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MOLTEN SALT SYNTHESIS OF MULTINARY SELENOPHOSPHATES

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Konstantinos Chondroudis

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MOLTEN SALT SYNTHESIS OF MULTINARY SELENOPHOSPHATES

By

Konstantinos Chondroudis

A DISSERTATION

Submitted to
Michigan State University
in partial fulfillment of the requirements

for the degree of

DOCTOR OF PHILOSOPHY

Department of Chemistry

1997

ABSTRACT

MOLTEN SALT SYNTHESIS OF MULTINARY SELENOPHOSPHATES

By

Konstantinos Chondroudis

We utilized the recently developed molten alkali polychalcogenide flux method to
synthesize new multinary selenophosphates. The in situ fusion of AzQ/P2Q5/Q (A=Alkali

metal, Q=S, Se) forms highly reactive [Psz]n- species solubilized in an excess of
polychalcogenide flux. These species in the presence of metal ions, coordinate and become
the building blocks of new polymeric structures. By studying the chemistry of these

systems, we discovered that the variation of the flux composition provides a way of
controlling the reaction outcome in the sense that we can select species with either P4+ or

P5+. New, previously unknown [Psz]n- ligands have been synthesized and their
coordination chemistry was studied. The structural diversity in the new compounds ranged
from one-dimensional to three-dimensional. By increasing the Lewis basicity of the flux,
we demonstrated that even discrete molecular species can be accessed. By applying this
method to various metal ions, we acquired a fairly comprehensive picture of the chemical
behavior of metals from the different areas of the periodic table.

In this dissertation, the synthesis, characterization and properties of these multinary
selenophosphates will be discussed. The synthetic work performed here provides the

ground for systematic synthesis and further exploration of these compounds.

DEDICATION

To my supporting and loving wife, Vicki.

ACKNOWLEDGMENTS

The guidance of my research advisor Mercouri G. Kanatzidis was invaluable and
gratefully acknowledged. His support, friendship, and faith in me, provided the optimum
environment for a challenging, enjoyable and fulfilling Ph.D. My interaction with him
made me a better scientist and person.

I would also like to thank Dr. Pinnavaia J. Thomas, Dr. Blanchard J. Gary, and
Dr. Baker L. Gregory for serving as members of my guidance committee (and for the
reference letters that they wrote/will write for me).

Through the timespan of four years that were required for this work I was fortunate
enough to have as colleagues some of the finest scientists and personalities. I thank them
for the unique experiences and the fruitful discussions we shared.

Throughout this difficult time, my beautiful wife, Vicki was the cornerstone of my
success. Her support and love was always a great relief after 14 strenuous lab-hours (with
an experiment that would not work!!!). I want to ask her forgiveness for the times I
burdened her with my frustrations and to thank her for the joy she shared whenever a new
crystal was discovered in my flask...

The National Science Foundation has generously supported this work.

iv

TABLE OF CONTENTS

LIST OF TABLES .................................................................................. xii
LIST OF FIGURES ............................................................................... xvi
CHAPTER 1

Introduction ....................................................................................... 1
1. Nature of chalcophosphate fluxes ............................................................... 8
2. Synthetic conditions and formation of [PyQZPI' units ...................................... 11
CHAPTER 2

Complex Multinary Compounds from Molten Alkali Metal
Polyselenophosphate Fluxes. Layers and Chains in A4Ti2(P28e9)2(P28e7),

and ATiPSe5 (A=K,Rb). Isolation of [PZSe9]4-, a Flux Constituent Anion

1. Introduction ...................................................................................... 28
2. Experimental Section ........................................................................... 29
2.1. Syntheses ............................................................................. 29
2.2. X-ray Crystallography .............................................................. 3O
3. Description of Structures ....................................................................... 36
Rb4Ti2(PZSe9)2(PZSe7) (I) .............................................................. 36
KTiPSe5 (II) ............................................................................... 36
CS4P28e9 (III) ............................................................................. 37
4. Physical Measurements ........................................................................ 37

5. Conclusions ..................................................................................... 44

CHAPTER 3
i[P3Se4']: A Novel Polyanion in K3RuP5Se10; Formation of Ru-P bonds

in a Molten Polyselenophosphate Flux

1. Introduction ...................................................................................... 46
2. Experimental Section ........................................................................... 47

2.1. Syntheses ............................................................................. 47

2.2. X-ray Crystallography .............................................................. 47
3. Description of Structure ........................................................................ 52

K3RuP58e10 ................................................................................ 52
4. Physical Measurements ........................................................................ 55
5. Conclusions ..................................................................................... 59
CHAPTER4

Chemistry of Gold in Molten Alkali Metal Polychalcogeno-phosphate
Fluxes. Synthesis and Characterization of the Low Dimensional

Compounds A3AuPZSe3 (A=K, Rb, Cs), A2Au2PZSe6 (A=K, Rb) and

A2AuP28e6 (A=K, Rb)
1. Introduction ...................................................................................... 61
2. Experimental Section ........................................................................... 62
2.1. Reagents .............................................................................. 62
2.2. Syntheses ............................................................................. 63
K3AuPZSe3 (I) ................................................................... 63
Rb3AuP28e3 (II) ................................................................ 63

vi

CS3AuP2563 (III) ................................................................ 64

KzAuzPZSe6 (IV) ................................................................ 64
szAu2P28e6 (V) ................................................................ 64

A2AuPZSe6 (VI) .................................................................. 64

2.3. Physical Measurements ............................................................. 65

3. Results and Discussion ......................................................................... 74
3.1. Description of Structures ........................................................... 74
Structure of K3AuP2Se3 (I) ..................................................... 74

Structure of KzAu2P28e6 (IV) ................................................. 75

Structure of szAuPZSe6 (VI) ................................................. 76'

3.2. Synthesis, Spectroscopy and Thermal Analysis ................................. 87

4. Conclusions ..................................................................................... 96

CHAPTER 5
Group-10 and 12 One-Dimensional Selenodiphosphates: AzMP23e6 (A=K,

Rb, Cs; M=Pd, Zn, Cd, Hg) and the Novel, Tetranuclear, Cluster Anions

[M4(Se2)2(PSe4)4]8- (M=Cd, Hg) with a Stellane-like core

1. Introduction ...................................................................................... 99
2. Experimental Section .......................................................................... 100
2.1. Reagents ............................................................................. 100

2.2. Syntheses ............................................................................ 100
CsdePZSeg (l) ................................................................. 100

KZZnPZSe6 (2) .................................................................. 101

K2CdP2Se6 (3) .................................................................. 101

szCdPZSe6 (4) ................................................................. 101

CsszPZSeg, (5) ................................................................. 102

vii

K2HgP2866 (6) .................................................................. 102

RbgHgPZSe6 (7) ................................................................ 102

Rbng4(Se2)2(PSe4)4 (8) ...................................................... 102

RbgHg4(Se2)2(PSe4)4 (9) ...................................................... 103

2.3. Physical Measurements ............................................................ 103

3. Results and Discussion ........................................................................ 111

3.1. Description of Structures .......................................................... 111

Structure of CsdeP28e6 (1) .................................................. 111

Structure of Rb2CdP28e6 (4) ................................................. 112

Structure of K2HgPQSe6 (6) .................................................. 112

Structure of RbgHg4(Se2)2(PSe4)4 (9) ....................................... 113

P-P Distance Versus M2+ Ionic Radius in AZMPZSe6 ....................... 115

3.2. Synthesis, Spectroscopy and Thermal Analysis ................................ 129

4. Conclusions .................................................................................... 134
CHAPTER 6

K41n2(PSe5)2(P28e6) and Rb3Sn(PSe5)(P28e6): One-Dimensional

Compounds with Mixed Selenophosphate Anions. Isolation of

[Sn(PSe5)3]5-, and [Sn28e4(PSe5)2]6-, the First Discrete Complexes from

Molten Alkali Metal Polyselenophosphate Fluxes

1. Introduction ..................................................................................... 137
2. Experimental Section .......................................................................... 139
2.1. Reagents ............................................................................. 139

2.2. Syntheses ............................................................................ 139
K41n2(PSe5)2(P2Se6) (I) ....................................................... 139
Rb3Sn(PSe5)(P28e6) (II) ...................................................... 140

viii

A5$n(PSes)3 (III) ............................................................... 140

A6Sn28e4(PSe5)2 (IV) ......................................................... 140

2.3. Physical Measurements ............................................................ 141

3. Results and Discussion ........................................................................ 151
3.1. Description of Structures .......................................................... 151
Structure of K41n2(PSe5)2(P2Se6) (I) ........................................ 151

Structure of Rb3Sn(PSe5)(P2Se6) (II) ........................................ 152

Comparison of Structures ....................................................... 153

Structure of A5Sn(PSe5)3 (HI) ................................................ 154

Structure of A6Sn28e4(PSe5)2 (IV) ........................................... 155

3.2. Synthesis, Spectroscopy and Thermal Analysis ................................ 166

4. Conclusions .................................................................................... 171

CHAPTER 7 .
New Lanthanide Polychalcophosphates. Synthesis and Characterization of

the molecular Rb9Ce(PSe4)4, l-D A3MPZSe3, and the 2-D A2MPZSe7 (A =

Rb, Cs; M = Ce, Gd)
1. Introduction ..................................................................................... 173
2. Experimental Section .......................................................................... 174
2.1. Reagents ............................................................................. 174
2.2. Syntheses ............................................................................ 174
Rb9Ce(PSe4)4 (I) ............................................................... 175
Rb3CeP2Se3 (II) ................................................................ 175
(:83de2863 (III) ............................................................... 176
szCeP28e7 (IV) ............................................................... 176
CszGdP28e7 (V) ................................................................ 176

2.3. Physical Measurements ............................................................ 177

3. Results and Discussion ........................................................................ 185

3.1. Description of Structures .......................................................... 185

Structure of Rb9Ce(PSe4)4 (I) ................................................. 185

Structure of Rb3CeP2Se3 (II) .................................................. 186

Structure of CszGdP28e7 (V) ................................................. 187

3.2. Synthesis, Spectroscopy and Thermal Analysis ................................ 198

4. Conclusions .................................................................................... 206
CHAPTER 8

Synthesis and Characterization of KzUP3Se9; the First Actinide

Selenophosphate. Stabilization of U5+ in Rb4U4P4Sez6; an Actinide

Compound with a Mixed Selenophosphate / Polyselenide and Ion-Exchange

Properties

1. Introduction ..................................................................................... 208

2. Experimental Section .......................................................................... 209
2.1. Syntheses ............................................................................ 209
2.2. X-ray Crystallography ............................................................. 210

3. Description of Structure ....................................................................... 216
KzUP3Se9 (I) ............................................................................. 216
Rb4U4P4Se26 (II) ........................................................................ 219

4. Physical Measurements ....................................................................... 221

5. Conclusions .................................................................................... 231

CHAPTER 9

Rb4Sn2Ag4(P2Se6)3: First Example of a Quintenary Selenophosphate and

an Unusual Sn--Ag s?-—d10 Interaction

1. Introduction ..................................................................................... 233
2. Experimental Section .......................................................................... 234
2.1. Syntheses ............................................................................ 234
2.2. X-ray Crystallography ............................................................. 234
3. Description of Structure ....................................................................... 238
Rb4Sn2Ag4(P2Se6)3 ...................................................................... 238
4. Physical Measurements ....................................................................... 240
5. Conclusions .................................................................................... 245
CONCLUSIONS-OUTLOOK ................................................................... 247

LIST OF TABLES

l- 1. Structure and coordination examples of the [Psz]n' units ............................. 14
2-1. Crystallographic data for Rb4Ti2(P2Se9)2(P2Se7), KTiPSes, and

CS4P2Se9 ...................................................................................... 31
2-2. Positional parameters and ch for Rb4Ti2(P2Se9)2(PZSe7) ............................. 32
2-3. Anisotropic Displacement Parameters for Rb4Ti2(P28e9)2(PZSe7) .................... 33
2-4. Positional parameters and ch for KTiPSe5 ............................................... 34
2-5. Anisotropic Displacement Parameters for KTiPSes ...................................... 34
2-6. Positional parameters and Beq for CS4P28e9 .............................................. 35
2-7. Anisotropic Displacement Parameters for CS4P2Se9 ..................................... 35
2-8. Selected Distances (A) and Angles (deg) for Rb4Ti2(P2Se9)2(PZSe7) ................. 42
29. Selected Distances (A) and Angles (deg) for KTiPSe5 .................................. 43
2-10. Selected Distances (A) and Angles (deg) for CS4P2Se9 ................................ 43
3-1. Crystallographic data for K3RuP5Se10 .................................................... 49
3-2. Positional parameters and Beq for K3RuP58e10 .......................................... 50
3-3. Anisotropic Displacement Parameters for K3RuP5Se10 ................................. 51
34. Selected Distances (A) and Angles (deg) for K3RuP58e10 .............................. 58
4-1. Crystallographic data for K3AuP28e3, K2Au2PZSe6, szAuP2Se6 ................... 68
4-2. Positional parameters and Beq for K3AuPZSe8 ........................................... 69
4-3. Anisotropic Displacement Parameters for K3AuP28eg .................................. 70
4-4. Positional parameters and Beq for KzAu2P28e6 .......................................... 71
4-5. Anisotropic Displacement Parameters for KzAu2P28e6 ................................. 71
4—6. Positional parameters and Beq for szAuP2Se6 .......................................... 72

4-7. Anisotropic Displacement Parameters for szAuPZSe6 ................................. 73

4—8. Selected Distances (A) and Angles (deg) for K3AuP2Seg ............................... 84
4-9. Selected Distances (A) and Angles (deg) for KzAu2P2Se6 .............................. 85
4-10. Selected Distances (A) and Angles (deg) for szAuPZSe6 ............................ 86

4-1 1. Synthetic conditions for the different [Psz]n- units. (M = metal,

A2Q= alkali chalcogenide) .................................................................. 91
4-12. Optical Band Gaps, Colors and Melting Point Data .................................... 91
4-13. Infrared Data for (I), (IV) and (VI) and Raman Data (cm-1) for (I),

and (IV) ....................................................................................... 92
5- 1. Crystallographic data for CsdePZSeG, RbngPZSeg, KzHgPZSe6 and

RbgHg4(Se2)2(PSe4)4 ...................................................................... 106
5-2. Positional parameters and Egg for CsdeP2Se6 .......................................... 107
5-3. Anisotropic Displacement Parameters for CsdePZSe6 ................................. 107
5-4. Positional parameters and Beq for szCdPZSe6 ......................................... 108
5-5. Anisotropic Displacement Parameters for szCszSe6 ................................ 108
5-6. Positional parameters and Beq for KzHgPZSe6 .......................................... 109
5-7. Anisotropic Displacement Parameters for K2HgP2Se6 ................................. 109
5-8. Positional parameters and Beq for RbgHg4(Se2)2(PSe4)4 .............................. 110
5-9. Anisotropic Displacement Parameters for RbgHg4(Se2)2(PSe4)4 ..................... 110
5-10. Selected Distances (A) and Angles (deg) for CsdePZSe6 ............................ 126
5-11. Selected Distances (A) and Angles (deg) for szCdPZSe6 ........................... 126
5-12. Selected Distances (A) and Angles (deg) for K2HgP2Se6 ............................ 127
5-13. Selected Distances (A) and Angles (deg) for RbgHg4(Sez)2(PSe4)4 ................ 128
5-14. Optical Band Gaps and Melting Point Data ............................................. 133

6-1. Crystallographic data for K41n2(PSe5)2(P28e6),
RD3SD(P865)(PZSC6), RbsSn(PSes)3 and C865n2864(PSe5)2 ........................ 143

xiii

6-2. Positional parameters and Beq for K41I12(PSCS)2(PZSD6) ............................... 144
6-3. Anisotropic Displacement Parameters for K4In2(PSe5)2(P28e6) ...................... 145
6-4. Positional parameters and Beq for Rb3Sn(PSe5)(P28e6) ............................... 146
6-5. Anisotropic Displacement Parameters for Rb3Sn(PSe5)(PZSe6) ...................... 147
6-6. Positional parameters and B‘s,q for Rb5Sn(PSe5)3 ....................................... 148
6-7. Anisotropic Displacement Parameters for Rb5Sn(PSe5)3 .............................. 149
6-8. Positional parameters and Beq for CS5SnZSe4(PSe5)2 .................................. 150
6-9. Anisotropic Displacement Parameters for Cs6Sn2Se4(PSe5)2 ......................... 150
6-10. Selected Distances (A) and Angles (deg) for K41n2(PSe5)2(P2Se(,) ................. 162
6-11. Selected Distances (A) and Angles (deg) for Rb3Sn(PSe5)(P28e6) ................. 163
6-12. Selected Distances (A) and Angles (deg) for RbSSn(PSe5)3 ......................... 164
6-13. Selected Distances (A) and Angles (deg) for Cs6Sn28e4(PSe5)2 .................... 165
7- 1. Crystallographic data for Rb9Ce(PSe4)4, Rb3CeP2Se3, and

CszGdPZSe7 ................................................................................. 180
7-2. Positional parameters and Egg for Rb9Ce(PSe4)4 ....................................... 181
7-3. Anisotropic Displacement Parameters for RbgCe(PSe4)4 .............................. 1782
7-4. Positional parameters and Beq for Rb3CeP28e3 ......................................... 183
7-5. Anisotropic Displacement Parameters for Rb3CeP2Se3 ................................ 183
7-6. Positional parameters and Beq for CszGdPZSe7 ......................................... 184
7-7. Anisotropic Displacement Parameters for CszGszSe7 ................................ 184
7-8. Selected Distances (A) and Angles (deg) for Rb9Ce(PSe4)4 ........................... 195
7-9. Selected Distances (A) and Angles (deg) for Rb3CeP2Se3 ............................. 196
7-10. Selected Distances (A) and Angles (deg) for CszGszSe7 ........................... 197
7-11. Optical Band Gaps, Colors, Melting Points and ueff Data ............................ 205
8-1. Crystallographic data for KZUP3Se9, and Rb4U4P4Se26 .............................. 211

xiv

8-2.
8-3.
8-4.
8-5.

