedra point in the same direction implying lack of center of symmetry. b)
Extended coordination sphere of En showing that it is coordinated by 6 AsS4 ligands
in a bicapped trigonal prismatic geometry. c) The distorted tetrahedral environment
around Ag (1) Coordination sphere of an ASS4 ligand

142

C.3 Structure description of Eu3AS283

Eu3AS2Sg belongs to a new structure type in which tetrahedral ASS43' ligands coordinate
to En to form a three dimensional framework, Figure 3a. The unique and interesting
feature of this structure is the arrangement of the ASS43' anions down the c- axis. Figure
5a shows the repeat unit of the ASS43' anions in a unit cell. As seen, the first two
tetrahedra, labelled m, are staggered by an angle of ~17°. The next two tetrahedra,
labelled n, are also staggered by ~ 17° with respect to each other. The second tetrahedron
of m and the first tetrahedron of n are staggered by about 60°. The Eu atoms are arranged
in a hexagonal fashion around the A884 tetrahedra.

Each Eu is bound to 8 S atoms in a bicapped trigonal prismatic geometry with Eu-S
distances of 2.9549(13), 3.0519(16), 3.0522(16), 3.1438(10) and 3.4309(14) A. The As-S
bond lengths are 2.1630(12) and 2.187(2) A, Table 4. S-As-S angles are almost an ideal
tetrahedral angles with values of 109.97° and 108.97°, Table 5. Figures 5b and SC Show
the coordination spheres around Eu and As atoms.

A number of compounds have the molecular formula A3B2X3 and consist of tetrahedral
anions coordinating to heavy metal cations. Some include Pb3P20354, Ca3AS20355,
Pb3V20356, Ba3AS20357, Ba3Nb20358, Sr3V20359 etc. These compounds also have the
tetrahedral ligands staggered with respect to each other however the repeat distance for
such staggering is only two anions compared to the four in Eu3AS2Sg.

It is very surprising indeed that this compound could be made so easily. The
corresponding chalcophosphate analog, Eu3P283 and Eu3P2Se3, have not yet been
reported. Similarly we were unable to make Pb3ASst. Though Pb3P28360 exists, the

structure of this compound is very different from Eu3AS283. Pb3P2Sg crystallizes in the

143

cubic space group P213. The structure of Pb3P2$3 viewed down the diagonal axis is
shown in Figure 3b. Figure 4 shows the unit cells of Eu3AS283 and Pb3P283 along the

[110] direction.

C.4 Magnetism

To determine the oxidation state of En conclusively and to check if it exhibits mixed
valency, we conducted magnetic susceptibility measurements on AgEuASS4 and
Eu3AS2sg. Figure 6 shows the plots of inverse magnetic susceptibility (l/xm) versus
temperature. Both the compounds follow Curie law from 2K to 300K. The effective
magnetic moment (11.3) for AgEuASS4 comes out to be 7.2 BM, which is very close to the
calculated 7.9 BM for Eu”, Figure 6a. The ~10% difference in the calculated and
experimental susceptibilities probably arise from the presence of minor amount of
impurities. The pen— for Eu3AS283 was 12.53 BM which agrees reasonably well with the

calculated 13.68 BM for 3 Eu2+ ions, Figure 6b.

C.5 Diffuse Reflectance Spectroscopy and Thermal Analysis

The ruby red crystals of Eu3AS283 were ground to a fine powder and loaded on a BaSO4
surface. The optical absorption Spectrum of this compound Showed a very strong
absorption onset at 1.9 eV, Figure 7. This corresponds very well to its red color. The
absorption spectrum of AgEuAsS4 indicated an energy gap at about 1.87 eV. However
the sample displayed considerable tailing near the edge due to the presence of BU3A8288
as an impurity. Hence we were not able to determine the band gap of AgEuAsS4

conclusively. Optically, AgEuAsS4 has a very similar color as Eu3AS2Sg and therefore the

144

bandgap of 1.87eV is probably close to its actual value.

We analyzed the thermal behavior of Eu3AS283 by differential thermal analysis. The DTA
plot is shown in Figure 8. The plot shows two melting and recrystallization points in both
the cycles. This is indicative of the decomposition of the sample on heating. To confirm
this observation, we compared the powder pattern of the sample after DTA to the one
before the experiment. The powder pattern revealed that along with the peaks due to the
parent compound, there were a couple other strong peaks belonging to an unidentified

phase. We can therefore conclude that Eu3AS283 melts incongruently on heating.

D. Concluding Remarks

AgEuASS4 and Eu3AS2Sg are valence-precise compounds built from tetrahedral ASS43'
building blocks. It is noteworthy that AgEuAsS4 can be conceptually obtained by an
addition of one equivalent of Ag3ASS4 to Eu3AS283. AgEuAsS4 crystallizes in a non-
centrosymmetric Space group and is air-stable. It can therefore be a promising non-linear
optical compound. Eu3As283 has a unique structure type and it needs to be seen if
Eu3AS2Seg and Eu3AS2Te3 can form with the same structure. Other rare earth metals like
Ce and Yb need to be investigated in view of their propensity to exhibit mixed valence

states.

145

a)

b)

 

Figure 3. a) Unit cell of EU3A82Ss viewed down the c- axis showing the hexagonal
arrangement of Eu atoms around the staggered AsS4 tetrahedra b) Unit cell view of
Pb3P2Sg down the diagonal.

146

 

 

13)

 

Figure 4. a) Unit cell view of Ell3ASst down the 110 direction. b) Unit cell view of
Pb3P2Sg down the 110 direction. The figure shows that the two compounds are
structurally different.

147

 

Figure 5. a) Unit cell view down the a- axis shows the repeating unit of four AsS4
tetrahedra. The pairs of tetrahedra labelled m and n are staggered 17° with respect
to each other. The second tetrahedron of m and the first tetrahedron of n are
staggered 60° with respect to each other. b) Extended coordination Sphere of Eu c)
Coordination of the ASS4 ligand.

148

 

 

a) 2.5 50

 

 

 

 

 

     
   
 

 

 

 

| y = 0.022323 + 0.15655x R2= 0.99999
2 1 —40
1 5 — 30
x5 3
3R
1 ~20
05“ M: 7.2 BM ‘ 1°
0 1 - — -- — o
0 50 100 150 200 250 300
Temperature (K)
b) 10 15
y = -0014773 + 0.050945x R2 = 0.99985
8
~10
6
x5 :3?
4
— 5
2 a... = 12.53 BM
0 0
0 50 100 150 200 250 300

Temperature (K)

Figure 6. Plots of the inverse magnetic susceptibility and magnetic susceptibility of a)
AgEuAsS4 showing a 11.5 of 7.2 BM b) Eu3AS283 Showing a pm of 12.53 BM.

149

 

absorbance (or/S)

 

 

 

l l

1
0 1 l 2 3 4 5
Energy, eV

 

Figure 7. Optical absorption spectrum of Eu3AS2sg shows that it absorbs strongly
at 1.9 eV corresponding to its red color.

 

 

 

 

l l l L l l l l

0 100 200 300 400 500 600 700 800

0
Temperature, C

 

Figure 8. DTA plot of EU3A8233 showing two melting and two recrystallization
points. The powder pattern of the residue after DTA indicated that the compound
decomposes on heating.

150

References

10.

11.

12.

13.

. Aitken, J. A.; Larson, P.; Mahanti, S. D.; Kanatzidis, M. G. Chem. Mater. 2001, I3,

4714.

Evenson, C. R.; Dorhout, P. K. Z. Anorg. Allg. Chem.2001, 627, 2178.

Lemoine, P.; Carre, D.; Guittard, M. Acta Cryst. 1986, C42, 390.

Evenson, C. R.; Dorhout, P. K. Inorg. Chem. 2001, 40, 2409.

Gauthier, G.; Jobic, S.; Boucher, F. ; Macaudiere, P.; Huguenin, D.; Rouxel, J .; Brec,
R. Chem. Mater. 1998, 10, 2341.

Gauthier, G.; Jobic, S.; Evain, M.; Koo, H. J.; Whangbo, M. H.; Fouassier, C.; Bree,
R. Chem. Mater. 2003, 15, 828.

Aitken, J. A.; Cowen, J. A.; Kanatzidis, M. G. Chem. Mater. 1998, 10, 3928.

Tampier, M.; Johrendt, D. J. Solid State Chem. 2001, 158, 343.

Aitken, J. A.; Chondroudis, K.; Young, V. G.; Kanatzidis, M. G. Inorg. Chem. 2000,
39, 1525.

Chondroudis, K.; McCarthy, T. J.; Kanatzidis, M. G. Inorg. Chem. 1996, 35, 840.

a) Evenson, C. R.; Dorhout, P. K. Inorg. Chem 2001, 40, 2875. B) Evenson, C. R.;
Dorhout, P. K. Inorg. Chem 2001, 40, 2884.

Aitken, J. A.; Evain, M.; Iordanidis, L.; Kanatzidis, M. G.; Inorg. Chem, 2002, 41 ,
180.

Chondroudis, K.; Kanatzidis, M. G. Inorg. Chem. Commun. 1998, I, 55.

151

14. Choi, K. S.; Iordanidis, L.; Chondroudis, K.; Kanatzidis, M. G. Inorg. Chem. 1997,

15.

16.

17.

18.

19.

20.

21.

22.

23.

24.

25.

26.

27.

36, 3804.

Chondroudis, K.; Kanatzidis, M. G. Inorg. Chem. 1998, 37, 3792.

Chen, J. H.; Dorhout, P. K.; Ostenson, J. E. Inorg. Chem. 1996, 35, 5627.

Huang, F. Q.; Mitchell, K.; Ibers, J. A. Inorg. Chem. 2001, 40, 5123.

Yang, Y.; Ibers, J. A. J. Solid State Chem. 1999, 14 7, 366.

Sutorik, A. C.; Albritton, -T. J .; Kannewurf, C. R.; Kanatzidis, M. G. J. Am. Chem.
Soc. 1994, 116, 7706.

Patschke, R.; Brazis, P.; Kannewurf, C. R.; Kanatzidis, M. G. Inorg. Chem. 1998, 37,
6562.

Patschke, R.; Heising, J .; Kanatzidis, M. G. Chem. Mater. 1998, 10, 695.

Carpenter, J. D.; ku, S. J. Inorg. Chem. 1995, 34, 4647.

Sutorik, A. C.; Albritton, -T. J.; Hogan, T.; Kannewurf, C. R.; Kanatzidis, M. G.
Chem. Mater. 1996, 8, 751.

Wu, P.; Ibers, J. A. J. Solid State Chem. 1993, 107, 347.

Sutorik, A. C.; Kanatzidis, M. G. Chem. Mater. 1997, 9, 387.

Patschke, R.; Heising, J .; Schindler, J.; Kannewurf, C. R.; Kanatzidis, M. G. J. Solid
State Chem. 1998, I35, 111.

Patschke, R.; Brazis, P.; Kannewurf, C. R.; Kanatzidis, M. G. J. Mater. Chem. 1999,
9, 2293.

152

28.

29.

30.

31.

32.

33.

34.

35.

36.

37.

38.

39.

40.

Komm, T.; Schleid, T. Z Anorg. Allg. Chem. 2004, 630, 712.

Mitchell, K.; Huang, F. Q.; Caspi, E. N.; McFarland, A. D.; Haynes, C. L.; Somers,
R. C.; Jorgensen, J. D.; Van Duyne, R. P.; Ibers, J. A. Inorg. Chem. 2004, 43, 1082.

Strobe], S.; Schleid, T. Angew. Chem. Int. Ed. 2003, 42, 4911.

Yao, J .; Deng, B.; Ellis, D. E.; Ibers, J. A. J. Solid State Chem. 2003, I76, 5.

Mitchell, K.; Ibers, J. A. Chem. Rev. 2002, 102, 1929.

Kumta, P. N.; Risbud, S. H. J. Mater. Sci. 1994, 29, 1135.

Adam, J. -L. Chem. Rev. 2002, 102, 2461.

a) Sutorik, A. C.; Kanatzidis, M. G. Prog. Inorg. Chem. 1995, 43, 151. b) Kanatzidis,
M. G. Curr. Opin. Solid State Mater. Sci. 1997, 2, 139.

a) Iyer, R. G.; Kanatzidis, M. G. Inorg. Chem. 2004, 43, 3656. b) Iyer, R. G.;
Kanatzidis, M. G. Inorg. Chem. 2002, 41, 3605.

Aitken, J. A. Ph. D Dissertation, Michigan State University, 2001.

a) Jansen, M. Angew. Chem. Int. Ed. 1987, 26, 1098. b) Kertesz, M.; Cui, C. X. Inorg.
Chem. 1990, 29, 2568.

a) Guadin, E.; Fischer, L.; Boucher, F.; Evain, M.; Petricek, V. Acta Cryst. 1997,
B53, 67. b) Chondroudis, K; Kanatzidis, M. G. Inorg. Chem. 1998, 37, 2848.

Loeken, S.; Tremel, W. Eur. J. Inorg. Chem. 1998, 2, 283.

153

41.

42.

43.

44.

45.

46.

47.

48.

49.

50.

51.

52.

Schimek, G. L.; Kolis, J. W. Acta Cryst. 1997, C53, 991.

Wood, P. T.; Schimek, G. L.; Kolis, J. W. Chem. Mater. 1996, 8, 721.

Chou, J. H.; Kanatzidis, M. G. J. Solid State Chem. 1996, 127, 186.

Schimek, G. L.; Kolis, J. W.; Long, G. J. Chem. Mater. 1997, 9, 2776.

Auemhammer, M.; Effenberger, H.; Irran, E.; Pertlik, F.; Rosenstingl, J. J. Solid State
Chem. 1993, 106, 421.

Pertlik, F. Monat. Chem. 1994, 125, 1311.

An, Y.; Li, X.; Liu, X.; Ji, M.; Jia, C. Inorg. Chem. Commun. 2003, 6, 1137.

Jerome, J. E.; Wood, P. T.; Pennington, W. T.; Kolis, J. W. Inorg. Chem. 1994, 33,
1733.

Bensch, W.; Duerichen, P. Chem. Ber. 1996, 129, 1489.

Llanos, J .; Mujica, C.; Sanchez, V.; Pena, O. J. Solid State Chem. 2003, 173, 78.

a) Wendlandt, W. W.; Hecht, H. G. Reflectance Spectroscopy; Interscience: New
York, 1966. b) Kotum, G. Reflectance Spectroscopy; Springer-Verlag, New York,
1969. c) Tandon, S. P.; Gupta, J. P. Phys. Status Solidi 1970, 38, 363.

SMART 5. 054, SAINT 6.36, SHELXT L 5.1: Bruker-Axs Inc., Madison, WI 1997.

53.JANA2000: Petricek, V.; Dusek, M. Institute of Physics AVCR, Praha, Czech

Republic, 2004.

54.Angel, R. J.; Bismayer, U.; Marshall, W. G. J. Phys. : Condens. Matter 2001, 13,

5353.

154

55. Gopal, R.; Calvo, C. Can. J. Chem. 1971, 49, 1036.

56. Kiat, J. M.; Garnier, P.; Pinot, M. J. Solid State Chem. 1991, 91, 339.

57. Bluhm, K.; Park, C. H. Z Naturforsch. 1996, 51 , 722.

58. Vanderah, T. A.; Collins, T. R.; Wong-Ng, W.; Roth, R. S.; Farber, L. J. Alloys de
2002, 346, 116.

59. Carrillo-Cabrero, W.; von Schnering, H. G. Z. Kristallogr. 1993, 205, 271.

60. Post, E.; Kraemer, V. Mater. Res. Bull. 1984, 19, 1607.

155

Chapter 6
Chemistry of Trivalent Main Group Metals: Discovery of A61nAs3SI3 (A = K, Rb,
Cs), A3BIASst (A = Rb, Cs) and A9BiAS4Sm (A = K, Rb) from Alkali

Polythioarsenate Fluxes

Abstract

The reactions of In in K, Rb and Cs thioarsenate fluxes yielded three new compounds
containing molecular anions with the general formula A6[In(AsS4)2(Asss)] (A = K, Rb,
Cs). They crystallize in the triclinic space group P-l with a = 10.959(3) A, b = 11.376(3)
A, c = 12.909(3) A, a = 64.822(4)°, [3 = 86.025(4)°, y = 63.805(3)° for A = K; a =
11.128(3) A, b = 11.532(3) A, c = 13.396(3) A, a = 65.102(4)°, fl = 85.987(4)°, y =
64.045(4)° for A = Rb; a = 10.959(3) A, b = 11.376(3) A, c = 12.909(3) A, a =
64.822(4)°, fl = 86.025(4)°, y= 63.805(3)° for A = Cs. The compounds form as yellow
crystals with band gaps in the 2.6 eV region. They decompose on dissolution in water.
The reactions of Bi in these fluxes yielded the one-dimensional phase A3Bi(AsS4)2 (A =
Rb, Cs) and the molecular phase AgBi(ASS4)4 (A = K, Rb). A3BiAS2Sg crystallizes in the
orthorhombic space group ana with a = 9.337(4) A, b = 7.002(3) A, c = 24.904(12) A
for A = Rb and a = 9.665(3) A, b = 7.152(2) A, c = 25.365(8) A for A = Cs. A9BiAs4$16
crystallizes in P21212 with a = 18.716(14) A, b = 9.109(8) A, c = 9.864(9) A for A = K
and a = 18.877(4) A, b = 9.351(2) A, c = 10.137(2) A for A = Rb. A3B1A8233 formed as
yellow needles whereas A9BiAs4Su; formed as red blocks/plates. A9BiAs4Sus dissolve in

water to form a reddish-brown colored solution that is stable for more than a day.

156

A. Introduction

Following our success in establishing the broad synthetic scope of polychalcophosphate
fluxes1 in stabilizing a variety of building blocks and diverse structures, we decided to
investigate how the corresponding polychalcoarsenate, in particular thioarsenate, fluxes
would perform. Our results with main group metals, Sn and Pb, gave enough evidence
that these fluxes were as rich and promising as their chalcophosphate counterparts and
their potential needed to be exploitedz’ 3 Sn gave compounds that were molecular
(CS2SnAS289), one-dimensional (NaSnASS4, KSnAsSs and RbSnAsSs) or two
dimensional (K2SnAS2S6 and Rb2SnAS286) with Sn in the +4 oxidation state. Pb reacted
very differently to give two-dimensional APbAsS4 and chains of A4PbAS2Sg (A = Rb, Cs)
with Pb in the +2 oxidation state. The marked difference between the compounds of these
two metals, other than their structures, was the type of thioarsenate ligand formed. In the
case of Sn, we isolated pyramidal B-ASS43' and AS853“ ligands, which feature AS in the +3
oxidation state and a disulfide unit, whereas in the case of Pb the well-known tetrahedral
A3843" ligand with As in the +5 oxidation state was observed. These results indicated that
the metal might have a significant role to play in defining the final thioarsenate ligand.
We therefore chose In and Bi to study the outcome of the reaction of M“ in
polythioarsenate fluxes and see what kind of ligands are generated.

The chemistry of indium and bismuth chalcogenides has been extensively investigated.
The photovoltaic material CuInSe24 and the thermoelectric material Bi2Te35 are probably
the most investigated compounds of Cu and Bi. While a major portion of research on
indium and bismuth chalcogenides have focussed on efforts to improve the efficiencies of

the above compounds, a significant amount of work has been done on discovering new

157

ternary and quaternary indium and bismuth chalcogenides. These metals display a rich
structural chemistry in their compounds. Indium has shown a great tendency to form open
cavity frameworks such as [In(Se6)2]', [M41n16S33]1°', [Cu3In17S33]l°' etc.6 Some other
known indium chalcogenides are AIn3SS, AInssg,7 AInS28 (A = alkali metal), KInGeS.;,9
KInSnSe4,lo [Fe(en)3]In2Te6ll etc. The field of bismuth chalcogenides has been advanced
to a great degree of complexity by our group in the last decade. We have gradually
increased the compositional and structural complexity to include KBi3Ss,12 K2Big;Se13,l3
CsBi4Te6,” CsMBi3Te6 (M = Pb, Sn),15 CSPb3Bi3Teg,'6 KSnsBi5$e13l7 etc.

Using In and Bi in a polychalc0phosphate flux we synthesized (Ph.;P)InP2Se(5,18
Cs51n(P2Se6)2,18 K4In2(PSe5)2(P2Se6),l9 KBiP2S7,2° KMP2Se6 (M = Sb, 131),21 [3-
131405329332 CS3Bi2(PS4)3, A3M(PS4)2, Namniuspzs.” and CSgM4(P2Se6)5.24 Other
known compounds include InPS4,25 KInP2S7,26 CuInP286,27 Im(P236)328 and BiPS4.29
Some of these compounds have shown interesting properties. InPS4 exhibits high NLO
susceptibility and piezo-coefficients,25 CuInP286 displays ferroelectric - paraelectric
transition27 and KSbP2Se6 shows reversible glass to crystal transformation.30
In comparison to the In and Bi chalcophosphates, the corresponding the chalcoarsenates
are woefully an extremely small class. Only a few compounds are known such as
CS.;BiAS3Se7,31 (Ph4P)2InAS3S7, (Me4N)2RbBiAs(5812.32 There are some solid solutions of
In, As and S however a concerted effort to discover new In and Bi chalcoarsenates has
been lacking. Here we report the synthesis and characterization of AslnAS3813,

A3BiAS2Sg and A9BiAS4816, which represent important additions to the quaternary

thioarsenate class of compounds.

158

B. Experimental Section

8.1 Reagents

All manipulations were done in a nitrogen-filled dri-vac glove box. Reagents: In
(99.999%; Cerac, Milwaukee, WI), Bi (99.999%; Noranda Advanced Materials, St.
Laurent, Quebec, Canada), AS283 (99.9%; Strem Chemicals, Newburyport, MA), As
(99.9%; Aldrich Chemical Co, Milwaukee, WI), S (99.9%; Strem Chemicals,
Newburyport, MA). N,N-dimethylformamide (Spectrum Chemicals, ACS reagent grade);
diethyl ether (CCI, ACS grade). K2S, Rb2S and C528 were prepared by dissolving the
alkali metal in liquid NH3 and reacting it with a stoichiometric amount of sulfur

according to a modified literature procedure.33

B.2 Physical Measurements

Powder X-ray Dififaction

X-ray powder diffraction patterns were recorded on a CPS 120 INEL diffractometer (Cu
Koc radiation) operating at 40kV/20mA and equipped with a position sensitive detector
and a flat-sample geometry.

Energy Dispersive Spectroscopy

Semiquantitative microprobe analyses on the compounds were done with a JEOL JSM-
6400V scanning electron microscope equipped with a Tracor Noran Energy Dispersive
Spectroscopy detector with an ultrathin window. Elemental compositions were obtained

from an average of three readings. Acquisition times were 303 or 45s per reading.

159

Diffuse Reflectance Spectroscopy

Solid state diffuse reflectance Spectra were measured using a Shimadzu UV-3101 PC
double-beam, double-monochromator spectrophotometer. BaSO4 was used as reference.
Finely ground sample was Spread on a sample holder preloaded with the reference.
Energy gap was determined from a plot of absorbance vs energy by converting
reflectance to absorbance using the Kubelka-Munk function.34

Infiared Spectroscopy

Far IR spectra of the compounds were recorded as CSI pellets on a Nicolet 740 F T-IR
spectrometer with a TSG/PE detector and silicon beam splitter. Raman spectra were
recorded on a Bio-rad F T- Raman spectrometer equipped with a Germanium detector and

using 633nm radiation from a HeNe laser for excitation with a 4cm'l resolution.

B.3 Synthesis

K6171ASjS/3 (I): K51flAS3S]3 was synthesized from a reaction mixture consisting of K28, In,
AS283 and 8 in the ratio 3/1/ 1/ 10. The mixture was loaded in a fused-silica tube and
sealed under vacuum (<10'4 Torr). The sealed tube was then placed in a computer-
controlled furnace and heated to 500°C. It was maintained at this temperature for 60h and
then cooled to 250°C at the rate of 5°C/h followed by fast-cooling to room temperature.
The product on isolation with N2-bubbled DMF revealed yellow crystals, colorless
crystals and pale brown crystals in equal amounts. The yellow crystals were air-sensitive
and decomposed in a few minutes. Energy dispersive spectroscopy (EDS) on the yellow
crystals gave an average reading of "K6_7In1,4AS2_3813_o2". The brown crystals were KIn82

while the colorless crystals were K3AsS4.

160

RbdnAS3S1 3 (II): Rb61flAS3Sl3 was obtained on heating Rb28, In, AS and 8 in the ratio
321:3:10 using the same heating profile as above. The product consisted of pale yellow
crystals of average composition "Rb5.7InAS2,1813,4" and pale orange crystals of RbIn82 as
determined by EDS. The product was air-stable however the yield of the compound was
very low (~15%).

Cs6InAs 3S, 3 (III): CsslnAS3813 was the product of the reaction of C328, In, AS283 and S in
the ratio 4/1/2/10. This mixture was heated at 500°C for 7days, after an initial isotherm at
250°C for 12h, followed by cooling to 200°C at the rate of 3°C/h and finally fast-cooling
to room temperature. Isolation of the product with degassed DMF gave yellow crystals,
which were stable in air. EDS on a several of the yellow crystals gave an average
composition of "CS62Ino3AS35814". Comparison of the powder pattern to that obtained
from Single crystal refinement indicated that this was the majority phase (~80%).

Rb 3BiAS2S3 (IV): Rb3BiAS2Sg was obtained as transparent yellow plates from a reaction
of Rb28(0.046g, 0.225mmol), Bi(0.031g, 0.15mmol), AS283(0.037g, 0.15mmol),
S(0.017g, 0.525mmol) in the ratio 1.5/l/1/3.5. The starting materials, loaded and sealed
in a fused-silica tube, were heated to 500°C and isothermed at that temperature for 60h.
This tube was then cooled to 250°C at the rate of 5°C/h, followed by rapid cooling to
room temperature. On isolation of the product with degassed DMF, transparent orange
plates and red cubic crystals were obtained. EDS on the plates gave an average
composition of "Rb3,4BiAS2_283.3" whereas the red cubes gave a reading of
"Rb3,3BiAS3,6815,7". The yield of the yellow plates was <10% of the total product.
CS3BlAS2Sg (V): CS3BiAS283 was obtained from a stoichiometric combination of the

starting materials C328, Bi, AS283 and S in the ratio 1.5/1/1/3.5 using the same heating

161

profile as above. The compound is isolated as transparent yellow plates in ~40% yield
along with red chunks and black rods. The average composition, as determined by EDS
analysis, was "CS3,lBiAS2_283,4" for the yellow crystals and ~"CscBiAs4816" for the red
chunks. The black rods were Bi283.

KgBiAs4Sl6 (V I): K9BiAs4816 was prepared by heating a mixture consisting of K28, Bi,
AS283 and 8 in the ratio 1.5/1/1/3.5 at 500°C according to the heating profile mentioned
above. The compound forms as red cubes with an average composition of
"K9B1A8398163" along with black wires of Bi2S3 in equal measure.

RboBiAs4S/6 (VII): RboBiAs4816 is the product of the reaction of a 2/1/1/10 ratio of
Rb28/Bi/As/S at 500°C. The procedure remains the same as the preceding compounds.
The compound is obtained as red plates (yield ~30%) along with black rods of Bi283. The

average composition from several red plates was "Rb9.3BiAS3,3816,3".

8.4 Single Crystal X-ray Crystallography

A full sphere of data comprising of 2424 frames, scanning 180 in 20 and a scan width of
03° in (1), was collected for all the compounds except KgBiAs4816 on a Bruker SMART
CCD diffractometer employing Mo K01 radiation. For KgBiAs4816, a hemisphere of data
was obtained. For K61flAS3SI3 and RbslnAS3813, the data were collected at 173K. The
remaining compounds were measured at room temperature. The data were merged using
the SAINT program and an absorption correction applied using SADABS. The structures
were solved by direct methods with the SHELXTL package of programs.35

For CS6IIIAS3813, after an initial round of least squares refinement, three high electron

density peaks were found close to 811 and 812. They were labeled 813, 814 and 815

162

respectively. 813 and 814 were 0.75 A and 1.575 A away from 811 and 2.056 A away
from each other. 814 was at a distance of 1.979 A from As3. Similarly 815 was at a
distance of 1.408 A from 812 and 2.350 A from A33. Therefore 813, 814 and 815 formed
an A585 unit along with 810 and 816. This ligand was disordered with the original ASS4
ligand formed by 810, 811, 812 and 816. After least squares refinement, the final
occupancy for the A384 ligand was 80% while the A885 ligand occupied 20% of the site.
Another disorder was found in the CS6 site. This position was disordered with another Cs
(CS7) at a distance of 0.723(8) A. The final R1/wR2 values, after anisotropic refinement,
were 0.0322/0.0744. The structures of K5111AS3S] 3 and RbslnAS3813 were solved Simlarly.
Cs3BiAS283 and Rb9BiAS4S|6 were solved in the orthorhombic space groups ana and
P21212 respectively. All the atoms were found in the first two least-squares cycles. The
thermal displacement parameter for Bi was found to be high and hence its occupancy was
released. Upon refinement, the Bi atom occupied only 50% of the Site and created another
equivalent site due to the presence of a mirror plane. Anisotropic refinement of all the
atoms gave final R1/wR2 values of 0.0404/0.0848 for CS3BIA8283 and 0.0433/0.0888 for
RbgBiAs4816.

Tables 1 to 9 list the crystallographic data, fractional atomic coordinates and anisotropic

thermal parameters for I to VII.