8-7.
9-1.

9-3.
9-4.

Positional parameters and Beq for K2UP3Se9 ............................................ 212

Anisotropic Displacement Parameters for K2UP3Se9 ................................... 213
Positional parameters and Beq for Rb4U4P4Se26 ........................................ 214
Anisotropic Displacement Parameters for Rb4U4P4Se26 ............................... 215
. Selected Distances (A) and Angles (deg) for K2UP3Se9 ............................... 229
Selected Distances (A) and Angles (deg) for Rb4U4P4Se26 ........................... 230
Crystallographic data for Rb4Sn2Ag4(P28e6)3 .......................................... 235
. Positional parameters and Beq for Rb4Sn2Ag4(P2Se6)3 ................................ 236
Anisotropic Displacement Parameters for Rb4Sn2Ag4(P2Se6)3 ....................... 237
Selected Distances (A) and Angles (deg) for Rb4Sn2Ag4(P28e6)3 .................... 244

XV

1-1:

1-2:

2-2:

2-3:

2-4:
3-1:

4-1:

4-2:

4-4:

LIST OF FIGURES

Unit cell of ABiP2S7 viewed down the a-axis. A+ cations omitted for

clarity ............................................................................................ 5

(A) A [MP28e6]n“‘ "double" layer. The dashed line indicates the two

centrosymmetrically related fragments that form the double layer. (B)

Polyhedral View of the layer showing the chains of corner-sharing

BiSe6 octahedra. Unit cell of ABiP287 viewed down the a-axis ......................... 6
: The structure of Rb4Ti2(P28e9)2(P28e7) viewed down the c-axis ..................... 38

The structure of Rb4Ti2(P28e9)2(P28e7) viewed down the b-axis ..................... 39

One chain of KTiPSe5 viewed down the c-axis ........................................... 40

Structure of the [P2Se9]4- anion ............................................................ 41

ORTEP representation of the unit cell of K3RuPSSe10 viewed down

the b axis ...................................................................................... 56

: ORTEP representation of a section of the —l—[Ru(P2Se6)(P3Se4)]3-

chain with labeling ........................................... 57
ORTEP representation and labeling of K3AuP2Se3 in a diagonal view.

Cations have been omitted for clarity. (80% probability ellipsoids) ................... 79
ORTEP representation and labeling of KzAu2P28e6 looking down the

b-axis. Cations have been omitted for clarity. (90% probability

ellipsoids) ..................................................................................... 80

: View of a single [AuszSe6]Zn- chain ...................................................... 81

The unit cell of AzAuPZSe6 looking down the b-axis. The packing of

the chains in the unit cell forms channels where the A+ cations are

xvi

4-8:

5-1:

5-2:

5-3:

5-5:

5-6:

5-7:

residing (open ellipses). In the infinite part of the structure, gold is
shown as octant shaded ellipses, selenium as open ellipses and

phosphorus as crossed ellipses with no shading ......................................... 82

: View showing a section of the chain in A2AuP28e6 with labeling ..................... 83

: Solid-state optical absorption spectra of K3AuP2Seg (I) and

K2AU2P2$C6 (IV) ............................................................................ 93

: Typical DTA diagram for the A3AuP2Se3 phases (A=Rb) .............................. 94

(A) DTA diagram for KzAuzPZSe6 (first cycle) (B) Second DTA cycle
of K2Au2P2Se6, showing two phases. (C) Third DTA cycle of
K2AU2P2$C6 .................................................................................. 95

(A) An isolated [PszSe6]n20- chain with labeling. (B) The disorder of

the P atoms in the [P2Se6]4- group. Bonds between P and Se atoms

are omitted for clarity ....................................................................... 116

ORTEP representation and labeling of a single [CdP28e6]n2n- chain
(70% probability) ........................................................................... 117

Projection of the [CdP2Se6]n2n- chain on the b-c plane ................................ 118

: ORTEP representation and labeling of a single [HngSe6]n2n- chain

(80% probability) ..................................................................... 119
Projection of the [HgPZSe6]n2"- chain on the b-c plane ................................. 120
(A) A single ngPZSe6 layer. (B) Removal of half of the Hg2+ ions

resulting in a hypothetical [HgPZSe6]n2n- layer. Dashed lines highlight

the possibility of chain formation by breaking the corresponding Hg-

Se bonds ..................................................................................... 121
ORTEP representation and labeling of a single [Hg4(Se2)2(PSe4)4]8-

molecule ...................................................................................... 122

xvii

5-8: Stereo view of a single [Hg4(Se2)2(PSe4)4]3- molecule ............................... 123
5-9: Perpendicular view of the same molecule. Dashed lines indicate Se-Se

interactions ................................................................................... 124
5-10: Diagram of the P-P distance versus M2+ ionic radius in A2MP28e6 ,,,,,,,,,,,,,,,,, 125
5-11: Optical absorption spectra of szCdPZSe6 (solid line) and of

szHgPZSe6 (dotted line) .................................................................. 131
5- 12: (A) Single crystal optical transmission spectrum of Rb2CdPZSe6

converted to absorption data. (B) The region close to the absorption .

edge is plotted for absorption“2 vs energy. (C) The same region is

plotted for absorption2 vs energy ......................................................... 132
6-1: Unit cell of K41n2(PSe5)2(P28e6) viewed down the a-axis. In the

infinite part of the structure, indium is shown as octant shaded

ellipses, selenium as open ellipses, and phosphorus as crossed

ellipses. The K+ ions located between the chains are shown as open

ellipses ........................................................................................ 156

6-2: An isolated [In2(PSe5)2(P2Se6)]n4n- chain with labeling ............................... 157
6-3: Unit cell of Rb3Sn(PSe5)(P2Se6) viewed down the b-axis. In the
infinite part of the structure, tin is shown as octant shaded ellipses,

selenium as open ellipses, and phosphorus as crossed ellipses. The

Rb+ ions located between the chains are shown as open ellipses ..................... 158

6-4: An isolated [Sn(PSe5)(PZSe6)]n3n- chain with labeling ................................. 159

6-5: ORTEP representation and labeling scheme of the structure of the

[Sn(PSe5)3]5' anion ( Mk5 enantiomorph ) ............................................ 160

6-6: ORTEP representation and labeling scheme of the structure of the

[Sn28e4(PSe5)2]6‘ anion ................................................................... 161

xviii

6-8:

7-1:

7-2:
7-3:

7-4:

7-5:

7-7:

7-8:

: Solid-state optical absorption spectra of K41n2(PSe5)2(P28e6) (dashed
line) and Rb3Sn(PSe5)(P2Se6) (solid line) ............................................... 169

DTA diagram for K41n2(PSe5)2(P28e6) (A) First cycle, (B) second

cycle .......................................................................................... 170

A single [Ce(PSe4)4]9- molecule with labeling (ORTEP view, 70%

ellipsoids) .................................................................................... l 89
The unit cell of Rb9Ce(PSe4)4 looking down the b-axis ................................ 190

ORTEP representation of Rb3CeP28e3 as viewed down the a-axis
(70% ellipsoids). In the infinite part of the structure Ce is shown as
octant shaped ellipses, selenium as open ellipses and phosphorus as

crossed ellipses with no shading. Rb cations between the chains are

shown as open ellipses ..................................................................... 191

(A) View of a single [CePZSe3]n3n- chain with labeling. (B) Bicapped

trigonal prismatic environment around Ce3+ ............................................. 192

ORTEP representation of CszGdP28e7 as viewed down the b-axis.
(80% ellipsoids). In the infinite part of the structure Gd is shown as
octant shaped ellipses, selenium as open ellipses and phosphorus as

crossed ellipses with no shading. Cs cations between the layers are

shown as open ellipses ..................................................................... 193
: (A) Perpendicular view (along [1 0 1]) of a [GdP28e7]n2n- layer with

labeling. (B) Square antiprismatic environment around Gd3+ ......................... 194

Solid-state optical absorption spectra of (A) Rb3CePZSe3 (II) and (B)

CSzGszSe7 (V) ............................................................................ 202
Far-IR spectra of (A) Rb3CePZSe3 (II) and (B) CszGdP28e7 (V) ................... 203

xix

8-1:

8-2:

8-3:

8-4:

8-5:

8-6:

9-1:

9-3:

Plot of the magnetic susceptibility x and llx vs. temperature for (A)

Rb3CeP2363 (II) and (B) CSzGszSe7 (V) ............................................ 204

The unit cell of K2UP3Se9 looking down the c-axis. The arrows

indicate the boundaries between two layers since the overlapping

selenium atoms from the two layers conceal them ...................................... 223

ORTEP representation and labeling scheme of the U2Se14 dimer

showing the disposition of the [P2Se6l4- ligands around it ............................ 224

One [U2(P28e6)3]4~ slab. It forms by the side-by-side arrangement of

9’

the chains packed in a bi-layer fashion to form accordion-like “pleats .

View down the chain axis .................................................................. 225

(A) Polyhedral representation of a (UZSe14)x chain in the [100]

direction. (B) The "dimer" in the chain with labeling of atoms,

including the side [PSe4]3' groups ........................................................ 226

The tunnel framework of Rb4U4P4Se26 looking down the b-axis.

Cations have been omitted for clarity ..................................................... 227

Polyhedral representation down the [100] direction showing the

smaller tunnels ............................................................................... 228

ORTEP representation of the unit cell of Rb4Sn2Ag4P6Se13 viewed

down the b-axis. Rb+ cations have been omitted for clarity. Tin and
silver atoms are shown as octant shaped ellipses, selenium as open

ellipses and phosphorus as crossed ellipses with no shading (90%

thermal ellipsoids) ........................................................................... 241
: View perpendicular to a single [SnzAg4P68e13]n4n- layer showing the

rings (stick model) .......................................................................... 242

View showing a section of the layer with labeling. Solid arrows

indicate connectivity to the rest of the layer .............................................. 243

XX

CHAPTER 1

Introduction

Solid state chemistry has been the foundation of many aspects of modern
technology. Existing technologies such as electronics or emerging areas such as nonlinear
optics, superconductivity, photovoltaic energy conversion, high energy density storage
batteries and others are relying on the development of existing solid state materials or the
discovery of novel materials with new and enhanced properties. Therefore, a lot of work is
dedicated to exploratory solid state synthesis.

One very important class of solid state compounds that has demonstrated interesting
properties is the chalcophosphate class MxPsz (M=metal, Q=S,Se). In 1965, Hahn and
Klingenl prepared and characterized for the first time a new family of compounds, the
thiophosphates of transition metal elements, with the general formula MPS3. Five years
earlier, Weiss and Schaeferz, determined the crystal structures of AlPS4, and BPS4. These
are the very first examples of the chalcophosphate family of compounds. The analogous Se
chemistry started later, in the early 70's, displaying similar chemistry.3 The important
MPQ3 (Q=S,Se) class of compounds,1t3s4,5»6s7 contains the ethane like [P2Q6]4- ligand.
Compounds based on this structural unit have been identified with monovalent (Li, Ag),
divalent (Cd, Sn, Hg, Pb, Fe, V, etc.), and trivalent (In) cations.l»3,4.5,6»7. Many of these
compounds displayed technologically interesting properties and some examples are given
below. Sn2P286 crystallizes in the acentric space group (Pc) and undergoes a second order,
exothermic phase transition from ferroelectric to paraelectric (P21/c) at 60°C.8 This

compound has been shown to be a promising ferroelectric material for use in memory

2

devices.9a The also acentric SnP2S6 displays significant second harmonic generation
efficiency.9b Another interesting material is In1,33PzSe6 which may be suitable for
photovoltaic devices. 10 Other members of the M2P2Q6 family have been studied for
rechargeable battery“ and ion-exchange applications.12 It has been also shown that these
materials give rise to an interesting, rather uncommon intercalation chemistry (either
chemically or electrochemically).l3 InPS4 7, 14 crystallizes in a noncentrosymmetric
tetragonal space group (13) which gives rise to a high non-linear optical susceptibility and
piezo—coefficients. 14 Members of the rare earth metals have been studied for luminescence
under UV-excitation.15 Furthermore, T13PSe416 is a promising material for use in accusto-
optic devices (optical filters, laser modulators, signal processors, etc.).

The great importance of the chalcophosphate class rendered further exploration of
these or related systems as highly desirable. Our lab undertook the detailed investigation of
the quaternary family of AlM/P/Q compounds (A=alkali metal, Q=S, Se) by exploiting the
knowledge gained from years of experience working with the AIM/Q polychalcogenide
fluxes.17 The new A/M/P/Q family appeared promising for many reasons. The possibility
of new structural chemistry that would depart from the thermodynamically stable and
structurally dense known compounds, the stabilization of novel metastable, lower
dimensionality compounds, and the variety of anisotropic electrical, optical and magnetic
behavior they may possess, led us to pursue the exploratory synthesis of these new phases.

The term "exploratory" accurately describes the fact that the solid state synthetic
chemist lacks in a great extent the predictability that other areas of chemistry enjoy. The
main reason is the employment of high temperatures in order to allow sufficient diffusion
between solids for a reaction to occur. This permits almost no kinetic control and the
thermodynamically stable products that are formed act as thermodynamic traps that are
difficult or impossible to avoid. One approach of circumventing this problem is the use of
low-melting salts such as the polychalcogenide Any (A=Alkali metal, Q=S,Se,Te) fluxes.

A review on the application of these salts towards the synthesis of AIM/Q compounds

(M=metal) provides a very good description of the properties and chemistry of such
systems.17

Utilizing this approach, we became interested to develop a general methodology by
which new quaternary A/M/P/Q (A=A1kali metal, M=metal, Q=S,Se) chalcophosphate
compounds could be systematically synthesized and studied. In this case the building
blocks of the structure would be [Psz]n' species that would act as ligands, coordinating to
the metal ions through their chalcogen coordination sites. To gain access into this chemistry
we modified the polychalcogenide flux technique by including phosphorus chalcogenide
compounds in the starting materials and by using intermediate temperatures that would not

force the system to a thermodynamic minimum.

The first compounds reported from a AxPySz flux reaction were the layered
' ABiP2S7 (A=K, Rb).18 The compound features corrugated layers that are separated by
eight-coordinate K+ ions. The layers are assembled from Bi3+ and multiply bonding
[P287]4* units forming irregular eight-membered Bi-S-P rings. The PS4 tetrahedron of the
[P287]4- unit coordinates in a bidentate chelating fashion to Bi and acts as a bridge to a
second Bi to form the top side of the eight-membered ring. The Bi atoms are connected at
the bottom of the ring by the PS4 tetrahedron of another [P287]4- unit that acts as a
tridentate to both Bi atoms, Figure 1-1. The rings are connected in two dimensions by P-S-
Bi linkages to form the layer. The layers stack with their eight-membered rings in registry
so that they form channels running down the a-axis. The seven coordinated Bi is in a
distorted capped trigonal prismatic arrangement. The distortion presumably arises from the
stereochemically active 632 lone pair of Bi3+. The remarkable ability of the fluxes to
stabilize different [PszPi- ligands allowed the synthesis of the 2-D KMPZSe6 (M=Sb,
Bi)19 and the 3-D C58M4(P2Se6)5 (M=Sb, Bi),20 representing very complicated new
structure types. The layers of KMPZSe6 (M=Sb, Bi) can be actually characterized as
"double" layers since they consist of two centrosymmetrically related, layered fragments,

Figure 1-2A. The [MP2Se6]nn- slabs are assembled from chains of distorted corner-sharing

4

BiSe6 octahedra along the b-axis, Figure l-2B. The [P28e6]4- unit trichelates to one Bi
while a fourth Se atom acts as a bridge between two other Bi atoms in the chain. The fifth
Se is non bonding while the sixth Se connects to a Bi on the neighboring chain to form a
layer in the b-c plane. Bismuth is six-coordinate and forms a distorted octahedron. The
distortion is attributed to the effect of the stereochemically active 6s2 lone pair.

Application of the flux method to the transition metals Mn and Fe, yields the l-D
A2MP28e6 (A=K, Rb, Cs; M=Mn, Fe),21 related to the TiI3 structure type. For
C52M2P28e6 (M=Cu, Ag), M+---M+ dimers were observed in the structure. Substitution
of K for Cs resulted in a dramatic change in the structure of the l-D CszAgzPZSe5 to the 3-
D K2Ag2P2Se6.21 The latter possesses a unique and complicated three-dimensional tunnel
framework which consists of AgSe4 tetrahedra linked by [P2Se6]4' units. The channels run
along the a-axis and are filled with K+ ions. There are two types of hexadentate [P28e6]4'
units both bridging four Ag atoms. These [P2Se6]4' are assembled into layers and link the
AgSe4 tetrahedra to form a dense three-dimensional network. No special Ag+---Ag'+
contacts were observed in this compound.

Attempts to synthesize a new substituted M2P286 compound via stoichiometric
synthesis yielded the 2-D RbVP2S7,22 but it was not possible to prepare the compound as
pure product. Its synthesis suggests that a thermodynamically stable quaternary

chalcophosphate can be synthesized by direct combination.

 

Figure 1- 1. Unit cell of ABiP287 viewed down the a-axis.

A+ cations omitted for clarity.

 

Chains of MSee
octahedra

Figure 1-2. (A) A [MP25e6]nn' "double" layer. The dashed line indicates
the two centrosymmetrically related fragments.
(B) Polyhedral view of the layer showing the chains of
comer-sharing MSe6 octahedra.