163

CsslnAS3813

empirical formula
fw

space group

a, A

b, A

c, A

01, deg

13. deg
Y, deg
V, A 3
Z

pcalcd, g/cm3
Au, mm‘1
T, K

,1, A
Total reflections
Total unique

R(int)

No. of parameters
Goodnes of fit on F 2
Refinement method
R1a

wR2b

Table 1. Crystallographic refinement details for K6111AS3813, RbéInAS3SI3 and

KslnAs3813 Rb61nA3381 3 CsalnAS3813
990.96 1279.60 1560.40
P-1 P-1 P-1
10.959(3) 11.128(3) 8.565(4)
11.376(3) 11.532(3) 11.026(5)
12.909(3) 13.396(3) 16.875(7)
64.822(4) 65.102(4) 78.3 88(7)
86.025(4) 85.987(4) 77.357(7)
63.805(3) 64.045(4) 80.454(12)
1292.8(6) 1388.2(6) 1510.7(11)
2 2 2
2.546 3.061 3.430
6.730 15.845 12.073
1 73(2) 173(2) 293 (2)
0.71073 0.71073 0.71073
12757 12361 15207
6025 6464 6876
0.0474 0.1296 0.0308
236 236 246
0.933 0.909 1.028

F ull-matrix least-squares on F2
0.0506 0.0628 0.0322
0.1055 0.0999 0.0744

164

0 R1 = z IIFel- IFeII/EIFOI- ” wR2 = {2 1w(F.2-F.2f1/2[w(F.2)21}”2

empirical formula
fw

space group
a, A

b, A

c, A

01, deg

13, deg

)1. deg

V, A 3

Z

pcalcd, g/cm3
#3 m"
T, K

11, A
Total reflections
Total unique

R(int)

No. of parameters
Goodnes of fit on F 2
Refinement method
R1a

wR2b

Table 2. Crystallographic refinement details for Rb3BiAS283 and Cs3BiAs2Sg

Rb3BiAS283 CS3BiAS2Sg
871.71 1014.03
ana ana
9.337(4) 9.665(3)
7.002(3) 7.152(2)
24.904(12) 25.365(8)
90 90
90 90
90 90
1628.2(13) 1753.3(9)
4 4
3.556 3.842
24.762 20.860
293(2) 293(2)
0.71073 0.71073
14223 17085
2131 2285
0.1122 0.0587
85 85
1.002 1.031
Full-matrix least-squares on F2
0.0518 0.0404
0.1058 0.0848

165

0 R1 = 2 "F.1- lFell/ZlFol- ” wR2 = {2 1w(F.2-F.2f1/21w(F.2)21}”2

Table 3. Crystallographic refinement details for KgBiAS4Su5 and RbgBiAs4816

empirical formula K9BiAs4816 RbgBiAS4S 16

fw 1373.52 1790.85
Space group P21212 P21212

a, A 18.716(14) 18.877(4)
b, A 9.109(8) 9.351(2)
c, A 9.864(9) 10.137(2)
0t, deg 90 90

[3, deg 90 90

7, deg 90 90

V, A 3 1682(2) 1789.3(7)
Z 2 2

owed, g/cm3 2.713 3.324

y, m" 11.256 21.695

T, K 293(2) 293(2)

/1, A 0.71073 0.71073
Total reflections 4852 153 81
Total unique 2900 4158
R(int) 0.0623 0.0751
No. of parameters 142 142
Goodnes of fit on F3 1.006 1.008
Refinement method F ull-matrix least-squares on F 2
R1a 0.0543 0.0433
wR2b 0.1004 0.0888

“ R1 = 2 lchl- tau/2w. 3 wR2 = {2 1w(F.3-F.3f1/21w(1~".3)’]}”3

166

(A2 x 103) for KélnAS3813, Rb6InAs3SI3 and Cs61nAS3813

Table 4. Fractional atomic coordinates and equivalent isotropic displacement parameters

 

 

Atom x y z Ueq“
K61flAS3Sl3
In(1) 0.6874(1) -0.0007(1) 0.2648(1) 15(1)
As(1) 0.4021(1) 0.3214(1) 0.2031(1) 14(1)
As(2) 1.0344(1) 0.0007(1) 0.2214(1) 17(1)
As(3) 0.7515(1) -0.3467(1) 0.3099(1) 32(1)
K(1) 0.6894(2) 0.4536(2) 0.1618(2) 25(1)
K(2) 0.8878(2) .0.2330(2) 0.6510(2) 29(1)
K(3) 1.1882(2) -0.2642(2) 0.0682(2) 28(1)
K(4) 1.1254(2) -0.3919(2) 0.3710(2) 30(1)
K(5) 0.4514(2) .0.2239(2) 0.4677(2) 30(1)
K(6) 0.7284(2) -0.1499(2) -0.0450(2) 37(1)
8(1) 0.5617(2) 0.2640(2) 0.0951(2) 23(1)
8(2) 0.9979(2) -0.0574(2) 0.4056(2) 23(1)
8(3) 0.8008(2) .0.2773(2) 0.4285(2) 22(1)
8(4) 0.2063(2) 0.4174(2) 0.1051(2) 22(1)
8(5) 0.9050(2) -0.0561(2) 0.1510(2) 17(1)
8(6) 0.4541(2) 0.1083(2) 0.3514(2) 21(1)
8(7) 1.2458(2) -0.1444(2) 0.2401(2) 22(1)
8(8) 0.4173(2) 0.4604(2) 0.2675(2) 20(1)

167

8(9)
S(10)
S(1 1)
S(12)
S(13)
S(14)
S(15)

S(16)

In(1)
As(1)
As(2)
As(3)
Rb(1)
Rb(2)
Rb(3)
Rb(4)
Rb(5)
Rb(6)
S(1)

S(2)

S(3)

0.9828(2)
0.7892(2)
0.5946(3)
0.9143(2)
0.6527(4)

0.5636(9)

0.7629(11)

0.5712(10)

0.6872(1)
0.4052(2)
1.0300(2)
0.7515(2)
0.1880(2)
0.6867(2)
0.1073(2)
0.4476(2)
1.1272(2)
0.2757(2)
1.2383(4)
0.4217(4)

0.9948(4)

0.2256(2)
0.0715(3)

-01 182(4)
-O.4226(3)

-0.4756(4)

-0.2398(10)
-0.5847(1 l)

-0.0458(13)

RbéInAS3 S 13

0.0030(1)
0.3187(2)
0.0067(2)
-0.3435(2)
0.7386(2)
0.4663(2)
0.2307(2)
.0.2213(2)
-0.3924(2)
0.1497(2)
-0.1353(4)
0.4556(4)

-0.0458(4)

168

0.1370(2)
0.3857(2)
0.1812(4)
0.2191(2)
0.3930(3)
0.2171(7)

0.4212(8)

0.1272(10)

0.2670(1)
0.2086(1)
0.2222(1)
0.3091(2)
0.0697(1)
0.1526(1)
0.3553(1)
0.4668(1)
0.3732(2)
0.0449(2)
0.2412(3)
0.2698(3)

0.3994(3)

23(1)
26(1)
22(1)
29(1)
32(1)
24(3)
31(3)

23(2)

14(1)
14(1)
14(1)
31(1)
26(1)
23(1)
25(1)
27(1)
29(1)
38(1)
19(1)
17(1)

18(1)

S(4)
8(5)
8(6)
8(7)
8(8)
8(9)
S(10)
S(1 1)
S(12)
S(13)
S(14)
S(15)

S(16)

Cs(1)
Cs(2)
Cs(3)
Cs(4)
Cs(5)
Cs(6)
Cs(7)

In(1)

0.9032(4)
0.5603(4)
0.2101(4)
0.4588(4)
0.9824(4)
0.7880(4)
0.7942(4)
0.91 18(4)
0.5964(7)
0.6545(10)
0.5668(14)
0.7420(20)

0.5763(16)

0.7623(1)
0.7541(1)
0.4431(1)
0.9588(1)
0.5029(1)
0.6851(6)
0.7604(12)

0.9698(1)

-0.0539(4)
0.2621(4)
0.4135(4)
0.1088(4)
0.2263(4)
0.0769(5)
-0.2701(4)
-0.4144(5)
-01 148(9)
-0.4679(10)
-0.2291(15)
-0.5610(20)

-00370(20)

CSfiInAS3S13
0.4363(1)
0.9937(1)
0.6389(1)
0.0643(1)
0.1022(1)
-0.3515(1)
-0.3818(9)

0.3777(1)

169

0.1596(3)
0.1022(3)
0.1 174(4)
0.3491(3)
0.1373(4)
0.3807(4)
0.4226(4)
0.2205(4)
0.1862(7)
0.3866(6)
0.2172(1 1)
0.4127(12)

0.1273(14)

-0.0014(1)
0.0555(1)
0.2283(1)
6.3353(1)
0.3283(1)
0.4695(1)
0.4809(3)

0.2645(1)

15(1)
19(1)
24(1)
18(1)
19(1)
22(1)
21(1)
29(1)
16(2)
29(2)
23(5)
26(5)

24(4)

37(1)
44(1)
49(1)
50(1)
57(1)
65(1)
91(2)

29(1)

As(1)
As(2)
As(3)
8(1)
8(2)
8(3)
S(4)
8(5)
8(6)
3(7)
S(8)
8(9)
S(10)
S(1 1)
S(12)
S(13)
S(14)
S(15)

S(16)

1.0666(1)
0.6902(1)
0.7795(1)
1.0635(2)
1.0370(2)
0.9055(2)
0.8898(2)
0.8658(2)
0.5395(2)
0.7137(2)
0.6371(2)
1.2746(2)
0.6764(2)
1.0417(4)

0.7506(4)

1.1281(14)
0.9841(10)

0.6013(14)

0.7131(3)

0.3058(1)
0.791 1(1)
0.2454(1)
0.2355(2)
0.5709(1)
0.2131(2)
0.2003(2)
0.5550(1)
0.7466(2)
0.6508(1)
0.9768(1)
0.1880(2)
0.3651(2)
0.2344(2)
0.3371(3)
0.2338(9)

0.2827(8)

0.2898(11)

0.0647(2)

—0.2130(1)
-0.1125(1)
0.4598(1)
0.0787(1)
0.3126(1)
0.1902(1)
-0.1323(1)
0.1536(1)
0.0051(1)
-0.1901(1)
.0.1712(1)
-O.2631(1)
0.3592(1)
0.3955(2)
0.5614(1)
0.3739(6)
0.4802(5)
0.5806(5)

0.4866(1)

26(1)
28(1)
43(1)
35(1)
33(1)
36(1)
38(1)
29(1)
40(1)
36(1)
38(1)
40(1)
38(1)
38(1)
73(1)
36(2)
40(2)
61(3)

70(1)

 

170

a Ueq is defined as one third of the trace of the orthogonalized Uij tensor.

(A2 X 103) for Rb3BiASzSg and CS3BiASzSg

Table 5. Fractional atomic coordinates and equivalent isotropic displacement parameters

 

 

Atom x y z Ueqa
Rb3BiASzSg
131(1) 0.5939(1) 0.1823(1) 0.4475(1) 24(1)
As(1) 0.6175(2) 0.2500 0.5896(1) 38(1)
As(2) 0.8440(1) 0.2500 0.3440(1) 21(1)
Rb(1) 1.2564(2) 0.2500 0.3154(1) 47(1)
Rb(2) 0.9809(2) -02500 0.4282(1) 49(1)
Rb(3) 0.3633(2) 0.2500 0.7159(1) 34(1)
8(1) 0.6858(4) 0.2500 0.6698(2) 36(1)
8(2) 0.8748(4) 0.2500 0.4324(2) 41(1)
8(3) 0.9334(3) -0.0005(4) 0.3103(1) 46(1)
8(4) 0.6875(3) -0.0008(5) 0.5473(1) 51(1)
8(5) 0.6124(4) 0.2500 0.3372(2) 46(1)
8(6) 0.6163(5) -0.1803(7) 0.4196(2) 26(1)
CS3BiASst
Bi(l) -0.0871(1) -O.1812(1) 0.9467(1) 24(1)
Cs(1) 0.2561(1) -o.2500 0.8172(1) 47(1)
Cs(2) 0.5326(1) -0.7500 0.9325(1) 46(1)
Cs(3) 0.3846(1) 0.2500 0.7185(1) 30(1)

171

As(1)
As(2)
8(1)
8(2)
S(3)
3(4)
S(5)

S(6)

0.1268(1)
0.1725(1)
0.0851(2)
.0.1022(3)
-0.3573(3)
-0.1006(4)
0.2073(3)

0.1865(3)

07500
-0.2500
-0.0035(4)
-02500
02500
0.1736(6)
-07500

-0.9970(5)

0.9152(1)
0.6566(1)
0.6889(1)
0.8367(1)
0.9301(1)
0.9196(2)
0.8382(1)

0.9576(1)

58(1)
21(1)
38(1)
36(1)
41(1)
27(1)
39(1)

62(1)

 

a Ueq is defined as one third of the trace of the orthogonalized Uij tensor.

172

(A2 x 103) for KgBiAS4816 and RboBiAS4816

Table 6. Fractional atomic coordinates and equivalent isotropic displacement parameters

 

 

Atom x y z Ueqa
K9BiAs4815
131(1) 0.0042(3) 0.5252(3) 0.7779(1) 21(1)
As(1) 0.1231(1) 0.2915(2) 0.9916(2) 22(1)
As(2) 0.1365(1) 0.7276(2) 0.5241(2) 20(1)
K(l) 0.0757(2) 0.1442(4) 0.5035(4) 37(1)
K(2) 0 0.5000 0.2695(5) 34(1)
K(3) 0.2685(3) -0.0180(6) 0.7390(4) 53(1)
K(4) 0.0869(2) 0.8745(4) 1.0196(4) 42(1)
K(5) 0.2482(2) .0.0024(5) 0.2520(3) 44(1)
8(1) 0.1026(2) 0.4973(5) 0.5613(4) 34(1)
8(2) 0.1071(2) 0.5294(4) 0.9828(5) 34(1)
8(3) 0.0843(3) 0.8096(5) 0.3446(4) 37(1)
8(4) 0.2509(3) 0.7300(5) 0.4994(6) 33(1)
S(5) 0.0821(3) 0.1979(5) 1.1756(4) 40(1)
S(6) 0.2335(3) 0.2350(5) 0.9721(5) 46(1)
3(7) 0.0546(3) 0.2106(7) 0.8295(5) 60(2)
8(8) 0.1027(3) 0.8597(6) 0.6923(5) 5 1 (2)

173

Bi(l)
Rb(1)
Rb(2)
Rb(3)
Rb(4)
Rb(5)
As(1)
As(2)
8(1)
8(2)
8(3)
S(4)
8(5)
8(6)
8(7)

8(8)

-0.0037(3)
0.0896(1)
0.2515(1)
0.2280(1)
0
0.0746(1)
0.1363(1)
0.1214(1)
0.1062(2)
0.2506(2)
0.0799(2)
0.0880(2)
0.1012(2)
0.2311(2)
0.0548(2)

0.1010(2)

Rb931AS4816

0.0218(3)
0.6255(1)
0.0001(1)
0.0121(2)
0
0.3484(1)
-0.2330(1)
0.2064(1)
.0.0253(3)
0.2633(3)
0.2968(3)
0.6908(3)
-0.0101(3)
0.2620(3)
0.2831(4)

0.63 86(4)

0.2765(1)
0.5142(1)
0.2489(1)
0.7608(1)
0.7676(1)
0.0001(1)
0.0233(1)
0.4886(1)
0.4783(3)
.0.0025(3)
0.6665(3)
—o.1555(2)
0.0612(3)
0.4738(3)
0.3264(3)

0.1854(3)

25(1)
35(1)
36(1)
45(1)
30(1)
33(1)
20(1)
20(1)
32(1)
30(1)
33(1)
30(1)
36(1)
43(1)
60(1)

51(1)

 

174

a Ueq is defined as one third of the trace of the orthogonalized Uij tensor.

Table 7. Anisotropic displacement parameters" (A2 x 103) for K61Ms3813, Rb6InAs3813

 

 

and CSGInAs3813

U11 U22 U33 U23 U13 U12

KélnAS3813

In(1) 13(1) 12(1) 18(1) -7(1) 3(1) -3(1)
As(1) 14(1) 11(1) 16(1) -6(1) 4(1) -4(1)
As(2) 16(1) 16(1) 20(1) -10(1) 6(1) -8(1)
As(3) 36(1) 58(1) 23(1) -23(1) 12(1) -34(1)
K(l) 24(1) 28(1) 31(1) -18(1) 10(1) -14(1)
K(2) 32(1) 25(1) 25(1) -10(1) 2(1) -11(1)
K(3) 34(1) 18(1) 21(1) -10(1) -2(1) -1(1)
K(4) 26(1) 20(1) 37(1) -7(1) 12(1) -10(1)
K(S) 25(1) 31(1) 24(1) -13(1) 3(1) -4(1)
K(6) 41(1) 32(1) 45(1) -23(1) 27(1) 20(1)
8(1) 21(1) 19(1) 18(1) -7(1) 8(1) -2(1)
8(2) 21(1) 30(1) 21(1) -15(1) 5(1) -10(1)
S(3) 26(1) 15(1) 19(1) -7(1) 4(1) -5(1)
8(4) 16(1) 18(1) 25(1) -6(1) -2(1) -6(1)
S(5) 16(1) 17(1) 20(1) -11(1) 7(1) -8(1)
8(6) 19(1) 12(1) 21(1) -4(1) 8(1) -3(1)
8(7) 15(1) 23(1) 28(1) -13(1) 2(1) -7(1)
8(8) 20(1) 17(1) 22(1) -12(1) 6(1) -6(1)

175

8(9)

S(10)
8(11)
8(12)
S(13)
8(14)
S(15)

S(16)

In(1)
As(1)
As(2)
As(3)
Rb(1)
Rb(2)
Rb(3)
Rb(4)
Rb(5)
Rb(6)
8(1)

8(2)

8(3)

22(1)
19(1)
18(2)
25(1)
48(2)
21(5)
50(7)

22(5)

14(1)
14(1)
17(1)
30(1)
37(1)
24(1)
31(1)
24(1)
25(1)
47(1)
17(2)
18(2)

18(2)

13(1)
37(1)
22(2)
24(1)
32(2)
28(5)
23(6)

18(6)

11(1)
14(1)
14(1)
61(1)
16(1)
25(1)
24(1)
31(1)
19(1)
31(1)
24(3)
11(2)

26(3)

35(1)
32(1)
28(2)
31(1)
30(2)
19(5)
30(5)

22(6)

Rb6InAS3 S 13

14(1)
12(1)
14(1)
18(1)
15(1)
28(1)
20(1)
20(1)
38(1)
44(1)
17(3)
19(3)

15(2)

-13(1)
25(1)
-15(2)
-18(1)
-15(2)
-10(4)
-5(4)

-7(5)

-5(1)
-5(1)
-6(1)
-21(1)
-8(1)
-17(1)
-8(1)
-10(1)
-8(1)
—21(1)

-9(2)

-7(2)

-11(2)

8(1)
9(1)
2(2)
2(1)
1 1(2)
1(4)
0(5)

41(4)

1(1)
4(1)
2(1)
10(1)
-2(1)
8(1)
2(1)
1(1)
13(1)
30(1)
3(2)
-1(2)

4(2)

-8(1)
-12(1)
-6(2)
0(1)
-29(2)
-7(4)
-31(6)

-5(5)

4(1)
-5(1)
-8(1)
-32(1)
-3(1)
-14(1)
-14(1)
-6(1)
-10(1)
-24(1)
-11(2)
-2(2)

-11(2)

8(4)
8(5)
8(6)
8(7)
8(8)
8(9)
S(10)
S(11)
S(12)
S(13)
S(14)
S(15)

S(16)

(:s(1)
(342)
(343)
<:s(4)
<:s(5)
(3(6)
<:s(7)

In(1)

16(2)
16(2)
21(3)
20(3)
21(3)
23(3)
25(3)
24(3)
16(4)
44(6)

31(9)

47(1 2)

33(10)

38(1)
37(1)
31(1)
59(1)
63(1)
78(2)
87(3)

36(1)

14(2)
14(2)
21(3)
8(2)

15(2)
31(3)
13(2)
23(3)
18(5)
28(5)

35(9)

38(12)

31(11)

35(1)
40(1)
77(1)
40(1)
64(1)

69(1)

139(3)

26(1)

16(2)
14(2)
24(3)
16(2)
20(3)
18(3)
22(3)
36(3)
17(5)
25(5)
19(9)
14(8)

9(9)

C85II’IAS3 S 13

41(1)
47(1)
44(1)
53(1)
52(1)
40(1)
56(1)

27(1)

177

-7(2)
-2(2)
-5(2)
-1(2)
-6(2)
-17(2)
-6(2)
-21(2)
-10(4)
-9(4)
-21(7)
-6(8)

-3(8)

-9(1)
-1(1)
-17(1)
4(1)
-15(1)
-9(1)
-45(2)

-3(1)

0(2)
4(2)
-3(2)
5(2)
2(2)
8(2)
7(2)
4(2)
-1(3)
4(4)
6(7)
8(8)

-6(8)

-16(1)
-1(1)
-7(1)
-18(1)
-26(1)
8(1)
-3(2)

-8(1)

-6(2)
-1(2)
-6(2)
-3(2)
-10(2)
-12(2)
-8(2)
1(2)
-5(3)
27(5)
-18(7)
4200)

-19(9)

-1(1)
3(1)
-13(1)
-12(1)
-10(1)
-6(1)
-21(3)

-7(1)

As(1) 26(1)

As(2) 26(1)

As(3) 59(1)

8(1)
8(2)
8(3)
8(4)
8(5)
8(6)
8(7)
8(8)
8(9)
8(10)
S(1 1)
S(12)
S(13)
S(14)
S(15)

8(16)

* The anisotropic displacement factor exponent takes the form:

-21t2[h2a*2Un + k2b*2U22 + 12c*2U33 + 2hka*b*U12 + 2klb*C*U23 + Zhla*C*U13]

30(1)
38(1)
37(1)
38(1)
32(1)
38(1)
36(1)
41(1)
36(1)
35(1)
35(1)
124(3)
28(5)
37(5)
66(7)

95(2)

24(1)
27(1)
42(1)
44(1)
33(1)
35(1)
34(1)
29(1)
39(1)
32(1)
27(1)
36(1)
48(1)
36(1)
61(2)
41(5)
53(5)
91(8)

66(1)

29(1)
31(1)
34(1)
34(1)
34(1)
40(1)
41(1)
31(1)
37(1)
46(1)
44(1)
47(1)
28(1)
42(1)
33(1)
32(4)
32(4)
26(4)

55(1)

178

-4(1)
-5(1)
-8(1)
-12(1)
-3(1)
-11(1)
2(1)
-6(1)
-1(1)
-13(1)
-2(1)
-15(1)
1(1)
4(1)
-18(1)
0(3)
-3(4)
-17(4)

23(1)

-7(1)
-9(1)
24(1)
-12(1)
-17(1)
-5(1)
-4(1)
-14(1)
-1(1)
-16(1)
-8(1)
-4(1)
-7(1)
-15(1)
-25(2)
4(4)
-11(3)
-5(4)

-30(1)

-6(1)
-2(1)
1(1)
2(1)
-9(1)
-13(1)
-14(1)
50)
~40)
-3(1)
-3(1)
0(1)
-8(1)
-5(1)
10(2)
0(4)
-9<4)
-6(6)

-47(1)

Table 8. Anisotropic displacement parameters* (A2 x 103) for Rb3BiASst and

 

 

C83BiA82Sg

U11 U22 U33 U23 U13 U12

Rb3BiA8283
131(1) 25(1) 27(1) 21(1) 0(1) 2(1) -2(1)
As(1) 21(1) 78(1) 16(1) 0 0(1) 0
As(2) 21(1) 21(1) 20(1) 0 2(1) 0
Rb(1) 33(1) 42(1) 66(1) 0 -6(1) 0
Rb(2) 39(1) 49(1) 60(1) 0 -13(1) 0
Rb(3) 33(1) 44(1) 25(1) 0 6(1) 0
8(1) 31(2) 55(3) 22(2) 0 -10(2) 0
8(2) 23(2) 79(3) 22(2) 0 -3(2) 0
8(3) 48(2) 27(2) 62(2) -14(2) 21(2) 0(1)
8(4) 53(2) 60(2) 41(2) -14(2) 10(2) -28(2)
8(5) 24(2) 81(3) 32(2) 0 -4(2) 0
8(6) 22(2) 26(3) 31(3) -9(2) -5(2) 2(2)
C83BiA8283

131(1) 24(1) 24(1) 24(1) 1(1) -2(1) -2(1)
Cs(1) 28(1) 46(1) 67(1) 0 5(1) 0
Cs(2) 34(1) 53(1) 53(1) 0 8(1) 0
Cs(3) 28(1) 38(1) 25(1) 0 1(1) 0

179

As(1)
As(2)
8(1)
8(2)
8(3)
3(4)
3(5)

8(6)

* The anisotropic displacement factor exponent takes the form:

-2n2[hza*2UH + k2b*2U22 + 12C*2U33 + 2hka*b*U12 ‘1' 2k1b*C*U23 ‘1' Zhla*C*Ul3]

20(1)
19(1)
36(1)
20(1)
21(2)
23(2)
30(2)

59(2)

136(2)

22(1)
26(1)
51(2)
80(3)
26(2)
63(3)

89(3)

17(1)
23(1)
52(2)
36(2)
22(2)
32(2)
24(2)

37(2)

180

0
0
-10(1)
0
0

7(2)

5(2)

1(1)
1(1)
12(1)
2(1)
0(1)
2(2)
9(1)
-2(1)

0

0

4(1)

2(2)

-42(2)

Table 9. Anisotropic displacement parameters* (A2 x 103) for KgBiAs4816 and

 

 

Rb913iAs..8l6
U11 U22 U33 U23 U13 U12
KoBiAs4816
Bi(l) 25(1) 15(2) 22(1) -1(1) -1(1) 12(2)
As(1) 25(1) 21(1) 21(1) -1(1) 2(1) -1(1)
As(2) 16(1) 24(1) 21(1) 3(1) 2(1) 2(1)
K(l) 46(3) 31(2) 32(2) 2(2) -1(2) -2(2)
K(2) 36(4) 29(3) 38(3) 0 0 5(3)
K(3) 65(4) 50(3) 44(2) 6(2) 22(2) -6(3)
K(4) 58(4) 35(2) 33(2) 2(2) -7(2) 2(2)
K(S) 49(4) 46(3) 37(2) -10(2) -6(2) 2(3)
8(1) 28(4) 27(2) 46(2) 3(2) 2(2) -7(2)
8(2) 41(4) 19(2) 43(2) 1(2) -4(2) 5(2)
8(3) 41(4) 43(3) 26(2) 7(2) -7(2) 1(3)
8(4) 15(3) 39(2) 46(2) 6(2) 6(2) -2(2)
8(5) 54(4) 37(3) 28(2) 9(2) 15(2) 6(3)
8(6) 35(4) 49(3) 55(3) 13(3) 12(3) 18(2)
8(7) 79(5) 73(4) 28(2) -21(3) 6(3) 47(4)
8(8) 64(5) 65(3) 26(3) -9(2) 7(2) 30(3)

181

131(1)
Rb(1)
Rb(2)
Rb(3)
Rb(4)
Rb(5)
As(1)
As(2)
8(1)
8(2)
8(3)
S(4)
S(5)
S(6)
S(7)

8(8)

* The anisotropic displacement factor exponent takes the form:

-21t2[hza*2U11 + k2b*2U22 + 12c*2U33 + 2hka*b*U12 + 2klb*C*U23 + Zhla*C*U13]

32(1)
47(1)
41(1)
62(1)
32(1)
37(1)
19(1)
26(1)
42(2)
21(1)
50(2)
35(2)
38(2)
34(2)
81(3)

62(2)

23(2)
26(1)
37(1)
38(1)
26(1)
32(1)
21(1)
16(1)
18(1)
33(1)
27(2)
36(2)
25(1)
43(2)
71(3)

69(2)

RbgBiAS4S 15

20(1)
30(1)
28(1)
35(1)
31(1)
30(1)
18(1)
18(1)
35(1)
35(1)
22(1)
20(1)
46(2)
50(2)
27(2)

22(2)

182

-3(1)
2(1)
-7(1)

3(1)

0(1)
-3(1)
2(1)
-1(1)
3(1)
-3(1)
-5(1)
-8(1)

-13(2)

17(2)

9(2)

1(1)
-5(1)
-1(1)

-14(1)

0
-1(1)
0(1)
3(1)
-2(1)
1(1)
11(1)
-8(1)
-3(1)
16(2)

4(2)

7(2)

-15(1)
0(1)
-2(1)
-10(1)
-3(1)
1(1)
-1(1)
1(1)
-8(1)
-1(1)
-2(1)
0(1)
14(1)
20(1)
47(2)

-28(2)

C. Results and Discussion

C.l Synthesis

The alkali metal indium thioarsenate system produced A61IlAS3813 as the only crystalline
phase. It was obtained from nearly all our reactions that involved changing the flux
basicity, reaction temperature and reaction profile. A number of other A28/In/AS2S3/s
ratios only yielded glassy products. We also attempted direct syntheses of A3InAS283,
AnlnAS3812, A3In2A83812 (A = K, Rb, Cs) but all of these reactions yielded glassy
products. We sought to crystallize the glasses by subjecting them to a differential thermal
analysis treatment, however the glasses did not transform through the entire range of the
DTA (1000°C). We tried to prepare M3InA8283, M61nAS3812 (M = Ag, Cu) but ended up
with AgInS2, AgAsS2, CU3ASS4 and CuInS2. Additionally all the ratios that produced the
title compounds also gave AInS2 or AIn583. Hence characterization of these materials
was difficult.

The reactions of Bi in potassium, rubidium and cesium thioarsenate fluxes always yielded
a mixture of products that included A3BiAS2$3 and A9BiA84816. We have evidence for
K3B1AS2$3 and CscBiAS4816 from EDS and cell parameters, but we haven't been able to
solve their structures due to bad crystal quality. Reaction parameters were changed by
adding more A28, changing AS283 with metallic As and varying the metal content.
However all the reactions produced A3BiAS283 or A9BiAs4816 along with Bi2S3 and/or
ABiS2. It seems that A9BiAs4816 is very stable under these conditions, since it was found
in nearly every reaction. Attempts to obtain pure phases were made by reacting

stoichiometric amounts of the elements, but these too gave a mixture of products.

183

Finally, the reactions of In and Bi in sodium thioarsenate fluxes resulted in phase
separation giving Na3AsS4, NaAsS2, NaInS2 and Bi283.

The solubility of the molecular compounds in water was determined. While A5111AS3313
dissolve in water, they decompose within a few minutes to give a white powdery
precipitate. AoBiAs4816 dissolve in water to generate a reddish-brown solution, which
remains stable for more than a day. KslnAs3813 is extremely air-sensitive whereas
Rb6InA83813 and CS6InAS3S| 3 are stable over several months. KgBiAs4816 and
RboBiA84816 remain stable under ambient conditions but they absorb moisture on

grinding.

C.2 Structure description of AnlnAS3813

Since all the three compounds are isostructural, we will focus on the description of
CsslnAS3813. This compound is composed of [In(AsS4)2(A885)]6' clusters that co-
crystallize with [In(AsS4)(A885)2]6' anions, with the former beings the major anion
(70%). Hence we will refer to this compound as CSGIDAS3313. Figure 1 shows the two
components of this molecule. As we can see, the In is coordinated octahedrally by two
tetrahedral A8843' anions and one A8853’ anion. Each anion uses two of its sulfur atoms to
coordinate to the metal. In the case of the A885 unit, it uses the disulfide arm and one
terminal sulfide to bind to the metal. The A835 anion is the distinct feature of this
compound. This ligand has not been observed previously in thioarsenate chemistry. The
selenophosphate analog, PSe53', of this anion has been reported.36 In has a distorted
geometry with In-S bond lengths in the range 2.574(2) A to 2.722(2) A. As-S distances

lie between 1.979(8) A to 2.350(9) A, while the 8-8 distance is 2.060(2) A. There are 6

184

crystallographically unique Cs atoms. Considering the Cs—S cutoff bond length as 3.9 A,
C81, C82, C85 and Cs6/Cs7 are seven-coordinate with distances ranging from 2.705( 12)
A to 3.874(15) A, CS3 and C84 sit in 8- coordinate sites with distances in the range
3.397(9) A to 3.879(2) A. S-In-S bond angles vary between 73.2(2) to 169.29(5). As(1)S4
and As(2)84 tetrahedra show a small deviation from ideal tetrahedral angles.
As(3)S4/As(3)85 tetrahedron however shows a large deviation due to the disorder.
Selected bond distances and angles for CSGInAs3813, Cs3BiAs283 and RbgBiAs4816 are
listed in Tables 10 and 11.

The compound Rbng2As4813, which was obtained from the reaction of Cd in Rb
thioarsenate flux, consists of two co-crystallized anions [Cd2(ASS4)4]8' and
[Cd2(AsS4)2(A885)2]8' with the latter being the major component.37a Another compound
that contains two different clusters in the lattice is C86M04823,6, which is made up of
[Mo4S4(S3)6]6' and [Mo4S4(S4)6]6’ anions.37b A compound very similar to this complex is
[In(en)2(A88e4)].en, which consists of octahedral In complexed by two ethylene diamine
ligands and one pyramidal ASSe43' ligand, in a bidentate fashion.38 The co-crystallization
of InAS38136' and InAS38146' implies that both the anions lie close to each other in terms of
stability and it might be possible to make them independent of each other by Slightly

changing conditions.

C.3 Structure description of A3BiA82Ss
Figure 2 displays the structure of CS3BiASst. This compound consists of one-
dimensional chains running down the c- axis. Figure 2b shows the chain, which is made

up of 5- coordinate Bi that is arranged in a zigzag fashion along the chain. The

185

stereochemical expression of the Bi 6s2 lone pair is evident in the structure. Each Bi is
coordinated by three tetrahedral A8843' anions, two of which coordinate using an edge
and one coordinates in a corner-sharing fashion. There are two different kinds of ASS4
ligands. As(1)84 coordinates to two Bi atoms by using an edge and comer. This ligand
also serves to propagate the chain. As(2)84 is a terminal ligand and uses an edge to bind
to a Bi atom.

Bi-S distances range from 2.632(4) A to 2.968(3) A. There are 2 long Bi-S lengths at
distances of 3.452(2) A and 3.517(2) A (not shown in Table 10). These are Shown as
dashed lines in Figure 2c. As -8 distances vary between 2.104(4) A to 2.267(4) A. C81 is
5- coordinate, C82 sits in a nine coordinate Site while CS3 is surrounded by 10 8 atoms.
The minimum and maximum Cs-S bond lengths are 3.434(4) A and 3.874(4) A.

The structure of A3BiAS283 is similar to A3BiP283 except that A3B1P233 crystallizes in the
non-centrosymmetric space group P212121 and does not exhibit Bi disorder. These chains
are also very Similar to K3LaP283,39 except that the La is 9- coordinated by 4 P843' units
in edge and face- sharing modes.

Based on the formation of A3BiA8283 and A9BiAs4815, a series of Bi compounds can be
predicted, similar to the series of Pb compounds, according to the general formula
(A3ASS4)n(BiASS4)m. This is shown in scheme 1. In the thiophosphate chemistry, we were
able to prepare CS3B12(PS4)3 while in the thioarsenate chemistry we were successful in
isolating the end member of the series, A9BiAs4815, which is the next topic of discussion.

Though BiPS4 exists, several attempts to prepare BiASS4 proved futile.

186

C.4 Structure description of A9BiAs4816
This compound is the end member of the series depicted in scheme 1. We will discuss the
structural details of RbgBiAs4816. This compound consists of molecular anions

[Bi(AsS4)4]9', that are packed as shown in Figure 3a. The individual molecule is shown

 

 

 

 

 

 

 

 

 

A3ASS4 . BiAsS
m = 1. n = >A3BIASZS3 4 +A3BizAS3312
‘ T
A3ASS4 BiAsS4
V
2 A A S '
BiASS4 3 S 4 >A6BiAS3SIZ 3 BIASS4
m = 1; n = 2
A3ASS4
3 A3ASS4 *

 

 

= 3 >AgBIAS4SI6

m=l;n

Scheme 1

in Figure 3b. As seen from this figure, Bi Sits in a distorted octahedral geometry ligated
by 4 A8843" anions. The Bi site is modeled as a split siteThere are two kinds of A834
ligands. One type coordinates to the metal using two sulfur atoms while the second type

is monodentate and uses one sulfur atom to bind to the metal.

187

This compound is very similar to the molecular anion [Ce(PSe4)4]9'.40 The Significant
difference between the title compound and the above compound is the coordination
geometry of the metal atom. Ce occupies a dodecahedral geometry compared to the
octahedral coordination of Bi. Another very related compound is K9-xLa1+x/3(PS4)4 which
contains alternating rows of [La(PS4)4]9' clusters and chains of [Lao_67(PS4)2]4'.39 The La
atoms in these clusters sit in an 8- coordinate square anti-prismatic site.

Bi-S distances are similar to the one reported above and range between 2.729(6) A to
3.052(6) A. As-S bond lengths are 2.142(3) A to 2.219(3) A. The five
crystallographically unique Rb atoms are coordinated by 8, 7, 6, 8 and 7 sulfur atoms

respectively. The cutoff Rb-S distance was taken as 3.8 A.

188

 

Figure 1. The two co-crystallized anions in the CS6InAS3813 lattice, [In(AsS4)2(Asss)]6'
and [In(AsS4)(A885)2]6'

189

 

    
 

@——-

  

 

 

Figure 2. a) The unit cell of CS3BiASst looking down the b- axis b) A single chain
showing the orientation of the 682 lone pair and coordination geometry around Bi

190

 

 

.. v 0
.101. c ’0 no \t ’

o 9 o
. 9 - e . ° 9
.&o\.oo'..o.oo'.

'9
o , ,o

'12 ool'°'~ 00..

 

 

b)

 

Figure 3. a) View down the b- axis of RbgBiAs4816. B) A Single cluster anion,
[Bi(ASS4)4]9' Showing the octahedral geometry of Bi. The split site is due to the
stereochemically active lone pair on Bi.

191

Table 10. Selected bond lengths for C861M83813, CS3BiA8283 and Rb9BiA84816

Cs(1)-S(1)
Cs(1)-S(5)
Cs(1)-S(6)
Cs(1)-8(7)
Cs(1)-8(4)
Cs(1)-S(5)
Cs(1)-S(6)
Cs(2)-8(8)
Cs(2)-8(4)
Cs(2)-S(6)
Cs(2)-8(9)
Cs(2)-S(1)
Cs(2)-8(4)
Cs(2)-S(6)
Cs(3)-S(15)
Cs(3)-8(9)
Cs(3)-S(5)
Cs(3)-S(2)
Cs(3)-S(12)

Cs(3)-8(4)

3.4364(18)
3.4812(17)
3.551(2)
3.624(2)
3.628(2)
3.6299(19)
3.641(2)
3.489(2)
3.5980(19)
3.623(2)
3.648(2)
3.6602(19)
3.744(2)
3.846(2)
3.397(9)
3.527(2)
3.594(2)
3.599(2)
3.616(3)

3.617(2)

CSéInAS3S 13

Cs(4)-S(1 1)
Cs(4)-S(16)
Cs(4)-S(13)
Cs(4)-S(3)
Cs(4)-8(9)
Cs(5)-S(13)
Cs(5)-8(8)
Cs(5)-S(16)
Cs(5)-S(16)
Cs(5)-S(10)
Cs(5)-8(9)
Cs(5)-8(7)
Cs(6)-Cs(7)
Cs(6)-S(15)
Cs(6)-S(14)
Cs(6)-S(12)
Cs(6)-8(9)
Cs(6)-S(2)
Cs(6)-S(10)

Cs(6)-S(12)

3.637(3)
3.665(3)
3.697(10)
3.709(2)
3.741(2)
3.290(1 1)
3.448(2)
3.459(2)
3.585(2)
3.642(2)
3.682(2)
3.7357(18)
0.723(8)
2.705(12)
3.370(9)
3.479(4)
3.557(3)
3.659(3)
3.746(3)

3.852(6)

192

Cs(7)-S(13)
Cs(7)-S(1 1)
Cs(7)-S(14)
In(1)-S(1 1)
In(1)-S(3)
In(1)-S(5)
In(1)-S(2)
In(1)-S(13)
In(1)-S(10)
In(1)-8(7)
As(1)-8(4)
As(1)-8(9)
As(1)-S(2)
As(1)-S(5)
As(2)-8(8)
As(2)-S(6)
As(2)-8(7)
As(3)-S(14)
As(3)-S(16)

As(3)-S(12)

3.567(10)
3.700(5)
3.874(15)
2.574(2)
2.5928(17)
2.6073(16)
2.6143(18)
2.639(9)
2.6748(18)
2.722(2)
2.1312(17)
2.1423(18)
2.1906(16)
2.2052(16)
2.1096(18)
2.1314(18)
2.1789(18)
1.979(8)
2.097(2)

2.110(3)

Cs(3)-S(6)

Cs(3)-8(7)

Cs(4)-S(14)

Cs(4)-8(8)

Cs(4)-S(12)

31(1)-31(1)
Bi(1)-S(4)
Bi(1)-S(3)
Bi(1)-S(2)
Bi(1)-S(6)
Bi(1)-S(6)
Cs(1)-S(2)
Cs(1)-S(1)

Cs(1)-S(5)

31(1)-31(1)
Bi(1)-S(7)
Bi(1)—S(1)
Bi(l)—S(5)

Bi(l)-S(1)

3.665(2)
3.879(2)
3.522(8)
3.558(2)

3.569(3)

0.9835(13)
2.632(4)
2.690(3)
2.837(4)
2.905(4)
2.968(3)

3.498(3)

2 x 3.639(3) Cs(3)-S(1)

2 x 3.6459(13)Cs(3)-S(1)

0.431(5)
2.729(6)
2.815(5)
2.858(5)

2.946(5)

As(3)-S(10) 2.1843(17)

As(3)-S(1 1)

As(3)-S(15)

S(1)-S(3)

Cs(3)-8(4)
Cs(3)-S(2)

As(1)-8(5)

2 x 3.7312(14)As(1)-S(6)

Cs(7)-S(14) 2.850(10)
Cs(7)-S(12) 3.130(10)
Cs(7)-S(2) 3.346(6)
Cs(7)-S(15) 3.413(16)
C83BiA8283

Cs(2)-8(4) 2 x 3.602(4)
Cs(2)-S(3) 3.874(4)
Cs(2)-S(1) 2 x 3.610(3)
Cs(2)-S(3)
Cs(2)-S(6) 2 x 3.836(3)
Cs(3)-S(5) 3.434(4)
Cs(3)-S(5) 3.485(3)

2 x 3.497(3)

2 x 3.543(2)

RboBiAs4816

Rb(2)-S(6) 3.368(3)
Rb(2)-S(5) 3.418(3)
Rb(2)-S(2) 3.543(3)
Rb(2)-S(6) 3.601(3)
Rb(2)-S(1) 3.605(3)

193

As(1)-8(4)
As(2)-S(1)
As(2)-S(2)

As(2)-8(3)

Rb(5)-8(8)
Rb(5)-8(7)
Rb(5)-S(2)
Rb(5)-S(3)

Rb(5)-S(5)

2.265(3)
2.350(9)

2.060(2)

2 x 3.550(4)
2 x 3.8420(17)
2.104(4)

2 x 2.147(4)
2.267(4)

2 x 2.119(2)
2.185(3)

2.220(4)

3.337(4)
3.384(3)
3.416(3)
3.417(3)

3.446(3)

Bi(1)-S(5)
Bi(1)-S(7)
Rb(1)-S(1)
Rb(1)-8(8)
Rb(1)-8(4)
Rb(1)-8(7)
Rb(1)-S(3)
Rb(1)-S(6)
Rb(1)-S(3)
Rb(1)-S(7)

Rb(2)-S(2)

2.963(5)
3.052(6)
3.301(3)
3.342(3)
3.403(3)
3.434(4)
3.444(3)
3.619(4)
3.626(4)
3.782(4)

3.338(3)

Rb(2)-8(4)
Rb(3)-S(2)
Rb(3)-S(2)
Rb(3)-S(6)
Rb(3)-8(8)
Rb(3)-S(1)
Rb(3)-S(6)
Rb(4)-S(3)
Rb(4)-8(4)
Rb(4)-S(5)

Rb(4)-S( 1 )

3.640(3)
3.385(3)
3.403(3)
3.422(3)
3.480(4)
3.690(3)

3.732(4)

2 x 3.321(3)
2 x 3.425(3)
2 x 3.538(3)

2 x 3.560(3)

194

Rb(5)-8(4)
Rb(5)-8(4)
As(1)-8(8)
As(1)-S(2)
As(1)-8(4)
As(1)-S(5)
As(2)-S(6)
As(2)-8(3)
As(2)-S(1)

As(2)-8(7)

3.471(3)
3.578(3)
2.142(3)
2.147(3)
2.150(3)
2.219(3)
2.140(3)
2.141(3)
2.188(3)

2.190(3)

Table 11. Selected bond angles for Cs6InA83813, C83BiAs283 and RbgBiAs4816

S(11)-In(1)-S(3)
S(11)-In(1)-S(5)
S(3)-In(1)-S(5)
S(1 1)-In(1)-8(2)
S(3)-In(1)-S(2)
S(5)-In(1)-S(2)
S(3)-In(1)-8(13)
S(5)-In(1)-8(13)
S(2)-In(1)-S(13)
8(1 1)-In(1)-8(10)
S(3)-In(1)-S(10)
S(5)-In(l)-S(10)
S(2)-In(1)-S(10)
S(13)-In(1)-S(10)
S(1 1)-In(1)-S(7)
S(3)-In(1)—S(7)
S(5)-In(l)-S(7)
8(2)-In(1)-S(7)
S(13)-In(l)-S(7)

S(10)-In(1)-S(7)

9972(7

167.75(7)

8967(6)

9062(7)

169.29(5)

8050(5)
101.1(2)
166.2(2)
88.1(2)

7931(8)
8710(6)
9343(5)
9764(6)
95.8(2)

8959(8)
9154(5)
9807(5)
8570(5)

73.2(2)

168.41(5)

CSéIl'lAS3S] 3

S(9)-As(1)-S(2)
S(4)-As(1)-S(5)
S(9)-As(1)-S(5)
S(2)—As(1)-S(5)
S(8)-As(2)-S(6)
S(8)-AS(2)-S(7)
8(6)-As(2)-S(7)
S(8)—A8(2)-S(1)
S(6)-As(2)-S(1)
8(7)-As(2)-S(1)
8(14)-A8(3)-S(16)
S(16)-As(3)—S(12)
S(14)-As(3)-S(10)
S(16)-As(3)-S(10)
S(12)-As(3)-S(10)
S(1 6)-As(3)-S(1 1)
S(12)-As(3)-S(1 1)
S(10)-As(3)-S(1 1)
S(14)-As(3)-S(15)

S(16)-As(3)-8(15)

195

1 1014(7)
112.09(7)
1 1 135(7)
100.26(6)
1 1341(7)
1 1469(7)
113.05(7)
109.68(7)
101.64(7)
102.90(6)
122.8(3)

1 16.05(12)
118.0(2)

1 1320(8)
111.48(10)
108.12(10)
108.53(13)
9771(8)
100.7(4)

88.9(3)

S(4)-As(1)-S(9)

S(4)-As(1)-S(2)

S(4)-Bi(1)-S(3)
S(4)-Bi(1)-S(2)
S(3)-Bi(1)-S(2)
S(4)-Bi(1)-S(6)
S(3)-Bi(1)-S(6)
S(2)-Bi(1)-S(6)
S(4)-Bi(1)-S(6)
S(3)-Bi(1)-S(6)
S(2)-Bi(1)-S(6)

S(6)-Bi( l )-S(6)

S(7)-Bi(1)-S(1)
S(7)-Bi(1)-S(5)
S(1)-Bi(1)-S(5)
S(7)-Bi(1)-S(1)
S(1)-Bi(1)-S(1)
S(5)-Bi(1)-S(1)

S(7)-Bi(1)-S(5)

111.91(7)

110.52(7)

9503(9)
84.75(10)
7643(9)

7718(12)
8366(9)

151.76(9)
68.92(12)
163.90(9)
102.40(8)

91 .23(9)

97.66(11)

115.89(12)

96.48(l9)
73.74(14)

88.93(12)

168.00(12)

87.46(17)

S(10)-As(3)-S(15)

CS3BiASzSg

S(5)-As(1)-S(6)
S(6)-As(1)-S(6)
S(5)-A8(l)-S(4)
S(6)-A8(1)-S(4)
S(6)-A8(1)-S(4)
S(5)-As(1)-S(4)
S(1)-As(2)-S(1 )
S(1)-As(2)—S(2)
S(1)-As(2)-S(3)

S(2)-As(2)-S(3)

RbgBIAS4S15

S(5)-Bi(l)-S(7)
S(8)-As(1)-S(2)
S(8)-A8(1)-S(4)
S(2)-As(1)-S(4)
S(8)-A8(1)-S(5)
S(2)-As(1)-S(5)

S(4)-As(l)-S(5)

196

105.0(3)

2 x111.47(11)
110.70(17)
113.88(16)

2 x 9214(14)
2 x 115.72(15)
113.88(16)
112.56(15)

2 x 111.55(9)
2 x 10936(9)

101.92(13)

103.85(11)
112.02(14)
109.24(13)
10948(12)
107.54(14)
109.18(11)

10934(12)

S(1)-Bi(1)—S(5)
S(5)-Bi(l)-S(5)
S(1)-Bi(1)—S(5)
S(7)-Bi(1)-S(7)
S(1)-Bi(1)-S(7)
S(5)-Bi(1)-S(7)

S(1)-Bi(1)—S(7)

174.76(15)
82.18(11)
91.46(17)
15903(13)
7094(13)
83.52(15)

88.17(10)

S(6)-As(2)-S(3)
S(6)-As(2)-S(l)
S(3)-As(2)-S(1)
S(6)-A8(2)-S(7)
S(3)-A8(2)-S(7)

S(1)-As(2)—S(7)

197

108.51(13)
111.37(12)
112.54(12)
115.01(15)
107.04(12)

102.29(14)

 

C.5 Spectroscopy

Diffuse reflectance spectra of CSGInAS3813, CS3BIASst and RbgBiAs4816 indicated that
these compounds were semiconductors with Sharp absorptions at 2.64 eV, 2.34 eV and
1.98 eV, which correspond well with their observed colors of light-yellow, golden-yellow
and red respectively, Figure 4. Though CS3B1A8233 and RbgBiAs4816 had impurities
(Bi2S3 mainly), we could identify their absorption because of a big difference in the
colors of the two phases (~1.2 eV for Bi2S3). In the case of the molecular phases, these
gaps are more appropriately described as HOMO-LUMO transtions, rather than as band
gaps.

Since RbgBiAS4S16 was soluble in water to give a reddish-brown solution, we decided to
conduct some solution UV-Vis spectroscopy to ascertain if the anions stay intact in water.
The spectrum of the solution showed a moderate absorption at 650nm (1.91 eV) which is
very close to the absorbance of the solid, which indicates that the cluster remains stable in
water.

The Far-IR spectra of CSfiIflAS3S13 and RbgBiAS4S16 are shown in Figure 5. The spectrum
of C86InAS3S13 shows a number of strong vibrational frequencies. Of these the peaks
appearing at 384, 402, 427 and 451 cm'1 can be attributed to AS-S stretching.“ The strong
peaks below 350 cm'1 can be due to Bi-S or As-S vibrations. The strong peak at 469cm'l
and the very weak peak at 502 cm'1 are due to the 8-8 asymmetric and symmetric
stretching modes respectively in the A885 ligand.42

The spectra of RboBiAs4816 shows diagnostic peaks at 406, 431 and 443 cm'1 due to the

stretching vibrations of the As-S bonds. Peaks at the same range have also been observed

198

for APbAsS4 and A4PbAS283 (A = Rb, Cs). The peaks below 400 cm'1 cannot be

definitely assigned due to the presence of Bi283 impurity in the sample.

D. Conclusion

The reactions of In and Bi in alkali polythioarsenate fluxes yielded the molecular
AGII'IAS3SI3 (A = K, Rb, Cs), A9BiAS4S15 (A = K, Rb) and the one-dimensional
A3BiAs283 (A = Rb, Cs). A5111AS3S13 represents the first example where a tetrahedral
A8853” ligand has been observed in a solid state compound. A3BiAS283 and A9BiAs4816
belong to the general series of compounds (A3ASS4)n(BiAsS4)m. The isolation of
molecular anions with high charge was facilitated by the use of a flux. A61HAS3Sl3
decomposes on dissolution in water however A9BiAs4816 remains stable suggesting that it
probably can be synthesized via solution chemistry. This stability can also render the
anion available for further chemistry in solution. A difficult problem in these systems has
been to optimize the synthesis to obtain pure compounds. Further studies are therefore
required to delineate the conditions in which these compounds can be obtained as single
phases. Based on our observations, it does seem that the metal has a definite role to play
in the determination of the ligands that are isolated in the product. To confirm this
hypothesis, extensive investigations involving gradual change of the reaction parameters

and metals are warranted.

199

 

 

 

 

 

 

 

 

 

 

 

 

 

Q
53
C.)
U
2:
B
5 Eg = 2.64 eV
U:
.0
C5
1 l I L 1
0 1 2 3 4 5
Energy, eV
b) <2)
<3 5
E". B
D V
5% §
e Eg = 2.34 eV .g
8 o
'9 .‘8
‘3 ca
1 l l J_ l . ‘ 1 l
0 1 2 3 4 5 0 I 2 3 4 5
Energy. eV Energy . CV

Figure 4. Optical absorption spectra of a) Cs6InAs3813 b) CS3BiA82Sg and c) RboBiAsnSu,
showing sharp absorption with onsets at 2.64 eV. 2.34 eV and 1.98 eV corresponding to
their light-yellow. golden-yellow and red colors

200

 

352 502

384

Transmittance

209
254

427 451

 

 

1 1 1 1
100 200 300 400 500 600

wavenumber (cm' 1)

 

 

b)

356

Transmittance

406

443
431

213
1 1 1 1

100 200 300 400 500 600
wavenumber (cm° 1)

 

 

 

Figure 5. Far-IR spectra of a) CSéInAS3SB, the peak at 469 cm'1 is due to 8-8 stretching
b) RboBiAs4816, the peaks above 400 cm"1 are due to As-S stretching.

201

References

1. a) Kanatzidis, M. G. Curr. Opin. Solid State Mater. Sci. 1997, 2, 139. b) McCarthy,
T. J.; Kanatzidis, M. G. Inorg. Chem. 1995, 34, 1257. c) Gauthier, G.; Jobic, 8.; Brec,
R.; Rouxel, J. Inorg. Chem. 1998, 37 (10), 2332. (1) Chen, J. H.; Dorhout, P. K.;
Ostenson, J. E. Inorg. Chem. 1996, 35, 5627.

2. a) Iyer, R. G.; Kanatzidis, M. G. Inorg. Chem. 2002, 41, 3605. b) Iyer, R. G.; Do, J .;
Kanatzidis, M. G. Inorg. Chem. 2003, 42, 1475.

3. APbAsS4 and A4PbASzSgI Iyer, R. G.; Kanatzidis, M. G. Unpublished results

4. a) Carmalt, C. J.; Morrison, D. E.; Parkin, I. P. J. Mater. Chem. 1998, 8, 2209. b)
Hirpo, W.; Dhingra, 8.; Sutorik, A. C.; Kanatzidis, M. G. J. Am. Chem. Soc. 1993,
115, 1597.

5. a) Boulouz, A.; Chakraborty, 8.; Giani, A.; Delannoy, F. P.; Boyer, A.; Schumann, J.
J. Appl. Phys. 2001, 89, 5009. b) Hong, S. J.; Chun, B. S. Mater. Res. Bull. 2003, 38,
599.

6. a) Dhingra, 8.; Kanatzidis, M. G. Science 1992, 258, 1769. b) Wang, C.; Li, Y.; Bu,
X.; Zheng, N.; Zivkovic, Q; Yang, C. 8.; Feng, P. J. Am. Chem. Soc. 2001, 123,
11506. c) Zheng, N.; Bu, X.; Feng, P. Nature 2003, 426, 428.

7. a) Deiseroth, H. J.; Reiner, C.; Schlosser, M. Z. Anorg. Allg. Chem. 2002, 628, 1641.
b) Deiseroth, H. J. Z. Kristallogr. 1986, 1 77, 307.

8. a) Schubert, H.; Hoppe, R. Z Naturforsch. 1970, 25b, 886. b) Kish, Z. Z.; Kanitseva,
S. 8; Mikhailov, Y. N.; Lazarev, V. B.; Semrad, E. E.; Peresh, E. Y. Dokl. Akad.
Nauk SSR 1985, 280, 398. c) Isaenko, L.; Vasilyeva, I.; Yelisseyev, A.; Lobanov, 8.;
Malakhov, V.; Dovlitova, L.; Zondy, J. J.; Kavun, I. J. Cryst. Growth. 2000, 218,
313.

9. Wu, P.; Lu, Y. J.; Ibers, J. A. J. Solid State Chem. 1992, 97, 383.

202

10. Hwang, 8. J.; Iyer, R. G.; Trikalitis, P. N.; Ogden, A. G.; Kanatzidis, M. G. Inorg.

11.

12.

13.

14.

15.

16.

17.

18.

19.

20.

21.

22.

23.

Chem. 2004, 43, 2237.

Li, J.; Chen, Z.; Wang, R. J.; Proserpio, D. M. Coord. Chem. Rev. 1999, 190-192,
707.

McCarthy, T. J .; Tanzer, T. A.; Kanatzidis, M. G. J. Am. Chem. Soc. 1995, 117, 1294.

McCarthy, T. J.; Ngeyi, S. P.; Liao, J, H.; DeGroot, D. C.; Hogan, T.; Kannewurf, C.
R.; Kanatzidis, M. G. Chem. Mater. 1993, 5, 331.

Chung, D. Y.; Hogan , T. P.; Rocci-Lane, M.; Brazis, P.; Ireland, J. R.; Kannewurf,
C. R.; Bastea, M.; Uher, C.; Kanatzidis, M. G. .I Am. Chem. Soc. 2004, 126, 6414.

Hsu, K. F.; Chung, D.Y.; Lal, 8.; Mrotzek, A.; Kyratsi, T.; Hogan, T.; Kanatzidis, M.
G. J. Am. Chem. Soc. 2002, 124, 2410.

Hsu, K. F.; Lal, 8.; Hogan, T.; Kanatzidis, M. G. Chem. Commun. 2002, 1380.

Mrotzek, A.; Kanatzidis, M. G. Inorg. Chem. 2003, 42, 7200.

Chondroudis, K.; Kanatzidis, M. G. Z. Anorg. Allg. Chem. 1998, 624, 975.

Chondroudis, K.; Kanatzidis, M. G. J. Solid State Chem. 1998, I36, 79.

McCarthy, T. J .; Kanatzidis, M. G. Chem. Mater. 1993, 5, 1061.

McCarthy, T. J.; Kanatzidis, M. G. Chem. Commun. 1994, 1089.

Aitken, J. A.; Brown, 8.; Chondroudis, K.; Jobic, 8.; Brec, R.; Kanatzidis, M. G.
Inorg. Chem. 1999, 38, 4795.

McCarthy, T. J.; Kanatzidis, M. G. J. Alloys de. 1996, 236, 70.

203

24.

25.

26.

27.

28.

29.

30.

31.

32.

33.

McCarthy, T. J .; Hogan, T.; Kannewurf, C. R.; Kanatzidis, M. G. Chem. Mater. 1994,
6, 1072.

a) Nitsche, R.; Wild, P. Mater. Res. Bull. 1970, 5, 419. b) Bridenbaugh, P. M. Mater.
Res. Bull. 1973, 8, 1055.