1. Nature of chalcophosphate fluxes

In the polychalcogenide systems the reactants are elemental metal M, alkali
chalcogenide AzQx (A=alkali metal) and elemental chalcogen Q (Q=S, Se, Te). The
reactions between the metals and the molten fluxes are performed in situ. The most obvious
way to incorporate phosphorus in these systems is to add elemental phosphorus in the
reactants. We chose instead to use Psz compounds that would provide preoxidized
phosphorus in the reaction system. The compounds of choice were the "P2S5" (or more
accurately P4S10) for the sulfur chemistry, and the amorphous P2Se5 for the corresponding
Se chemistry. The former compound has been reported as existing in a mixture with P489
and S323 and its adamantane type structure is shown in Scheme 1A. In this structure P is
formally 5+. The amorphous P2Se5 is a glassy material and 31P NMR studies indicate the
presence of significant amounts of P-P bonding.24 Crystalline P28e5 is known to possess
the structure shown in Scheme 1B with a formal charge of 3+ on P.25

A typical reaction mixture includes M/PzQ5/A2Q and Q (M=elemental metal; Q=S,
Se; A=alkali metal). The powdered reagents are mixed under inert atmosphere and loaded
into reaction vessels of pyrex or quartz. The tubes are evacuated to a pressure of about 5 x
104 mbar and then flame sealed. Once sealed the tubes are subjected to the desired heating
program in a computer controlled furnace. Upon heating the components of the tube fuse
together to form the flux. The exact compositional nature of such molten fluxes remains
unclear. The redox reactions that occur are quite complex but to obtain some insight, one
can rely on the principles known from polychalcogenide chemistry.

It is known that A2Q reacts with x amount of Q to form A2Qx+1 fluxes. In these

systems (Qx)2- chains of various lengths coexist and undergo complicated self-redox

equilibria of the type shown in Scheme 2.17

Scheme 1

l

P
s/s' \s Se
| ' I l Se

P
P//\ P Se Se
3 s'/S\s \s S \ /

(A) l34310 (B) P2395

 

 

Schemez
. a 2-
. . 2- 2-
Q 2' 0’0 9 ’0
ll + . —-_ . + ,
‘Q . Q. Q

 

 

These mixtures are extremely reactive towards metals because they are very strong
oxidants. This phenomenon arises from the fact that although the terminal atoms of the
(Qx)2- chains are formally 1-, the internal atoms are all formally zero valent. Metals are
solubilized by being oxidized by these internal atoms, which, upon reduction break apart

into smaller fragments.

The presence of the P2Q5 component renders the above Lewis acid-base equilibria
more elaborate. The P2Q5 reacts with the AzQx mixture to yield Ax[Psz] species. These
highly charged [Psz]n- fragments, solubilized in excess flux, increase its basicity. The
already solvated metal cations are then coordinated by these basic fragments forming

different kinds of soluble intermediates. This is followed by nucleation into solid crystals

9

which is in equilibrium with the soluble intermediates. Therefore, a solvation-
reprecipitation effect (mineralizer effect), similar to that in polychalcogenide fluxes, occurs.
This highly desirable phenomenon helps in the growth of good quality single crystals,
since the flux can redissolve small or poorly formed crystallites and then reprecipitate the
species onto larger, well-formed crystals.

The multicomponent M/P2Q5/A2Q and Q (M=elemental metal; Q=S, Se; A=alkali
metal) system is very flexible in allowing control of the reaction outcome as opposed to the
direct elemental synthesis reactions employed so far in the M/P/Q systems. The
composition of the M/P2Q5/A2Q and Q mixture is one very important variable that can be
easily manipulated. These manipulations can alter the basicity of the flux leading in
different reactivities with the metal. The main guiding principles to alter the flux
characteristics are : (a) the amount of elemental Q which is directly proportional to the flux
acidity, (b) the amount of A2Q which is inversely proportional to the flux acidity, (c) the
amount of P2Q5 which as we discovered is a crucial parameter in the stabilization of
specific [Pszln- ligands, (d) the amount of metal which regulates the stabilization of metal-
rich or -poor structures. In addition, it further plays an important role on the stabilization of
the aforementioned ligands. Finally, e) by changing the cation, the flux basicity is also
altered and the trend is the bigger the cation the more basic the flux. Cation size effects
should also be considered. Varying the composition of the polychalcophosphate flux is
similar to varying the pH in aqueous solutions, and is equivalent to having a variety of
solvents in which to perform reactions, each one having different reactivity. The changes in
the basicity initiate complex changes in the reactivity and the solubility by altering the
equilibria mentioned above. The most important consequence of these alterations is the

formation of different [Psz]n- species. The latter are the building blocks of the structure

and by controlling their stabilization direct control on the reaction outcome is plausible.

10

2. Synthetic conditions and formation of [Psz]n‘ units.

Quantitative 31P and 6.7Li high resolution solid state NMR studies of Li2S-P2S5
glasses26 provide some useful insight in the stabilization of the [PySz]n- structural units in

various glassy or crystalline compositions. For example, Scheme 3 contains the proposed

[PySz]n- units for different values of x in the system (Li28)x(P285)1-x.

 

Scheme 3
glass crystal x
- 2-
\ ,5 Sspfis S 0 50
\S’P‘S/ S’ \S’ \S
4- s s 4-
S‘p’s 8‘ S s—‘P-P-‘S o 67
\ .
s’ \s/ \s s’ s
3- 3-
s s s
29$ )3: 0.75
S S s s

For the crystalline state, high concentrations of Li2S (basic conditions) favor the
stabilization of the tetrahedral [PS4]3- unit, whereas [P286]2- and [P286]4- are favored at
lower LiZS content. The [P2S7]4- group appears unstable in the crystalline state and
disproportionates to [P2S6]4-. Nevertheless, compounds with the [P2S7]4- are not that
uncommon. Complex, Lewis acid-base equilibria reactions that have been suggested to

occur in metal sulfide-phosphorus sulfide systems include those of Scheme 4.27

11

Scheme 4
32- 2-
P2352‘ :— 2 P83’ :1: P2874‘ :5: 2 PS43' (Eq. 1)

P2852” + 32' z: P2864' + 3 (Eq. 2)
The stabilization of the tetrahedral [PSe4]3- unit at higher Li2Se content, as opposed

to [P28e6]4- at lower LiZSe, appears to hold true in the Li-P-Se system as well.28 The type

of equilibria at Scheme 5 has been proposed to occur in melted P-Se glasses.29

Scheme 5
\ \
\Se" p— Se~ §e 89—" P— 89/
P P
/ \ / \ P
39 i 59 Se/ |\Se
P 8'6 :21“ I SIG I
39- P— — P
Se/ \P / P\/ 89/ \ P/
P $6 I SQ Se~ ‘Se
,Se \ 39‘ P/Se- Se
/

The most important advantages of the polychalcophosphate flux method over the
high temperature direct combination reactions are : a) Use of low-intermediate temperatures
(300-550 0C) that allows the stabilization of metastable phases and isolation of new
[Psz]n- ligands; b) the dual nature of the fluxes (i.e. reactants and mineralizers), allows
the isolation of high quality crystalline products that can be easily characterized, c) by
optimizing the starting composition, the basicity of the flux can be altered allowing control
of the stabilization of specific [PySezPI- building blocks. In addition, careful control of the
A2Se amount in the starting composition can drive to different dimensionality or even

molecular compounds, d) the [PySeZ]n- species act as ligands with an astonishing bonding

12

versatility yielding novel structural frameworks, and e) after the end of the reaction the
residual flux can easily be removed with polar solvents yielding pure crystalline products.

The [PyQZ]n- polyanions play the most important role in this chemistry since their
coordination to the metal centers is a cmcial factor in dictating the structure. They can be
regarded as building blocks that link the different metal centers to construct the final solid-
state or molecular framework. The diversity of chalcophosphate phases that have been
prepared owe their existence in the great variety of the [Psz]n- units. In addition, the
astonishing bonding versatility of these units further enhances their ability to coordinate in
numerous ways, trying to adopt to such parameters as the coordination number and
geometry of the metal, and the size of the charge balancing countercations. In this respect,
the chalcophosphate flux method is essential in designing compounds since it allows
control of the reaction outcome by controlling the stabilization of specific [Psz]n- units. To
better demonstrate the remarkable bonding and structural features of the [Psz]n- units we
have constructed Table 1-1, in which we classified the units and the different bonding
modes that have been observed, and also provided one example for each case. Many of the
entries of this table have been observed for the first time in compounds synthesized by the
polychalcophsophate flux method.

In this dissertation, the synthesis, characterization and properties of many new
multinary selenophosphates will be discussed. To acquire a good unterstanding of the
underlying chemistry and to probe different metal systems we chose to explore
representatives from the different areas of the periodic table such as p-block elements (i.e.
In, Sn, Pb), d-block (i.e. Ti, Ru, Pd, Ag, Au, Zn, Cd, Hg), and f-block elements (i.e. Ce,
Eu, Gd, U). Many of these systems were also chosen because their ternary counteparts had
demonstrated interesting properties. Some other systems such as Au and Ru were chosen
in order to establish their selenophosphate chemistry since no chalcophosphates had ever
been prepared containing these metals. The synthetic work performed here provides the

ground for systematic synthesis and further exploration of these compounds.

Table 1-1. Structure and coordination examples of the [Psz]n‘ units.

 

 

 

 

 

 

 

 

‘P .w
‘.~'\ [PSe2]- in
Ses
Se [WSe(PSe4)(PSe2)]2-,30
Sr
‘. P—S
S/‘t / [PS3l3' in Po.2V3231
\R‘A
O
M / | [WP in K4Pd(PS4)2.32
E) /P‘""'Q [PSe4]3- in CS4Pd(PSe4)232
_ Q
Q
l [PS4]3- in AzAuPS4 (A=K, Rb),33
Q/ P""""Q--M [PSe4l3- in Rb8M4(PSC4)4(Sez)2
_Q—M (M=Cd, Hg)34
Q
Ni/ ' [PS4]3- in CS3Bi2(PS4)318
'3'"an
Q/
_ Q—M
M ’5'
\S /P""""S \ [PS4]3‘ in Ti4P3$2935
S~M
S
M / l
\ /Pq"us -—M [PS4]3- in GaPS436
S
.. S—M
Qz—M . .
| M l [P3413111 C83312(PS4)3.18
Q /P‘m(|2llQ [PSe4]3- in KTiPSe5,37

 

[P864]3' in Rb3Ce(PSe4)233

 

 

(Cont)

 

 

14

 

Table 1-1. (Continued)

 

 

 

 

 

 

 

S — M
| \M l
p..... us [PS4l3' in Pd3(PS4)239
S/ ‘3‘,“
Sim-T [PSe4l3- in A4Ln2(PSe4>2(stes)
p...» it Se (A=Rb, Cs; Ln=Ce, Gd)33
M _Se’ ‘ 9
lil
M .
..... u [PS4]3‘ 1n CrPS44O
\S /P‘ S
/ S
M
M /Si _M [PS4]3- in TISnPS441
\ P "ms
3 / \
\ S—M
/
M
/ Se .
M I [PSe4]3- 1n AMPSe4
\ /P""" Se—M (A=K, Rb; M=Pb, Eu)33. 42
Se Se \
\ M
M
M —S —'M
l | ‘M l
..... PS 3' in Pb3(PS4)243
s ’ P‘ "i\ [ 4]
\\ ST”
\
M M
Se
,1
/ ""Wz ’ [Pse4l3’ in K4Cus(PSe4)2<P28es)44
M\Se \Se 89‘
/ I M
M M

 

 

 

(Cont.)

 

 

15

 

Table 1-1. (Continued)

 

[PS4]3- in AanPS445

 

[PQ4l3‘ in C1131’Q43a

 

[13365]} in A6Snzse4(PSes)2
(A=K, Rb)46

 

[PSe5]3- in a-,b-A58n(PSe5)3
(A=K, Rb)46

 

[PSesl3' in K41n2(P365)2(P2366)47

 

[P23612411 Ti4P852935

 

 

[PZS6I2' in Z114(P256)348

 

 

(Cont)

 

 

l6

 

Table 1-1. (Continued)

 

[P236l2' in Ag21’23649a1

 

[P286]2‘ in T12P28649b

 

[PZSe6]4- in A2AuPZSe6 (A=K, Rb)SO

 

[P2366]4’ in Rb4Sn5862(P2866)338

 

[P236]4' in K2MP237
(M=V, Cr)51

 

[P2366]4‘ in A2AUP2866 (A=K, Rb)50

 

 

 

 

(Cont)

 

 

17

Table l- 1. (Continued)

 

 

[P2366]4' in Rb3Sn(PSes)(P2866)47

 

 

 

 

 

 

 

Se\ $86
3“ Se—M
P—-P

Set? \

Se
SGAM/
Se\ §Se
f..— Se
/Se“)P— P\ S / [PZSC6I4’ in 1<Z4U2(P2S¢6)352
e
M -— Se \
\M
M
Se/ \ée [P2Se6]4- in A2MP2$e5
\P P’f’Se (A=K, Rb, Cs; M=Hg, Pd)32
367 \
Se\ /Se
M
M
Q/ X [st614 in K2MP286 (M=Mn,Fe),53
Okla—PLO [stefij4' in A2MP2$C6
Q’\ \Q (A=K, Rb, Cs;
\M/ =Mn, Fe, Zn, Cd)?“
M—Se s86
\ 3" Se
Se“““'P P\ \ [P28e6]4- in A2AuPZSe6 (A=K, Rb)50
I S / M
SexM e
M
/ [P28e6]4- in C53M4(ste6)5
Se \SG
\ ,.-“ Se (M=Sb, Bi)20
M Seyp— P\
Se
M — Se
(Cont)

 

 

 

 

 

 

 

 

 

 

 

 

 

18
Table 1-1. (Continued)
M
Se/ Se”M
\ is s [P2Se6]4- in KYPZSe654
Seé"”P—P<‘ 9
Se
Se \M/
M
\ i/S [P286]4- in 11158655
“nu-"P P \
S A \ /M
I /s s
M
Se $Se—M
\ bSe—M .
M_ 867P_P\ [P2Se6]4- ln A2Au2P2Se6 (A=K,Rb)33
M—Se 86
M —- Se\ $567M
S .P—p<-"‘ Se leSesl4- in K4U2(stes>352
e
/ / Se—M
M — Se
T;S\ y“? S [Passl4- in MP2$6
“av” P— P, I — 56
guilty M I (M—U, Zr, Th)
/
S —M
M " 39\ s89 /M [P2Se6l4- in KMPZSe6 (M=Sb, Bi)19
...P—P’“Se\M
Set? \
Se
SQ ‘EM /
M
Se/ \~‘Se
M \ f’ Se [P2866]4' in CSzCu2P236621
\Se“"'P— F,\ \M
86/ Se
\ M/ (Cont.)

 

 

 

Table l- 1. (Continued)

 

[P236614' in K4U2(PZSC6)352

 

[P2366]4‘ in KLnP2566
(Ln=La, Ce, Pr)54

 

[P2366]4' in K3Ag3P386921

 

 

[P25614' in Zn4(P2Sts)3,48

[P2866]4' in K3Ag3P336921

 

[P236]4‘ in SnszS657

 

 

 

(Cont.)

 

 

20

 

Table 1-1. (Continued)

 

[P28614' in M2P236.58
[PZSe6I4’ in K4CU6(PSC4)2(P2366),44

 

[P236614' in Nao.leBil.28P23613

 

[P236]4- in mono-Ag4pzs659

 

M
I -
M—QQI4>P—F?;
M_Q€M \0 M
M, —
/

M

IP2Q6I4‘ in ortho-Ag4P2Q64a, 59

 

 

 

(Cont.)

 

 

21

 

Table 1-1. (Continued)

 

 

 

 

 

M M
M \SI M
I M——-—§e—-
M M‘ 39/ £5 \/\ _
/\ 3 M [P2866]4‘ In T14PZSC66O
M \S I... SQ /
a ’ E3"\""°"D"-P\ \’\M
M \ / M
S
M’sle\ / B‘M
M M
M/SI” I — \ “‘\S\ [P23712' in Ti4P882935
\ l
\ I 393/
Q . .
\ .9 \M [P237l4-ln K4T12(PZS7)(P289)2,61
Q—P' o o
M/ :P/ \Q/ [13256714111 A4T12(P28e7)(P28e9)2
\Q Q (A=K, Rb)37
SI” 8
I... S “\\
\ / \ / \ / [P237]4- in RbVPZS722
S S\ /s S
M
M
M- S\ 8// [P237l4- in ABiP287 (A=K, Rhys

P/S \ P_/.. .nIIIIS

I'w/ ‘
M

 

,s s— M
M\S,M M\ /
\ s S
“a” P/ \ P4|II||“ S '- M
M—8“ 1 \
M—S s—M

 

[1’23714'in H821323762

 

 

(Cont.)

 

 

22

 

Table 1- 1. (Continued)

 

M M M M

 

 

 

 

 

s . /
S\ \S M
M .P/S\ / S,
‘sfl" PW ‘M [P287]4- in 1x41325763
’ l\ \
M /s M S—M
M I \ / \
M M M
M—S —-
I M/ I ?\M I [P288]4' in M2P810 (M=V, Nb)64~ 65
----P S\
S“"|"'/ PRMIIIIS
S S
M
Se I [steg]4- in A3AuP256333
I ‘\\Se Se
.. / (A=K, Rb, Cs)
M _ 86/ P ’ Pas-III" Se
59— Se \3
e
M—S
M/ | S S [P28914- in Psz482166
SIIII Inn/'"P-S/ \S—li’"'.""|""8
M
S s/ M
Se ‘
I [P236914' in A4Ti2(P2367)(P2369)2
se _ 0““ 36
l x39 P \ (A=K, Rb)37
\ zM
Se“""’P\ ’89 59
/ Se
M " Se

 

 

 

[P436 10]4' in K2CU2P4861044

 

 

(Cont.)