Kopnin, E.; Coste, 8.; Jobic, 8.; Evain, M.; Brec, R. Mater. Res. Bull. 2000, 35, 1401.

a) Maisonneuve, V.; Evain, M.; Payen, C.; Cajipe, V. B.; Molinie, P. J. Alloys de.
1995, 218, 157. b) Simon, A.; Ravez, J.; Maisonneuve, V.; Payen, C.; Cajipe, V. B.
Chem. Mater. 1994, 6, 1575.

Diehl, R.; Carpentier, C. D. Acta Cryst. 1978, B34, 1097.

Zimmermann, H.; Carpentier, C. D.; Nitsche, R. Acta Cryst. 1975, B31, 2003.

Breshears, J. D.; Kanatzidis, M. G. .I. Am. Chem. Soc. 2000, 122, 7839.

Wachhold, M.; Kanatzidis, M. G. Z. Anorg. Allg. Chem. 2000, 626, 1901.

Chou, J. H.; Kanatzidis, M. G. Inorg. Chem. 1994, 33, 1001.

Feher, F. In Handbuch der Pra'parativen Anorganischen Chemie; Brauer G., Ed.;
Ferdinand Enke: Stuttgart, Germany, 1954; vol. 1, pp 280—281.

34.3) Wendlandt, W. W.; Hecht, H. G. Reflectance Spectroscopy; Interscience: New

York, 1966. b) Kotum, G. Reflectance Spectroscopy; Springer-Verlag, New York,
1969. c) Tandon, 8. P.; Gupta, J. P. Phys. Status Solidi 1970, 38, 363.

35.SMART, SAINT, SHELXTL: Data Collection and Processing Software for the

SMART-CCD system; Siemens Analytical X-ray Instruments Inc., 1997.

36.a) Zhao, J.; Pennington, W. T.; Kolis, J. W. Chem. Commun. 1992, 265. b)

Chondroudis, K.; Kanatzidis, M. G. Chem. Commun. 1996, 1371.

204

37. a) Iyer, R. G.; Kanatzidis, M. G. Inorg. Chem. 2004, 43, 3656. b) Mironov, Y. V.;
Gardberg, A. 8.; Ibers, J. A. Inorg. Chem. 2002, 41, 1333.

38. Smith, D. M.; Pell, M. A.; Ibers, J. A. Inorg. Chem. 1998, 37, 2340.
39. Evenson, C. R.; Dorhout, P. K. Inorg. Chem. 2001, 40, 2884.
40. Chondroudis, K.; Kanatzidis, M. G. Inorg. Chem. Commun. 1998, 1, 55.

41.a) Chou, J. H.; Kanatzidis, M. G. Inorg. Chem. 1994, 33, 5372. b) Siebert, H. Z.
Anorg Allg. Chem. 1954, 225, 275. c) Nakamoto, K. Infiared and Raman Spectra of
Inorganic and Coordination Compounds. 5th ed.; John Wiley & Sons, Inc. 1997.

42. Jaroudi, O. E.; Picquenard, E.; Demortier, A.; Lelieur, J. P.; Corset, J. Inorg. Chem.
2000, 39, 2593.

205

Chapter 7

[Mn2(AsS4)4] 8' and [Cd2(AsS4)2(A885)2]8’: Discrete Clusters with High Negative

Charge from Alkali Polythioarsenate Fluxes

Abstract

The reaction of Mn and Cd in alkali polythioarsenate fluxes afforded four new
compounds featuring molecular anions. K3[Mn2(A884)4] (I) crystallizes in the monoclinic
space group P2/n with a = 9.1818(8) A, b = 8.5867(8) A and c = 20.3802(19) A, B =
95.095(2)°. Rb3[Mn2(ASS4)4] (II) and C83[Mn2(AsS4)4] (111) both crystallize in the
triclinic space group P-l with a = 9.079(3) A, b = 9.197(3) A, c = 11.219(4) A, CL =
105.958(7)°, B = 103.950(5)° and y = 92.612(6)° for 111 and a = 9.420(5) A, b = 9.559(5)
A, c = 11.496(7) A, or = 105.606(14)°, B = 102.999(12)° and y = 92.423(14)° for III. The
discrete dimeric [Mn2(AsS4)4]8' clusters in these compounds are composed of two
octahedral Mn2+ ions bridged by two {ASS4]3' units and chelated each by a [AsS4j3' unit.
Rb3[Cd2(ASS4)2(A885)2] (IV) crystallizes in P-l with a = 9.122(2) A, b = 9.285(2) A, c =
12.400(3) A, a = 111.700(6)°, B = 108.744°, y = 90.163(5)°. Owing to the bigger size of
Cd than Mn, the Cd centers in this compound are bridged by [A885]3' units. The
[Cd2(A884)4]8' cluster is a minor component cocrystallized in the lattice. These

compounds are yellow in color and soluble in water.

206

A. Introduction

Traditionally "all-inorganic" cluster compounds have been prepared in solution near
room temperature using standard precipitation techniques and aided by the use of organic
counter-ions.l Inorganic clusters have often been thought of as thermally too sensitive to
be stable at high temperatures and highly charged clusters have been exceedingly difficult
to deal with in water or organic solvents. The development of low temperature techniques
including the solventothermal method and the molten alkali flux method has made it
easier to isolate compounds with discrete clusters. Although primarily designed for
extended solids, the molten alkali polychalcogenide flux method2 can be a promising
synthetic technique for molecular chalcogenides as well. For example, alkali
polychalcophosphate fluxes have yielded several such compounds including
K6[Cr2(PS4)4]3, Rb3[M4(Se2)2(PSe4)4] (M = Cd, Hg)‘, C85[In(P28e6)2]5, K9[Ce(PS4)4]°,
Rb9[Ce(PSe4)4]7, A5[Sn(PSe5)3] ( A = K, Rb)“, A6[Sn28e4(PSe5)2] (A = Rb, C8)8,
A5[An(PS4)3] (A = K, Rb, Cs; An = U, Th)9, C810[Pd(PSe4)4]‘°, K4[Pd(PS4)2]‘°,
C84[Pd(PSe4)2]'°. Molecular salts are best obtained under highly basic flux conditions.2 It
is noteworthy that access to these highly charged anions would be extremely difficult
using "wet" chemistry.

Since the broad synthetic scope of polychalcophosphate fluxes11 in discovering new
materials has been established, we decided to investigate how the corresponding
chalcoarsenate fluxes might behave. Our initial experiments with main group metals, in
alkali thioarsenate flux yielded us CS28nAS2Q9 (Q= 8, Se) 12 and A6[InA83313] 13 (A = K,
C8) which contain discrete molecular complexes of [Sn(AsS4)(A885)]2' and

[In(ASS4)2(AsSs)]6‘ respectively.

207

We report here that the reactivity of Mn and Cd in alkali polythioarsenate fluxes (i.e.
molten AAsSx (A=alkali)) affords salts containing the highly charged molecular
thioarsenate complexes [Mn2(ASS4)4]8' and [Cd2(AsS4)2(AsSs)2]8'. It is interesting that
these salts are subsequently soluble in water. In addition, the cadmium complex presents

a rare example of a sulfur-coordinated Cd2+ with a full octahedral geometry.

B. Experimental Section

B.1 Reagents

The following reagents were used as obtained: Rb, CS metals (analytical reagent, Johnson
Matthey / AESAR Group, Seabrook, NH), K metal (analytical reagent, Aldrich Chemical
Company, Milwaukee, WI), 8 (99.9%, Strem Chemicals, Newburyport, MA), Cd, Mn
(Johnson Matthey / AESAR Group, Seabrook, NH), A8283 (99.9%; Strem Chemicals,
Newburyport, MA). K28, Rb28 and C828 were made by the reaction of the alkali metal

and sulfur in liquid ammonia using a modified literature procedure.l4

B.2 Physical Measurements

Powder X ~ray Dififiction

A calibrated CPS 120 INEL X-ray powder diffractometer equipped with a position-
sensitive detector, operating at 40kV/25mA with a flat geometry and employing Cu K01
radiation, was used to obtain diffractograms. Observed powder patterns were compared

with powder patterns calculated using the Cerius2 software package.

208

Energy Dispersive Spectroscopy

Energy Dispersive Spectroscopy (EDS), to analyze the composition of the compounds,
was done on a JEOL JSM-35C Scanning Electron Microscope (SEM) equipped with a
Tracor Northern detector. Data were acquired with an accelerating voltage of 20kV and
accumulation time of 458.

UV/Vis/near IR and Infiared Spectroscopy.

Optical diffuse reflectance measurements were made at room temperature using a
Shimadzu UV-3101 PC double-beam, double-monochromator spectrophotometer
operating in the 200-2500 nm region using a procedure described elsewhere in detail.15

F T-IR spectra were recorded as solids in a CsI matrix. The samples were ground with dry
C81 into a fine powder and pressed into translucent pellets. The spectra were recorded in
the far-IR region (600-100cm'l, 4cm'l resolution) using a Nicolet 740 F T-IR spectrometer
equipped with a TGS/PE detector and a silicon beam splitter.

Magnetic Susceptibility Measurements

Magnetization measurements as a function of applied magnetic field and temperature
were made on a MPMS Quantum Design SQUID susceptometer in the temperature range
of 2 to 300 K and magnetic fields of 0 to 3:55 kG. The samples consisted of a few (5 or 6)
large single crystals.

Dijfirential Thermal Analysis

Thermal studies were performed on Shimadzu DTA-50 thermal analyzer. Typically
samples were heated to 600°C at the rate of 10°C/min, held there for a minute, followed

by cooling to 100°C at the rate of -10°C/min. Residues of the DTA experiments were

209

examined by powder X-ray diffraction. Multiple heating/cooling cycles were run to

ascertain the reproducibility of the results.

B.3 Synthesis

K3[Mn2(AsS4)4] (I) was prepared by reacting a mixture of K28 (0.055g, 0.5 mol), Mn
(0.014g, 0.25mmol), A8283 (0.062g, 0.25mmol) and S (0.08g, 2.5mmol) in the ratio
2/1/1/10. All manipulations were done in a glove box under nitrogen atmosphere. The
reactants were loaded in fused silica tube and sealed under vacuum (<10'4 Torr). The tube
was then inserted in a furnace and heated to 500°C in 10 h. It was isothermed at this
temperature for 60 h before cooling down to 250°C at the rate of 5°C/h, followed by
rapid quenching to room temperature. Isolation of the product using N2-bubbled N, N -
Dimethyl F ormamide revealed large golden yellow crystals (~70% yield based on Mn)
and green micro-crystals. Energy Dispersive Spectroscopy revealed an average
composition of “K6,4Mn3As4814,4” and “K2Mn2,3AsS4,7” for the golden yellow crystals
and the green micro-crystals respectively. The powder diffraction pattern of the yellow
crystals compared very well to the simulated pattern obtained from single crystal
refinement.

Rb3[Mn2(AsS4)4] (II) was synthesized from a Rb2S/Mn/AS2S3/8 ratio of 3/1/1/10 using
the same heating profile as above. The product consisted of bright yellow, colorless and
black crystals. Electron microscopy analysis on several of the yellow crystals gave an
average composition of “Rbm2Mn2As48136”. The colorless and the black crystals were

Rb3AsS4 and MnS respectively.

210

C88[Mn2(AsS4)4] (III) was obtained from a reaction of C828/Mn/A82S3/S in the ratio
2/1/1/10. The method used was identical as mentioned above and the product consisted of
yellow, colorless and black crystals. Elemental analysis using EDS on the yellow crystals
confirmed the presence of all four elements with an average composition of
“CS79MI115AS433159”.

Rbg[Cd2(AsS4) 2(AsSs) 2] (IV) was the product of the reaction of Rb2S/Cd/AS2S3/S in the
ratio 2/1/1/10. The synthetic conditions remained the same as above and along with the
title compound were obtained colorless crystals of Rb3AsS4 and Rb28. The impurities
were a minor part of the product as determined from powder diffraction pattern. EDS

measurements on the yellow crystals gave an average value of “Rb9,6Cd2As4_5819,6”.

3.4 Single Crystal X-ray Crystallography

A Bruker SMART Platform CCD diffractometer, operating at 50kV/40mA and
employing graphite monochromatized Mo K01 radiation was used to collect crystal
diffraction data. A full Sphere of data was collected for all the compounds with scan
widths of 03° in (n and an exposure time of at least 308 per frame. Data was collected
using the SMART program and integrated with the program SAINT using the orientation
matrix obtained from SMART. An empirical absorption correction was done with the
program SADABS and all refinements were carried out with the SHELXTL16 package of
crystallographic programs. Based on systematic absences and intensity statistics, the
space group was determined to be P2/n for I, P-l for I], III and IV. Refinement of I, II
and III was straightforward to give final R1/wR2 values of 188/439, 227/54] and

4.28/ 12.24 respectively. For IV, after the initial round of least squares, one Cd, four Rb,

211

two AS and nine 8 atoms were found with R1/wR2 = 8.85/20.66. At this point, a high
electron density peak (assigned A822) was observed at a distance of 0.72 A from A82.
Two more peaks, one close to the disulfide arm at 0.72 A from S7 and 1.65 A from S3
(assigned 810), and one 1.22 A away from S9 (assigned 899), were observed. 810 and
899 were respectively 2.09 A and 2.13 A away from A822. Therefore a disordered model
was considered and structure refinement led to an occupancy of 85% for the [A885]3'
ligand and 15% for the [A884]3' ligand. Anisotropic refinement gave final R1/wR2 values
of 5.01/1 1.19. Crystallographic refinement details, fractional atomic coordinates with
isotropic temperature factors and anisotropic displacement parameters for all compounds
are given in Tables 1, 2 and 3. Selected distances and angles for K3[Mn2(ASS4)4] and

Rb3[Cd2(AsS4)2(A885)2]are given in Tables 4 and 5.

C. Results and Discussion

C.1 Synthesis

The synthesis of K3[Mn2(AsS4)4] was achieved by reaction of a mixture of a 2:1:1:10
ratio of K28/Mn/AS2S3/S at 500°C. The compound forms as large golden yellow crystals.
The product was contaminated with green micro-crystals of another quaternary phase of
approximate composition “K2Mn2,3AsS4_7” (based on EDS). The reaction involved the
oxidative dissolution of the metal in the basic melt and the subsequent coordination of the
divalent metal cations with the present [AsSx]3° anions. Reaction parameters were varied
through the addition of K28 and AS283. Increasing the basicity of the flux, by adding K28,
led to the formation of K3ASS4 along with the title compound. Our attempts to obtain

pure Rb3[Mn2(AsS4)4] and C83[Mn2(AsS4)4] were unsuccessful as the compounds always

212

formed with some amount of A3ASS4 and MnS. This effect is more pronounced on
increasing the flux basicity by adding more alkali sulfide. Increasing the fraction of
A8283 always led to glassy products. No other phases were detected in any of the
reactions.

The reactivity of Zn in potassium and rubidium thioarsenate fluxes was also explored.
Using the same reaction conditions as above, we obtained A3AsS4 and ZnS. Further work
needs to be done in order to establish an optimal synthetic ratio for isolating the Zn
analogs of these clusters.

Rbg[Cd2(ASS4)2(ASSs)2] was isolated from a reaction of Rb28/Cd/AS2S3/S ratio of
2/1/1/10. This system was more prone to give Rb3AsS4 and CdS on increasing the
basicity of the reaction (i.e. increasing the fraction of Rb28). A8 with the Mn chemistry
above, increasing the fraction of A8283 yielded glassy phases.

The cluster compounds reported here are soluble in water but insoluble in ethanol and
DMF. The aqueous solution of the AganAS4S15 is initially yellow-brown in color but
rapidly becomes colorless. This discoloration is so rapid that no absorption is observed in
the UV-Vis spectrum. After about an hour, the solution becomes milky. For the
Rbng2As4813 compound, a yellow precipitate is observed after about half a day. The
powder pattern of this yellow precipitate shows that it is CdS. These observations
indicate that the clusters do not remain intact in solution and precludes their formation by

wet chemistry. The clusters were found to be stable in air for at least a month.

213

Table 1. Crystallographic refinement details of KgMn2As4816, RbgMn2A84816,

CSsMn2A84S 16 and Rbst2A84S 13

empirical formula

space Group
a, A

b, A

c, A

01, deg

B. deg

7, deg

Z, V

posted, g/cm3
T, K
A, A

11, mm"

Total reflections

Total unique
R(int)

No. of parameters

Refinement method

R1“
wR2 b
GOF on F2

K3MI‘12AS4S16
9.1818 (8)
8.5867 (8)
20.3802 (19)

95.095(2)

4, 1600.5(3)

RbganAS4S 16

P-l
9.079 (3)
9.197 (3)
11.219 (4)
105.958 (7)
103.950 (5)
92.612 (6)
2, 867.8(5)
3.074

293
0.71073
16.620
8668

3921
0.0198

145

Full-matrix least-squares on F 2

0.0227
0.0541
1.000

CSsanAS4S16

P-l
9.420 (5)
9.559 (5) ‘
11.496 (7)
105.606 (14)
102.999 (12)
92.423 (14)
2, 965.5 (9)
3.415

293

0.71073
12.353

9201

4210

0.0266

136

0.0428
0.1224
1.053

" R1 = 2 "F.1- Ian/2118.1. ” wR2 = {2 1w(F.3-F.3f1/21w(Fo3)3]}”3

214

Rbng2As4S 13
P-l

9.122 (2)
9.285 (2)
12.400 (3)
111.700 (6)
108.744 (5)
90.163 (5)
2, 915.2(4)
3.239

173
0.71073
16.349
9225

4291
0.0502

173

0.0501
0.1119
1.042

Table 2. Fractional Atomic Coordinates and Isotropic Displacement Parameters (A2 x

103) for KgMn2As4816 RbgMn2As4816, CssMn2As4816 and Rbng2As4813.

 

 

Atom x y z Ueqa
K3Mfl2AS4S15
As(1) .0.0034(1) 0.3349(1) 0.6138(1) 12(1)
As(2) -0.4502(1) 0.1907(1) 0.3747(1) 12(1)
Mn(1) -O.1690(1) 0.3701(1) 0.4582(1) 14(1)
K(l) -0.1058(1) 0.3837(1) 0.8652(1) 22(1)
K(2) -02500 011910) 0.2500 30(1)
K(3) -0.8699(1) 0.1049(1) 0.3349(1) 27(1)
K(4) 0.2867(1) 1146(1) 5155(1) 21(1)
K(5) -0.2500 0.4114(1) 0.2500 26(1)
8(1) -O.583(1) 0.1610(1) 0.5389(1) 15(1)
8(2) -0.4491(1) 0.3393(1) 0.4614(1) 14(1)
8(3) -0.5567(1) 0.3064(1) 0.2908(1) 23(1)
8(4) 0.2284(1) 0.3880(1) 0.6182(1) 16(1)
8(5) —0.056l4(1) -0.0240(1) 0.3903(1) 24(1)
8(6) -0.2166(1) 0.1507(1) 0.3664(1) 15(1)
8(7) -0.1080(1) 0.5467(1) 0.5713(1) 15(1)
8(8) -0.0708(1) 0.2647(1) 0.7067(1) 20(1)

215

As(1)
As(2)
Rb(1)
Rb(2)
Rb(3)
Rb(4)

Rb(5)

Mn(1)

8(1)
8(2)
8(3)
S(4)
8(5)
8(6)
8(7)

8(8)

Cs(1)
Cs(2)
Cs(3)

Cs(4)

RbganAS4S l6

0.1316(1) 0.3130(1)
0.5478(1) 0.8874(1)
0.5657(1) 0.4804(1)
-0.1020(1) 0.2608(1)
-0.2631(1) 0.0179(1)
0.1082(5) 0.6838(5)
0.1 186(4) 0.6828(5)
0.3489(1) 0.1381(1)
0.5281(1) 1.1202(1)
0.3975(1) 0.8325(1)
0.3061(1) 0.4153(1)
0.4858(1) 0.7387(1)
0.0932(1) 0.0764(1)
0.2134(1) 0.3316(1)
-0.0745(1) 0.4199(1)
0.7719(1) 0.8666(1)
CssMnAs4S16
0.0722(1) 0.4763(1)
0.2410(1) 0.0227(1)
0.4013(1) 0.2589(1)
-0.6145(1) 0.3151(1)

0.2444(1)
0.2716(1)
0.2474(1)
0.4813(1)
0.0398(1)
0.1300(4)
0.1170(4)
0.4268(1)
0.2721(1)
0.3829(1)
0.4240(1)
0.0809(1)
0.2447(1)
0.0851(1)
0.2406(1)

0.3840(1)

0.7494(1)
0.5451(1)
0.9876(1)

0.3761(1)

216

20(1)
20(1)
31(1)
38(1)
34(1)
65(1)
34(1)
24(1)
25(1)
24(1)
28(1)
36(1)
29(1)
28(1)
38(1)

32(1)

33(1)
34(1)
38(1)

45(1)

Mn(1) 0.1509(1) 0.8618(1) 1.0727(1) 11(1)
As(1) 0.0470(1) 0.8878(1) 0.7744(1) 22(1)
As(2) -0.3643(1) 0.3088(1) 0.7449(1) 23(1)
S(1) 0.0237(2) 0.1128(2) 0.7733(2) 28(1)
8(2) 0.3975(2) -0.0804(2) 0.2519(2) 31(1)
8(3) -0.2817(2) 0.3288(3) 0.5903(2) 30(1)
8(4) 0.2015(3) 0.5917(2) 1.0784(2) 31(1)
8(5) -0.0068(3) 0.7446(3) 0.5885(2) 37(1)
8(6) -0.0961(2) 0.8342(3) 0.8857(2) 29(1)
8(7) 0.2646(3) 0.8675(3) 0.8816(2) 34(1)
8(8) 0.4328(3) 0.4092(3) 0.7375(3) 36(1)
Rbng2As4813
Cd(1) 0.3520(1) 0.3068(1) 0.4365(1) 18(1)
Rb(1) -0.1068(1) 0.2218(1) 0.4734(1) 19(1)
Rb(2) 0.4705(1) 0.1904(1) 0.7446(1) 20(1)
Rb(3) -O.2316(1) -0.0634(1) -0.0023(1) 23(1)
Rb(4) 0.0466(1) 0.5106(1) 0.8377(1) 29(1)
As(1) 0.1044(1) -O.388(1) 0.2686(1) 11(1)
As(2) 0.5734(2) 0.3607(2) 1.2344(2) 12(1)
As(22) 0.5628(14) 0.4050(13) 1.2725(12) 20(2)
8(1) 0.1424(3) -0.2010(2) 0.1077(2) 20(1)
8(2) 0.3116(2) 0.0155(2) 0.4330(2) 15(1)

217

S(4) 0.0684(2) 0.1873(2) 0.2553(2) 17(1)
8(5) -0.0980(2) -0.1370(2) 0.2843(2) 19(1)
8(6) 0.2384(3) 0.4602(3) 0.6210(2) 24(1)
8(3) 0.6447(3) 0.5242(3) 0.7932(2) 14(1)
8(7) 0.3479(4) 0.5671(4) 0.3844(3) 14(1)
8(8) 0.5242(2) 0.1819(2) 0.2917(2) 17(1)
8(9) 0.5972(3) 0.2775(3) 1.0586(2) 20(1)
8(99) 0.5340(30) 0.3840(20) 1.0920(20) 61(7)
S(10) 0.3970(30) 0.5460(20) 0.3580(17) 23(4)

 

“ Ueq is defined as one third of the trace of the orthogonalized Uij tensor.

218

 

 

Table 3. Anisotropic displacement parameters” (A2 x 103) for KgMn2As4816
RbgMn2As4816,C83Mn2A84816 and Rbng2As4813.

Ull U22 U33 U23 U13 11.2

KgMn2As4816

As(1) 12(1) 13(1) 11(1) 0(1) 0(1) -1(1)
As(2) 11(1) 12(1) 13(1) -3(1) -1(1) 0(1)
Mn(1) 14(1) 15(1) 13(1) 1(1) -2(1) -2(1)
K(l) 20(1) 16(1) 29(1) 0(1) 3(1) -1(1)
K(2) 34(1) 22(1) 31(1) 0 -15(1) 0
K(3) 21(1) 29(1) 28(1) 8(1) -5(1) -1(1)
K(4) 18(1) 26(1) 20(1) -2(1) 2(1) —1(1)
K(5) 38(1) 24(1) 16(1) 0 8(1) 0
8(1) 17(1) 14(1) 14(1) -1(1) -2(1) -2(1)
8(2) 14(1) 17(1) 12(1) -3(1) 1(1) -1(1)
8(3) 25(1) 26(1) 15(1) -2(1) -7(1) 7(1)
8(4) 11(1) 17(1) 19(1) 0(1) -2(1) -1(1)
8(5) 17(1) 14(1) 39(1) -2(1) -1(1) -4(1)
8(6) 13(1) 18(1) 16(1) 2(1) 1(1) 1(1)
8(7) 16(1) 15(1) 15(1) 1(1) 0(1) 2(1)
8(8) 26(1) 24(1) 11(1) 2(1) 4(1) 2(1)

219

As(1)
As(2)
Rb(1)
Rb(2)
Rb(3)
Rb(4)

Rb(5)

18(1)
25(1)
28(1)
36(1)
32(1)
72(2)

28(1)

Mn(1) 26(1)

8(1)
8(2)
8(3)
S(4)
8(5)
8(6)
8(7)

8(8)

Cs(1)
Cs(2)
Cs(3)

Cs(4)

32(1)
24(1)
34(1)
58(1)
27(1)
31(1)
25(1)

26(1)

29(1)
33(1)
36(1)

44(1)

20(1)
19(1)
26(1)
37(1)
35(1)
29(1)
33(1)
26(1)
20(1)
27(1)
22(1)
29(1)
21(1)
33(1)
42(1)

38(1)

28(1)
34(1)
39(1)

34(1)

RDgMIleS4S 16

22(1)
19(1)
38(1)
39(1)
35(1)
64(2)
34(1)
21(1)
28(1)
20(1)
21(1)
21(1)
35(1)
22(1)
54(1)

36(1)

(:83an29184515

40(1)
35(1)
38(1)

44(1)

7(1)
7(1)
11(1)
10(1)
10(1)
17(1)
9(1)
9(1)
12(1)
3(1)
4(1)
3(1)
10(1)
10(1)
22(1)

18(1)

9(1)
6(1)
8(1)
11(1)

3(1)
7(1)
4(1)
10(1)
7(1)
-38(1)
-3(1)
4(1)
10(1)
4(1)
0(1)
12(1)
-1(1)
6(1)
14(1)

9(1)

4(1)
9(1)
11(1)

-12(1)

3(1)
4(1)
4(1)
5(1)
6(1)
-12(1)
1(1)
7(1)
6(1)
-3(1)
3(1)
6(1)
-2(1)
4(1)
16(1)

10(1)

4(1)
4(1)
5(1)
4(1)

Mn(1) 12(1)

As(1)
As(2)
8(1)
8(2)
8(3)
S(4)
8(5)
8(6)
5(7)

8(8)

Cd(1)
Rb(1)
Rb(2)
Rb(3)
Rb(4)
As(1)

As(2)

26(1)
21(1)
34(1)
29(1)
31(1)
37(1)
57(2)
28(1)
26(1)

26(1)

23(1)
20(1)
20(1)
23(1)
39(1)
13(1)

14(1)

As(22) 33(4)

8(1)
8(2)

25(1)

16(1)

15(1)
21(1)
22(1)
22(1)
23(1)
34(1)
27(1)
29(1)
34(1)
37(1)

38(1)

13(1)
18(1)
17(1)
22(1)
17(1)
9(1)
8(1)
3(4)
19(1)

14(1)

6(1)
21(1)
24(1)
30(1)
37(1)
24(1)
24(1)
23(1)
23(1)
39(1)

49(1)

RbngzAS4S13

14(1)
15(1)
23(1)
18(1)
21(1)
10(1)
11(1)
23(6)
11(1)

10(1)

221

3(1)
6(1)
5(1)
11(1)
7(1)
7(1)
2(1)
4(1)
6(1)
13(1)

15(1)

2(1)
4(1)
9(1)
7(1)
0(1)
2(1)
1(1)
8(4)
0(1)
3(1)

1(1)
7(1)
4(1)
12(1)
2(1)
7(1)
1(1)
12(1)
6(1)
6(1)
14(1)

6(1)
5(1)
7(1)
-1(1)
9(1)
3(1)
4(1)
4(4)
6(1)

0(1)

7(1)
3(1)
4(1)
7(1)
0(1)
5(1)
2(1)
6(1)
-5(1)
9(1)
13(1)

-5(1)
1(1)
2(1)
-4(1)
-2(1)
0(1)
-1(1)
-5(3)
2(1)
-2(1)

8(4)
8(5)
8(6)
8(3)
3(7)
8(8)
8(9)
8(99)

S(10)

* The anisotropic displacement factor exponent takes the form:

-2n2[hza*2U” + k2b*2U22 + 120*2U33 + 2hka*b*U12 + 2klb*C*U23 '1” 2hla*c*U13]

21(1)
17(1)
24(1)
17(1)
19(2)
:20(1)

25(1)

120(20)

43(12)

12(1)
18(1)
17(1)
12(1)
10(1)
10(1)

21(1)

25(10)

14(7)

18(1)
20(1)
24(1)
11(1)
12(2)
20(1)

9(1)

39(12)

9(8)

222

8(1)
6(1)
-3(1)
4(1)
-1(1)
6(1)
0(1)
5(8)

-2(6)

4(1)
6(1)
12(1)
3(1)
9(1)
5(1)
8(1)

39(13)

12(7)

1(1)
-3(1)
-8(1)
2(1)
1(1)
0(1)
-2(1)
-17(11)

9(7)

The thermal response of I and II was measured using a Differential Thermal Analyzer.
The data revealed that I and II melt incongruently at 480°C and 520°C respectively. The
powder X-ray diffraction pattern of the residue taken after DTA showed the presence of

MnS and amorphous K(Rb),‘AsySz along with the parent compound.

C.2 Structure description of K3[Mn2(ASS4)4]

The structure of A3[Mn2(A884)4] contains the discrete molecular [Mn2(ASS4)4]8' clusters
and charge-compensating A+ cations. We will discuss the structural details of
K3[Mn2(ASS4)4]. The clusters are centrosymmetric and consist of octahedrally
coordinated Mn2+ ions linked by tetrahedral [A884]3' units, Figure 1. Each Mn center is
connected to three [A884]3' ligands and each ligand uses two of its 8 atoms to bind the
metal. There are two different kinds of [A884]3' ligands, terminal and bridging. The
terminal [A884]3' ligand uses two of its sulfur arms to chelate to a Single Mn atom. The
bridging [A884]3‘ ligand uses three of its sulfur atoms, two binding to two Mn atoms and
the third 8 atom forming a bridge between the metals. The fourth 8 atom remains non-
bonding. Alternatively, two Mn86 octahedra edge share with four ASS4 tetrahedra to form
the binuclear cluster.

The intra-core Mn-Mn distance is 4.070(1) A. Mn-S distances range from 2.5812(6) A to
2.7739(6) A. (Table 2) As-S distances are normal between 2.1306(6) A and 2.1984(5) A
for the terminal unit and 2.1378(6) A to 2.1936(6) A for the bridging ligand. Mn86 is a
distorted octahedron with S-Mn-S bond angles varying from 79.174(18)° to l67.96(2)°.

The [A884]3' tetrahedra are also distorted from ideal tetrahedral geometry with S-As-S

223

bond angles between 103.12(2)° and 115.64(2)° for bridging A884 and between
102.70(2)° and 113.08(2)° for the terminal ligand. (Table 3)

There are 5 crystallographically unique K+ ions. K1 sits in a nine coordinate pocket
created by 8 S atoms and an AS atom with distances between 3.1142(8) A and 3.6755(6)
A. K2 is coordinated to 6 8 in the range 3.2489(7) A to 3.5346(7) A. K3 is coordinated to
7 S atoms with bond distances ranging from 3.1167(7) A to 3.5654(8) A. K4 is connected
to 8 S atoms and an A8 atom at distances 3.1292(8) A - 3.7104(7) A. K5 is hepta-
coordinated by 6 S atoms and an As atom ranging from 3.1385(7) A to 3.7765(5) A.

Figure 2 shows the coordination environments of the K cations.

224

 

Figure l. The molecular anion [Mn2(AsS4)4]8'. The black circles are Mn, the white
circles are S and the grey circles are A8.

S6 86
S8
33 81
$6 37
K3
K2 S3 85
S4 S3

 

Figure 2. Coordination environments of the five cyrstallographically unique K+ ions.

225

Table 4. Selected bond distances for K3MII2AS4Sl6, and Rbst2As4813.

KgMn2As4816
As(1)-8(8) 2.1306(6) K(l)-S(2) 3.3272(7) K(3)-S(5) 3.1548(8)
As(1)-S(1) 2.1626(5) K(1)-S(2) 3.5447(8) K(3)-S(6) 3.3263(8)
As(1)-8(4) 2.1715(6) K(l)-S(3) 3.1142(8) K(3)-8(7) 3.5654(8)
As(1)-8(7) 2.1984(5) K(l)-S(4) 3.4509(7) K(3)-8(8) 3.3175(8)
As(2)-S(3) 2.1378(6) K(1)-S(5) 3.1515(8) K(4)-S(1) 3.2697(8)
As(2)-S(5) 2.1443(6) K(1)-S(7) 3.3381(7) K(4)-S(1) 3.2883(7)
As(2)-S(2) 2.1793(5) K(1)-S(8) 3.3526(8) K(4)-S(2) 3.3613(7)
A8(2)- 8(6) 2.1936(6) K(1)-S(8) 3.4300(8) K(4)-S(4) 3.2210(7)
Mn(1)-S(1) 2.5812(6) K(l)-As(l) 3.6755(6) K(4)-S(5) 3.2417(8)
Mn(1)-S(2) 2.5920(6) K(2)-8(4) 2x3.5346(7) K(4)-S(5) 3.1292(8)
Mn(1)-8(4) 2.6238(6) K(2)-S(6) 2x3.3112(8) K(4)-S(6) 3.4158(7)
Mn(1)-S(6) 2.6635(6) K(2)-8(8) 2x3.2489(7) K(4)-S(7) 3.7104(7)
Mn(1)-8(7) 2.7591(6) K(3)-S(1) 3.5442(7) K(4)-As(2) 3.6785(6)
Mn(1)-8(7) 2.7739(6) K(3)-S(3) 3.1167(7) K(5)-S(3) 2x3.1385(7)
Mn(1) - Mn(1)4.070(l) K(3) - S(3) 3.5402(8) K(5) - 8(4) 2 x 3.1828(7)

K(5)-As(2) 3.7765(5) K(5)-S(6) 2x3.2566(7)

Rbng2As4813

As(1)-S(1) 2.143(2) Rb(1)-S(2) 3.599(2) Rb(3)-S(1) 3.382(2)
As(1)—S(5) 2.152(2) Rb(1)-8(4) 3.479(2) Rb(3)-S(1) 3.667(2)
As(1)-S(2) 2.177(2) Rb(1)-S(5) 3.359(2) Rb(3)-S(3) 3.650(3)

226

As(1) - 8(4)

As(2) - As(22) 0.536(13)

2.183(2)

As(2) - 8(99) 1.79(2)

As(2) - S(9)
As(2) - 8(8)
As(2) - 8(6)

As(2) - 8(3)

As(22) - S(6) 1.956(11)

As(22) - S(3) 2.023(12)

2.111(3)
2.130(3)
2.174(3)

2.250(3)

As(22) - 8(99) 211(2)

As(22) - 8(8) 2.210(10)

As(22) - S(10) 227(3)

Cd(1) - S(10) 2.70(2)

Cd(1) - 8(8)
Cd(1) - S(2)
Cd(1) - 8(4)
Cd(1) - S(7)

Cd(1) - S(6)

Cd(1) - S(10) 2.811(19)

Cd(1) - 8(7)

2.705(2)
2.711(2)
2.716(2)
2.720(3)

2.732(2)

2.819(3)

Cd(1) - Cd(1) 3.960(1)

Rb(1) - S(5)
Rb(1) - 8(6)
Rb(1) - S(6)
Rb(1) - 8(7)

Rb(1) - 8(8)

Rb(1) - As(1) 3.8262(12)

3.309(2)
3.380(2)
3.634(3)
3.428(4)

3.324(2)

Rb(1) - As(2) 4.031(2)

Rb(1) - As(22)4.065(11)

Rb(2) - S(1)
Rb(2) - 8(2)
Rb(2) - 8(2)
Rb(2) - 8(3)
Rb(2) - 8(5)
Rb(2) - 8(6)
Rb(2) - S(7)
Rb(2) - 8(8)

Rb(2) - 8(9)

3.397(2)
3.379(2)
3.489(2)
3.235(2)
3.317(2)
3.727(3)
3.836(3)
3.319(2)

3.453(3)

Rb(2) - S(99) 372(2)

Rb(2) - 8(99) 384(2)

Rb(2) - S(10) 3.51(2)

S(3) - 8(7)

2.071(4)

227

Rb(3) - 8(4)
Rb(3) - 8(4)
Rb(3) - 8(5)
Rb(3) - 8(8)
Rb(3) - 8(9)

Rb(3) — 8(9)

3.705(2)
3.458(2)
3.688(2)
3.482(2)
3.606(3)

3.471(3)

Rb(3) - 8(99) 364(2)

Rb(3) - As(1) 3.6801(13)

Rb(3) - As(2) 3.733(2)

Rb(4) - S(1)
Rb(4) - S(1)
Rb(4) - 8(3)
Rb(4) - S(4)
Rb(4) - 8(5)
Rb(4) - 8(6)
Rb(4) - S(7)

Rb(4) - 8(9)

3.259(2)
3.722(2)
3.537(3)
3.455(2)
3.335(2)
3.550(2)
3.634(4)

3.389(3)

Rb(4) - 8(99) 368(3)

Rb(4) - S(10) 391(2)

Rb(4) - As(2) 4.123(2)

Table 5. Selected bond angles for K3MD2AS4Sl6, and RbngzAs4813.

S(8) - As(1) - S(1)
8(8) - As(1) - S(4)
S(1) - As(1) - 8(4)
8(8) - As(1) - S(7)
S(1) - As(1) - 8(7)
8(4) - As(1) - S(7)
S(5) - As(2) - S(6)
S(2) - As(2) - S(6)
S(3) - As(2) - S(5)
S(3) - As(2) - S(2)
S(5) - As(2) - S(2)

S(3) - As(2) - S(6)

S(1) - Mn(1) - S(7)

S(2) - Mn(1) -S (7)

S(2) - As(1) - S(4)
S(1) - As(1) - S(5)
S(1) - As(1) - S(2)

S(5) - As(1) - S(2)

KganAs4316
111.38(2) S(1) - Mn(1) -S(7) 79.174(18)
112.56(2) S(4) - Mn(1) - S(7) 79.224(17)
109.90(2) S(6) - Mn(1) - S(7) 97.290(18)
115.64(2) S(1) - Mn(1) - S(2) 104.37(2)
103.12(2) S(1) - Mn(1) - S(4) 167.96(2)
103.58(2) S(2) - Mn(1) - S(7) 99.32708)
111.00(2) S(2)-Mn(1)-S(4) 86.625(18) '
102.70(2) S(4) - Mn(1) - S(7) 94.387(19)
109.14(2) S(6) - Mn(1) - S(7) 168.10(2)
110.19(2) S(2) - Mn(1) - S(6) 81.041(17)
110.60(2) S(1)-Mn(1)-S(6) 89.19(2)
113.08(2) S(7) - Mn(1) - S(7) 85.296(18)
90.03809) S(4) - Mn(1) - S(6) 9751(2)
165.44(2)

RbstzAs4813
103.95(8) S(8)-Cd(l)-S(7) 8137(9)
108.08(9) S(10)-Cd(l)-S(8) 94.1(5)
111.02(9) S(2)-Cd(1)-S(7) 102.93(8)
112.61(9) S(10)-Cd(1)-S(2) 103.7(4)

228

S(1) - As(1) - S(4)
S(5) — As(1) - S(4)
S(10) - As(22) - S(9)
S(3) - As(22) - S(8)
S(6) - As(22) - S(10)
S(8) - As(22) - S(10)
8(99) - As(22) - 8(8)
S(6) - As(22) - S(99)
S(3) - As(22) - 8(99)

S(6) - As(22) - 8(8)

1 1 109(9)
1 1008(8)
139.7(7)
1 10.0(5)
100.5(7)
101.6(7)
1 15.2(7)
105.8(8)
73.0(9)

117.5(5)

8(99) - As(22) - S(10)115.7(10)

S(6) - As(22) - S(9)
S(3) - As(22) - 8(9)
8(8) - As(22) - S(9)
8(99) - As(2) - 8(8)
S(6) - As(2) - S(3)
S(9) - As(2) - S(8)
8(99) - As(2) - S(6)
S(9) - As(2)- S(6)
S(8) - As(2) - S(6)
8(99) - As(2) - S(3)
S(9) - As(2) - 8(3)

8(8) - As(2) - S(3)

103.5(5)
95.0(5)
95.4(5)
136.9(6)
106.76(12)
114.47(13)
109.5(7)
114.28(12)
111.76(13)
74.0(9)
103.67(13)

104.73(11)

229

8(4) - Cd(1) - 8(7)
3(8) - Cd(1) - S(2)
S(7) - Cd(1) - S(7)
S(10) — Cd(1) - S(4)
S(6) - Cd(1) - 8(7)
8(8) - Cd(1) - S(4)
S(10) - Cd(1) - S(7)
S(2) - Cd(1) - S(4)
S(10) - Cd(1) - 8(7)
8(8) - Cd(1) - S(7)
S(2) - Cd(1) - 8(7)
8(4) - Cd(1) - S(7)
S(10) - Cd(1) - S(6)
8(8) - Cd(1) - S(6)
S(2) - Cd(1) - S(6)
S(4) - Cd(1) - S(6)
S(7) - Cd(1) - S(6)
S(10) - Cd(1) - S(10)
8(8) - Cd(1) - S(10)
S(2) - Cd(1) - S(10)
S(4) - Cd(1) - S(10)

S(6) - Cd(1) - S(10)

177.09(9)
85.00(6)
88.78(10)
169.5(5)
86.48(9)
9630(7)
84.9(4)
7852(6)
89.2(4)
90.63(9)
166.70(9)
8951(8)
73.7(5)
167.85(7)
97.81(7)
95.84(7)
8909(9)
88.1(6)
77.9(4)
160.0(4)
92.9(4)

101.1(4)

In the case of the Rb and Cs analogs the structure of the core remains the same however
the octahedral angles in the Mn86 and AsS4 groups are more distorted presumably due to
the slightly different packing forces arising from the presence of the bigger alkali metals.
This also leads to a lowering of symmetry in the overall structure from monoclinic P2/n
for KganAs4Sw to P-l for the Rb and Cs phases. Mn-Mn distance within the core

increases to 4.176(1) A and 4.327(1) A for the Rb and Cs compounds, respectively.

C.3 Structure description of Rbs[Cd2(AsS4)2(Asss)2]

The structure of Rbg(Cd2(AsS4)2(Asss)2 presents an interesting case of ligand size
adjustment to counter the size of the transition metal. The structure of this compound is
similar to the Mn phase and consists of [Cd2(A885)2(AsS4)2]8' clusters. (Figure 3) The
interesting aspect in this structure is the presence of the tetrahedral [AsSs]3' ligand which
is derived from the [AsS4]3' tetrahedron by substituting a terminal S atom with a disulfide
Szz'unit. The presence of the larger Cd2+ ion in place of a Mn” probably puts a strain on
the bridging [AsS4]3’ ligand causing the system to release this strain by taking in an
additional S atom from the flux to form [AsSs]3' and the ensuing molecular
[Cd2(As85)2(AsS4)2]8' unit. Thus this cluster is composed of two Cd atoms coordinated to
two [A884]3’ units and bridged by two [AsSs]3' units. This is by no means to say that
[Cdz(AsS4)4]8' doesn’t exist. The refinement of this structure showed that the
[Cd2(Asss)2(AsS4)2]8' anion is disordered with [Cd2(AsS4)4]8' (15%) though the
percentage of the former (85%) is much greater. Our attempts to isolate pure

Rbg[Cd2(AsS4)4] were however unsuccessful.

230

 

Figure 3. a The molecular [Cd2(AsS4)2(As85)2]8' anion. b) The co-crystallized
[Cd2(ASS4)4] - anion.

231

The octahedral geometry of Cd” ions observed in [Cd2(AsSS)2(AsS4)2]8' is indeed
unusual for a sulfur based coordination environment. In the vast majority of cases this
metal ion prefers the standard tetrahedral geometry.”

In this structure, Cd-S bond distances range from 2.705(2) A to 2.819(3) A. As-S
distances vary from 2.112(3) A to 2.250(3) A for A385 and 2.143(2) A to 2.183(2) A for
AsS4. (Table 2) S-S distance is normal at 2.071(4) A. Cd-Cd distance within the core is
3.960(1) A The formation of the A885 ligand reduces the distortion of the Cd86 octahedra
with S-Cd-S bond angles being closer to 90° and 180°. S-As-S bond angles are slightly
distorted ranging from 103.95(8)° to 112.61(9)°. (Table 3)

The Mn and Cd clusters are reminiscent of the clusters encountered in K.;Cr2(PS.t)43
which also consists of a binuclear Cr center that is bonded by 4 PS4 units in an identical
fashion as described above. The one-dimensional compound K3Cr2P3Stz18 has the same
core that shares edges with another core through the terminal PS4 tetrahedron. It is
interesting to note that K6Cr2P4SI6 can be conceptually obtained from K3Cr2P3Su by
addition of one equivalent of K3PS4. A dimeric core can be seen in A5An(PS4)3 (An = U,
Th).8 However in these compounds, there are two terminal [PS4]3' units per metal ion.
This structural motif seems to be very stable and is observed in the chains of

A3RE(PSe4)219 and K3Pu(PS4)22° and the layers of Cs3Bi2(PS4)3.2'

C.4 Spectroscopy
Large crystals of K8 [Mn2(AsS4)4], Rbs [Mn2(AsS4)4], CSs[Mn2(ASS4)4] and
Rbg[Cd2(AsS4)2(Asss)2] were hand-picked and ground to powder for diffuse reflectance

spectroscopic examination. All compounds are yellow in color with energy gaps

232

commencing at 2.25eV for I, 2.33eV for 11, 2.26eV for 111 and 2.67eV for IV. (Figure 4)
Since these are molecular complexes, it is less meaningful to talk about band gaps, rather
it is very likely that the energy gap arises from "localized" energy levels and can be
assigned to S—>M charge transfer transitions.

Infrared spectra for I and IV are shown in Figure 5. I shows frequencies at 426(m-s),
413(m), 384(m) cm'1 which can be assigned to As-S stretching. These frequencies are
analogous to those observed in the clusters of [Pt3(AsS4)3]3' and other reports.22 There are
several weak peaks below 3000m", which are contributed by Mn-S stretching modes. IV
displays peaks at 468(3), 431, 411, 385, 362, 243 cm'l. The peaks at 431, 411 and 385
cm'1 are due to As-S stretching while below that are due to Cd-S vibrations. The peak at

468 cm'1 is attributed to S-S stretching.

C.5 Magnetism

K3[Mn2(AsS4)4] is paramagnetic, nearly obeying the Curie-Weiss law over the
temperature range 20-300K. Figure 6a shows the plot of the reciprocal molar
susceptibility (l/xm) against temperature. The estimated pm value of 5.4 BM confirms the
Mn2+ nature of the metal even though it is slightly lower than the ideal 5.9 calculated for
high-spin Mn2+ ions. Figure 6b shows the dependence of x," in the range O-50K. As seen
in the figure, the susceptibility shows a maximum indicating antiferromagnetic coupling.
The maximum is observed at ~ 6K with a Weiss constant, 0 ~ -19 K suggesting that the
antiferromagnetic interactions are weak in nature and this is in accordance with the long

intra-core Mn-Mn distance of 4.070(1)A.

233

 

 

    

 

 

 

 

 

 

 

 

 

3)
C58[Mn2(ASS4)4]
2?
d
r; Rbsan2(ASS4)4]
U
5
'8
8
..o
(6
Eg = 2.26eV
E =2.33eV
i 1 l
1 2 3 4 5 6
Energy, eV
Q
S
D
O
5
"E
8
'8
E = 2.67eV
1 is 1 1
1 2 3 4 5 6
Energy, eV

Figure 4. a) Optical absorption spectra of Css[Mn2(AsS4)4] and Rbg[Mn2(AsS4)4]
showing energy gaps at 2.26 and 2.33eV respectively. b) Optical absorption spectra of
Rbg[Cd2(AsS4)2(As85)2] with an onset at 2.67eV.

234

 

Transmittance

 

 

 

l l l l l

200 250 300 350 400 450 500
Wavenumbers (cm'l)

 

 

b)

Transmittance

 

431

 

 

l l l l l

200 250 300 350 400 450 500

 

Wavenumber (cm")

Figure 5. a) Far IR spectrum of K3[Mn2(AsS4)4] b) Far IR spectrum of
Rbg[Cd2(AsS4)2(Asss)2]. The peak at 468 cm’1 is attributed to S-S stretching.

235

 

l/x

 

 

 

 

0 l 1 l l l I
0 50 100 150 200 250 300 350
Temperature, K

 

0.11
b)
0.1 h

0.09 ~

9. 0.08 -

0.07 ‘

0.06 ”

 

 

 

O 05 l l l l
0 10 20 30 40 50

Temperature, K

Figure 6. a) Plot of inverse molar susceptibility against temperature for
K3[Mn2(AsS4)4] showing a nearly Curie-Weiss behavior till 20K. b) Plot of molar
susceptibility against temperature from O-SOK. The susceptibility reaches a maximum
at 6K.

236

D. Concluding Remarks

Discrete molecules such as the anionic clusters [Mn2(AsS4)4]8' and [Cd(AsS4)2(As85)2]8'
form under essentially solution conditions inside a molten flux, and crystallize as their
alkali salts. Such outcomes in metal reactivity stress the utility of a flux approach in
preparing not only complex solid state compounds but, in many cases, also phases with
discrete molecular species. The high negative charge of these clusters would have made it
more difficult for them to be obtained via conventional solution techniques. The alkali
thioarsenate flux is equally promising as its thiophosphate counterpart in exploring
complex chalcogenides and further investigation is called for in order to realize the full

potential of these fluxes.

237

References

10.

11.

12.

. a) Kanatzidis, M. G.; Huang, S. P. Coord. Chem. Rev. 1994, 130, 509. b) Chung, D.

Y.; Huang, S. P.; Kim, K. W.; Kanatzidis, M. G. Inorg. Chem. 1995, 34, 4292. c)
Eichhom, B. W.; Mattamana, S. P.; Gardner, D. R.; Fettinger, J. C. J. Am. Chem. Soc.
1998, 120, 9708. d) Bollinger, J. C.; Ibers, J. A. Inorg. Chem. 1995, 34, 1859. e)
Wang, C.; Haushalter, R. C. Inorg. Chim. Acta 1999, 288, 1.

Sutorik, A. C.; Kanatzidis, M. G. Prog. Inorg. Chem. 1995, 43, 151.

Derstroff, V.; Kwenofontov, V.; Gutlich, P.; Tremel, W. Chem. Commun. 1998, 187.

Choundroudis, K.; Kanatzidis, M. G. Chem. Commun. 1997, 401.

Chondroudis, K.; Chakrabarty, D.; Axtell, E. A.; Kanatzidis, M. G. Z. Anorg. Allg.
Chem. 1998, 624, 975.

Gauthier, G.; Jobic, S.; Danaire, V.; Bree, R.; Evain, M. Acta. Cryst. 2000, C56, 117.

Chondroudis, K.; Kanatzidis, M. G. Inorg. Chem. Commun. 1998, 55.

Chondroudis, K.; Kanatzidis, M. G. Chem. Commun. 1996, 1371.

. Hess, R.; Abney, K. D.; Burris, J. L.; Hochheimer, H. D.; Dorhout, P. K. Inorg.

Chem. 2001, 40, 2851.

Chondroudis, K.; Kanatzidis, M. G.; Sayettat, J.; Jobic, S.; Bree, R. Inorg. Chem.
1997, 36, 5859.

Kanatzidis, M. G. Curr. Opin. Solid State Mater. Sci. 1997, 2, 139.

Iyer, R. G.; Do, J.; Kanatzidis, M. G. Inorg. Chem. 2003, 42, 1475.

238

13. Iyer, R. G.; Kanatzidis, M. G. manuscript in preparation

14. Feher, F. In Handbuch der Praparativen Anorganischen Chemie; Brauer, G., Ed.;
Ferdinand Enke: Stuttgart, Germany, 1954; vol. 1, pp 280-281.

15. Aitken, J. A.; Chondroudis, K.; Young, V. G.; Kanatzidis, M. G. Inorg. Chem. 2000,
39, 1525.

16.SMART, SAINT, SHELXT L: Data Collection and Processing Software for the
SMART -C CD system; Siemens Analytical X-ray Instruments Inc., 1995.

17. a) Axtell, E. A.; Kanatzidis M. G. Chem. Mater. 1996, 8, 1350. b) Axtell, E. A.;
Kanatzidis M. G. Chem. Eur. J. 1998, 4, 2435. c) Axtell, E. A.; Liao, J.-H.;
Pikramenou, Z.; Kanatzidis M. G. Chem. Eur. J. 1996, 2, 656. d) Greenwood, N. N;
Earnshaw, A. "Chemistry of the elements" 1997, Elsevier Science.

18. Coste, S.; Kopnin, E.; Evain, M.; Jobic, S.; Payen, C.; Bree, R. J. Solid State Chem.
2001, 162, 195.

19. Chondroudis, K.; Kanatzidis, M. G. Inorg. Chem. 1998, 37, 3792.

20. Hess, R.; Gordon, P. L.; Tait, D. C.; Abney, K. D.; Dorhout, P. K. J. Am. Chem. Soc.
2002, 124, 1327.

21. McCarthy, T. J .; Kanatzidis, M .G. J. Alloys Compd. 1996, 236, 70.

22.3) Chou, J. H.; Kanatzidis, M. G. Inorg. Chem. 1994, 33, 5372. b) Siebert, H. Z.
Anorg Allg. Chem. 1954, 225, 275. e) Nakamoto, K. Infiared and Raman Spectra of
Inorganic and Coordination Compounds. 5th ed.; John Wiley & Sons, Inc. 1997.

239

Chapter 8
CstoCuzAs4819, CszMAsss (M = Cu, Ag) and CszAuAsS4: Low Dimensional Coinage
Metal Compounds from Cesium Thioarsenate Fluxes

Abstract

The reactions of Cu, Ag and Au in cesium polythioarsenate fluxes yielded
Csto[{Cu2(Asss)3}(AsS4)], CszMAsss (M = Cu, Ag) and CszAuAsS4. CstoCuzAs4Sw (I)
crystallizes as yellow rods in space group P21/c with a = 15.967(4) A, b = 9.581(3) A, c =
29.636(8) A, B = 97.233(4)°. CszMAsSS (II and III) crystallizes in space group I4/m with
a = 16.710(3) A, c = 7.4313(18) A for M = Cu (orange rods) and a = 17.211(5) A, c =
7.397(3) A for M = Ag (yellow needles). CszAuAsS4 (IV) crystallizes as bright yellow
needles in space group Pbcm with a = 6.9320(14) A, b = 20.272(4) A, c = 7.1037(15) A.
The structure of CstoCuzAs4819 comprises of two co-crystallized anions, [Cu2(AsSS)3]7'
and AsS43’. CszMAsss consist of the tetranuelear cluster anion [M4(A385)4]8' whereas
CszAuAsS4 consists of chains formed by AsS43' ligands coordinating to Au. The first
three compounds have the tetrahedral AsSs3' building block whereas the Au compound
features the tetrahedral AsS43' anion. These compounds are semiconductors with energy
gaps of 2.1, 2.41 and 2.54 eV for CSzCllASSs, CszAgAsss and CszAuAsS4 respectively.

CszCuAsss and CszAgAsss decompose on dissolution in water.

240

A. Introduction

Coinage metal (Cu, Ag, Au) chalcogenides are among the most widely compounds.
According to the ICSD, there are over a thousand binary, ternary and quaternary
chalcogenides of the Group 11 metals.1 The affinity of these metals for S, Se and Te is
not surprising considering that the name "chalcogen" comes from Greek and means
"copper-forming". Among the preparative techniques, the solvothermal method2 and the
molten flux method3 have been particularly successful in isolating a wide variety of
compounds with diverse structural features. The structures differ in the coordination
modes of the ligands and the geometry around the metal atom. Another important
parameter aiding the structural diversity is the tendency of these metals to show mixed
valency. Thus Au‘il strictly prefers a linear geometry whereas Au3+ likes to be square
planar.4 Cu and Ag occur mostly in linear,5 trigonal planar6 and tetrahedral geometries.7
We have isolated a number of coinage metal- containing chalcogenides and
chalcophosphates by utilizing the polychalcogenide and polychalcophosphate fluxes.8
Some of these compounds include KCuS4,9 CsCuS(5,10 AzAuPS4, AAuP2$7 (A = K, Rb,
Cs),“ AuCuSe...12 AAgTeS3 (A = K, Rb, Cs),l3 A3CUgTeto (A = Rb, Cs),14 CscuCes_-.,15
KzAggCeTe4,l6 KzAu4CdS4 etc.” Naturally we were interested in exploring how these
metals performed in polythioarsenate fluxes. There are very few known quaternary
thioarsenates of Cu, Ag and Au. These are KCuzAsS3, KCu.tAsS4,18 CszAgAsS4,l9
KAg3Asz85,2° KAngsS4,21 [Fe(NH3)6]AgAsS4,22 (NH4)Ag2AsS4,23 and KzAuAsS4.24 Of
these, K2AuAsS4 is the only compound that has been synthesized by a solid state
reaction. The other compounds have been prepared using the solvothermal technique. It is

therefore clear the wide scope that the alkali polythioarsenate fluxes hold in discovering

241

new Group 11 thioarsenates. The syntheses and characterization of CsloCuzAs4819,
CszMAsss (M= Cu, Ag) and CszAuAsS4 are described in this chapter. These compounds

are predecessors to what will likely develop into a substantial subclass of thioarsenates.

B. Experimental Section

B.l Reagents

All manipulations were done in a nitrogen-filled dri-vac glove box. Reagents: Ag (99.99
%; Liberty Coins, Lansing, MI), Cu (Fisher Scientific Company, Fair Lawn, NJ), Au(325
mesh, 99.9%, Cerac, Miwaukee, WI), AS283 (99.9 %; Strem Chemicals, Newburyport,
MA), As (99.9%; Aldrich Chemical Co, Milwaukee, WI), S (99.9 %; Strem Chemicals,
Newburyport, MA). N,N-dimethylformamide (Spectrum Chemicals, ACS reagent grade);
diethyl ether (CCI, ACS grade). CszS was prepared by dissolving the alkali metal in
liquid NH3 and reacting it with a stoichiometric amount of sulfur according to a modified

literature procedure.”

B.2 Physical Measurements

Powder X-ray Dijfiaction

X-ray powder diffraction patterns were recorded on a CPS 120 IN EL diffractometer (Cu
Koc radiation) operating at 40kV/20mA and equipped with a position sensitive detector
and a flat sample geometry.

Energy Dispersive Spectroscopy

Semiquantitative microprobe analyses on the compounds were done with a JEOL J SM-

6400V scanning electron microscope equipped with a Tracor Noran Energy Dispersive

242

Spectroscopy detector. Elemental compositions were obtained from an average of three
readings. Acquisition times were 303 or 45s per reading.