 

 

 

Table 1-1. (Continued)

 

[P4512]4' in 3D-P2Nb3367

 

 

[P431316' in V2P431368

 

 

[P3564lnn' in

K3RU(P2366)(P3364)69

 

 

 

10.

11.

12.

13.

14.

24

References

(a) Hahn, H.; Klingen, W. Naturwissenschaften 1965, 52, 494. (b) Hahn, H.;
Ott, R.; Klingen, W. Z. Anorg. Allg. Chem. 1973, 396, 271-278.

(a) Weiss, A.; Schafer, H. Z. Naturwissenschaften 1960, 47, 495. (b) Weiss, A.;
Schafer, H. Z. Naturforsch. 1963, 18b, 81-82.

(a) Garin, J .; Parthe, E. Acta Crystallogr., 1972, 128, 3672-3674. (b) (a) Klingen,
W.; Eulenberger, J.; Hahn, H. Z. Anorg. Allg. Chem. 1973, 401, 97-112.

(3) Toffoli, P.; Khodadad, P.; Rodier, N. Acta Crystallogr. 1978, B34, 1779-
1781. (b) Jandali, G.; Eulenberger, J.; Hahn, H. Z. Anorg. Allg. Chem. 1978,
447, 105-118.

(a) Ouvrard, G.; Bree, R.; Rouxel, J.; Mater. Res. Bull. 1985, 20, 1181-1189.
(b) Lee, S.; Colombet, P.; Ouvrard, G.; Bree, R. Inorg. Chem. 1988, 27, 1291-
1294. (C) Lee, S.; Colombet, P.; Ouvrard, (3.; Bree, R. Mater. Res. Bull. 1986,
21, 917-928. ((1) Durand, E.; Ouvrard, G.; Evain, M.; Bree, R. Inorg. Chem.
1990, 29, 4916-4920.

Carpentier, C. D.; Nitsehe, R. Mater. Res. Bull. 1974, 9, 401-410.
Diehl, R.; Carpentier, C. D. Acta Crystallogr. Sect.B, 1978, 34, 1097-1105.

Scott, B.; Pressprieh, M.; Willet, R. D.; Clearly, D. A. J. Solid State Chem.
1992, 96, 294-300.

a) Arnautova, E.; Sviridov, E.; Rogaeh, E.; Savchenko, E.; Greeov, A. Integrated
Ferroelectrics, 1992, I, 147-150. b) Wang, Z.; Willet, R. D.; Laitinen, R. A.;
Cleary, D. A. Chem. Mater. 1995, 7, 856-858.

(a) Etman, M.; Katty, A.; Levy-Clement, C.; Lemasson, P. Mater. Res. Bull.
1982, 17, 579-584. (b) Katty, A.; Soled, S.; Wold, A. Mater. Res. Bull. 1977,
12, 663-666.

(a) Thompson, A. H.; Whittingham, M. S.; US Patent 4,049,879 1977. (b)
Bree, R.; Le Mehaute', A. Fr.Patents 7,704,519 1977. (e) Evain, M; Bree, R.;
Whangbo, M. -H. J. Solid State Chem. 1987, 71, 244-262.

(a) Clement, R. J. Chem. Soc., Chem. Commun. 1980, 647-648. (b)
Miehalowiez, A.; Clement, R. Inorg. Chem. 1982, 21, 3872-3877. (e) Joy, P.;
Vasudevan, S. J. Am. Chem. Soc., 1981, 114, 7792-7801.

(a) Clement, R.; Green, M. L. H. J.C.S. Dalton Trans. 1980, 15, 189. (b)
Audiere, J. P.; Clement, R.; Mathey, Y.; Mazieres, C. Physica B. 1980, 99, 133.
(e) Mehaute, A.; Ouvrard, G.; Bree, R.; Rouxel, J. Mat. Res. Bull. 1977, 12,
1191. ((1) Thompson, A. H.; Whittingham, M. 8. Mat. Res. Bull. 1977, 12, 741.

Bridenbaugh, P. M. Mat. Res. Bull. 1973, 8, 1055-1060.

15.

l6.

17.

18.

19.

20.

21.
22.
23.
24.
25.
26.
27.
28.

29.

30.

31.

32.
33.

34.

25

(a) Volodina, A.N.; Koubehinova, T. B.; Maximova, S. I. Zh. Neorg. Khim.
USSR, 1987, 32, 2899. (b) Rolland, B.; McMillan, P.; Molinié, P.; Colombet, P.
Eur. J. Solid State Inorg. Chem. 1990, 27, 715-724.

(a) Gottlieb, M.; Isaacs, T. J.; Feiehtner, J. D.; Roland, G. W. J. Appl. Phys.
1974, 45, 5145-5151. (b) Alkire, R. W.; Vergamini, P. J.; Larson, A. C. Acta
Crystallogr. 1984, C40, 1502-1506.

Sutorik, A.; Kanatzidis, M. G. Progr. Inorg. Chem. 1995, 43, 151-265 and
references therein.

(a) McCarthy, T. J.; Kanatzidis, M. G. J. Alloys Camp. 1996, 236, 70-85. (b)
McCarthy, T. J.; Kanatzidis, M. G. Chem. Mater. 1993, 5, 1061-1063.

McCarthy, T. J.; Kanatzidis, M. G. J. Chem. Soc. Chem. Commun. 1994, 1089-
1090.

McCarthy, T. J.; Hogan, T. C.; Kannewurf, R.; Kanatzidis, M. G. Chem. Mater.
1994, 6, 1072-1079.

McCarthy, T. J.; Kanatzidis, M. G. Inorg. Chem. 1995, 34, 1257-1267.
Durand, E.; Evain, M.; Bree, R. J. Solid State Chem. 1993, 102, 146-155.
Eckert, H.; Liang, C. S.; Stucky, G. D. J. Phys. Chem. 1989, 93, 452-457.
Eckert, H.; Lathrop, D. J. Am. Chem. Soc. 1989, 111, 3536-3541.

Eckert, H.; Francisco, R. H. P. J. Solid State Chem. 1994, 112, 270-276.
Eckert, H.; Zhang, Z.; Kennedy, J. H. Chem. Mater. 1990, 2, 273-279.
Menzel, P.; Ohse, L.; Brockner, W. Heteroatom. Chem. 1990, 1, 357-362.

Francisco, R. H. P; Tepe, T.; Eckert, H. J. Solid State Chem. 1993, 107, 452-
459.

Maxwell, R.; Eckert, H. J. Am. Chem. Soc. 1993, 115, 4747-4753.

(a) O'Neal, S. C. 0.; Pennington, W. T.; Kolis, J. W. Angew. Chem. Int. Ed.
Engl. 1990, 29, 1486-1488. (b) Zhao, J.; Pennington, W. T.; Kolis, J. W. J.
Chem. Soc, Chem. Commun. 1992, 265-266.

(a) Bree, R.; Ouvrard, G.; Fréour, R.; Rouxel, J. Mat. Res. Bull. 1977, I8, 689-
696. (b) Bree, R.; Ouvrard, G. Solid State Ionics, 1983, 9&10, 481-484.

Chondroudis, K.; Kanatzidis, M. G. Bree, R. Inorg. Chem. In Press.

Chondroudis, K.; Hanko, J. A.; Kanatzidis, M. G. Inorg. Chem. 1997, 36,
2623-2632.

Chondroudis, K.; Kanatzidis, M. G. J. Chem. Soc., Chem. Commun. 1997,
401-402.

35.

36.
37.
38.

39.

40.
41.

42.
43.
44.
45.

46.

47.
48.

49.

50.
51.
52.

53.

26

Jandali, Von M. Z.; Eulenberger, G.; Hahn, H. Z. Anor. Allg. Chem. 1985, 530,
144-154.

Buck, P, Carpentier, C. D. Acta Crystallogr. 1973, B29, 1864-1868.
Chondroudis, K.; Kanatzidis, M. G. Inorg. Chem. 1995, 34, 5401-5402.

Chondroudis, K.; Kanatzidis, M. G. Materials Research Society, Fall 1996
Meeting, Boston, MA.

Simon, A.; Peters, K.; Peters, E. M.; Hahn, H. Z. Naturforsch. 1983, 38b, 426-
427.

Diehl, R.; Carpentier, C. D. Acta Crystallogr. 1977, B33, 1399-1404.

Becker, R.; Brockner, W.; Eisenmann, B. Z. Naturforsch. 1987, 42a, 1309-
1312.

Chondroudis, K.; McCarthy, T. J.; Kanatzidis, M. G. Inorg. Chem. 1996, 35,
840-844.

Post, E.; Kramer, V. Mat. Res. Bull. 1984, 19, 1607-1612.
Chondroudis, K.; Kanatzidis, M. G. Manuscript in preparation.

Toffoli, P. P.; Rouland, J. C.; Khodadad, P.; Rodier, N. Acta Crystallogr. 1985,
C41, 645-647.

Chondroudis, K.; Kanatzidis, M. G. J. Chem. Soc., Chem. Commun. 1996,
1371-1372.

Chondroudis, K.; Kanatzidis, M. G. J. Solid State Chem. In Press.

Bouchetiere, P. M.; Toffoli, P.; Khodadad, P.; Rodier, N. Acta Crystallogr.
1978, B34, 384-387.

(a) Toffoli, P. P.; Khodadad, P.; Rodier, N. Acta Crystallogr. 1978, B34, 3561-
3564. 0)) Wibbelmann C.; Brockner, W.; Eisenmann, B.; Sehéifer, H. Z.
Naturforsch. 1983, 38b, 1575-1580.

Chondroudis, K.; McCarthy, T. J.; Kanatzidis, M. G. Inorg. Chem. 1996, 35,
3451-3452.

Tremel, W.; Kleinge, H.; Derstroff, V.; Reisner, C. J. Alloys Camp. 1995, 219,
73-82.

Chondroudis, K.; Kanatzidis, M. G. C. R. Acad. Sci. Paris, Series B, 1996, 322,
887-894.

(a) Menzel, F.; Brockner, W. Carrillo-Cabrera, W.; Sabmannhausen, J. Z. Anor.
Allg. Chem. 1994, 620, 1081-1086. (b) Carrillo-Cabrera, W.; Sabmannhausen,
J.; Sehnering, H. G.; Menzel, P.; Brockner, W. Z. Anor. Allg. Chem. 1994, 620,
489-494.

54.

55.

56.

57.

58.

59.

60.

61.
62.

63.

64.

65.

66.

67.
68.

69.

27

Chen, J. H.; Dorhout, P. K.; Ostenson, J. E. Inorg. Chem. 1996, 35, 5627-
5633.

Jandali, Von M. Z.; Eulenberger, G.; Hahn, H. Z. Anor. Allg. Chem. 1985, 470,
39-44.

(a) Junghwan, D.; Jungwook, K.; Sangmoo, L.; Hoseop, Y. Bull. Korean Chem.
Soc., 1993, 14(6), 678-681. (b) Simon, A.; Peters, K.; Peters, E.; Hahn, H. Z.
Anor. Allg. Chem. 1982, 491, 295-299.

(a) Brockner, W.; Becker, R. Z. Natmforsch. 1987, 42a, 511-512. (b) Nitsehe,
R.; Wild, P. Mat. Res. Bull. 1970, 5, 419-423.

(a) Bree, R. Solid State Ionics, 1986, 22, 3-30. (b) Becker, R.; Brockner, W.;
Schafer, H. Z. Naturforsch. 1983, 38a, 874-879.

(a) Mercier, R.; Malugani, J. P.; Fahys, B.; Douglade, J .; Robert, G. J. Solid State
Chem. 1982, 43, 151-162. (b) Cyvin, S. J.; Cyvin, B.N.; Wibbelmann, C.;
Becker, R.; Brockner, W.; Parensen, M. Z. Naturforsch. 1985, 40a, 709-713. (C)
Toffoli, P. P.; Miehelet, A.; Khodadad, P.; Rodier, N. Acta Crystallogr. 1982,
B38, 706-710.

Brockner, W.; Ohse, L.; Patzmann, U.; Eisenmann, B.; Schafer, H. Z.
Naturforsch. 1985, 40a, 1248-1252.

Do, J.; Lee, K.; Yun, H. J. Solid State Chem. 1996, 125, 30-36.

Jandali, Von M. Z.; Eulenberger, G.; Hahn, H. Z. Anor. Allg. Chem. 1978, 445,
184-192.

(a) Toffoli, P. P.; Khodadad, P.; Rodier, N. Acta Crystallogr. 1977, B33, 1492-
1494. (b) Menzel, F.; Ohse, L.; Brockner, W. Heteroatom. Chem. 1990, 1, 357-
362.

(a) Fiechter, S.; Kuhs, W. P.; Nitsehe, R. Acta Crystallogr. 1980, B36, 2217-
2220.

(a) Bree, R.; Ouvrard, G.; Evain, M.; Grenouilleau, P.; Rouxel, J. J. Solid State
Chem. 1983, 47, 174-184. (b) Queignec, M.; Evain, M.; Bree, R.; Sourisseau, C.
J. Solid State Chem. 1986, 63, 89-109. (c) Bree, R.; Grenouilleau, P.; Evain, M.;
Rouxel, J. Rev. Chim. Miner. 1983, 20, 295-304.

Bree, R.; Grenouilleau, P.; Evain, M.; Grenouilleau, P.; Rouxel, J. Rev. Chim.
Miner. 1983, 20, 283-294.

Evain, M.; Bree, R.; Ouvrard, G.; Rouxel, J. Mat. Res. Bull. 1984, 19, 41-48.

Evain, M.; Bree, R.; Ouvrard, G.; Rouxel, J. J. Solid State Chem. 1985, 56, 12-
20.

Chondroudis, K.; Kanatzidis, M. G. Angew. Chem. 1997, 36, 1324-1325.

CHAPTER 2

Complex Multinary Compounds from Molten Alkali Metal Polyselenophosphate Fluxes.
Layers and Chains in A4Ti2(PZSe9)2(P2Se7), and ATiPSe5 (A=K,Rb). Isolation of

[P2Se9]4-, a Flux Constituent Anion

1. Introduction

Recently, we suggested the use of polychalcophosphate fluxes for the synthesis of
new ternary and quaternary thiophosphate and selenophosphate complexesl‘3 These
fluxes are formed by simple in situ fusion of AzQ/PzQs/Q and contain [Psz]n- ligands
(Q=S,Se) which in the presence of metal ions coordinate to give, interesting new materials.
We have shown that novel solid state structures can be constructed from [P2S7]4-, [PS4]3-,
and [P2Se(,]4-.1v2 Of course, quaternary compounds of this type have been prepared earlier
by non-flux procedures at higher temperatures.3 The first compound reported from a
AxPySz flux reaction was ABiPZS7 (A=K,Rb).2 The selenide containing fluxes gave rise
to several unusual compounds such as A2MPZSe6,3-4-5 KMPZSe6 (M=Sb,Bi),4
CSgM4(P2Se6)5 (M=Sb,Bi),3 APbPSe4,6 A4Pb(PSe4)2,6 (A=Rb,Cs) and K4Eu(PSe4)2.6
We have now investigated early transition metals such as Ti to explore whether this flux
technique is applicable in this area of the periodic table and because it appears that no
Ti/P/Q ternary or quaternary phases are known. Here we report the synthesis, structural
characterization, optical and thermal properties of the first selenophosphate quaternary
titanium compounds, Rb4Ti2(P2Se9)2(P2Se7) and KTiPSes. One of the possible ligand

anions that is present in these fluxes, namely [P28e9]4- has been isolated as the Cs+ salt

28

29

and its structure is reported here. All compounds feature novel structures containing the
rare [PSe4]3- as well as the polyselenido [P28e9]4- and [P28e7]4- ligands. The isostruetural

K4Ti2(P28e9)2(P28e7) and RbTiPSe5 have also been prepared. The ability to vary the flux

composition allows for control of basicity and consequently of the reaction pathway.“-6

One way is to vary the flux basicity by varying the amount of Azse in the starting

compositioné. In this case, however, access to each phase was achieved by modification of
the P28e5 amount. Specifically, to obtain A4Ti2(PZSe9)2(PZSe-;), a ratio of 123:2:10 of
Ti/P2Se5/AZSe/Se was used. Changing the ratio of P2Se5 to 1:222:10 gave ATiPSe5.

2. Experimental Section

2.1. Syntheses.

Azse (A=K, Rb, Cs; Q=S, Se) were prepared by reacting stoichiometric amounts
of the elements in liquid ammonia as described elsewhere.5

P2Se5 The amorphous phosphorus selenide glass "P28e5", was prepared by
heating a stoichiometric ratio of the elements as described elsewhere.5

Preparation of A4Ti2(P2Se9)2(PZSe7) (I). A4Tiz(P2Se9)2(PZSe-/)
(A=K,Rb) were synthesized from a mixture of Ti (0.3 mmol), P28e5(0.9 mmol), A28e

(0.60), and Se (3 mmol) that was sealed under vacuum in a Pyrex tube and heated to 490

0C for 4 d followed by cooling to 150 0C at 4 0C h-l. The excess AXPYSez flux was
removed with DMF to reveal black needles (88% yield based on Ti). The crystals are air-

and water- stable.

30
Preparation of ATiPSe5 (II). ATiPSe5 were synthesized from a mixture of Ti

(0.2 mmol), P28e5(0.4 mmol), A2Se (A=K, Rb) (0.40), and Se (2 mmol) with the same
heating conditions and isolated as above. The black, plate-like crystals (79% yield based on
Ti) are air- and water- stable.

Preparation of CS4P2Se9 (III). The red, air- and water- sensitive CS4P28e9
was synthesized from a mixture of P2Se5(0.45 mmol), C52Se (1.20), and Se (3 mmol)

with the same aforementioned heating conditions (80% yield based on P).

2.2. X-ray Crystallography

Intensity data for (I-III) were collected using a Rigaku AFC6S four-circle

automated diffractometer equipped with a graphite crystal monochromator. An empirical

absorption correction based on I]! scans was applied during initial stages of refinement.

The space groups were detemlined from systematic absences and intensity. No crystal

decay was detected in any of the compounds. The structures were solved by direct methods
using SHELXS-86 software7a (for all compounds), and full matrix least squares

refinement was performed using the TEXSAN software package?b For (I) the
phosphorus atoms were refined isotropieally.

Complete data collection parameters, details of the structure solution and
refinements for all compounds are given in Table 2-1. The coordinates of all atoms,
average temperature factors, anisotropic displacement parameters and their estimated

standard deviations are given in Tables 2-2 to 2-7.

31

Table 2-1. Crystallographic data for Rb4Ti2(P28e9)2(P28e7), KTiPSes, and CS4P2869

 

 

Formula Rb4Tiz(P28e9)2(P28e7) KTiPSes CS4P28e9
FW 2597.51 512.77 1304.21
a, A 3555(1) 18.430(1) 10.163(1)
b, A 37.315(8) 7.364(2) 10.582(2)
e, A 6.574(7) 6.561(1) 19.655(2)
a (deg) 90.00 90.00 90.00
B(deg) 90.00 9808(1) 9402(1)
7 (deg) 90.00 90.00 90.00
2, (103,3) 4; 8722(10) 4; 881.6(2) 4; 2108.7(5)
7t (Mo 1(a), A 0.71069 0.71069 0.71069
space group Fdd2 (#43) C2/m (#12) C2/c (#15)
Dcalc, g/cm3 3.956 3.863 4.108
19. cm-1 255.74 219.69 223.28
Temp (0C) -100 -122 25
Final R/wa’ % 4.1/4.1 5.9/8.1 3.3/5.0
Total Data 2185 869 2105
Measured
Total Unique Data 2185 840 1979
(ave)
Data F02>3O(F02) 766 381 1420
150 46 70

No. of Variables

Crystal Dimen.,
mm

0.56 x 0.08 x 0.08

0.72 x 0.23 x 0.05

em = £(1F01 - IFc|)/ZIF0|, Rw = {ZWUFOI - IFCI)2/ZWIF012} 10.

0.67 x 0.39 x 0.34

32

Table 2-2. Positional parameters and Beqa for Rb4Tiz(P2Se9)2(P28e7)

 

 

Atom X Y Z B equ2
Rb( 1) 0.0524(2) 0.1454(1) -0. 1666( l) 2.7(3)
Rb(2) 0.1774(1) 0.1763(1) 0.3194(9) 2.1(3)
Se(l) 0.0808(1) 0.1542(1) 0.334(1) 1.5(3)
Se(2) 0.0169(1) 0.2267(1) -0.5332(9) 1.6(2)
Se(3) 0.0194(1) 0.3058(1) -0.2644( 1) 1.3(2)
Se(4) 0.0782(1) 0.2359(1) 0.0267(1) 1.3(3)
Se(5) 0.1127(1) 0.2445(1) 0.5118(8) 1.2(2)
Se(6) 0.0766(1) 0.3283(1) -0.6678(8) 1.5(3)
Se(7) 0.0249(1) 0.3621(1) 01 139(9) 1.3(3)
Se(8) 0.1518(1) 0.1630(1) -0.1798(1) 1.6(2)
Se(9) 0.1202(1) 0.3223(1) -0. 125( 1) 1.3(3)
Se(10) 0.1747(1) 0.2508(1) -0.013(1) 1.4(2)
Se(l 1) 0.1776(1) 0.3107(1) 0.3875(8) 1.4(3)
Se(12) 0.2510(1) 0.1819(1) -0.025(1) 1.8(3)
Se( 1 3) 1/4 1/4 0.374(1) 1.5(4)
Ti 0.1227(2) 0.2823(2) 0.189(2) 1.3(4)
P(l) 0.0735(3) 0.2112(3) 0.329(2) 1.4(3)
P(2) 0.0823(3) 0.3583(3) 0.044(2) 1.2(3)
P(3) 0.2145(3) 0.2844(3) 0.159(2) 1.2(2)

a B values for anisotropieally refined atoms are given in the form of the isotropic
equivalent displacement parameter defined as Beq = (4/3)[aZB( l , l) + sz(2, 2) + c23(3,
3) + ab(cosy)B(l,2) + ac(cosB)B(l,3) + bc(cos0t)B(2, 3)]

33

Table 2-3. Anisotropic Displacement Parameters for Rb4T12(P28e9)2(P28e7)

 

 

Atom U1 1 U22 U33 U12 U13 U23
Rb(l) 0.044(4) 0.035(3) 0.022(4) -0.010(3) 0.004(3) 0.001(3)
Rb(2) 0.025(3) 0.031(3) 0.022(3) 0.002(3) 0.004(3) 0.005(3)
Se(1) 0.020(3) 0.014(3) 0.022(3) -0.001(2) 0.005(3) 0.002(3)
Se(2) 0.014(3) 0.024(3) 0.022(4) -0.002(3) 0.008(3) -0.007(3)
Se(3) 0.019(3) 0.018(3) 0.014(3) —0.003(2) 0.001(3) -0.005(3)
Se(4) 0.0 l 4( 3) 0.020(3) 0.015(4) -0.003(2) -0.002(3) 0.004(3)
Se(5) 0.019(3) 0.021(3) 0.007(3) -0.006(2) -0.001(3) -0.002( 3)
Se(6) 0.021(3) 0.016(3) 0.020(4) 0.003(2) 0.007(3) 0.000(3)
Se( 7) 0.0 1 5( 3) 0.013(3) 0.020(4) 0.002(2) -0.002( 3) -0.006(3)
Se(8) 0.023(3) 0.016(3) 0.021(3) 0.006(3) 0.002(3) -0.004(3)
Se(9) 0.017(3) 0.014(3) 0.019(4) 0.004(2) 0.008(3) 0.001(3)
Se(lO) 0.016(3) 0.017(3) 0.019(3) -0.002(3) -0.003(3) -0.001(3)
Se(] 1) 0.015(3) 0.015(3) 0.023(4) 0.001(2) -0.005(3) -0.004(3)
Se(12) 0.016(3) 0.025(3) 0.027(4) -0.004(2) -0.006(3) -0.008(3)
Se(13) 0.020(4) 0.013(4) 0.024(5) -0.000(3) 0 0
Ti 0.013(5) 0.010(5) 0.027(6) 0.004(4) 0.005(5) 0.005(4)

P( 1) 0.018(4)

P(2) 0.015(3)

P(3) 0.015(3)

34

Table 2-4. Positional parameters and Beq for KTiPSes

 

 

 

 

Atom X Y Z B eq A2
Se(1) 0.0850(2) 0 0.8832(5) 0.9(2)
Se(2) 0.0866( 1) 0.2409(4) 1.3405(4) 1.2( 1)
Se(3) 0.2548(2) 0 1.2584(6) 1.5(2)
Se(4) 0.0620(2) -1/2 0.81 14(5) 1.0(2)
Ti 0 -0.276( 1) 1.0000 0.7(3)
K( 1) 0.2673(5) 0 0.766(1) 1.9(4)
P(l) 0.1378(6) 0 1.214(1) 1.1(5)
Table 2-5. Anisotropic Displacement Parameters for KTiPSe5
Atom U1 1 U22 U33 U12 U13 U23
Se(1) 0.012(3) 0.014(3) 0.010(2) 0 0.003(2) 0
Se(2) 0.016(2) 0.015(2) 0.012(2) 0.003(1) -0.002( 1) -0.003( 1)
Se(3) 0.013(3) 0.026(3) 0.018(2) 0 0.003(2)
Se(4) 0.016(3) 0.010(3) 0.012(2) 0 0.003(2) 0
Ti -0.000(4) 0.013(4) 0.013(4) 0 0.000(3) 0
1((1) 0.024(6) 0.028(6) 0.020(5) 0 0.000(4) 0
P( 1) 0.023(7) 0.010(6) 0.013(6) 0 0.01 1(5) 0

35

Table 2-6. Positional parameters and Egg for CS4P2509

 

 

 

 

Atom X Y Z Beq A2

Cs( 1) 0.15991(9) 0.4046(1) 0.32832(5) 340(5)

Cs(2) 0.03 334(8) 0.75144(9) 0.47575(5) 250(4)

Se(1) 0.1303(1) 0.6228(1) 0.18062(7) 250(6)

Se(2) 0.0333(1) 0.0261(1) 0.34824(7) 230(6)

Se(3) 1/2 0.4020(2) 1/4 254(8)

Se(4) 0.1963(1) 0.2980(1) 0.14585(7) 223(6)

Se(5) 0.2487(1) 0.0374(1) 0.48489(7) 242(6)

P( 1) 0.2575(3) -0.0073(3) 0.3769(2) 1.5( 1)

Table 2-7. Anisotropic Displacement Parameters for CS4P2369
Atom U1 1 U22 U33 U12 U13 U23
Cs( 1) 0.0366(5) 0.0594(7) 0.0335(6) 0.0132(5) 0.0051(4) 0.0050(5)
Cs(2) 0.0298(5) 0.0306(5) 0.0342(5) -0.0047(4) -0.001 1(4) 0.0027(4)
Se(1) 0.0383(8) 0.0243(8) 0.0334(8) 0.0045(6) 0.0089(6) -0.0039(6)
Se(2) 0.0230(7) 0.0333(8) 0.031 1(8) 0.0060(6) 0.0012(6) -0.0063(6)
Se(3) 0.040(1) 0.024(1) 0.031(1) 0 -0.0101(9) 0
Se(4) 0.0378(8) 0.0190(7) 0.0280(8) -0.0053(6) 0.0036(6) 0.0022(6)
Se(5) 0.0343(7) 0.0330(8) 0.0246(8) -0.0047(6) 0.0027(6) -0.0085(6)
P( 1) 0.023(2) 0.020(2) 0.015(2) 0.002(1) 0.001(1) -0.002(1)

36

3. Description of Structures

Structure of Rb4Tiz(P28e9)2(PZSe7) (1). Compound (I) has a layered
structure; see Figure 2-1. The [T12(P28e9)2(P2Se7)]4- layers are separated by six-
coordinate Rb(1)+ [Rb(l)-Se mean=3.6(l)A] and eight-coordinate Rb(2)+ ions [Rb(2)-Se
mean=3.6(l)A]. The layers form a perforated network made of TiSe6 octahedra linked in
two dimensions by [P28e7]4- and [P28e9]4- anions. The latter is a rare ligand and

possesses a Se-Se-Se chain linking two phosphorus atoms. The sulfur analog of this anion
has been observed in the two-dimensional P2Nb4S21.8 These layers contain very large 44-

membered rings made of six titanium atoms, two [P2Se7]4- , and four [P28e9]4- units
(Ring Dimensions: 26.61A along a-axis, 6.57A along c-axis), Figure 2-2. The layers have
a corrugated structure and they stagger by being offset along the a-axis by a 1/2 translation.
This is as well the reason that the large rings do not form channels running down the b-

axis. In a polyhedral description the titanium octahedra share edges with three phosphorus
tetrahedra. Two of these tetrahedra belong to [PZSe9]4- units whereas the third one belongs

to a [P28e7]4- unit. The Ti-Se distances range from 2.554(9)A to 2.58(1)A. The P-Se

distances range from 213(1) to 2.29(1)A and compare well with those found in

APbPSe4,.6 Selected distances and angles are given in Table 2-8.
Structure of KTiPSes (11). Compound (11) has the one-dimensional

structure shown in Figure 2-3. The chains consist of centrosymmetric Ti2(PSe4)2 dimeric
cores which are bridged by two tig—Sez- ions. In these cores two [PSe4]3- ligands bridge

two titanium atoms employing three selenium atoms each. The fourth selenium remains
non-bonding. The titanium atoms are in a distorted octahedral environment. The shortest

Ti-Ti distance is between metals of adjacent dimers at 3.29(1)A. The Ti-Se distances range

37
from 2.438(6)A to 2.742(6)A and compare well with those found in (I). The P-Se

distances range from 2.13(l) to 2.222(7)A similar to those of (1). Finally, the chains are

separated by eight coordinate K+ ions [K-Se mean 3.5(2)A]. Selected distances and angles
are given in Table 2-9.

Structure of CS4P2Se9 (III). Compound (III) is a molecular compound
that was obtained in our attempt to isolate one of the various [PyQZ]n- ligands thought to be

present in polychalcophosphate fluxes. It consists of isolated [P23e9]4- units which in turn
are made of two PSe4 subunits connected via a monoselenide (see Figure 2-4). This
arrangement gives rise to a triselenide unit in this anion. The molecule is sitting on a 2-fold
axis going through Se(3). There are two crystallographically independent Cs+ ions, both
having eight-coordinate environment [Cs(1)-Se mean 3.80(9)A], [Cs(2)-Se mean
3.74(7)A]. The potassium and rubidium analogs were also prepared and they are very air

and moisture sensitive. Selected distances and angles are given in Table 2-10.

4. Physical Measurements

The optical spectra of the compounds show sharp optical gaps consistent with
semiconductors. The Rb4Ti2(P28e9)2(P2Se7) shows a band-gap, Eg, of 1.38 eV, while
KTiPSe5 and CS4P2Se9 show 1.06 and 1.78 eV respectively. The Raman spectra of (I)
display absorptions at ~504, ~400, ~266, ~228, ~186, and ~156 cm-1.9 Compound (III)
displays absorptions at ~475,~357,~265,~228 and ~159 cm-l. The shifts at ~266 and ~265
cm-1 in (I) and (HI) are attributed to Se-Se stretching vibrations. Those at higher energies
are due to P-Se vibrations. DTA analysis shows that (I) and (H) melt incongruently at 403
and 525 0C respectively yielding TiSe2 and amorphous AxPySex. This further highlights
the value of the alkali polychalcophosphate flux which allows the synthesis of compounds

at relatively low temperatures. Compound (III) melts congruently at 446 oC.

38

 

 

 

V

(s " \
8612 8611860

 

1/
Q
Q.

 

P

 

Figure 2-1: The structure of Rb4Ti2(P2Se9)2(P28e7) viewed down the c-axis

 

39

VA 5 1'. f0 8. (4 8:1 to
It IL ‘L It
‘ U '
Am r‘ A~ r‘ A~‘c.‘ -- r‘
1' D ‘P ' ‘7 V! 1' i
ll. ‘5 IL ‘L
U I
4' .‘ 0' .‘ a! .‘ 0', §

it

'0

 

 

it

 

 

 

 

s. to a. Co
5 L
‘D 1 I
“A... a....,
‘7 V.
t h
‘7 ‘ I
0' .3 a! .3 a! .3 0', g

The structure of Rb4Ti2(P28e9)2(P28e7) viewed down the b-axis

Figure 2-2

An
C.

A~
\

V!
I

1 Q at." .‘u 1. a
'6 .v Q”

 

on on . a?» 6 in “u
4.0; .“ IS aruksrl

\
fix

 

One chain of KTiPSe5 viewed down the c-axis

Figure 2-3:

Se(1)
‘7

PO) 7“

7 " K
43 {17)
Se(5) Se(4)

Figure 2-4:

41

6’44
O
Q 1;
Se(2) Se(3)
‘=.:m 4”

Structure of the [P28e9]4- anion

Table 2-8. Selected Distances (A) and Angles (deg) for Rb4Ti2(PZSe9)2(PZSe7)

42

Ti-Se(4) 2.58(1) Sc(4)-Ti-Se(5) 83.6(3)
Ti-Se(5) 2.57( 1) Se(4)-Ti-Se(6) 102.1(3)
Ti-Se(6) 2.554(9) Se(4)-Ti-Se(9) 92.1(3)
Ti-Se(9) 2.55( l) Se(4)-Ti-Se(10) 85.4( 3)
Ti-Se( 10) 2.56(1) Se(4)-Ti-Se(1 1) 162.1(4)
Ti-Se(1 1) 2.5 8( l ) Se(5)-Ti-Se(6) 88.6(3)
P(1)-Se( l) 2. 14( 1) Se(5)-Ti-Se(9) 169.8(4)
P(1)-Se(2) 2.28(1) Se(5)-Ti-Se( 10) 106.1(3)
P(1)-Se(4) 2.20(1) Se(5)-Ti-Se(1 1) 85.0(3)
P( 1 )-Se(5) 2.22(1) Se(6)-Ti-Se(9) 83.2(3)
P(2)-Se(6) 2.21( l ) Se(6)—Ti-Se( 10) 164.3(4)
P(2)-Se(7) 2.29(1) Se(6)-Ti-Se( 1 l) 91 .3(3)
P(2)-Se(8) 2. l 3( 1) Se(9)-Ti-Se( 10) 82.7(3)
P(2)-Se(9) 2.20( 1) Se(9)-Ti-Se(l 1) 101.2(3)
P(3)-Se( 10) 2.20(1) Se(10)-Ti-Se(l l) 84.5(2)
P(3)-Se(] 1) 2.22( 1) Se(2)-Se(3)-Se(7) 103.7(2)
P(3)-Se( 12) 2. 1 3( l) Se(1)-P(1)-Se(2) 1 10.5(5)
P(3)-Se( l 3) 2.29( 1) Se(1)-P(l)-Se(4) 1 14.9(6)
Se(2)-Se(3) 2.333(6) Se(1)-P(1)-Se(5) 118.1(6)
Se(2)-P( 1 )-Se(4) 108.7(6)

Se(2)-P( l )-Se(5) 101.4(5)

Se(4)-P(1 )-Se(5) 102.1(5)

43

Table 2-9. Selected Distances (A) and Angles (deg) for KTiPSe5

Ti-Se(l) 2.742(6) Se(2)-Ti-Se(2') 168.3(3)
Ti-Se(2) 2.570(3) Se(2)-Ti-Se(4) 103.4(2)
Ti-Se(4) 2.438(6) Se(2)-Ti-Se(4') 84.6(1)
P(l)-Se(1) 2.25( 1) Se(4)-Ti-Se(4') 95.0(3)
P(l)-Se(2) 2.222(7)}. Se(1)-P(1)Se(2) 102.2(4)
P(1)Se(3) 2.13(1)A Se(1)-P(l)—Se(3) 114.9(5)
Se(2)-P(l )-Se(2') 105.9(4)

Se(1)-Ti-Se(1') 84.2(2) Se(2)-P( l)-Se(3) l 15.0(3)
Se(1)-Ti-Se(2) 81.8(1) Ti-Se(l)-Ti 95.8(2)
Se(1)-Ti-Se(2') 89.5(2) Ti-Se( 1 )P( 1) 85.2(2)
Se(1)-Ti-Se(4) 9188(9) Ti-Se(2)-P(l) 90.1(3)
Se(1)-Ti-Se(4') 165.9(1) Ti-Se(4)-Ti 85.0(3)

Table 2-10. Selected Distances (A) and Angles (deg) for CS4P28e9

P(l)-Se(1) 2.157(4) Se(1)-P(l)-Se(5) 115.5(1)
P(l)-Se(2) 2.335(3) Se(2)-P(1)-Se(4) 108.4(1)
P(l)-Se(4) 2.166(4) Se(2)-P(IISe(5) 95.5(1)
P(l )-Se(5) 2.183(3) Se(4)-P(1rSe(5) 1 15.5( I)
Se(2)-Se(3) 2.340(2) P( 1 )‘S€(2)-SC(3) 101 312(9)

Se(2)-Se(3)-Se(2) l l 1.7( l)
Se(1)-P(l)-Se(2) 108.6(1 )
Se( 1)-P(1)-Se(4) 1 1 1 .6( l)

5. Conclusions

The first selenophosphate titanium compounds have been prepared in molten
polyselenophosphate Ax[PySez] fluxes. The non-centrosymmetric A4Ti2(P2Se9)2(P28e7)
may be potentially interesting non-linear optical materials. In the Ax[PySez] system, unlike
other fluxes (e.g. halide or metal fluxes), control of the flux composition permits to a
certain degree control of the reaction outcome and thus can be exploited productively in
synthetic solid-state chemistry. Selenophosphate systems containing different transition or
main metal ions have also yielded novel solid-state structures.10 Furthermore, certain flux
conditions can promote the crystallization of various [PySez]n- anions present in it. The
isolation and identification of such anions will help understand better the nature of these

fluxes and will provide useful insight into how the various multinary compounds form.