Difluse Reflectance Spectroscopy

Solid state diffuse reflectance spectra were measured using a Shimadzu UV-3101 PC
double-beam, double-monochromator spectrophotometer. BaSO4 was used as reference.
Finely ground sample was spread on a sample holder preloaded with the reference.
Energy gap was determined from a plot of absorbance vs energy by converting
reflectance to absorbance using the Kubelka-Munk function.26

Infi'ared Spectroscopy

Far IR spectra of the compounds were recorded as CsI pellets on a Nicolet 740 FT—IR
spectrometer with a TSG/PE detector and silicon beam splitter. The spectra were
obtained in the 600-100cm'l range with 4cm"l resolution.

Diflerential Thermal Analysis

The thermal behavior of the compounds was investigated by differential thermal analysis
using a Shimadzu DTA-50 thermal analyzer. Typically a sample (~20 mg) of ground
crystalline material was sealed in a silica ampule under vacuum. A similar ampoule of
equal mass filled with A1203 was sealed and placed on the reference side of the detector.
The sample was heated to the desired temperature at 10°C/min, and after 1-3 min it was
cooled at a rate of -10°C/min to 50°C. Residues of the DTA experiments were examined
by X-ray powder diffraction. Reproducibility of the results was checked by running

multiple heating/ cooling cycles.

243

B.3 Synthesis

CsmCuzAs4Sm (I) and C szCuAsss (II) were synthesized as yellow and red rods,
respectively, from a reaction of Cs;SlCu/A82$3/S in the ratio 4/2/1/10. The reagents were
loaded in a fused-silica tube inside a N2- filled glove box. The tube was sealed under
vacuum (<10‘4 Torr) and placed in a computer-controlled fumace. The tube was heated to
600°C and held at that temperature for 96h. This was followed by cooling to 200°C at the
rate of 5°C/h followed by fast cooling to room temperature. The excess of flux was
washed with degassed N,N- dimethylformamide to reveal red rods, yellow rods and
colorless crystals. The yellow rods were a minor phase (<20%) whereas the red rods were
the major phase (~ 50%). Energy dispersive spectroscopy measurements on several of the
yellow crystals revealed an average composition of "Cs; 1CuAss,4Stg" and "Csz.1CuAs85,t"
for the red rods. The colorless crystals were Cs3AsS4. The powder diffraction pattern of
the product was compared with the theoretical powder patterns calculated from single
crystal structures of CstoCuzAs4Stg, CszCuAsSs and CS3ASS4, which indicated that it was
a mixed phase.

CszAgAsss (III) was obtained as almost single phase by heating a mixture of Cszs
(0.179g, 0.6mmol), Ag(0.032g, 0.3mmol), A32S3(0.074g, 0.3mmol) and S(0.077g,
2.4mmol) at 500°C. The reaction was maintained at this temperature for 60h, followed by
cooling to 250°C at the rate of 5°C/h and fast cooling to room temperature. Afier washing
the flux with DMF, yellow needles of CszAgAsss were produced in nearly 80% yield.
The powder pattern of the product matched very well with the simulated pattern obtained
from single crystal refinement. EDS measurements on a few crystals gave an average

composition of "Csz,6Ago_9Aso,9S4,7".

244

CszAuAsS.. (IV) was synthesized as a single phase from a reaction of C528, Au, AS283
and S in the ratio 2:1:1:10. The reactants were loaded in a fused-silica tube and heated
according to the profile given for 111. On washing the excess flux away, yellow needles
were obtained as the only product in about 70% yield. The powder pattern of the product
matched perfectly with the simulated pattern obtained from single crystal refinement.

EDS analysis on the needles gave an average composition of "CszAuAsS4,6".

B.4 Single crystal X-ray crystallography

For CstoCuzAS4Sm, a yellow rod with dimensions of 0.02 x 0.02 x <0.02 mm; was glued
to a glass capillary fixed to an aluminum pin and mounted on a goniometer head. A full
sphere of data was collected on a Bruker SMART system operating at 293K and
equipped with Mo Ka radiation and CCD detector. The data was integrated using SAINT
and an absorption correction was applied using SADABS. The structure was solved in the
monoclinic space group P21/c using the SHELXTL package of programs.27 All the atoms
were found within the first 3 least-squares cycles. All atoms were refined anisotropically
to give final Rl/wR2 values of 0.0602/0.1227.

A red rod of CszCuAsss with dimensions 0.02 x 0.02 x 0.1 mm3 was used for data
collection. Based on systematic absences and Ez-l statistics, the possible space groups
were 1-4 and I4/m. The CF OM (Combined Figure of Merit) value for the former was
lower and hence it was chosen as the space group. The program PLATON28 indicated a
missed center of symmetry and suggested the space group l4/m. Hence the structure
refinement was redone in the space group I4/m. One Cu, one As, two Cs and four S

atoms were found of which the Cu, and two S atoms occupied general positions. At this

245

point, the isotropic displacement parameters for Cul and S4 were found to be very high.
Therefore they were allowed to refine freely. They refined to 50% occupancy with a
significant decrease in their thermal parameters. Cul generates another Cu at a distance
of 0.82 A. This distance precludes the two atoms to be present at the same time. There are
two 81 atoms linked to As (Sla and Slb). Depending on which Cu is present, atom S4 is
connected to either Sla or Slb with an occupancy of 100%. Hence 8] is both terminal
and part of the disulfide arm of the AsSs3' anion. The average structure determined from
X-ray diffraction however shows that S4 is attached to both Sla and Slb with 50%
occupancy. All the atoms were anisotropically refined to give final R1/wR2 values of
0.0408/0.0740. CszAgAsss was solved and refined in the same manner. We probed for
the existence of super-cells in both the compounds by taking zone photos with exposure
times of 5 min. However no super-cell reflections were observed.

The structure solution of CszAuAsS4 was straight-forward. All the atoms were found in
two rounds of least squares refinement. After anisotropic refinement of all atoms, the
final R1/wR2 values were 0.0221/0.0463.

The crystallographic refinement data along with the fractional atomic coordinates and

aniostropic displacement parameters for all the compounds are listed in Tables 1, 2 and 3.

246

Table 1. Crystallographic data and refinement details for CstoCuzAs4Sm, CSzCllASSs,

CSzAgA885, and CSzAuASS4

empirical formula
fw

space group

a, A

b, A

c, A

0:, deg

B, deg
Y.deg
V, A 3
Z

pcatcd, g/cm3
thrnnf'
T, K
A, A
Total reflections
Total unique
R(int)

No. of parameters

Goodnes of fit on F2

Refinement method

R18|
wR2b

CSloCU2AS4slg
2365
P21/c
15.967(4)
9.581(3)
29.636(8)
90
97.233(4)
90
4498(2)

4

3.493
12.731
293(2)
0.71073
41522
10309
0.1416
317

0.855

0.0602
0.1227

CszCuAsss CszAgAsSS
564.58 608.91
I4/m I4/m
16.710(3) 17.211(5)
16.710(3) 17.211(5)
7.4313(18) 7.397 (3)
90 90
90 90
90 90
2075(7) 2191(14)
8 8
3.614 3.692
13.116 12.268
173(2) 293(2)
0.71073 0.71073
10825 10755
1384 1392
0.0653 0.0573
59 65
1.144 1.306

F ull-matrix least-squares on F 2
0.0408 0.0658
0.0740 0.1548

0 R1 = 2 IIFol- chll/EIFOI. ” wR2 = {z 1w(F.2-F.2f1/2[w(F02)21}”2

247

CszAuAsS4
1002.02
Pbcm
6.9320(14)
20.272(4)
7.1037(15)
90

90

90
998.3(4)

2

3.334
16.856
173(2)
0.71073

1 1 159
1329
0.0387

45

1.090

0.0221
0.0463

103) for CsloCuzAs4819, CszCuAsSs, CszAgAsss, and CszAuAsS4.

Table 2. Fractional Atomic Coordinates and Isotropic Displacement Parameters (A2 x

 

 

Atom x y z Ueq“
CstoCuzAs4Sto
Cs(1) 0.1585(1) 0.173(1) 0.1819(1) 34(1)
Cs(2) 0.3758(1) 0.128(1) 0.585(1) 32(1)
Cs(3) 0.5989(1) 0.392(1) 0.1888(1) 37(1)
Cs(4) 0.8562(1) -0.5355(1) 0.0571(1) 39(1)
Cs(5) 0.5732(1) -0.3477(1) 0.0411(1) 39(1)
Cs(6) 0.3818(1) 0.388(1) 0.3009(1) 39(1)
Cs(7) -0.0683(1) -0.0176(2) 0.0606(1) 42(1)
Cs(8) 0.3574(1) 0.3743(1) 0.1648(1) 36(1)
Cs(9) 0.0979(1) -0.3530(1) 0.2605(1) 41(1)
Cs(10) 0.2041(1) -0.3249(1) 0.0851(1) 43(1)
As(1) 0.3934(1) -0.1991(2) 0.1890(1) 23(1)
As(2) 0.6133(1) 0.2361(2) 0.0639(1) 24(1)
As(3) 0.1678(1) 0.2257(2) 0.3141(1) 24(1)
As(4) 0.1422(1) 0.2433(2) 0.0537(1) 25(1)
Cu(l) 0.9718(2) -0.5181(3) 0.1619(1) 35(1)
Cu(2) 0.7264(2) -0.0524(3) 0.1056(1) 34(1)
S(1) 0.3699(3) 0.0201(5) 0.1764(2) 30(1)
S(2) 0.5080(3) 0.2804(6) 0.2545(2) 34(1)

248

S(3)
S(4)
S(5)
S(6)
3(7)
5(8)
8(9)
S(10)
S(1 1)
S(12)
S(13)
S(14)
S(15)
S(16)
S(17)
S(18)

S(19)

Cs(1)
Cs(2)
As(1)
Cu(1)

S(1)

0.4324(3)
0.2799(3)
0.6061(3)
0.7072(3)
0.7981(3)
0.5015(3)
0.3480(3)
0.2196(3)
0.7553(3)

0.1356(3)

-0.0446(3)

0.0168(3)
0.1348(3)
0.2571(3)
1.0325(3)
0.0171(3)

0.1493(3)

0.3589(1)
0.1049(1)
0.2617(1)
0.4338(1)

0.5213(1)

0.2973(6)
0.3001(5)
0.0085(5)
0.2924(5)
0.1400(6)
0.3317(6)
0.3166(5)
0.3278(6)
0.2719(5)
0.0104(5)
0.1661(5)
0.3080(6)
0.3354(5)
0.3403(5)
0.6956(6)
0.2792(5)
0.0194(5)
CszCuAsSs
0.3252(1)
0.3893(1)
0.0931(1)
0.3727(1)

0.2705(1)

249

0.1291(2)
0.2065(2)
0.0638(2)
0.1243(2)
0.1293(2)

0.0808(2)

-0.0028(2)

0.2613(2)
0.1205(2)
0.2982(2)
0.1779(2)
0.1412(2)
0.1235(2)
0.0406(2)
0.0103(2)
0.1400(2)

0.0597(2)

0.4449

0.2654

36(1)
35(1)
31(1)
35(1)
42(1)
40(1)
34(1)
40(1)
39(1)
36(1)
34(1)
37(1)
34(1)
35(1)
41(1)
34(1)

33(1)

22(1)
24(1)
13(1)
20(1)

31(1)

S(2)
S(3)

S(4)

Cs(1)
Cs(2)
Ag( 1)
As(2)
As(1)
S(1)
S(2)
S(3)

S(4)

Cs(1)
Cs(2)
Au(l)
As(1)
S(1)
S(2)

S(3)

0.3127(1)
0.3879(1)

0.3924(2)

0.1806(1)
0.1161(1)
0.1250(5)
0.1205(10)
0.0955(1)
0.0277(3)
0.1988(3)
0.3878(4)

0.1161(5)

0.7070(1)
0.1025(1)
0.3923(1)
0.2236(1)
0.0457(3)
0.2046(3)

0.3916(2)

0.3020(1)
0.1129(1)

0.4868(2)

CSzAgASS 5

0.1424(1)
0.3974(1)
0.0600(5)
0.0647(9)
0.2629(1)
0.2345(3)
0.1943(3)

0.1151(4)

0.0146(5)

CSzAuASS4

0.0142

0.3345

0.2500

0.1131

0.1622

0.5078

0.3626

-0.5000

0

0.2993

0

0

0.5712(16)
0.5000
0.5000
0.2590(7)

-0.5000

0

-0.7418(13)

0.2500

0.2500

0

0.2500

0.2500

0.2500

0.0039

18(1)
22(1)

13(1)

35(1)
52(1)
39(3)
37(6)
22(1)
42(1)
28(1)
45(2)

28(2)

16(1)
24(1)
16(1)
12(1)
20(1)
15(1)

19(1)

 

250

a Ueq is defined as one third of the trace of the orthogonalized Uij tensor.

Table 3. Anisotropic displacement parameters“ (A2 x 103) for CstoCuzAs4Sw,

CSzCUASSs, CSzAgA855, and CSzAuASS4

 

 

U11 U22 U33 U23 U13 U12
CSloCuzAS4319

Cs(1) 31(1) 36(1) 36(1) 5(1) 6(1) 4(1)
Cs(2) 31(1) 34(1) 32(1) -1(1) 6(1) 0(1)
Cs(3) 37(1) 40(1) 37(1) 2(1) 14(1) 0(1)
Cs(4) 36(1) 43(1) 36(1) 2(1) 2(1) 2(1)
Cs(5) 42(1) 28(1) 44(1) -1(1) -4(1) -2(1)
Cs(6) 37(1) 38(1) 43(1) 2(1) 13(1) 2(1)
Cs(7) 38(1) 50(1) 37(1) -5(1) 9(1) 0(1)
Cs(8) 37(1) 28(1) 43(1) 1(1) 0(1) 1(1)
Cs(9) 43(1) 40(1) 37(1) 8(1) 0(1) -1(1)
Cs(10) 51(1) 32(1) 48(1) 3(1) 15(1) 3(1)
As(1) 24(1) 21(1) 24(1) 1(1) 4(1) 0(1)
As(2) 25(1) 22(1) 24(1) 1(1) 4(1) 0(1)
As(3) 21(1) 22(1) 28(1) 0(1) 2(1) -2(1)
As(4) 27(1) 22(1) 28(1) 2(1) 7(1) 3(1)
Cu(1) 36(2) 35(2) 33(1) -6(1) 2(1) 11(1)
Cu(2) 34(1) 36(2) 33(1) 3(1) 4(1) 9(1)
S(1) 32(3) 22(3) 35(3) 6(2) 3(2) 4(2)
S(2) 30(3) 42(3) 28(3) -1(2) -3(2) -2(2)

 

S(3)
3(4)
S(5)
S(6)
8(7)
8(8)
8(9)
S(10)
S(11)
S(12)
S(13)
S(14)
S(15)
S(16)
S(17)
S(18)

S(19)

(35(1)
Cs(2)
145(1)
(:u(1)

S(1)

44(3)
28(3)
32(3)
45(3)
30(3)
38(3)
38(3)
43(3)
44(3)
44(3)
28(3)
30(3)
34(3)
32(3)
34(3)
31(3)

35(3)

14(1)
18(1)
9(1)

16(1)

48(1)

37(3)
35(3)
25(3)
30(3)
47(4)
35(3)
38(3)
33(3)
28(3)
30(3)
34(3)
42(3)
35(3)
29(3)
46(4)
29(3)

25(3)

27(1)
23(1)
11(1)
21(1)

17(1)

29(3)
45(3)
33(3)
31(3)
47(3)
50(3)
28(3)
48(3)
140(3)
37(3)
43(3)
42(3)
34(3)
47(3)
44(3)
47(3)

39(3)

CszCuAsss

26(1)
31(1)
18(1)
24(1)

27(1)

252

-3(2)
8(3)
0(2)
-1(2)
-9(3)
4(3)
3(2)
5(3)

4(2)

-12(2)

2(2)
-4(3)
-5(2)
0(3)

14(3)
-1(2)

3(2)

13(2)
14(2)
-4<2)
2(2)

-5(3)
19(3)
10(2)

19(3)

-16(3)

14(2)
9(2)

18(2)
11(2)
16(3)
5(3)

18(2)

2(2)

-2(3)
-1(2)
-2(2)
1(3)
2(3)
5(3)
-3(2)
4(3)
3(2)
-9(2)
-5(2)
4(2)
-3(2)
-3(2)
11(3)
0(2)

6(2)

-1(1)
-1(1)
0(1)
1(1)
2(1)

 

 

 

S(2)
S(3)

3(4)

Cs(1)
Cs(2)
Ag(l)
As(2)
As(1)
S(1)
S(2)
S(3)

S(4)

Au(l)
Cs(1)
Cs(2)
As(1)
S(1)
S(2)

S(3)

* The anisotropic displacement factor exponent takes the form:

-zfimzaflun + k2b*2U22 + 12c*2U33 + 2hka*b*U12 + 2klb*c*U23 + 2hla*e*U13]

12(1)
12(1)

14(1)

32(1)
52(1)
52(4)
45(5)
20(1)
48(3)
23(3)
33(3)

28(4)

18(1)
16(1)
36(1)
17(1)
18(1)
19(1)

29(1)

10(1)
21(1)

13(1)

28(1)
34(1)
42(3)
29(4)
21(1)
34(2)
25(3)
22(3)

26(4)

11(1)
16(1)
18(1)
9(1)

17(1)
9(1)

12(1)

32(1)
34(1)

12(2)

CszAgAsss

46(1)
70(2)

23(8)

37(18)

26(1)
42(3)
38(4)
82(6)

29(5)

CSzAuASS4

17(1)
17(1)
19(1)
10(1)
24(1)
18(1)

15(1)

253

0
0

1

0

0

2(1)

0
0

-6(1)

1(1)
-2(1)

-2(1)

-3(1)
-6(1)
1 1(3)
0(3)
0(1)
-3(2)
3(2)
-2(3)

-1(3)

-1(1)
4(1)
1(1)
6(1)
-1(1)
-1(1)

C. Results and Discussion

C.1 Synthesis

CstoCuzAs4Sm was first obtained from a reaction of CszS/Cu/As283/S in the ratio 4/1/1/ 10
as the minor product, the major product being CszCuAsS5. A direct combination of the
reactants to produce CstoCuzAs4819 gave a mixture of this compound with Cs;CuAsSs.
CszCuAsss is a molecular based salt with [Cu4(As85)4]8' clusters. CsloCuzAs4Stg is a
mixed salt with eo-crystallized anions [Cu2(As85)3]7' and AsS43'. We also observed a new
phase (EDS: ~Cs4CuAS286) on changing the amount of C528 to 2 equivalents. This was
obtained as a pure phase but we were unable to solve the structure. Other ratios of €823
usually gave CszCuAsss along with CU3ASS4 and CS3ASS4.

In the case of CszAgAsss, a pure phase was obtained from a reaction of 2/1/1/8 of
CszS/Ag/Aszsg/S. Changing the reaction parameters like the flux basicity, the amount of
metal or the amount of A82S3 usually led to the formation of CszAgAsss and/or glassy
matrices. Similar behavior was observed in the reactions with Au. Pure CszAuAsS4 was
obtained from a ratio of 2/1/1/10 of CSzS/Au/A82S3/S. Increasing the amount of C828
usually gave the CszAuAsS4 along with CS3ASS4 or Cs4Aszsto.

The reactions of Cu, Ag and Au in corresponding potassium and rubidium fluxes
produced mostly Cu3AsS4, KAngsS4, RbAngsS4, KzAuAsS4 and A3AsS4.
CsloCuzAs4Sto, CszCuAsss, CszAgAsss and CszAuAsS4 are stable in air and insoluble in
DMF and ethanol. However CszCuAsss (along with CstoCuzAs4819) and CszAgAsss
dissolve in water and form a clear, pale yellow solution after a few minutes, which turns

milky in about half an hour. This indicates that the clusters decompose in water.

254

 

‘ fl)“,1

 

The [Cu2(AsSS)3]7' and [Cu4(As85)4]8' clusters differ only by a Cu atom and it would be

expected that the latter might form in regions of slightly higher Cu+ concentrations:

[Cu2(Asss)3]7' + Cu+ —+ "[Cu3(As85)3]6"' —> 3/4[Cu4(A585)4]8'

C.2 Structure description of CswCuzAs4819

The unit cell of CstoCuzAs4Sm is shown in Figure 1a. The structure contains two co-
crystallized anions, [Cu2(As85)3]7' and A8843", charge balanced by Cs+ cations. Figure 1b
shows a clearer view of the disposition of the two anions in the unit cell. The two anions
are shown in Figure 1c. The [Cu2(Asss)3]7' anion is a very unusual species and consists of
two Cu+ ions coordinated by three tetrahedral AsSs3 ' ligands in a trigonal planar
geometry. The AsSs3' anion is derived from the tetrahedral AsS43' unit by substituting a
terminal sulfur atom with a disulfide arm. Each Cu+ ion is linked to two AsS53' ligands.
One of these ligands is terminal, while the other serves to bridge the two Cu cations. The
bridging AsSs3' ligand uses an edge to bind to Cu(l) and a comer to link to Cu(2). The
terminal AsSs3 ' ligand attached to Cu(l) uses its disulfide end to coordinate in a
monodentate fashion to complete the trigonal planar geometry. The terminal AsSs3'
ligand on Cu(2) uses its disulfide arm and a monosulfide end to coordinate in a bidentate
chelating mode.

The co-crystallized anion in this lattice is the tetrahedral AsS43' unit. It is surprising that
this anion chose to crystallize along with the other anion rather than find a cation like Cs+
or Cu+ to form the well-known CS3ASS4 or Cu3AsS4. A possible explanation for this

behavior could be that CstoCuzAs4819 is an intermediate compound that crystallizes first.

255

In our reactions, CsloCuzAs4Sw always forms with CszCuAsss, which is probably a
thermodynamically more stable compound.

The Cu-S bond lengths in [Cu2(AsSs)3]7' are normal at 2.199(6) A, 2.221(6) A, 2.248(6)
A for Cu(l) and 2.187(6) A, 2.228(5) A and 2.236(6) A for Cu(2). As-S distances range
from 2.157(5) A to 2.175(5) A for As(1), 2.121(6) A to 2.251(5) A for As(2), 2.102(5) A
to 2.262(5) A for As(3) and 2.122(5) A to 2.264(5) A for As(4). The S—S bond lengths are
2.064(7) A, 2.072(7) A and 2.050(8) A. There are Cs-Cu distances comparable to Cs-S
distances. S-Cu—S angles are distorted from the ideal trigonal planar angle of 120°. S-As-
S angles deviate slightly from the tetrahedral angle of 109°. A list of selected bond
distances and angles for I, II, and IV is given in Tables 4 and 5.

A compound, similar to the [Cu2(As85)3]7' anion, and consisting of five member rings
containing Cu is (Ph4P)4[Cu28e14].29 This compound has a tetra-selenide ligand, 893' that
ligates to the Cu+ ion in a bidentate fashion. This creates a five-member ring. Two such

rings are bridged together by a hexaselenide ligand, Se62'.

256

 

 

 

showmg a clear new of
ions have been removed

unit cell

7' and AsS43'. Cs+
amons

Figure 1. a) The unit cell of CSloCU2AS4819 b) The
7' and the AsS43'

the two co-crystallized anions C112AS3815

for clarity. b) The Cu2(Asss)3

257

Table 4. Selected bond distances for CstoCuzAs4819, CS2CuAs85 and CszAuAsS4.

Cu(1)-S(18)
Cu(l)-S(12)
Cu(l)-S(14)
Cu(2)-S(1 1)
Cu(2)-S(5)
Cu(2)-8(7)
As(1)-S(2)
As(1)-S(1)
As(1)-S(3)
As(1)-8(4)
As(2)-8(8)
As(2)-8(9)
As(2)-S(5)
As(2)-S(6)
As(3)-S(10)
As(3)-S(1 1)
As(3)-S(12)
As(3)-S(13)
As(4)-S(17)
As(4)-S(16)

As(4)-S(19)

2.199(6)
2.221(6)
2.248(6)
2.187(6)
2.228(5)
2.236(6)
2.157(5)
2.158(5)
2.168(5)
2.175(5)
2.121(6)
2.131(5)
2.184(5)
2.251(5)
2.102(5)
2.160(5)
2.163(5)
2.262(5)
2.122(5)
2.136(5)

2.154(5)

CS]0CU2AS4S]9

Cs(2)-S(16)
Cs(2)-8(8)
Cs(2)-S(5)
Cs(2)-S(3)
Cs(3)-S(2)
Cs(3)-Cu(2)
Cs(3)-S(2)
Cs(3)-S(1)
Cs(3)-S(6)
Cs(3)-S(10)
Cs(3)-S(5)
Cs(3)-8(4)
Cs(4)-Cu(l)
Cs(4)-S(17)
Cs(4)-S(17)
Cs(4)-S(1 1)
Cs(4)-S(6)
Cs(4)-S(16)
Cs(4)-8(9)
Cs(4)-S(l8)

Cs(5)-S(5)

3.669(5)
3.670(6)
3.675(5)
3.681(5)
3.459(5)
3.499(3)
3.551(5)
3.634(5)
3.655(5)
3.689(6)
3.732(5)
3.773(5)
3.412(3)
3.596(6)
3.630(6)
3.643(6)
3.680(5)
3.720(5)
3.729(5)
3.768(5)

3.505(5)

258

Cs(6)-S(10)
Cs(7)-8(7)
Cs(7)-S(19)
Cs(7)-S(17)
Cs(7)-S(19)
Cs(7)-Cu(2)
Cs(7)-S(13)
Cs(7)-S(14)
Cs(7)-S(17)
Cs(8)-S(1)
Cs(8)-S(2)
Cs(8)-S(3)
Cs(8)-8(8)
Cs(8)-S(15)
Cs(8)-8(4)
Cs(8)-S(16)
Cs(8)-S(10)
Cs(9)—S(7)
Cs(9)-S(4)
Cs(9)-S(13)

Cs(9)-S(10)

3.872(6)
3.474(6)
3.495(5)
3.548(6)
3.636(5)
3.707(3)
3.731(5)
3.804(6)
3.865(6)
3.414(5)
3.472(5)
3.573(5)
3.619(5)
3.629(5)
3.631(6)
3.838(5)
3.847(5)
3.474(5)
3.526(5)
3.602(5)

3.622(6)

As(4)-S(15)
Cs(1)-S(1)
Cs(1)-S(18)
Cs(1)-S(15)
Cs(1)-S(12)
Cs(1)-S(19)
Cs(1)-8(4)
Cs(1)-S(13)
Cs(1)-S(10)
Cs(2)-S(1)
Cs(2)-S(19)
Cs(2)-8(9)

Cs(2)-S(5)

Cu(l)—Cu(l)
Cu(l)-S(4)
Cu(l)-S(4)
Cu(1)-S(2)
Cu(l)-S(1)
Cu(1)-S(4)
S(1)-3(4)

As(1)-S(1)

2.264(5)
3.399(5)
3.497(5)
3.502(5)
3.513(5)
3.605(5)
3.630(5)
3.678(5)
3.842(6)
3.508(5)
3.622(5)
3.640(5)

3.661(5)

0.820(3)
2.298(3)
2.342(3)
2.378(3)
2.615(2)
2.780(3)

2.058(3)

Cs(9)-S(l4)
Cs(9)-S(13)
Cs(9)-S(12)
Cs(9)-Cu(1)

Cs(9)-S(l 8)

Cs(10)-S(19)
Cs(10)-S(14)

Cs(10)-S(16)

Cs(10)-8(4)

Cs(10)-S(15)

Cs(10)-8(9)

Cs(10)-S(3)

Cs(1)-Cu(1)

Cs(2)-S(3)

2 x 3.4779(18)Cs(2)-S(1)

Cs(5)-8(8) 3.531(6)
Cs(5)-S(11) 3.576(5)
Cs(5)-8(8) 3.663(6)
Cs(5)-8(9) 3.680(5)
Cs(5)-S(3) 3.684(5)
Cs(5)-8(9) 3.685(5)
Cs(5)-S(16) 3.855(5)
Cs(6)-S(2) 3.465(6)
Cs(6)-S(2) 3.558(5)
Cs(6)-S(6) 3.646(5)
Cs(6)-S(1) 3.677(5)
Cs(6)-S(3) 3.745(6)
Cs(6)-S(1 1) 3.845(6)
CSZCuAsss

As(1)-S(2) 2.148(2)
As(1)-S(3) 2.135(2)
Cs(1)-S(1)
Cs(1)-8(4) 2 x 3.543(3)
Cs(1)-S(1) 2 x 3.556(2)
Cs(1)-S(2) 3.570(2)
Cs(1)-S(3) 3.582(2)

2 x 3.585(3)

2 x 2.1839(18)Cs(1)-S(4)

259

Cs(2)-S(3)
Cs(2)-S(3)
Cs(2)-S(1)

Cs(2)-S(2)

3.635(5)
3.668(5)
3.683(5)
3.689(3)
3.878(5)
3.472(5)
3.604(5)
3.610(5)
3.656(5)
3.664(5)
3.685(5)

3.723(6)

2 x 3.6229(16)
3.639(2)

2 x 3.711(2)

2 x 3.7178(9)
3.725(2)

2 x 3.824(2)

3.481(2)

 

 

1T"

 

Au(1)-S(3)
As(1)-S(1)
As(1)-S(2)
As(1)-S(3)

Cs(1)-S(1)

CSzAuASS4

2 x 2.2818(14)Cs(l)-S(2)
2.1 16(2) Cs(1)-S(2)
2.1381(19) Cs(1)-S(2)
2 x 2.2026(14)Cs(1)—S(3)

3.456(2) Cs(1)-S(3)

3.485(2) Cs(2)-S(2)
3.452(2) Cs(2)-S(1)
2 x 3.6319(8) Cs(2)-S(1)
2 x 3.6025(15)Cs(2)-S(3)

2 x 3.7781(15)

260

3.5850(19)
3.514(2)
2 x 3.5743(8)

2 x 3.8876(16)

 

 

 

C.3 Structure description of CszMAsss (M = Cu, Ag)

CszCuAsss and CszAgAsss are isostructural. Therefore we will only discuss the
structural details of CSZCuAsss. Figure 2a shows the unit cell of this compound. As we
can see, the compound consists of discrete, molecular tetrameric [Cu4(Asss)4]8' anions
which sit on the crystallographic 4/m site. The four metal centers define a perfect square
with sides of 3.390(1) A. Within each tetramer, Cu is tetrahedral and coordinated by two
AsSs3' ligands. Figure 2b shows an individual cluster. Each AsSs3° ligand uses two of its
monosulfide arms to coordinate to two adjacent Cu atoms. The terminal sulfur atom of
the disulfide arm forms a direct bridge between the same pair of Cu atoms. The
remaining sulfur atom in the AsSs3' ligand is terminal and non-bonding.

Cu occupies a distorted tetrahedral site with Cu-S bond lengths ranging from 2.298(3) A
to 2.780(3) A, Table 4. S-Cu-S angles vary between 100.91(10)° to 118.94(16)°, Table 5.
The tetrahedral As consists of As-S bond distances in the range 2.135(2) to 2.1839(18) A.
S-As-S angles vary from 105.97(12)° to 116.48(9)°. S-S distance is 2.058(3) A. Cs-Cu
bond lengths that are similar to Cs-S distances are observed.

The [Cu4(Asss)4]8' cluster is structurally related to that of another tetranuelear cluster
anion, [Hg.t(Se2)2(PSe4)4]8'.30 This compound crystallizes in P42/n, which is a non-
isomorphic sub group of I4/m. The compound consists of tetrahedral Hg2+ ions that are
coordinated and bridged by tetrahedral PSe43' ligands. In addition, the Hg atoms are also
bridged by Sezz' dumbbells. The structure of this compound is shown in figure 2c. The
non-bonding Se atoms on the PSe43' ligand interact with the diselenide ligand. In
C52CuAsS5, the disulfide ligand that connects two trans-metal atoms is absent, instead it

is present as one of the arms of the thioarsenate ligand and bridges two cis-metal atoms.

261

t
r
J

1.
I

 

The structure of the [Cu4(As85)4]8' cluster can be derived from the structure of the
[Hg4(Se2)2(PSe4)4]8’ cluster. The transformation involves the reductive cleavage, by 4e',
of the diselenide bonds followed by oxidative coupling of the resulting 4 Sez' ions to one
of the terminal Se atoms on the PSe43' ligand. Since the reduction of two diselenide bonds
requires 4e' whereas the coupling of 4Se2‘ ions involves 8e', there is a net gain of 4e'.
This difference is accounted for by reducing the charge on the cation by substituting Hg2+

with Cu+. A schematic representation of this transformation is shown in Figure 3.

C4 Structure description of CszAuAs54

The structure of CszAuAsS4 is very simple and shown in Figure 4. The compound
consists of one dimensional [Au(AsS4)]2' chains propagating down the c- axis. The chains
are composed of a linear A111+ coordinated by two A5843“ ligands. Each AsS4 unit ligates
to two Au atoms. The linear coordination of Au+ prevents the anion in this compound to
adopt the cluster structure of the Cu and Ag analogs.

This compound is isostructural to its thiophosphate counterpart, CszAuPsdll and similar
but not isostructural to KzAuAsS424. Au—S distance of 2.2818(14) A compare well with
the above mentioned compounds. As-S bond lengths vary from 2.116(2) to 2.2026(14).
The distance between two Au atoms in a chain is 3.552(1) A ruling out any significant
Au---Au interactions. Cs(1) is surrounded by 9 S atoms at distances ranging from
3.456(2) to 3.7781(15) A while Cs(2) interacts with 6 S atoms at distances between
3.514(2) to 3.8876(16) A. Au is linear with S-Au—S bond angle of l79.77(7)°. Similarly,

S-As-S angles deviate very slightly from the tetrahedral angle.

262

 

 

 

 

 

Figure 2. a) The unit cell of CS2CuAsss. b) The single tetrameric cluster anion
[ed.(Asss).]8‘ c) The [Hg4(PSe4)4(Se2)2]8' cluster.

263

 

 

 

Reductive cleavage by 4e- of the
two diselenide linkages followed
by oxidative coupling by 8e-

 

 

Figure 3. Schematic representation of the transformation of [Hg4(Se2)(PSe4)4]8‘ cluster
to [Cu4(A885)4]8' cluster. The dotted lines indicate the breaking of the Se-Se bond in the

former cluster followed by the formation of the diselenide bond in the thioarsenate
ligand in the latter compound.

264

0..f‘

 

 

 

 

b) 82
O 0
As]
S3. . O O '. 0
31

Au]

Figure 4. a) The unit cell of CszAuAsS4 looking down the c- axis. b) A single
chain of 1..[AuAsS4]2' running along the c- axis.

265

1113.! C...“: . .

 

A... .—,-I_

 

Jr

 

Table 5. Selected bond angles for CsloCu2A54819, CszCuAsss and CszAuAsS4.

CstoCuzAs4Sm
S(18)-Cu(l)-S(12) 124.8(2) S(8)-As(2)-S(6) 101.9(2)
S(1 8)-Cu(1)-S(14) 125.6(2) S(9)-As(2)-S(6) 1 10.7(2)
S(12)-Cu(1)-S(14) 109.3(2) S(5)-As(2)-S(6) 105.71(19)
S(1 1)-Cu(2)-S(5) 120.6(2) S(10)-As(3)-S(1 1) 1 15.5(2)
S(1 l)-Cu(2)-S(7) 130.0(2) S(10)-As(3)-S(12) 1 12.7(2)
S(5)-Cu(2)-S(7) 109.3(2) S(11)-As(3)-S(12) 107.3(2)
S(2)-As(1)-S(1) 108.5(2) S(10)-As(3)-S(13) 107.1(2)
S(2)-As(l)-S(3) 109.8(2) S(11)-As(3)-S(l3) 107.7(2)
S(1)-As(1)-S(3) 1 10.0(2) S(12)-As(3)-S(13) 105.9(2)
S(2)-As(1)-S(4) 108.9(2) S(17)-As(4)-S(16) 1 15.6(2)
S(1)-As(1)-S(4) 110.0(2) S(17)-As(4)-S(19) 1 10.8(2)
S(3)-As(l)-S(4) 109.6(2) S(16)-As(4)-S(19) 1 14.2(2)
S(8)-As(2)-S(9) 1 12.7(2) S(17)-As(4)-S(15) 108.2(2)
S(8)-As(2)-S(5) 1 12.7(2) S(16)-As(4)-S(15) 98.1(2)
S(9)-As(2)-S(5) 1 12.3(2) S(19)-As(4)-S(15) 108.7(2)

 

: In -_ ~fi 'yf1.4_ml.fi

 

CszCuAsss
S(4)-Cu(1)-S(2) 1 1432(9) S(3)-As(1)-S(2) 116.48(9)
S(4)—Cu(l)-S(4) 1 15.83(14) S(3)-As(1)-S(1) 109.15(6)
S(4)-Cu(1)-S(1) 1 18.04(10) S(2)-As(1)-S(1) 107.79(7)

S(4)—Cu(1)-S(l) 100.91(10) S(3)-As(1)-S(1) 109.15(6)

266

S(2)-Cu( l )-S( 1)
S(4)-Cu( 1 )-S(4)

S(4)-Cu(1)-S(2)

S(3)-Au(1)-S(3)
S(1)-As(1)-S(2)

S(1)-As(1)-S(3)

103.83(8)
118.94(16)

103.75(10)

CSzAUASS4
l79.77(7)
1 14.55(8)

2x111.15(5)

S(2)-As(l)-S(l)

S(1)-As(1)-S(1)

S(2)-As(1)-S(3)

S(3)-As(l )-S(3)

267

107.79(7)

105.97(12)

2 x 104.85(5)

109.92(8)

 

 

 

C.5 Spectroscopy

Diffuse reflectance spectra in the UVNis/near-IR region of CszCuAsss, CszAgAsSs and
CszAuAssa are shown in Figure 5. The spectra show sharp absorption onsets at 2.1, 2.41
and 2.54 eV respectively corresponding to their orange and yellow colors. In the case of
CszCuAsss and CszAgAsss, since there are no strong inter-cluster forces, the absorption
must be intra-cluster in nature and as such an appropriate description would be a HOMO-
LUMO type of transition.

F ar-IR spectra of the three compounds are shown in Figure 6. The spectra of CszCuAsss
and CszAgAsss are very similar. The peaks occurring between 380-450 cm'1 are
attributed to As-S stretching vibrations.31 The weak peak at 470 cm’1 in figure 5a and the
strong peak at 488 cm'1 in figure 5b are due to S-S asymmetric stretching.32 Noticeably
this peak is absent in the spectrum of CszAuAssa corresponding to the lack of S-S bond
in this structure. Also, we can correlate the peaks due to As-S stretching in this
compound to the other two. Similar frequencies are observed for the compounds
APbAsSa and A4PbASZSg, both of which feature the tetrahedral AsS43’ ligand.33 Table 6

lists the peaks observed for the three compounds. The vibrations below 380 cm'1 can be

assigned to M-S stretching or As-S bending modes.

Table 6. Comparison of IR frequencies of CszCuAsss, CszAgAsss and CszAuAssa.
Compound IR frequency (cm'l,w = weak; m= medium; s= strong)

CszCuAsss 188(3), 211(3), 359(m), 414 (m-s), 430(m-s), 451(m), 470(w-m)
CszAgAsss 184(3), 198(3), 227(3), 357(3), 395(3), 435(m-s), 450(m-s), 488(3)

CszAuAssa 194(3), 208(m), 253(m-s), 310(m-s), 356(3), 386(3), 422(3), 433(3), 450(3)

268

absorbance (on/S)

 

 

 

 

b)

    

absorbance (oz/S)

Eg=2.10eV Eg=2.41eV

 

 

l L

—

   
 

 

 

 

 

 

 

 

 

2 3 4 5 6 l 2 3 4 5
Energy, eV Energy, eV
C)
Q
3
8
5
..D
8
.D
(6
E3 = 2.54 eV
1 1 1
1 2 1 3 4 5 6
Energy, eV

Figure 5. Diffuse reflectance spectra of a) C32CuA385 showing a sharp absorption
at 2.10 eV b) CszAgASSS showing an absorption at 2.41 eV. The molecular nature
of these clusters implies that the absorption is HOMO-LUMO transition. c)
CszAuAsS4 displays a steep slope at 2.54 eV corresponding to its bright yellow
color.

269

 

Transmittance

 

 

 

 

 

 

 

13)

 

 

i
"" 488
5 184 357
g 227
E‘ 198
395
414 435 450
l l l 430 l l l l l
200 300 400 500 600 200 300 400 500
-1 .1
wavenumber (cm ) wavenumber (cm )

 

Transmittance

 

 

 

 

l l l l
200 300 400 -1 500 600
wavenumber (cm )

600

Figure 6. Far— IR spectra of a) CszCuAsss, b) CszAgAsss and c) CszAuAsS4. The
peak at 470 cm'1 for 11 and 488 cm’1 for 111 are due to S-S asymmetric stretching.

The peaks between 400 and 450 cm'1 are due to As-S stretching.

270

C.6 Differential Thermal Analysis

CszAuAssa melts at ~470°C and recrystallizes upon cooling at 430°C. Figure 7 displays
the differential thermal analysis plot showing the two events. The first cycle shows an
endothermic melting peak at 474°C and an exothermic recrystallization peak at 430°C. In
the second cycle, the melting point shifts slightly to 467°C while the recrystallization
temperature remains the same. This shift in the melting peaks in the two cycles is due to
the very fast heating rates (10°C/min) used in the DTA. The powder pattern of the residue
taken after the DTA matches the one taken before the start of the experiment indicating
congruent melting.

We also measured the thermal behavior of CszAgAsss. This compound decomposes at

346°C to give CszAgAssa, C34Aszsro and AgZS according to the following reaction:

3 CszAgAsss ——> CszAgAssa + C34A32$to + Ang

271

 

 

430

exo —>

uV

 

467

O

“O

f:

0 ~. .
l ‘ ‘ k

l 474 . _

1 1 1 1
100 200 300 400 500 600

Temperature, 0C

 

 

 

Figure 7. Differential Thermal Analysis of CszAuAsS4 showing a melting point at
~470°C and an exothermic crystallization peak at 430°C. The powder pattern of the

product after the DTA matched the one before indicating a congruently melting
compound.

272

D. Concluding Remarks

The reactions of main group metals In, Sn, Pb and Bi in thioarsenate fluxes have shown
that the basicity of the metal was an important parameter in determining the oxidation
state of As and the presence of disulfide linkages in the resulting thioarsenate ligands. In
general, we observed that for a given flux, as the size of the metal increases the tendency
to form A35+ increases and the tendency to form S-S bonds decreases. Thus the very
acidic Sn“ promotes the formation of As3+ and S-S linkages in its compounds while the
basic Bi3+ forms compounds containing the tetrahedral A3843' anion. This observation
holds true in the chemistry of coinage metals in cesium thioarsenate fluxes. As we go
from Cu to Au, the thioarsenate ligand changes from the AsSs3' anion, which contains a
disulfide arm, to the AsSa3' ligand. This understanding of the flux chemistry is a step
ahead in the rational design of new compounds by using molten fluxes. CstoCu2A34Sm is
an intermediate product leading to the more stable C32CuAsSs. It may be possible to
obtain the Au compounds with Au in +3 oxidation state by utilizing a highly acidic flux.
It might also be possible to connect the [Cu4(A385)4]8‘ clusters in a three-dimensional
network by the use of smaller alkali cations like Na+ and Li+. Further work is therefore

needed to explore these possibilities.

273

 

 

 

References

l.

ICSD: Inorganic Crystal Structure Database, FIZ, Karlsruhe, 2004.

a) Wachhold, M.; Sheldrick, W. S. Z. Naturforsch., B 1997, 52, 169. b) Wachhold,
M.; Sheldrick, W. S. Z. Naturforsch., B 1996, 51 , 32. c) Chou, J.-H.; Hanko, J. A.;
Kanatzidis, M. G. Inorg. Chem. 1997, 36, 4. (1) Wood, P. T.; Pennington, W. T.;
Kolis, J. W. Inorg. Chem. 1994, 33, 1556.

a) Rumpf, C.; Naether, C.; Bensch, W. Inorg. Chem. 1999, 38, 4612. b) Sutorik, A.
C.; Kanatzidis, M. G. Prog. Inorg. Chem. 1995, 43, 151. c) Sunshine, S. A.; Kang,
D.; Ibers, J. A. J. Am. Chem. Soc. 1987, 109, 6202 .

a) Chung, D. Y.; Huang, S. P.; Kim, K. W.; Kanatzidis, M. G. Inorg. Chem. 1995, 34,
4292. b) Park, Y.; Kanatzidis, M. G. J. Alloys des. 1997, 25 7, 137.

. a) Klepp, K. O.; Sing, M.; Boller, H. J. Alloys des. 1992, I84, 265. b) Huster, J.;

Bonsmann, B.; Bronger, W. Z Anorg. Allg. Chemie 1993, 619, 70.

a) Chondroudis, K.; Kanatzidis, M. G. Inorg. Chem. 1998, 37, 2098. b) Huang, S. P.;
Kanatzidis, M. G. Angew. Chem. Int. Ed. Engl. 1989, 28, 1513.

a) Chen, X.; lDilks, K. J .; Huang, X.; Li, J. Inorg. Chem. 2003, 42, 3723. b) Tampier,
M.; Johrendt, D. Z. Anorg. Allg. Chemie 2001, 627, 312.

a) Sutorik, A. C.; Kanatzidis, M. G. Prog. Inorg. Chem. 1995, 43, 151. b) Kanatzidis,
M. G. Curr. Opin. Solid State Mater. Sci. 1997, 2 139.

Park, Y.; Kanatzidis, M. G. J. Am. Chem. Soc. 1989, II 1, 3767.

10. McCarthy, T. J .; Xiang, Z.; Kanatzidis, M. G. Inorg. Chem. 1993, 32, 2944.

11. Chondroudis, K.; Hanko, J. A.; Kanatzidis, M. G. Inorg. Chem. 1997, 36, 2623.

274

 

 

 

12. Park, Y.; Kanatzidis, M. G. Inorg. Chem. 2001, 40, 5913.

13. Zhang, X.; Kanatzidis, M. G. J. Am. Chem. Soc. 1994, 116, 1890.

l4.Zhang, X.; Park, Y.; Hogan, T.; Schindler, J. L.; Kannewurf, C. R.; Seong, S.;
Albright, T.; Kanatzidis, M. G. J. Am. Chem. Soc. 1995, 117, 10300.

15. Sutorik, A. C.; Albritton-Thomas, J .; Hogan, T.; Kannewurf, C. R.; Kanatzidis, M. G.
Chem. Mater. 1996, 8, 751. r.-

 

16. Patschke, R.; Brazis, P.; Kannewurf, C. R.; Kanatzidis, M. G. Inorg. Chem. 1998, 37
6562.

i-HI .I I:i' “lit-flute

 

17. Axtell, E. A.; Kanatzidis, M. G. Chem. Eur. J. 1998, 4, 2435.

l

18. Jerome, J. E.; Wood, P. T.; Pennington, W. T.; Kolis, J. W. Inorg. Chem. 1994, 33,
1733.

19. Wood, P. T.; Schimek, G. L.; Kolis, J. W. Chem. Mater. 1996, 8, 721.

20. Chou, J. H.; Kanatzidis, M. G. J. Solid State Chem. 1996 127, 186.

21. Schimek, G. L.; Kolis, J. W. Acta Cryst. 1997 C53, 991.

22. Schimek, G. L.; Kolis, J. W. Chem. Mater. 1997, 9, 2776.

23. Auemharnmer, M.; Effenberger, H.; Irran, E.; Pertlik, F.; Rosenstingl, J. J. Solid State
Chem. 1993, 106 421.

24. Loken, S.; Tremel, W. Eur. J. Inorg. Chem. 1998, 283.

25.Feher, F. In Handbuch der Pra‘parativen Anorganischen Chemie; Brauer G., Ed.;
Ferdinand Enke: Stuttgart, Germany, 1954; vol. 1, pp 280-281.

275

 

26.a) Wendlandt, W. W.; Hecht, H. G. Reflectance Spectroscopy; Interscience: New
York, 1966. b) Kotum, G. Reflectance Spectroscopy; Springer-Verlag, New York,
1969. c) Tandon, S. P.; Gupta, J. P. Phys. Status Solidi 1970, 38, 363.

27.SMART, SAINT, SHELXTL: Data Collection and Processing Software for the
SMART -CCD system; Siemens Analytical X-ray Instruments Inc., 1997.

28. PLA TON: Spek, A. L. J. Appl. Cryst. 2003, 36, 7.

29. Kanatzidis, M. G. Comments Inorg. Chem. 1990 10, 161.

30. Chondroudis, K.; Kanatzidis, M. G. Chem. Commun. 1997, 401.

31.Nakamoto, K. Infrared and Raman Spectra of Inorganic and Coordination
Compounds, 5th ed.; John Wiley and Sons: New York, 1997.

32. Jaroudi, O. E.; Picquenard, E.; Demortier, A.; Lelieur, J. P.; Corset. J. Inorg. Chem.
2000, 39, 2593.

33. Iyer, R. G.; Kanatzidis, M. G. Unpublished results

276

 

APPENDIX
During the course of discovering new quaternary thioarsenates and their analogs, we
isolated C34A32Sto, TlgSntoSb16Se43 and A3CeA3283 (A = Rb, Cs). C34AszSto and
A3CeAszsg were obtained from thioarsenate fluxes while TlsSnroSwae43 was obtained
while attempting to prepare leSDszsefi. These compounds could not be included in the
main body of the dissertation since they did not fit in the flow. Hence the syntheses,

structures and properties of these compounds are included in the appendix.

Synthesis and Structure of Cs4Aszsro
C34A32$10 was initially obtained from a reaction of CszS, Sn, A3283 and S in the ratio
2/1/1/10 at 500°C. The compound was isolated as yellow plates. A pure synthesis can be
achieved by reacting a stoichiometric amount of the starting materials, C32S, As and S.
C34A32S10 crystallizes in the monoclinic space group P2t/c and is isostructural to
CsaPZSm.l The structure of this compound is shown in Figure A-l. Table A-1 gives
complete single crystal refinement details. Tables A-2, A-3, A-4 and A-5 list the
fractional atomic coordinates, the aniostropic displacement paramters, selected bond

distances and bond angles, respectively.

 

1 Aitken, J. A.; Canlas, c.; Weliky, D. P.; Kanatzidis, M. G. Inorg. Chem. 2001, 40,
6496.

277

Table A-1. Crystallographic refinement details for CsaAszslo.

empirical formula
fw

space group
a, A

b, A

c, A

0:, deg

8. deg

Y, deg

V, A 3

Z

pared, g/cm3
u. m“
T, K
)1, A

0 range, deg
Refinement method
R1a

wR2b

CmAaSm
501.04
P21/c
l7.669(4)
7.1936(15)
24.171(5)
90
94.256(4)
90
3063.6(1 1)
12

3.259

1 1.296
173(2)
0.71073
1.69-28.30
F ull-matrix least-squares on F 2
0.0493
0.0919

“ 81 = 2 llFoI- lFall/ZIFOI. ” wR2 = {2 lw(F.2-F.’f]/21w(F.2)2]}”2

278

Table A-2. Fractional Atomic Coordinates and Isotropic Displacement Parameters (A2 x

 

 

103) for cs4Aszsm.

Atom x y z Ueq
Cs(1) 0.4076(1) 0.7155(1) 0.0381(1) 26(1)
Cs(2) 0.2594(1) 0.2955(1) 0.1361(1) 36(1)
Cs(3) 0.1508(1) 0.8431(1) 0.0007(1) 36(1)
Cs(4) 0.1003(1) 0.2000(1) 0.2156(1) 37(1)
Cs(5) 0.1499(1) 0.3258(1) 0.3549(1) 36(1)
Cs(6) 0.4553(1) 0.5774(2) 0.3339(1) 52(1)
As(1) 0.6673(1) 0.7785(2) 0.0269(1) 20(1)
As(2) 0.3318(1) 0.7399(2) 0.2006(1) 21(1)
As(3) 0.0055(1) 0.7353(2) 0.1359(1) 38(1)
3(1) 0.3136(2) 0.9706(4) 0.0718(1) 26(1)
3(2) 0.4378(2) 0.6253(5) 0.1817(1) 35(1)
3(3) 0.2755(2) 0.5942(4) 0.2612(1) 32(1)
3(4) 0.2586(2) 0.8109(4) 0.1297(1) 24(1)
3(5) 0.2296(2) 0.3518(4) 0.0097(1) 32(1)
3(6) 0.6052(2) 0.5784(4) 0.0840(1) 30(1)
3(7) 0.4193(2) 1.2133(4) 0.0397(1) 27(1)
3(8) 0.3812(2) 0.0050(4) 0.2435(1) 32(1)
8(9) 0.3125(2) 0.0481(4) 0.3648(1) 30(1)
S(10) 0.0765(2) 0.2949(5) 0.21 16(2) 44(1)

279

3(11)
3(12)
S(13)
S(14)
S(15)

S(16)

0.1099(2)
0.3007(2)
0.0178(2)
0.0629(3)
0.0212(7)

0.0462(6)

0.6662(5)
0.1028(4)
1.01 19(5)
0.5041(8)
0.41 18(12)

0.5922(14)

0.1388(1)
0.2922(1)
0.0922(1)
0.0894(2)
0.0310(6)

0.0053(9)

280

40(1)
39(1)
43(1)
107(2)
48(4)

71(5)

Table A-3. Anisotropic displacement parameters“ (A2 x 103) for C34AszSto.

Cs(1)
Cs(2)
Cs(3)
Cs(4)
Cs(5)
Cs(6)
As(1)
As(2)
As(3)
3(1)
3(2)
3(3)
3(4)
3(5)
S(6)
3(7)
8(8)
3(9)
3(10)
3(1 1)

3(12)

 

 

U11 U22 U33 U23 U13 U12
33(1) 22(1) 24(1) 1(1) 5(1) 3(1)
57(1) 21(1) 30(1) 0(1) 11(1) 1(1)
33(1) 44(1) 31(1) 5(1) 5(1) -8(1)
32(1) 35(1) 45(1) 7(1) 11(1) 7(1)
34(1) 35(1) 38(1) -5(1) -3(1) 8(1)
34(1) 94(1) 28(1) 8(1) 6(1) 28(1)
23(1) 20(1) 18(1) -1(1) 3(1) 0(1)
22(1) 21(1) 20(1) 2(1) 2(1) 1(1)
27(1) 35(1) 51(1) -1(1) 7(1) 4(1)
30(2) 23(2) 26(2) -6(1) 3(1) -3(1)
33(2) 48(2) 24(2) -2(2) 5(1) 14(2)
28(2) 39(2) 29(2) 12(2) 2(1) -9(1)
26(2) 24(2) 22(2) 3(1) 1(1) 3(1)
30(2) 32(2) 35(2) 2(1) 10(1) 7(1)
28(2) 32(2) 29(2) 3(1) 1(1) -2(1)
33(2) 24(2) 22(2) 3(1) -3(1) -4(1)
37(2) 38(2) 23(2) -4(1) 4(2) -13(2)
38(2) 27(2) 25(2) 1(1) 7(1) 1(1)
35(2) 37(2) 59(2) -10(2) -3(2) -7(2)
34(2) 41(2) 44(2) 0(2) 2(2) 10(2)
60(2) 32(2) 25(2) 3(1) 5(2) 20(2)

281

3(13)
S(14)
3(15)

S(16)

* The anisotropic displacement factor exponent takes the form:

44(2)
1 12(4)
58(7)

47(6)

43(2)
103(4)
39(5)

70(7)

44(2)
104(4)
48(8)

96(14)

-8(2)
33(3)
0(4)

56(7)

12(2)
-3(3)
9(6)

-10(7)

1 1(2)
-74(3)
1(4)
-9(5)

2131112820.. + 181921122 + 120*2U33 + 2hka*b*U12 + 2klb*c*U23 + 2hla*c*Un]

282

Table A-4. Selected bond distances for C34Aszsro.

As(1)-S(5)
As(1)-S(1)
As(1)-8(7)
As(1)-S(6)
As(2)-S(3)
As(2)-S(2)
As(2)-3(4)

As(2)-8(8)

As(3)-S(1 1)
As(3)-S(13)
As(3)-S(10)

As(3)-S(14)

Cs(1)-S(2)
Cs(1)-S(1)
Cs(1)-8(7)
Cs(1)-3(7)
Cs(1)-S(6)
Cs(1)-8(4)
Cs(1)-S(6)
Cs(1)-S(7)
Cs(2)-3(4)

Cs(2)-S(5)

2.116(3)
2.120(3)
2.137(3)
2.326(3)
2.110(3)
2.126(3)
2.131(3)
2.312(3)
2.105(3)
2.122(4)
2.152(4)
2.287(5)
3.531(3)
3.539(3)
3.587(3)
3.619(3)
3.625(3)
3.628(3)
3.718(3)
3.743(3)
3.490(3)

3.547(3)

Cs(2)-S(3) 3.703(3)

Cs(2)-8(4) 3.711(3)

Cs(2)-As(2) 3.7399(14)

Cs(2)-S(10) 3.829(4)
Cs(2)-3(7) 3.839(3)
Cs(2)-S(14) 3.851(6)
Cs(2)-8(8) 3.861(3)
Cs(3)-8(4) 3.568(3)
Cs(3)-S(1) 3.577(3)
Cs(3)-S(13) 3.582(3)

Cs(3)-S(11) 3.595(3)

Cs(3)-S(16) 3.645(10)

Cs(3)-S(15) 3.679(9)
Cs(3)-S(13) 3.725(4)
Cs(3)-S(14) 3.727(5)
Cs(3)-S(5) 3.811(3)

Cs(3)-S(15) 3.893(9)

Cs(3)-S(16) 3.916(11)

Cs(3)-S(5) 3.927(3)
Cs(4)-S(11) 3.519(3)
Cs(4)-S(3) 3.533(3)

Cs(4)-S(13) 3.563(4)

283

Cs(4)-S(10)

Cs(4)-8(4)

Cs(4)-S(10)
Cs(4)-S(10)
Cs(4)-S(14)
Cs(5)-S(12)

Cs(5)-S(13)

Cs(5)-S(1)

Cs(5)-S(10)

Cs(5)-S(1 1)

Cs(5)-S(5)

Cs(5)-S(1 1)

Cs(5)-S(3)
Cs(5)-3(9)
Cs(6)-S(3)
Cs(6)-S(1)
Cs(6)-3(8)
Cs(6)-S(2)
Cs(6)-3(7)
Cs(6)-S(2)

Cs(6)-S(9)

Cs(6)-As(2) 3.9333(14)

3.586(4)
3.606(3)
3.658(4)
3.696(4)
3.772(6)
3.546(3)
3.573(4)
3.592(3)
3.613(3)
3.614(3)
3.694(3)
3.728(4)
3.812(3)
3.930(3)
3.517(3)
3.525(3)
3.595(3)
3.686(3)
3.768(3)
3.794(4)

3.802(3)

 

Table A-5. Selected bond angles for CsaAsleo.