10.

45

References
Sutorik, A.; Kanatzidis, M. G. Progr. Inorg. Chem 1995, in press.

(a) McCarthy, T. J.; Kanatzidis, M. G. Chem. Mater. 1993, 5, 1061-1063. (b)
McCarthy, T. J.; Hogan, T.; Kannewurf, C. R.; Kanatzidis, M. G. Chem. Mater.
1994, 6, 1072-1079

For examples see: (a) P. Toffoli, P. Khodadad, N. Rodier, Acta Cryst. 1977,
B33, 1492-1494. (b) M. Z. Jandali, G. Eulenberger, H. Hahn, Z. Anorg. Allg.
Chem. 1978, 445, 184-192. (c) Durand, E.; Evain, M.; Bree, R. J. Solid State
Chem. 1992, 102, 146-155. ((1) Toffoli, P.; Miehelet, A.; Khodadad, P.; Rodier,
N. Acta Cryst. 1982, B38, 706-710. (e) D’ordyai, V. S.; Galagovets, I. V.;
Peresh, E. Yu.; Voroshilov, Yu. V.; Gerasimenko, V. S.; Slivka, V. Yu. Russ. J.
Inorg. Chem., 1979, 24, 1603-1606.

McCarthy, T. J.; Kanatzidis, M. G. J. Chem. Soc. Chem. Commun. 1994,
1089-1090.

McCarthy, T. J.; Kanatzidis, M. G. Inorg. Chem. 1995, 34, 1257-1267.
Chondroudis, K.; Kanatzidis, M. G. Submitted for publication.

(a) Sheldrick, G. M., in Crystallographic Computing 3 ; Sheldrick, G. M., Kruger,
C., Doddard, R., Eds.; Oxford University Press: Oxford, England, 1985, p 175.
(b) Gilmore G. J ., Appl. Crystallogr. 1984, 17, 42.

Bree, R.; Evain, M; Grenouilleau, P; Rouxel, J. Rev. ChimMiner. 1983, 20,
283-294.

Reliable Raman spectra could not be obtained from ATiPSe5 due to strong
fluorescence.

Chondroudis, K.; Kanatzidis, M. G. To be submitted for publication.

CHAPTER 3

i[P3Se4']: A Novel Polyanion in K3RuP58610; Formation of Ru-P bonds in a Molten

Polyselenophosphate Flux

1. Introduction

Very recently, progress in the polychalcophosphate flux technique has resulted in
many novel quaternary chalcophosphate compounds.1 The in situ fusion of AzQx, and
P2Q5 (Q=S, Se), yields various [Psz]n- units (Q=S, Se). These highly anionic ligands, in
the presence of metal ions, coordinate via the Q atoms in an astonishing number of ways
forming new materials.1 By fine-tuning the flux composition various ligands have been
stabilized, such as [PQ4]3-, {PSe5]3-, [P2Q6]4-, [P2Q7]4-, and [P2Se9]4-,1-ll which
become the building blocks of various polymeric, solid-state or even molecular structures.8
Examples of compounds synthesized this way include ABiP287 (A=K,Rb),2 A3M(PS4)2
(A=Rb, Cs; M=Sb, Bi),3 A2M2P2Se6 (A=K, Cs; M=Cu, Ag),l KMPZSe6 (M=Sb, Bi),4
C53M4(P28e6)5 (M=Sb, Bi),5 APbPSe4,6 Rb4Ti2(PZSe9)2(P28e7),7 A5Sn(PSe5)3 (A=K,
Rb),3, szAuPZSe6,9 K2UP3Se9,10 and K(RE)P28e6 (RE=Y, La, Ce, Pr, Gd).11 An
inspection of the entire class of chalcophosphate compounds reveals a conspicuous absence
of any ruthenium containing members, eventhough several iron compounds are known.
Furthermore, in all compounds the metal atoms form exclusively M-Q bonds. Given that
Ru belongs to the noble metal group it seemed that the highly reactive polychalcogenide

fluxes would serve as an excellent tool to access its chemistry.

46

47
Here we report on the first structurally characterized Ru selenophosphate

compound, K3RuP5Se10, which surprisingly, shows a significant departure from the

chemistry of any other metal studied in the P/Q systems.

2. Experimental Section

2.1. Syntheses

Preparation of K3RuP5Se10. K3RuP5Se10 was synthesized from a mixture of
Ru (0.15 mmol), P28e5(0.45 mmol), K28e (0.225 mmol), and Se (1.5 mmol) that was
sealed under vacuum in a Pyrex tube and heated to 490 0C for 10 (1 followed by cooling to

50 0C at -2 0C h-l. The excess KxPySez flux was removed with DMF under N2
atmosphere. The product was then washed with tri-n-butyl phosphine to remove residual
elemental Se, and ether. Black, rodlike crystals were obtained (75% yield based on Ru).
The crystals appear air- and water-stable. Semiquantitative microprobe analysis on single

crystals gave K2,3RuP4.98e9.7 (average on four data acquisitions).

2.2. X-ray Crystallography

A Siemens SMART Platform CCD diffractometer was used to collect data from a

crystal of 0.28 x 0.04 x 0.04 mm dimensions and MoKOt (A = 0.71073 A) radiation.

Lorentz polarization effects correction and an empirical absorption correctioana were

applied to the data (min/max. transmission=0.519). The structure was solved with

SHELXS-8612b and refined by full-matrix least squares techniques of the TEXSAN12C

48

package of crystallographic programs. The space groups were determined from systematic
absences and intensity. N 0 crystal decay was detected.

Complete data collection parameters, details of the structure solution and
refinements for all compounds are given in Table 3-1. The coordinates of all atoms,
average temperature factors, anisotropic displacement parameters and their estimated

standard deviations are given in Tables 3-2 and 3-3.

49

Table 3-1. Crystallographic data for K3RuP58e10

 

 

Formula K3RuP5Se10
FW 1 162.83
a, A 11.2099(2)
b, A 7.2868(1)
c, A 12.3474(2)
Ct (deg) 90.00
[3 (deg) 93.95 8(1 )
7 (deg) 90.00
2. V(A3) 2; 1006.18(2)
it (Me 1(a), A 0.71073
space group P21/m (#11)
Dcalc- g/cm3 3.838
11, cm'1 198.70
Temp (0C) 23
Final R/Rw,a % 3.4/3.6
Total Data 8462
Measured
Total Unique Data 1966
(ave)
Data F02>36(F02) 1575
No. of Variables 104

Crystal Dimen.,
mm

0.28 x 0.04 x 0.04

are = sum - chl)/ZIF01, Rw = {swam - IFCI)2/ZWIF012}1/2.

50

Table 3-2. Positional parameters and Beqa for K3RuP58e10

 

 

Atom X Y Z B equ2
Ru 0.34951(7) 0.2500 0.1 1656(7) 079(2)
Se( 1) 0.18477(7) 0.0218(1) 0.16935(7) 1.43(2)
Se(2) 0.9603(1) 0.2500 0.3334(1) 221(3)
Se(3) 0.43928( 10) 0.2500 0.31654(9) 173(3)
Se(4) 0.25761 (9) 0.0025(1) 0.50225( 8) 305(2)
Se(5) 0.66176(7) -0.0081(1) 0.16599(6) 151(2)
Se(6) 0.08995( 10) 0.2500 -0. 12099( 10) 199(3)
Se(7) 0.61909(9) 0.2500 -0. l 1915(9) 1.20(2)
K( 1) 0.9007(3) 0.2500 0.0670(2) 281(7)
K(2) 0.0097(3) 0.2500 -0.3905(3) 387(8)
K(3) 0.5262(3) 0.2500 -0.3886(3) 394(8)
P( 1) 0.1341(2) 0.2500 0.2737(2) 1.15(6)
P(2) 0.2757(3) 0.2500 0.41 10(2) 150(6)
P( 3) 0.2756(2) 0.2500 -0.0608(2) 1.01 (6)
P(4) 0.4777(2) 0.0194(3) 0.0849(2) 099(4)

a B values for anisotropically refined atoms are given in the form of the isotropic

equivalent displacement parameter defined as ch = (4/3)[azB( l , l) + sz(2, 2) + czB(3,

3) + ab(cosy)B(l ,2) + ac(cosB)B( 1 ,3) + bc(cosa)B(2, 3)]

51

Table 3-3. Anisotropic Displacement Parameters for K3RuP5Se10

 

 

Atom U 1 l U22 U33 U12 U13 U23
Ru 0.0046(4) 0.0106(5) 0.0153(4) 0.0000 0.0027(3) 0.0000
Se( 1) 0.01 19(4) 0.0157(4) 0.0274(5) -0.0031(3) 0.0065(3) -0.0041(3)
Se(2) 0.0103(6) 0.0449(9) 0.0297(7) 0.0000 0.0087(5) 0.0000
Se(3) 0.0107(6) 0.0356(8) 0.0195(6) 0.0000 0.0009(5) 0.0000
Se(4) 0.0370(6) 0.0392(6) 0.0402(6) 0.0006(5) 0.0063(5) 0.0209(5)
Se(5) 0.0106(4) 0.0170(4) 0.0215(4) 0.0010(3) -0.0025(3) -0.0035(3)
Se(6) 0.0068(6) 0.0419(8) 0.0264(7) 0.0000 -0.001 1(5) 0.0000
Se(7) 0.0099(5) 0.0121(6) 0.0238(6) 0.0000 0.0039(5) 0.0000
K( 1) 0.025(2) 0.048(2) 0.034(2) 0.0000 0.003(1) 0.0000
K(2) 0.061(2) 0.050(2) 0.035(2) 0.0000 0.003(2) 0.0000
K(3) 0.055(2) 0.057(2) 0.037(2) 0.0000 -0.002(2) 0.0000
P( 1) 0.008(1) 0.016(2) 0.020(1) 0.0000 0.004(1) 0.0000
P(2) 0.015(2) 0.024(2) 0.019(2) 0.0000 0.004(1) 0.0000
P(3) 0.006(1) 0.014(1) 0.018(1) 0.0000 0.000(1) 0.0000
P(4) 0.0076(9) 0.01 1( 1) 0.020(1) 0.0004(8) 0.0031(8) 0.0001(8)

52

3. Description of Structure

Structure of K3RuP5Se10. K3RuP58e10 has an one-dimensional structure with
Ru in the 2+ oxidation state, see Figure 3-1. It contains [P28e6]4- and l/oo[P3Se4-] anions
and so it can be described as K3+Ru2+(PZSe6)4-(P3Se4)-. There are two unprecedented
features in this compound. First the mixed P/Se coordination of the Ru centers and second
the stabilization of a novel polymeric l/oo[P3Se4-] anion with P atoms in two different
oxidation states (P2+, P3+), and which binds exclusively via P atoms. Hitherto in all the
known polychalcophosphates, the [Psz]n- units coordinate to the metal centers via the
negatively charged Q atoms (Q=S, Se). K3RuP5Se10 is the first polychalcophosphate with
bonding between the metal center and the P atoms of the [PszPi- unit. The strong
preference of Ru2+ for binding to phosphorus is reminiscent of the coordination of
ruthenium centers by phosphanes (R3P) in organometallic complexes. The selection of
phosphorus from a "sea" of selenide anions for bonding is remarkable and, at first
unexpected. It can be rationalized by soft acid/soft base arguments, if we assign a softer

basic character to the bound phosphorus centers than to the Se atoms of the [P2Se6]4-

anions.

The i[Ru(P28e6)(P3Se4)]3- chain structure is essentially based upon the -1—-[P3Se4-]

unit, a novel infinitely long, anionic ligand, which has not been observed before. Formally,
it can be viewed as resulting from the polymerization of the cyclic [P3Se4] (Scheme 1). The
conformation of the chain presents triangular binding pockets made of P atoms which
accommodate the Ru centers. The formal oxidation states can be assigned as P2+ for the P-
P bonded pair of atoms (e.g. P4) and P3+ for the remaining atom (e.g. P3). Both the P2+
and P3+ atoms in the chain are bound via their lone pairs of electrons. Therefore, they are

electronically more similar to the phosphorus atoms in phosphine ligands which are so

53

abundant in Ru coordination chemistry. The remaining coordination sphere of Ru is

completed by a tridentate [PZSe6]4-unit.

Scheme1
Se\ ’89 /
Se\ /Se / P / Se\P/Se
/ P /Se\ / /
P/SG\P ’Pi P\ Pp/Se\p\

Se/I \Se 89’ ‘\SeP
Se Se
Se Se Se
Se / Se
Se\P/Se \p// Se\P/Se
p// 39‘ P/ / P/ 86‘ P P// SB\P/
/ \‘R" 1 \ R“! \
Ru / /
I V4
/P‘f‘Se’/P /P; ‘Se7p
Se’Fl,\Se Se’ \\Se
Se Se

It is noteworthy, that the 2+ and 3+ oxidation states for P are among the lowest yet

observed in chalcophosphate chemistry. The infinite i[Ru(P3Se4)+] "ladder" shaped

structure that is formed by the coordination of the —l-[P3Se4-] to the Ru centers is the

backbone of the one-dimensional structure of K3RuP58e10 and propagates along the [010]

direction. The i[P3Se4-] unit can be considered as an infinite chelating ligand which

creates a cage structure around each Ru center. These cages are formed by the fusion of
two 5- and two 6-membered rings and consists of one Ru, five P and three Se atoms.
Every Ru2+ center is in an octahedral coordination environment with three Se and three P

atoms in a fac configuration (Scheme 2).

54

The Ru-P bonds in K3RuP58e10 are very short [Ru-P(3) 2.288(3)A, Ru-P(4')
2.262(2)A], and comparable only to the shortest distances found in some Ru phosphides
such as RuP3,13 and RuP4,14 and the shortest distances found in phosphine complexes

such as mer-[Ru(PEt2Ph)3Cl3]-. 15

Scheme 2

 

The chains are separated by three, crystallographically independent, K cations, see
Figure 3-2. K(l) has an unusually high coordination environment with 11 Se and one P
atoms in its coordination sphere with an average K(1)-Se distance of 3.59A and a K(1)-P
distance of 3.526(4)A. K(2) is 8-coordinate [av. K(2)-Se 3.62A]. K(3) is 9-coordinate
with eight Se [av. K(3)-Se 3.61A] and one P atom [K(3)-P 3.613(4)A]. Other selected

bonds and distances are given in Table 3-4.

55

4. Physical Measurements

K3RuP58e10 melts incongruently at 661 0C yielding a mixture of amorphous
KxPySez glass and residual K3RuP58e10. Some RuSez or Rqu should also be formed but
they are either amorphous or in concentrations and particle sizes undetectable by our XRD
analysis. We have been unable to prepare K3RuP58e10 by a direct stoichiometric reaction
for several days at 560 OC. Far—IR measurements reveal vibrational modes at ~515, ~453,
~441, ~40] cm-1 and ~360 cm-1 that can be assigned to the 1/oo[P3Se4-] unit, whereas the

ones at ~486 and ~313 cm'1 are assigned to the [P28e6]4- group.

56

 

 

 

 

 

Figure 3-1: ORTEP representation of the unit cell viewed down the b axis.