S(5)-As(1)-S(1)
S(5)-As(1)-S(7)
S(1)-As(1)-S(7)
S(5)-As(1)-S(6)
S(1)-As(1)-S(6)
S(7)-As(l)-S(6)
S(3)-As(2)-S(2)
S(3)-As(2)-S(4)

S(2)-As(2)-S(4)

111.80(13)
116.33(13)
116.04(12)
107.06(12)
106.65(12)
96.94(11)

115.15(13)
112.80(12)

114.35(12)

S(3)-As(2)-S(8)
S(2)-As(2)-S(8)

S(4)-As(2)-S(8)

3(1 1)-As(3)-S(13)
S(1 l)-As(3)-S(10)
S(13)-As(3)-S(10)
3(1 1)-As(3)-S(14)
S(13)-As(3)-S(14)

S(10)-As(3)-S(14)

284

106.23(12)
96.15(13)
110.49(12)
110.74(14)
116.92(14)
115.78(14)
108.1(2)
108.2(2)

95.34(17)

 

 

 

Figure A-l. Unit cell view of Cs4A32810 down the b-axis. Cs atoms have been removed
for clarity. The figure shows two crystallographically distinct As23104' anions.

285

 

 

 

Synthesis and Structure of TkSntoSbmSe43

TlgsnloSb15364g was achieved by heating T1, Sn, Sb28e3 and Se in the stoichiometric ratio
at 500°C. The reactants were loaded in a fused silica tube in a nitrogen atmosphere and
tube sealed under vacuum. The tube was then heated to 500°C in 10h, held at that
temperature for 60h and cooled down to 250°C at the rate of 5°C/h followed by rapid
cooling to room temperature. The compound was obtained as black plates and the powder
pattern of the product showed 100% phase purity.

Intensity statistics and systematic absence conditions pointed to the monoclinic space
group, C2/m. Sb and Sn are indistinguishable by X-ray, therefore assignment of atoms in
TlgSntoSb16Se43 were made on the basis of coordination geometry and charge-balancing
requirements. All atoms were refined anisotropically to give final Rl/wR2 value of
5.72/12.90. Crystal refinement details are given in Table A-6. Fractional atomic
coordinates and anisotropic displacement parameters are listed in Tables A-7 and A-8.
Selected bond distances and angles are given in Tables A-9 and A-10.

The structure of TlgSntoSb16Se4g consists of two different kinds of layers, Figure A-2a.
The first layer is the SnSe; structure type and consists of octahedral Sn and Sb bonded to
Se atoms. This layer can be formulated as (Sn5Sb28e14)2', Figure A-2b. The second layer
is similar to the structure of SnSe with two Sn atoms removed periodically and replaced
by T1 atoms slightly above and below the layer. This layer can be written as (Sb6Sero)2'
and consists of only Sb bonded to 5 Se atoms in a square pyramidal geometry, Figure A-
2c. The layers are arranged in an ABABA fashion.

The DTA and diffuse reflectance spectrum of TlgsntoSbmSeag are shown in Figure A-3.

The compound melts at 433°C and recrystallizes at 372°C. There are two additional small

286

' .1I‘E 3'!
I.

 

 

peaks, labelled m and n, in the DTA plot, which maybe due to the presence of a little
amount of impurities. The powder pattern of the product after the DTA matches the one
taken before showing that the compound does not decompose on heating. The diffuse
reflectance spectrum shows an energy gap of 0.64 eV, Figure A-3b.

Given the low band gap of the compound, we performed Seebeck measurement. The
sample was in the form of a pressed pellet. Figure A-4 shows the plot of the Seebeck
coefficient against temperature. The compound has a room temperature Seebeck

Coefficient of ~-400p.V/K. The negative sign indicates that it is an n-type semiconductor.

287

 

Table A-6. Crystallographic refinement details for TlgSntoSbmSeag.

Formula
Space Group
a, A

b, A

c, A

on, deg

B. deg

16 deg

Z, V

D, mg/m3
Temp, K

A, A
u. m‘
F(000)
0mm deg

1

Total reflections

Total unique reflections
No. of parameters
Refinement Method
Final R indices(I>23(I))
R indices (all data)
Goodness of fit on F 2

a 81 = 2 IlFol- lFeII/ZlFol- b wR2 =

TlgSnthnge4g

CZ/m

42.95 (3)

3.967 (2)

13.369 (8)

90

98.813 (11)

90

6, 2251 (2)

5.510

293

0.71073

41.109

3108

28.21

5347

2768

125

Full-matrix least-squares on F 2
R1= 0.0572, wR2 = 0.1290
R1= 0.1179, wR2 = 0.1551
0.954

{2 [W(F02-Fc2)2]/2 [W(F02)2] } 1/2

288

 

Table A-7. Fractional Atomic Coordinates and Isotropic Displacement Parameters (A2 x

103) for Tlssmosowsm.

 

 

Atom x y z Ueq
T1(1) 0.2923(1) 0.5000 0.4084(1) 36(1)
T1(2) 0.0024(1) -2.5000 0.1464(1) 36(1)
Sn(l) 0.3591(1) 0 0.1954(2) 19(1)
Sn(2) 0.5000 -1.0000 0.5000 21(1)
Sn(3) 0.2876(1) 0.5000 0.0567(2) 20(1)
Sb(1) 0.1895(1) -1.5000 0.2935(2) 23(1)
Sb(2) 0.0885(1) -25000 0.0879(2) 24(1)
Sb(3) 0.1109(1) -2.0000 0.3635(2) 28(1)
Sb(4) 0.4307(1) 0.5000 0.3380(2) 21(1)
se(1) 0.3670(1) 0.5000 0.3401(2) 20(1)
Se(2) 0.1372(1) -2.0000 0.2009(2) 22(1)
Se(3) 0.4341(1) -1.0000 0.4822(2) 24(1)
Se(4) 0.0697(1) 0.5000 0.2648(2) 21(1)
Se(5) 0.2969(1) 0 0.2046(2) 22(1)
Se(6) 0.2292(1) -10000 0.3720(3) 28(1)
Se(7) 0.3517(1) 0.5000 0.0496(2) 26(1)
Se(8) 0.5048(1) -1.5000 0.6526(2) 25(1)
Se(9) 0.3422(1) -1.0000 0.5534(2) 22(1)
Se(10) 0.0458(1) -3.0000 0.0285(2) 25(1)
Se(] 1) 0.4229(1) 0 0.1917(2) 24(1)

289

 

 

IHET _
\

 

Se(12) 0.2753(1) -10000 0.0858(2) 27(1)

290

 

Table A-8. Anisotropic displacement parameters“ (A2 x 103) for TlsSnroSbmSeag.

T1(1)
T1(2)
Sn(l)
Sn(2)
Sn(3)
Sb(1)
Sb(2)
Sb(3)
Sb(4)
Se(l)
3e(2)
Se(3)
3e(4)
3e(5)
Se(6)
Se(7)
Se(8)

Se(9)

 

 

Se(lO) 19(2)

U11 U22 U33 U23 U13 U12
30(1) 32(1) 45(1) 0 3(1) 0
28(1) 40(1) 39(1) 0 5(1) 0
13(1) 16(1) 29(1) 0 -1(1) 0
15(2) 17(2) 30(2) 0 -3(1) 0
14(1) 16(1) 28(1) 0 -3(1) 0
19(1) 21(1) 31(1) 0 7(1) 0
21(1) 21(1) 30(1) 0 5(1) 0
32(1) 23(1) 30(1) 0 12(1) 0
13(1) 19(1) 29(1) 0 -1(1) 0
17(2) 21(2) 23(2) 0 3(1) 0
22(2) 19(2) 27(2) 0 7(1) 0
22(2) 28(2) 24(2) 0 6(1) 0
16(2) 22(2) 24(2) 0 2(1) 0
14(2) 27(2) 26(2) 0 4(1) 0
14(2) 23(2) 45(2) 0 0(1) 0
23(2) 28(2) 26(2) 0 5(1) 0
26(2) 23(2) 27(2) 0 8(1) 0
17(2) 19(2) 30(2) 0 2(1) 0
20(2) 33(2) 0 -3(1) 0
28(2) 27(2) 0 5(1) 0

Se(l 1) 18(2)

 

Se(12) 25(2) 31(2) 27(2) 0 8(1) 0
* The anisotropic displacement factor exponent takes the form:

-27'c2[h2a*2U11 + K2b*2U22 + 120*2U33 + 2hka*b*U12 + 2klb*C*U23 + 2hla*c*U13]

292

 

Table A-9. Selected bond distances for TlgSntoSbmSeag.

T1(1)-Se(6)
T1(2)-Se(4)
Sn(1)-Se(5)
Sn(1)-Se(1 1)
Sn(1)-Se(l)
Sn(1)-Se(7)
Sn(2)-Se(3)
Sn(2)-Se(8)
Sn(3)-Se(12)
Sn(3)-Se(7)
Sn(3)-Se(5)

Sn(3)-Se(12)

3.210(4)
3.255(4)
2.695(4)
2.746(4)
2 x 2.755(3)
2 x 2.766(3)
2 x 2.804(4)
4 x 2.830(2)
2 x 2.745(3)
2.770(4)
2 x 2.786(3)

2.788(4)

Sb(1)-Se(9)
Sb(1)-Se(6)
Sb(1)-Se(2)

Sb(2)-Se(4)

Sb(2)-Se(10)

Sb(2)-Se(2)
Sb(3)-Se(2)
Sb(3)-Se(4)
Sb(3)-Se(9)
Sb(4)-Se(1)
Sb(4)-Se(8)

Sb(4)-Se(3)

Sb(4)-Se(1 1)

293

2.625(4)
2 x 2.720(3)
2 x 3.108(2)
2.613(4)
2 x 2.735(3)
2 x 3.102(2)
2.600(4)
2 x 2.844(3)
2 x 2.924(3)
2.741(4)
2.751(4)
2 x 2.754(3)

2 x 2.770(3)

 

Table A-10. Selected bond angles for TlgsnloSb16SC4s.

Se(5)-Sn(1)-Se(l 1)

Se(5)-Sn(l )-Se( 1)

Se(l 1)-Sn(1)-Se(1)

Se(1)-Sn(1)-Se(1)

Se(5)-Sn(1)-Se(7)

Se(l 1)-Sn(1)-Se(7)

Se(l)-Sn(1)-Se(7)
Se(l)-Sn(1)-Se(7)

Se(7)-Sn(1)-Se(7)

Se(12)-Sn(3)-Se(12)
3e(12)-36(3)-3e(7)
Se(12)-Sn(3)—Se(5)

Se(12)-Sn(3)-Se(5)

Se(7)-Sn(3)-Se(5)

Se(5)-Sn(3)-Se(5)

Se(12)-Sn(3)-Se(12)
Se(7)-Sn(3)-Se(l2)

Se(5)-Sn(3)-Se(12)

Se(1)-Sb(4)-Se(8)
Se(1)-Sb(4)-Se(3)
Se(8)-Sb(4)-Se(3)

Se(3)-Sb(4)-Se(3)

178.47(12)
2 x 89.09(10)
2 x 8984(9)
92.12(11)

2 x 9138(9)

2 x 8969(10)
2 x 17947(13)
2 x 8811(8)
91.65(12)
92.53(12)

2 x 93.60(10)
2 x 176.83(13)
2 x 8825(8)

2 x 8941(9)
90.81(11)

2 x 90.54(10)
174.01(12)

2 x 8639(10)
176.84(12)

2 x 8646(9)

2 x 9135(9)

92.13(12)

Se(3)-Sn(2)-Se(3)
Se(3)-Sn(2)-Se(8)
Se(3)-Sn(2)-Se(8)
Se(8)-Sn(2)-Se(8)
Se(8)-Sn(2)-Se(8)
Se(8)-Sn(2)-Se(8)
Se(9)-Sb(1)-Se(6)
Se(6)-Sb(1)-Se(6)
Se(4)-Sb(2)-Se(10)
Se(10)-Sb(2)-Se(10)
Se(2)-Sb(3)-Se(4)
Se(4)-Sb(3)-Se(4)
Se(2)-Sb(3)-Se(9)
Se(4)-Sb(3)-Se(9)
Se(4)-Sb(3)-Se(9)
Se(9)-Sb(3)-Se(9)
Se(8)-Sb(4)-Se(1 1)
Se(1)-Sb(4)-Se(1 1)
Se(3)-Sb(4)-Se(1 1)
Se(3)-Sb(4)-Se(l 1)

Se(11)-Sb(4)-Se(1 1)

294

180.0

4 x 9130(8)

4 x 8870(8)

2 x 88.99(10)
2 x 179.996(1)
2 x 91 .01(10)
2 x 93.89(11)
93.65(12)

2 x 88.67(10)
9296(12)

2 x 8603(10)
88.45(11)

2 x 87.41(10)
2 x 9268(7)

2 x 173.25(12)
85.42(11)

2 x 92.57(10)
2 x 8963(9)

2 x 8806(8)

2 x 176.07(12)

91.48(12)

 

    
 
   
 

b)

  
  
 
 

    

It..\° ii..." 1.3' 2.. '
\ «or. a: a!

;.$.H.§'Hg.
\ I. .\ I. .‘

    

C)

 

Figure A-2. a) Unit cell view down the b- axis of T13SnloSb168e4g showing the two
different kinds of layers constituting the cell. b) The (Sn58b2Se14)2' layer c) The
(Sb6Se10)2' layer. The large light gray circles are Tl, small dark gray circles are Sb, black
circles are Sn and open circles are Se.

295

40

 

 

 

 

_2 1 L 1 1 1
100 200 300 400 500 600 700

T. °C

 

b)

 

 

absorbance (oz/S)

E8 = 0.64 eV

 

 

l l l l l

0 0.5 l 1.5 2 2.5 3
Energy, eV

 

Figure A-3. a) Differential Thermal Analysis of TlgSntoSb16Se43 showing a melting
point of 433°C and a recrystallization point of 372°C. The peaks labeled m and n

are due to minor impurities. b) The diffuse reflectance spectrum showing a narrow
band gap of 0.64 eV.

296

-100

 

~200 -

C»
o
o
l

-400[j- E] El
-500 -

-600 —

Seebeck Coefficient (uV/K)

-700 —

 

1

1

 

1 l 1 l 1

 

-800

300 350 400

450 500 550 600 650 700
T, °K

Figure A-4. A plot of the Seebeck coefficient of TlgSntoSb15Se43 against
temperature shows that it is a n-type semiconductor with a room temperature value

of ~-400 uV/K.

297

Synthesis and Structure of A3CeA3283 (A = Rb, Cs)

Orange needles of Rb3CeA32St; were obtained from a reaction of Rb28/Ce/A3233/S in the
ratio 4/1/2/10 at 500°C. The reaction mixture was loaded in a fused silica tube in a N2
filled glove box. The tube was sealed under vacuum (<10'4 Torr) and heated in a
computer-controlled furnace at 500°C for 60h. The tube was cooled to 250°C at the rate
of 5°C/h and then fast-cooled to room temperature. The excess of flux was washed away
with DMF, previously degassed with N2, to reveal orange needles and transparent yellow
crystals. Semiquantitative analysis using EDS gave an average reading of "Rb3.2CeA32Ss"
for the orange needles and "RbmoCeAsdsSts" for the yellow crystals.

CS3CCAstg was obtained as yellow crystals on heating a reaction mixture containing
C32S, Ce, A32S3 and S in the ratio 2:1 :1.5:10 at 500°C using the same heating profile and
isolation procedure as above. EDS on several crystals gave an average composition of
"C32,6Ceo,3A32S7,9". Relevant single-crystal refinement details for A3C6ASzSg are given in
Table A-1 1. Fractional atomic coordinates and anisotropic displacement parameters are
listed in Tables A-12 and A-13. Selected bond distances and angles are given in Tables
A-14 and A-15.

The structure of A3CeA32S3 is shown in Figure A-5. The unit cell consists of [CeA32Sg]'
chains running down the b- axis. A single chain is shown in Figure A-5b. The chain is
made up of CeSg bicapped trigonal prisms fused together by means of tetrahedral AsS43'
ligands. There are two kinds of A3843' ligands. The first type is terminal and uses three S
atoms to bind to one Ce atom. The other type serves to bridge two Ce atoms and form the

chain.

298

Table A-1 1. Crystallographic refinement details for Rb3CCASzSg and C33CeAs2S3.

Formula
Space Group
a, A

b, A

e, A

0t, deg

B. deg

Y. deg

Z, V

D, mg/m3
Temp, K
A, A

1*, mm'
F (000)
GM, deg

1

Total reflections

Total unique reflections
No. of parameters
Refinement Method
Final R indices(I>23(I))

R indices (all data)

Goodness of fit on F 2

Rb3CeA3283 C33CeA3283
P21 P21/m

9.901 (3) 10.059 (3)
6.893 (2) 7.001 (2)
11.620 (3) 11.875 (4)
90 90

90.807 (5) 90.223 (6)
90 90

2, 793 (2) 2, 836.3 (5)
3.363 3.753

293 293

0.71073 0.71073
17.175 14.047

726 834

23.29 28.30

5569 8763

2213 2150

127 82
Full-matrix least-squares on F 2
R1= 0.0197, R1= 0.0302,
wR2 = 0.0390 wR2 = 0.0604
R1= 0.0245, R1= 0.0473,
wR2 = 0.0403 wR2 = 0.0639
1.029 0.975

° R1 = 2 llFol- 1811/2181. b wR2 =12 1w(F£-F£>Zl/21w(Faz)’li”2

299

Table A-12. Fractional Atomic Coordinates and Isotropic Displacement Parameters (A2 x

103) for Rb3CeAs2Sg and C33CeA3283.

 

 

Atom x y z Ueq
Rb3CeA3283
Ce(1) 0.8850(1) 0.1444(1) 0.6516(1) 18(1)
Rb(1) 0.5989(1) 0.1259(2) 1.1532(1) 28(1)
Rb(2) 0.3649(1) 0.1311(2) 0.5874(1) 49(1)
Rb(3) 0.8447(1) 0.6268(2) 0.9360(1) 40(1)
As(1) 0.9082(1) 0.1080(1) 0.13371(1) 17(1)
As(2) 0.6253(1) 0.1247(2) 0.8180(1) 19(1)
3(1) 0.6491(3) 0.3797(3) 0.7093(3) 28(1)
3(2) 0.4329(2) 0.1 182(4) 0.8958(1) 30(1)
3(3) 0.7267(1) 0.1284(4) 0.4365(1) 26(1)
3(4) 0.6562(3) 0.1216(3) 0.7050(3) 27(1)
3(5) 1.0993(2) 0.3577(3) 0.7729(2) 26(1)
S(6) 0.8051(2) 0.1300(4) 0.9246(1) 29(1)
3(7) 1.0677(2) 0.1349(3) 0.7652(2) 30(1)
8(8) 1.0703(2) 0.0483(3) 0.4602(2) 22(1)
C33CeA32Sg
Ce(1) 0.1086(1) 0.2500 0.8487(1) 15(1)
Cs(1) 0.4006(1) 0.2500 0.6567(1) 15(1)
Cs(2) 0.1506(1) 0.2500 0.5571(1) 20(1)
Cs(3) 0.3714(1) 0.2500 0.9196(1) 22(1)

300

As(1)
As(2)
3(1)
3(2)
3(3)
3(4)
3(5)

S(6)

0.3658(1)
0.0927(1)
0.1883(2)
0.4436(2)
0.2689(2)
0.3366(2)
0.0869(2)

0.0675(3)

0.2500

0.2500

0.2500

0.2500

0.2500

0.0023

0.0009

0.1642

0.6847(1)
1.1575(1)
0.5813(2)
0.6080(2)
1.0552(2)
0.7930(1)
0.7383(1)

1.0404(2)

301

10(1)
18(1)
16(1)
16(1)
14(1)
16(1)
32(1)

13(1)

Table A-l3. Anisotropic displacement parameters“ (A2 x 103) for Rb3CCASzSg and

 

 

Cs3CeA3283.
U11 U22 U33 U23 U13 U12
Rb3CeA32Sg
Ce(1) 15(1) 20(1) 20(1) 1(1) 1(1) -1(1)
Rb(1) 28(1) 31(1) 27(1) 1(1) 1(1) 2(1)
Rb(2) 39(1) 40(1) 68(1) -5(1) -25(1) 2(1)
Rb(3) 40(1) 31(1) 50(1) -2(1) 14(1) -2(1)
As(1) 15(1) 16(1) 20(1) -1(1) 0(1) 0(1)
As(2) 18(1) 18(1) 23(1) 1(1) 5(1) 0(1)
3(1) 32(2) 19(1) 35(2) 3(1) 11(1) 3(1)
3(2) 19(1) 36(1) 34(1) -1(1) 9(1) 1(1)
3(3) 13(1) 38(1) 25(1) -2(2) 1(1) -1(1)
3(4) 29(2) 20(1) 32(2) -7(1) 6(1) -5(1)
3(5) 32(1) 21(1) 27(1) 6(1) -9(1) -7(1)
S(6) 21(1) 32(1) 36(1) -2(2) -3(1) 0(1)
3(7) 39(2) 22(1) 28(1) -5(1) -6(1) 8(1)
8(8) 15(1) 29(1) 22(1) -3(1) -2(1) 2(1)
Cs3CeA32Ss
Ce(1) 10(1) 25(1) 10(1) 0 1(1) 0
Cs(1) 16(1) 16(1) 13(1) 0 0(1) 0
Cs(2) 22(1) 15(1) 23(1) 0 5(1) 0

 

Cs(3) 20(1)

As(1) 11(1)

As(2) 10(1)

3(1)
S(2)
3(3)
5(4)
5(5)

S(6)

* The anisotropic displacement factor exponent takes the form:

-27r2[hza*2U11 + k2b*2U 22 + 12c*2U33 + 2hka*b*U12 + 2klb*c*U23 + 2hla*c*Ut3]

16(1)
11(1)
11(1)
20(1)
51(1)

13(1)

19(1)
10(1)
36(1)
12(1)
17(1)
18(1)
11(1)
28(1)

14(1)

28(1)
11(1)
9(1)

19(1)
20(1)
14(1)
17(1)
18(1)

12(1)

303

-9(1)
3(1)
0(1)
-3(1)
5(1)
-1(1)
3(1)
9(1)
-2(1)

 

Table A-14. Selected bond distances for Rb3CCASzSg and C33CeA3283.

Ce(1)-S(5)
Ce(1)-S(1)
Ce(1)-S(3)
Ce(1)-3(7)
Ce(1)-8(8)
Ce(1)-8(4)

Ce(1)-3(8)

Ce(1)-As(2)

Ce(1)-S(6)
Rb(1)-S(6)
Rb(1)-S(2)
Rb(1)-S(1)
Rb(1)-S(2)
Rb(1)-3(4)

Rb(1)-S(3)

Ce(1)-S(3)
Ce(1)-S(5)
Ce(1)-S(6)
Ce(1)-8(4)

Ce(1)-S(6)

2.927(3)
2.929(3)
2.9331(17)
2.942(2)
2.9771(18)
2.987(3)
3.106(2)
3.2420(9)
3.2820(18)
3.3735(17)
3.3931(19)
3.401(3)
3.454(3)
3.498(3)

3.5099(18)

2.930(2)

2 x 2.934(2)
2 x 2.951(3)
2 x 2.953(2)

2 x 3.212(3)

Rb3CeA3288
Rb(1)-S(2) 3.559(3)
Rb(1)-S(5) 3.607(3)
Rb(1)-3(7) 3.798(3)
Rb(2)-8(8) 3.301(2)
Rb(2)-S(3) 3.556(3)
Rb(2)-S(1) 3.570(3)
Rb(2)-S(3) 3.591(3)
Rb(2)-3(4) 3.620(3)
Rb(2)-S(2) 3.638(2)
Rb(2)-S(5) 3.763(3)
Rb(2)-8(4) 3.804(3)
Rb(2)-S(1) 3.859(3)
Rb(3)-S(2) 3.3954(17)
Rb(3)-3(7) 3.411(3)
Rb(3)-S(6) 3.449(3)

CS3C€AS2Sg
Cs(1)-S(3) 3.663(2)
Cs(1)-S(5) 2 x 3.736(2)
Cs(2)-S(1) 2 x 3.533(2)
Cs(2)-S(2) 3.546(2)
Cs(2)-S(5)

Rb(3)-S(6)
Rb(3)-S(1)
Rb(3)-S(5)
Rb(3)-8(4)
Rb(3)-S(5)
Rb(3)-S(6)
As(1)-S(5)
As(1)-S(7)
As(1)-S(3)
As(1)-8(8)
As(2)-S(2)
As(2)-S(6)
As(2)-3(4)

As(2)-S(1)

Cs(3)-3(4)
Cs(3)-S(2)
Cs(3)-3(4)

As(1)-S(2)

2 x 3.669(2) As(1)-S(1)

304

3.493(3)
3.667(3)
3.677(3)
3.683(3)
3.772(3)
3.8065(19)
2.148(3)
2.150(3)
2.1538(15)
2.174(2)
2.1206(16)
2.1542(17)
2.170(3)

2.180(3)

2 x 3.7227(18)
3.768(3)

2 x 3.858(2)
2.126(2)

2.163(2)

 

Ce(1)-S(1)
Cs(1)-S(2)
Cs(1)-S(1)
Cs(1)-S(4)

Cs(1)-S(2)

3.279(2)
3.507(2)
3.549(2)
2 x 3.572(2)

2 x 3.574(1)

Cs(2)-S(1)
Cs(2)-8(4)
Cs(2)-S(5)
Cs(3)-S(6)

Cs(3)-S(3)

3.779(2)
2 x 3.798(2)
2 x 3.967(2)
2 x 3.425(3)

2 x 3.661(1)

305

As(1)-8(4)
As(2)-S(5)
As(2)-S(3)

As(2)-S(6)

2 x2.1791(16)
2.1496(19)
2.153(2)

2 x 2.208(3)

 

Table A-15. Selected bond angles for Rb3CCASst and CS3CCASst.

S(5)-As(1)-S(7)
S(5)-As(1)-S(3)
S(7)-As(1)-S(3)
S(5)-As(l)-S(8)
S(7)-As(l)-S(8)
S(3)-As(1)-S(8)
S(2)-As(2)-S(6)
S(2)-As(2)-S(4)
S(6)-As(2)-S(4)
S(2)—As(2)-S(1)
S(6)-As(2)—S(1)
S(4)-As(2)-S(l)
S(5)-Ce(1)-S(1)
S(5)-Ce(1)-S(3)
S(1)-Ce(1)-S(3)
S(5)-Ce(1)-S(7)

S(1)-Ce(1 )-S(7)

S(3)-Ce(1)-S(5)
S(5)-Ce(1)-S(5)

S(3)-Ce(1)-S(6)

Rb3CeA3283
109.64(8) S(3)-Ce(1)-S(7)
110.46(11) S(5)-Ce(1)-S(8)
110.05(11) S(1)-Ce(1)-S(8)
105.00(9) S(3)-Ce(1)-S(8)
115.66(9) S(7)—Ce(1)-S(8)
105.86(7) S(5)-Ce(1)-S(4)
119.69(7) S(1)-Ce(l)-S(4)
112.11(11) S(3)-Ce(1)-S(4)
103.83(1 1) S(7)-Ce(1)-S(4)
1 11.66(1 1) S(8)-Ce(1)-S(4)
102.96(1 1) S(5)-Ce(1)-S(8)
105.24(7) S(1)-Ce(1)-S(8)
100.76(8) S(3)-Ce(1)-S(8)
143.55(7) S(7)-Ce(1)-S(8)
7833(7) S(8)-Ce(1)-S(8)
7106(6) S(4)-Ce(1)-S(8)
138.31(8)
C33CeA32Sg

2 x 137.73(4) S(4)-Ce(1)-S(6)

7295(8)

S(6)-Ce(1)-S(6)

2 x 71 .62(7) S(3)-Ce(1)-S(1)

306

132.50(8)
9122(7)
142.75(7)
7151(5)
7894(6)
13904(8)
7150(5)
7589(7)
8818(8)
11972(6)
6919(6)
7364(6)
7582(7)
133.15(6)
7813(3)

138.59(6)

2 x 7031(6)

129.05(10)

132.43(6)

 

S(5)-Ce(1)-S(6)
S(5)-Ce(l)-S(6)
S(3)-Ce(l)-S(4)
S(5)-Ce(1)-S(4)
S(5)-Ce(l)-S(4)
S(6)-Ce(1)-S(4)
S(6)-Ce(1)-S(4)
S(4)-Ce(1)-S(4)
S(3)-Ce(1)-S(6)
S(5)-Ce(l)-S(6)
S(5)-Ce(1)-S(6)
S(6)-Ce(l)-S(6)
S(6)-Ce(l)-S(6)

S(4)-Ce(1)-S(6)

2 x 93.60(7) S(5)-Ce(1)-S(l)
2 x 7967(7) S(6)-Ce(1)-S(1)
2 x 7623(5) S(4)-Ce(l)-S(l)
2 x 140.23(5) S(6)-Ce(l)-S(1)
2 x 9404(5) S(2)-As(l)-S(1)
2 x 121.50(7) S(2)-As(l)-S(4)
2 x 13960(7) S(1)-As(1)-S(4)
7192(6) S(4)-As(1)-S(4)
2 x 7423(5) S(5)-As(2)-S(5)
2 x 6387(6) S(5)-As(2)-S(3)
2 x 129.27(7) S(5)-As(2)-S(6)
2 x 7783(5) S(5)-As(2)-S(6)
2 x 54.66(10) S(3)-As(2)-S(6)
2 x 136.33(6) S(5)-As(2)-S(6)

S(5)-As(2)-S(6)

307

2 x 7452(5)
2 x 153.76(7)
2 x 6577(4)

2 x 115.43(5)
120.01(9)

2 x 112.12(6)
2 x 102.84(6)
105.46(9)
109.60(10)

2 x 110.42(6)
9684(9)
124.32(10)

2 x104.19(10)
124.32(10)

96.84(9)

 

 

 

 

b)

 

Figure A-5. a) Unit cell of Rb3CeA32Sg looking down the b-axis. The large light gray
circles are Rb, the small dark gray circles are As, the black circles are Ce and the open
circles are S. b) The [CeA3283]' chain showing the bicapped trigonal prismatic Ce
coordinated by two different kinds of A3843' ligands.

308

 

IIIIIIIIIIIIIIIIIIIIIIIIIIIIIII

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