57

 

.mczonfl £39 £20 -mzfimmmvfiommmvsém 05 we cocoa a he 55953.9: may—O ”Wm Sawm—

 

 

 

58

Table 3-4. Selected Distances (A) and Angles (deg) for K3RuP58e10

Ru-Se(1) 2.601(1) P(3)-Se(6) 2.161(3)
Ru-Se(3) 2.601 ( l) P(4)-Se(5) 2.240(2)
Ru-P(3) 2.288(3) P(4)-Se(7) 2.297(2)
Ru-P(4') 2.262(2) P(4)-P(4) 2.206(4).
P( 1 )-Se( 1) 2.202(2)
P(1)-Se(2) 2.130(3) Se(1)-Ru-Se( 1') 7948(4)
P(1)-P(2) 2.241(4) Se(1)-Ru-Se(3) 8983(4)
P(2)-Se(3) 2.240(3) Se(1)-Ru-P(4') 9223(5)
P(2)-Se(4) 2. 144(2) Se(1)-Ru-P(4") 171.29(6)

P(3)-Se(5) 2.326(2) Se(1)-Ru-P(3) 91 .34(6)

59

5. Conclusions

That metal centers can choose their own coordination sphere and even dictate the final
structure of a compound is well known, but seldom in flux reaction chemistry do they play
a prominent role in determining which ligand will form. This is mostly determined by the
reactive flux composition, the reaction temperature and the nature of the counterion. In
K3RuP58e10 we observe an extreme case where the Ru exhibits a protagonistic role in
stabilizing a ligand, which otherwise is unstable under the experimental conditions,
according to its coordination chemistry needs. The exclusively P-bound [P3Se4] ligand

with its low oxidation state phosphorus atoms seems tailor-made for Ru binding.

 

10.

ll.

12.

13.

14.
15.

60

References

a) T. J. McCarthy, M. G. Kanatzidis, Inorg. Chem. 1995, 34, 1257-1267. b) A.
Sutorik, M. G. Kanatzidis, Progr. Inorg. Chem. 1995, 43, 151-265.

T. J. McCarthy, T. Hogan, C. R. Kannewurf, M. G. Kanatzidis, Chem. Mater.
1994, 6, 1072-1079.

T. J. McCarthy, M. G. Kanatzidis, J. Alloys Camp. 1996, 236, 70-85.

T. J. McCarthy, M. G. Kanatzidis, J. Chem. Soc. Chem. Commun. 1994, 1089-
1090.

T. J. McCarthy, M. G. Kanatzidis, Chem. Mater. 1993, 5, 1061-1063.

K. Chondroudis, T. J. McCarthy, M. G. Kanatzidis, Inorg. Chem. 1996, 35 ,
840-844.

K. Chondroudis, M. G. Kanatzidis, Inorg. Chem. 1995, 34, 5401-5402.

K. Chondroudis, M. G. Kanatzidis, J. Chem. Soc. Chem. Commun. 1996, 1371-
1372.

K. Chondroudis, T. J. McCarthy, M. G. Kanatzidis, Inorg. Chem. 1996, 35,
3451-3452.

K. Chondroudis, M. G. Kanatzidis, C. R. Acad. Sci. Paris, Series B, 1996, 322,
887-894.

(a) J. H. Chen, P. K. Dorhout, Inorg. Chem. 1995, 34, 5705-5706. (b) J. H.
Chen, P. K. Dorhout, J. E. Ostenson, Inorg. Chem. 1996, 35, 5627-5633.

a) R. H. Blessing, Acta Cryst. 1995, A51, 33-38. b) G. M. Sheldrick, In
Crystallographic Computing 3; (Eds: G. M. Sheldrick, C. Kruger, R. Doddard),
Oxford University Press: Oxford, England, 1985, p. 175-189. c) TEXSAN:
Single Crystal Structure Analysis Software (1981 & 1992). Molecular Structure
Corporation, The Woodlands, TX 77381.

W. anle, R. Kremer, H. G. Von Sehnering, Z. Kristallogr. 1987, 179, 443-
453.

V. D. J. Braun, W. Jeitschko, Z. Anorg. Allg. Chem. 1978, 445, 157-166.

E. A. Seddon, K. R. Seddon, The Chemistry of Ruthenium, Elsevier Science
Publishers B.V., New York, 1984, p. 503-511.

CHAPTER 4

Chemistry of Gold in Molten Alkali Metal Polyehalcogeno-phosphate Fluxes. Synthesis

and Characterization of the Low Dimensional Compounds A3AuP2Se3 (A=K, Rb, Cs),

A2AuszSe6 (A=K, Rb) and A2AuP2$e6 (A=K, Rb)

1. Introduction

The polychalcophosphate fluxes provide the best set of experimental conditions for

the synthesis of new ternary and quaternary thiophosphate and selenophosphate

compounds.l These fluxes form by the in situ fusion of A2Q/P2Q5/Q and contain [Psz]n-
(Q=S, Se) units which, in the presence of metal ions, coordinate to give interesting new
materials. These materials tend to be structurally and eompositionally complex and often

cannot be made by standard solid state chemistry methods. After the initial report on
ABiPZS7 (A=K, Rb),2 the following unusual compounds were reported: A3M(PS4)2
(A=Rb, Cs; M=Sb, Bi),3 CS3Biz(PS4)3,3 Na0_16Bi1.2gP286,3 AzMP28e6 (A=K, Rb;
M=Mn, Fe),l A2M2P28e6 (A=K, Cs; M=Cu, Ag),1 KMPZSe6 (M=Sb, Bi),4
C53M4(P28e6)5 (M=Sb, Bi),5 APbPSe4,6 A4M(PSe4)2 (A=Rb, Cs; M=Pb, Eu),6
Rb4Tiz(P28e9)2(PZSe7),7 KTiPSe5,7 A5Sn(PSe5)3 (A=K, Rb),8 and A6Sn28e4(PSe5)2
(A=Rb, Cs).8 More recently, K2UP3Se9,9 and the K(RE)PZSC6 (RE=Y, La, Ce, Pr,

Gd)lo series were also reported. Extension of this chemistry to Au looked appealing

because no structurally characterized compounds have been reported. The only reported

61

62

compound is the ternary AuPS4,ll whose structure remains elusive. Based on vibrational
spectroscopy, a polymeric chain structure consisting of alternating edge-sharing PS4
tetrahedra and square AuS4 planes was proposed.

Here we report the synthesis, structural characterization, optical and thermal
properties of the new quaternary gold selenophosphate compounds, A3AuPZSe3 (A=K,
Rb, and Cs), AzAu2P28e6 (A=K, and Rb) and A2AuP28e6 (A=K, and Rb). Access to
each phase was achieved by modifying the flux basicity, by means of varying the amount

of AzQ and P2Q5 in the starting composition (see Syntheses).1. 6-9.12

2. Experimental Section

2.1. Reagents

The reagents mentioned in this study were used as obtained unless noted otherwise:
(i) Au metal (99.99%) was acquired from Liberty Coins, Lansing MI. (ii) phosphorus
pentasulfide (P285) 99.999% purity, Aldrich Chemical Co., Milwaukee, Wi.; (iii) red
phosphorus powder, Morton Thiokol, Inc., -100 mesh, Danvers, MA. (iv) cesium metal,
analytical reagent, Johnson Matthey/AESAR Group, Seabrook, NH; (v) rubidium metal,
analytical reagent, Johnson Matthey/AESAR Group, Seabrook, NH; (vi) potassium
metal, analytical reagent, Aldrich Chemical Co., Milwaukee, Wi.; (vii) sulfur powder,
sublimed, J .T. Baker Chemical Co., Phillipsburg, NJ; (viii) selenium powder, 99.5+%
purity -100 mesh, Aldrich Chemical Co., Inc., Milwaukee, Wi.; (ix) N,N-
Dimethylformalide (DMF) reagent grade, EM Science, Inc., Gibbstown, NJ .; (x) diethyl
ether, ACS anhydrous, EM Science, Inc., Gibbstown, NJ; (xi) Methanol (MeOH) ACS

anhydrous, EM Science, Inc., Gibbstown, NJ.

63
Finely divided Au metal. A Canadian Maple Leaf gold coin, (99.99%, 31.1g) was

dissolved in 400 ml of aqua regia (300 ml concentrated HCl and 100 ml concentrated
HNO3). The solution was boiled in an acid-resistant fume hood to a volume of
approximately 100 ml. The solution was neutralized with ammonium hydroxide and the
gold was reduced with excess hydrazine hydrochloride, dissolved in 100 ml of distilled
water. The resulting black suspension was gently heated, with stirring, for one hour to
allow particle aggregation. After filtering the suspension, and washing it with copious

amounts of distilled water and acetone, the resulting gold powder was heated in air for 2

hours at 200°C to drive off any remaining impurities, yielding 30.9g of Au powder. Note:

heating too long or at higher temperature results in impractical grain sizes.

2.2. Syntheses

AzQ (A=K, Rb, Cs; Q=S, Se) were prepared by reacting stoichiometric amounts

of the elements in liquid ammonia as described elsewhere.1a.2

P2Se5 The amorphous phosphorus selenide glass "P28e5", was prepared by

heating a stoichiometric ratio of the elements as described elsewhere.1
Preparation of K3AuP28e3 (I). A mixture of Au (0.3 mmol), P2Se5 (0.6

mmol), K2Se (1.2 mmol), and Se (3.0 mmol) was sealed under vacuum in a Pyrex tube

and heated to 4400C for 4d followed by cooling to 150°C at 40C h-l. The excess
Ax[PySez] flux was removed by washing with DMF to reveal analytically pure orange-
yellow plates (87% yield based on Au). The crystals are only stable for some days in air
and water. Microprobe analysis carried out on several randomly selected crystals gave an

average composition of K2.9AuP1,3Se3,1.

64
Preparation of Rb3AuP2Se3 (II). A mixture of Au (0.3 mmol), P2Se5 (0.6

mmol), RbZSe (1.2 mmol), and Se (3.0 mmol) was sealed under vacuum in a Pyrex tube
and heated as in (I). The flux was removed as in (I) to reveal analytically pure orange-
yellow plates (84% yield based on Au). The crystals are only stable for some days in air
and water. Microprobe analysis gave an average composition of Rb2,gAuP1_9Se7,9.

Preparation of CS3AuP2Se3 (III). A mixture of Au (0.3 mmol), P25e5 (0.6
mmol), CszSe (1.2 mmol), and Se (3.0 mmol) was sealed under vacuum in a Pyrex tube
and heated as in (I). The flux was removed as in (I) to reveal analytically pure orange-
yellow plates (81% yield based on Au). The crystals are stable in air and water (signs of
decomposition are apparent only after several weeks). Microprobe analysis gave an
average composition of C82,7AuP2,oSe3_o.

Preparation of KzAuzPZSeg (IV). KzAu2P28e6 was synthesized from a less

Lewis basic mixture, of Au (0.3 mmol), P28e5 (0.3 mmol), Kzse (0.33 mmol), and Se
(3.0 mmol) that was sealed under vacuum in a Pyrex tube and heated to 4600C for 4d

followed by cooling to 1500C at 40C h-l. The excess Ax[PySez] flux was removed as
above to reveal red rods (72% yield based on Au). The crystals are air- and water-stable.
Microprobe analysis gave an average composition of K1_7Au2_0P1.3Se6,2.

Preparation of szAu2P28e5 (V). szAu2P28e6 was also synthesized from
a less Lewis basic mixture, of Au (0.3 mmol), P2Se5 (0.3 mmol), RbQSe (0.33 mmol),
and Se (3.0 mmol) that was sealed under vacuum in a Pyrex tube and heated as in (IV).
The excess AxPySez flux was removed as above to reveal red rods (55% yield based on
Au). The crystals are air- and water-stable. Microprobe analysis gave an average
composition of Rb1,3Au2_oP1.7Se6,1.

Preparation of A2AuP2Se5 (VI). A2AuP28e6 (A=K,Rb) was synthesized

from a mixture of Au (0.3 mmol), P28e5(0.9 mmol), A25e (0.60 rmnol), and Se (3 mmol)

which was sealed under vacuum in a Pyrex tube and heated to 4900C for 4 (1, followed by

65
cooling to 150°C at 4 0C h-l. The excess A,(P),SeZ flux was removed with DMF. The

black, shiny, rod-like crystals are air- and water- stable (~90% yield based on Au).
Semiquantitative microprobe analysis on single crystals gave K2,1AuP1.3Se5_9 and

szAquSeaz (average on four data acquisitions).

2.3. Physical Measurements

Powder X-ray Diffraction. Analyses were performed using a calibrated Rigaku-
Denki/RW400F2 (Rotaflex) rotating anode powder diffractometer controlled by an IBM

computer, operating at 45 kW 100 mA and with a 10/min scan rate, employing Ni-filtered

Cu radiation in a Bragg-Brentano geometry. Powder patterns were calculated with the

CERIUS2 software.l3 Calculated and observed XRD patterns are deposited with the

Supplementary Material.
Infrared Spectroscopy. Infrared spectra, in the far-IR region (600-50 cm-l), were

recorded in 4 cm-1 resolution on a computer controlled Nicolet 750 Magna-IR Series II
spectrophotometer equipped with a TGS/PE detector and a silicon beam splitter . The

samples were ground with dry CsI into a fine powder and pressed into translucent pellets.

Raman Spectroscopy. Raman spectra, in the far-Raman region (700-100 cm-1 ),
were recorded on a BIO-RAD FT Raman spectrometer equipped with a Spectra-Physics
Topaz T10—106c 1.064 nm YAG laser, and a Ge detector. The samples were ground into a
fine powder and loaded into glass tubes.

Solid State U V/Vis/Near IR Spectroscopy. Optical diffuse reflectance
measurements were performed at room temperature using a Shimadzu UV-3101PC double
beam, double monochromator spectrophotometer. The instrument is equipped with an

integrating sphere and controlled by a personal computer. BaSO4 was used as a 100%

66

reflectance standard for all materials. Samples were prepared by grinding them to a fine
powder and spreading them on a compacted surface of the powdered standard material,
preloaded into a sample holder. The reflectance versus wavelength data generated were

used to estimate a material's band gap by converting reflectance to absorption data as

described earlier. 14

Differential Thermal Analysis (DTA). UI‘ A experiments were performed on a
computer-controlled Shimadzu DTA-50 thermal analyzer. Typically a sample (~ 25 mg) of
ground crystalline material was sealed in quartz ampoules under vacuum. A quartz

ampoule of equal mass filled with A1203 was sealed and placed on the reference side of the
detector. The samples were heated to the desired temperature at 10 0C/min, then

isothermed for 10 minutes and finally cooled to 50 0C at the same rate. Residues of the
DTA experiments were examined by X-ray powder diffraction. To evaluate congruent
melting we compared the X-ray powder diffraction patterns before and after the DTA
experiments. The stability/reproducibility of the samples were monitored by running
multiple heating/cooling cycles.

Semiquantitative microprobe analyses. The analyses were performed using a JEOL
JSM-6400V scanning electron microscope (SEM) equipped with a TN 5500 EDS detector.
Data acquisition was performed with an accelerating voltage of 20kV and thirty seconds
accumulation time.

Single crystal X-ray Crystallography. Intensity data were collected using a Rigaku
AFC6S four-circle automated diffractometer equipped with a graphite crystal
monochromator. Crystal stability was monitored with three standard reflections whose
intensities were checked every 150 reflections, and unless noted, no crystal decay was

detected in any of the compounds. The space groups were determined from systematic

absences and intensity statistics. An empirical absorption correction based on 11! scans was

applied to all data during initial stages of refinement. An empirical DIFABS correction was

67

applied as recommended15 after full isotropic refinement, after which full anisotropic

refinement was performed. The structures were solved by direct methods using SHELXS—
86 software16a (for all compounds), and full matrix least squares refinement was

performed using the TEXSAN software package16b. After full refinement the final R/Rw
for K3AuP2Se3 were 3.4/3.8%. Since the structure is non-centrosymmetric refinement was
attempted on the other enantiomorph which converged with R/Rw = 3.9/45%.
Accordingly, the first solution was retained. The K2Au2P28e6 crystal habit to grow as rods
that consist of very thin needles, complicated the selection of an appropriate single crystal.
The great majority of these crystals gave a=6.145(1)A, which is only half the correct
length. Long exposure axial photographs revealed weak spots indicating the presence of a
2xa supercell but the supercell reflections were too weak to collect. Consequently, many
crystals were tested (about 15), until one with strong enough reflections was discovered.
The complete data collection parameters and details of the structure solution and
refinement are given in Table 4-1. The coordinates of all atoms, average temperature
factors, anisotropic displacement parameters and their estimated standard deviations are

given in Tables 4-2 to 4-7.

68

Table 4-1. Crystallographic data for K3AuP25e3, K2Au2P28e6, szAUstefi

 

 

Formula K3Austeg KzAu2P2566 szAuPzSe6
FW 1007.89 1007.84 903.61
a, A 7.122 (2) 12.289 (2) 11.961 (2)
b. A 12.527 (3) 7.210(1) 10.069 (2)
c, A 18.666 (4) 8.107 (1 ) 32.137 (3)
01 (deg) 90.00 90.00 90.00
B(deg) 96.06 (2) 115.13 (1) 91.37(l)
y (deg) 90.00 90.00 90.00
2, V(A3) 4; 1655.9 (7) 2; 650.3 (2) 12; 3869(2)
A (Mo K01), A 0.71069 0.71069 0.71069
space group Ce (#9) C2/m (#12) P21/n (#14)
Dale, g/cm3 4.043 5.147 4.653
11’ cm-l 271.86 399.36 356.36
Temp (0C) 23 25 -120
Final R/Rw,a % 3.4/3.8 4.5/5.4 4.0/4.8
Total Data 1722 662 5724
Measured
Total Unique Data 1545 630 5419
(ave)
Data F02>30(F02) 927 443 3524
No. of Variables 126 33 289

Crystal Dimen.,
mm

0.49 x 0.42 x 0.25

0.39 x 0.28 x 0.17

9R = 2(1F01 - Inn/£11901. Rw = {£w(IF0l - IFC|)2/ZWIF0|2}1/2.

0.92 x 0.11 x 0.08

69

Table 4-2. Positional parameters and Beqa for K3AuP2Se8

 

 

Atom X Y Z B equZ
Au 1 0.0491(1) 1/2 218(5)
Se(1) 1.0751(5) 0.0041(3) 0.6258(2) 2.4(2)
Se(2) 1.4795(6) -0. 1416(3) 0.7198(2) 3.0(2)
Se(3) 1.5538(5) 0.0433(3) 0.5764(2) 2.7(2)
Se(4) 1.3189(5) -0.2216(3) 0.5597(2) 2.2(2)
Se(5) 1.2172(5) -O. 1695(3) 0.4415(2) 2.5(2)
Se(6) 1.2294(5) 0.3177(3) 0.4193(2) 2.5(2)
Se(7) 0.9173(5) 0.0907(3) 0.3742(2) 2.6(2)
Se(8) 1.3382(5) 0.1570(3) 0.7767(2) 2.6(2)
K( 1) 1.794(1) 0.1037(7) 0.7457(5) 3.7(4)
K(2) 1.307(1) 0.2752(7) 0.6039(5) 3.4(4)
K(3) 1.432(1) 0.0695(7) 0.3939(5) 3.2(4)
P( 1) 1.365(1) -0.0638(7) 0.6227(5) 1.9(3)
P(2) 0.951(1) 0.2681(7) 0.3767(4) 1.6(3)

a B values for anisotropically refined atoms are given in the form of the isotropic

equivalent displacement parameter defined as Baq = (4/3)[azB(1, 1) + bZB(2, 2) + czB(3,

3) + ab(cosy)B(1,2) + ac(cosB)B(1,3) + bc(cosot)B(2, 3)]

70

Table 4-3. Anisotropic Displacement Parameters for K3AuP28e3

 

 

Atom U1 1 U22 U33 U12 U13 U23
Au 0.0261(6) 0.0267(7) 0.0298(8) 0.0022(7) 0.0024(5) 0.0035(7)
Se( 1) 0.027(2) 0.037(2) 0.027(2) 0.008(2) 0.008(2) -0.001(2)
Se(2) 0.054(2) 0.038(2) 0.021(2) 0.010(2) -0.001(2) 0.004(2)
Se(3) 0.030(2) 0.038(2) 0.036(3) -0.007(2) 0.006(2) 0.005(2)
Se(4) 0.039(2) 0.019(2) 0.028(2) -0.001(2) 0.012(2) -0.001(2)
Se(5) 0.020(2) 0.039(2) 0.035(2) 0.006(2) -0.000( 1) -0.006(2)
Se(6) 0.025(2) 0.035(2) 0.036(2) -0.009(2) 0.001(2) 0.000(2)
Se(7) 0.041(2) 0.024(2) 0.032(2) -0.002(2) -0.001(2) -0.002(2)
Se( 8) 0.038(2) 0.034(2) 0.025( 2) 0.002( 2) -0.001(2) -0.004(2)
K( 1) 0.057(5) 0.052(5) 0.036(5) 0.002(4) 0.021(4) -0.002(4)
K(2) 0.044(5) 0.048(5) 0.037(5) 0.003(4) 0.001(4) 0.000(4)
K(3) 0.046(5) 0.042(5) 0.037(6) 0.002(4) 0.01 1(4) 0.003(4)
P( 1) 0.027(4) 0.023(5) 0.021(5) 0.003(4) 0.007(4) 0.001(4)
P(2) 0.022(4) 0.025(4) 0.013(5) -0.001 ( 3) -0.001(3) 0.000(4)

71

Table 4-4. Positional parameters and Beq for KzAu2P25e6

 

 

 

 

Atom X Y Z B eq )2
Au 0 0.2564(2) 0 l . 15(4)
Se(1) -0.2144(3) 0 0.1994(4) 1.7(1)
Se(2) 0.0727(2) 0.2531(3) 0.3262(3) 189(8)
P -0.0224(6) 0 0.350(1) 0.7(2)
K 0.2988(7) 0 0.260(1) 25(3)
Table 4-5. Anisotropic Displacement Parameters for K2Au2P28e6
Atom U1 1 U22 U33 U 12 U13 U23
Au 0.0146(6) 0.0163(7) 0.0134(6) 0 0.0065(4) 0
Se( 1) 0.008(2) 0.031(2) 0.021(1) 0 0.003(1) 0
Se(2) 0.037(1) 0.016(1) 0.017(1) -0.01 8( 1) 0.010(1) -0.002(1)
P 0.010(4) 0.007(4) 0.012(3) 0 0.006(3) 0
K 0.031(5) 0.038(5) 0.022(4) 0 0.007(3) 0

72

Table 4-6. Positional parameters and Beq for szAuP28e6

 

 

Atom X Y Z B eq A2
Au(1) 1/2 0 1/2 100(5)
Au(2) 0.65469(9) 0.0544(1) 0.41960(3) 207(5)
Au(3) 0.482050) 0.06017(9) 0.32786(2) 068(4)
Au(4) 0 1/2 1/2 052(5)
Rb(l) 0.2963(2) 0.5267(2) 0491030) 1.5(1)
Rb(2) 0.7987(2) 0.0448(2) 0322300) 1.5(1)
Rb(3) 0.7956(2) 0.9523(2) 0.51552(6) 1.4(1)
Rb(4) 0.7270(2) 0.5425(2) 0333670) 1.7(1)
Rb(S) 0.1721(2) 0.0549(3) 0330200) 1.8(1)
Rb(6) 0.2234(2) 0.5554(2) 0.32517(7) 1.5(1)
Se(1) 0.4901(2) 0.2383(2) 049976(7) 1.1(1)
Se(2) 0.7113(2) 0.8161(2) 0.41765(7) 1.3(1)
Se(3) 0.5212(2) 0.5305(2) 041541(7) 1.3( 1)
Se(4) 0.2500(2) 0.7777(2) 0.41389(7) 1.3(1)
Se(5) 0.4343(2) 0.0620(2) 0.40281(6) 0.9(1)
Se(6) 0.4618(2) 0.8155(2) 0.33174(6) 1.1(1)
Se(7) 0.5175(2) 0.0312(2) 0.25348(6) 1.1(1)
Se(8) 0.9968(2) 0.1971(2) 0.83341(6) 1.2(1)
Se(9) 0.9767(2) 0.7550(2) 0.33265(6) 1.0(1)
Se(10) 0.7360(2) 0.2895(2) 0.249190) 1.2(1)
Se(l 1) 0.0074(2) 0.0635(2) 0239260) 1.3(1)
Se(12) 0.2232(2) 0.8067(2) 0.24833(7) 1.5(1)
Se(13) 0.7466(2) 0.2688(2) 041901(7) ' 1.2(1)
Se(14) 0.9689(2) 0.0108(2) 0420180) 1.0(1)
Se(15) 0.9682(2) 0.2585(2) 0.50004(6) 0.9(1)
Se(16) 0.9778(2) 0.3372(2) 0.33409(6) 1.1(1)
Se(17) 0.9654(2) 0.5441(2) 0.42448(6) 1.0(1)
Se(18) 0.7978(2) 0.6879(2) 0.58835(7) 1.3(1)
P(l) 0.5484(5) 0.7316(6) 0.4337(2) 0.8(2)

P(2) 0.4121(5) 0.8410(6) 0.3974(2) 0.8(2)

P(3) 0.9328(5) 0.7358(6) 0.2675(2) 0.8(2)

P(4) 0.0543(5) 0.8604(6) 0.2318(2) 0.9(2)

9(5) 0.9221(5) 0.2121(6) 0.4335(2) 07(2)

P(6) 0.0288(5) 0.3508(6) 0.3983(2) 0.7(2)

73

Table 4-7. Anisotropic Displacement Parameters for szAuPzSe6

 

 

Atom U1 1 U22 U33 U12 U13 U23
Au( 1) 0.0128(7) 0.0127(7) 0.0125(7) 0.0017(6) 0.0002(5) -0.0029(5)
Au(2) 0.0292(6) 0.0265(6) 0.0233(5) -0.0107(5) 0.0000(4) 0.0001(5)
Au(3) 0.0097(5) 0.01 12(5) 0.0056(4) 0.0004(4) 0.0006(3) 0.0000(4)
Au(4) 0.0073(7) 0.0059(6) 0.0066(6) 0.0004(5) -0.0000(5) -0.0002(5)
Rb(l) 0.015(1) 0.019(1) 0.023(1) 0.001(1) 0.001(1) -0.001(1)
Rb(2) 0.019(1) 0.019(1) 0.020( 1) 0.000( 1) -0.001 (1 ) -0.004( 1)
Rb(3) 0.015(1) 0.021(1) 0.018(1) -0.000( 1) -0.003( 1) 0.000( 1)
Rb(4) 0.017(1) 0.023(1) 0.025(1) -0.002( 1) 0.004(1) 0.002(1)
Rb(5) 0.01 5( 1) 0.029(1) 0.024(1) 0.003(1) -0.005(1) -0.007( 1)
Rb(6) 0.020(1) 0.017(1) 0.021(1) 0.000( 1) 0.004(1) -0.001( 1)
Se(1) 0.020(1) 0.014(1) 0.009(1) 0.001(1) 0.001(1) -0.000(1)
Se(2) 0.009( 1) 0.021(1) 0.021(1) -0.000(1) 0.004(1) -0.001( 1)
Se(3) 0.020( 1) 0.008( 1) 0.021(1) 0.001(1) 0.003(1) -0.004(1)
Se(4) 0.009( 1) 0.017(1) 0.021(1) -0.001 ( 1) 0.001 (1 ) 0.002(1)
Se(5) 0.013(1) 0.012(1) 0.009( 1) 0.002( 1) 0.001(1) 0.000(1)
Se(6) 0.021(1) 0.012(1) 0.008( 1) -0.000( 1) 0.001 ( 1) -0.002(1)
Se(7) 0.020(1) 0.012(1) 0.008(1) 0.001( 1) 0.002( 1) -0.001( 1)
Se(8) 0.022(1) 0.013(1) 0.009( 1) 0.003(1) 0.000( 1) 0.002(1)
Se(9) 0.016(1) 0.015(1) 0.009( 1) 0.000( 1) -0.002( 1) -0.002( 1)
Se( 10) 0.007( 1) 0.021(1) 0.016( 1) 0.001(1) -0.002( 1) -0.001 ( 1)
Se(11) 0.019(1) 0.011(1) 0.018(1) 0.001(1) -0.002(1) 0.001(1)
Se( 12) 0.009(1) 0.023( 1) 0.025(1) 0.001(1) 0.002( 1) 0.009( 1)
Se( 13) 0.007( 1) 0.017(1) 0.023( 1) 0.002(1) -0.001(1) 0.000(1)
Se( 14) 0.013(1) 0.007(1) 0.019(1) 0.000( 1) -0.000(1) -0.001(1)
Se( 15) 0.01 8( 1) 0.008( 1) 0.009( 1) -0.003( 1) -0.000( 1) 0.000( 1)
Se(16) 0.016(1) 0.016(1) 0.008(1) 0.001(1) -0.001(1) -0.001(1)
Se(17) 0.019(1) 0.010(1) 0.009( 1) 0.002( 1) -0.003( 1) -0.000( 1)
Se(18) 0.010(1) 0.020( 1) 0.019(1) -0.002( 1) -0.001 ( 1) 0.002( 1)
P( 1) 0.011(3) 0.010(3) 0.009(3) 0.003(3) 0.003(2) 0.001(2)
P(2) 0.012(3) 0.010(3) 0.008(3) 0.004( 3) -0.001(2) 0.004(2)
P(3) 0.009(3) 0.012(3) 0.010(3) 0.001(3) -0.001(2) -0.003(2)
P(4) 0.009(3) 0.01 1(3) 0.016(3) -0.000(3) 0.002(2) 0.003(3)
P(5) 0.009(3) 0.012(3) 0.006(3) -0.002(3) 0.002(2) 0.002(2)
P(6) 0.008(3) 0.01 1(3) 0.008(3) -0.001(3) -0.002(2) 0.001(2)

74

3. Results and Discussion

3.1. Description of Structures

Structure of A3AuP2Se3. Compounds (I-IH) are isostructural but since the

single-crystal structure determination was performed on the K+ salt (I), the discussion will
refer mainly to this compound. The novel one-dimensional structure is shown in Figure 4-

1. The monovalent Au cation is linearly coordinated. This class of compounds expands the
repertoire of the (poly)selenophosphate ligands introducing the new [P2Se3]4- unit. To the
best of our knowledge, this is the first example of the [P2Se3]4- unit in a selenOphosphate
compound. The [P28e3]4- unit is formed by the condensation of two [PSe4]3- units

through the formation of a Se-Se bond. Kolis et al.17 have observed the related [P28e3]2-
which consists of a six membered P28e4 ring with each phosphorus atom containing two

terminal selenide atoms, see Scheme 1.

Scheme 1
Se Se
Se’ I!’\ / Tm” Se
Se—Se Se Se
Se—Se
\ P/ 39 se\ P',,...t\\\\ Se
\
P S 12- I 4 I Se
[ 2 68 39 [P2568] ' Se

The sulfur analog [P283]4- has been observed in the ternary thiophosphates PV231018 and

PNb2810.19 In those compounds the [P283]4- unit is coordinatively saturated, whereas in

75
([—111) only two coordination sites of the [P28e3]4- are utilized [Se(1), Se(7)] presumably

because of the low coordination preference of the gold centers. In this way, every

[PzSeg]4- group links two Au centers creating infinite zig-zag [AuP2Se3]n3n- chains. These
Chains run in [110] and [2b20] directions and are almost mutually perpendicular to each
other, in a criss-cross fashion, an unusual packing for 1-D compounds. Another
interesting feature of this arrangement is that it crystallizes in a polar non-centrosymmetric
Spacegroup which makes the compound a possible candidate for non-linear optical
measurements. The polarity of the structure can be easily seen by inspecting the
perpendicular chains in Figure 4-1, which in a projection resemble the letter "C". In the
same figure one can observe that all the "C"s face the same direction. The Au-Se distances
have an average distance of 2.418(4)A and compare very well with those found in
szAuP28e6,12 KAuSe5,208 and CsAuSe3,20b all featuring linearly coordinated Au+. The
P-Se distances range from 2.141(9) to 2.307(9)A with the terminal selenium atoms

displaying the shorter distances. The torsion angle around Se(4)-Se(5) is 117.1(3)0. The

[AuPZSe3]n3n- chains are separated by A+ ions that are located in three different sites. In
K3AuPZSeg, K(l) is coordinated by six Se atoms [range of K(l)—Se distances, 3.394(9)-
3.51(1)A; av. 3.462A], K(2) is also six-coordinate [3.45(1)-3.54(1)A; av. 3.484A], and
K(3) is seven-coordinate [3.424(9)-3.654(9)A; av. 3.520A]. Tables of selected distances
and angles for K3AuPZSe3 are given in Table 4-8.

Structure of AzAuzPZSeg. Compounds (IV) and (V) are isostructural but
since the single-crystal structure determination was performed on the K+ salt (IV), the
discussion will refer mainly to this compound. The one—dimensional structure is shown in
Figure 4-2, and Figure 4-3. The chains propagate along the [001] direction. The
monovalent Au is also linearly coordinated. The structure features the ethane like [P2Se6]4-

unit. The formation of the P-P bond reduces the oxidation state of the phosphorus from

P5+ (as observed in [P2Seg]4-) to P”. The presence of this unit was expected since low

76
flux basicity was used for the synthesis of A2Au2P2Se6. The [P28e6]4- adopts the

staggered conformation and employs four selenium atoms (two from each phosphorus) to

c: oordinate with four Au+ centers forming an interesting pseudo-cyclohexane ring in a chair

C: onfiguration as shown in Scheme 2. A similar, though rather distorted, ring conformation

has been observed for the molecular [Au2(WS4)2]2-.21

Scheme 2

Se2'" Au

 

 

 

 

 

PM

There is a crystallographic center of symmetry located in the middle of every P-P bond (P-
P distance is 2.25(l) A). The staggered conformation and the way the ligand coordinates
dictate the "staircase" chain propagation, see Figure 4-2. The Au-Au' distance in this ring is
3.697(3)A which does not indicate any significant interactions. The Au-Se(2) distance is

2.405(2)A and compares very well with those mentioned above. The P-Se(1) distance is

2.147(4)A, shorter than the P—Se(2) distance of 2.221(4)A. The [Au2P28e6]nZn- chains are

separated by six-coordinated A+ ions [for KzAuzPZSe6 range of K—Se distances, 3.413(9)-
3.640(7)A; av. 3566A]. Tables of selected distances and angles for K2Au2P28e6 are given
in Table 4-9.

Structure of AzAuP2Se6. A2AuP2Se6 is an unusual mixed-valent compound

which, as it will become clear below, can be written as A6Au11_5Au1111,5(P28e6)3. Views of

the structure along any axis give the impression of a three- or at least two— dimensional

77
material because of extensive overlap of the atoms, see Figure 4—4. The compound, in fact,

possesses unique chains with a complicated one-dimensional sinusoidal structure. The

chains feature the [P2Se6]4- group which acts as bridging multidentate ligand coordinating
to four different gold atoms, see Figure 4-5. Each chain possesses two different

crystallographic centers of symmetry residing in atoms Au(l) and Au(4). There are three

types of [P2Se6]4- ligands in the structure. Each type coordinates to one, two and three
metal centers respectively. The overall description of the one-dimensional structure can be
characterized as a sinusoidal backbone with side groups attached to it, as illustrated in

Figure 4-5. Atoms Au(l), Au(2) and Au(4) are part of the sinusoidal backbone, while

atom Au(3) and its associated [P2Se6]4- group involving atoms P(3) and P(4) make up the
side groups. Atoms Au(3) and Au(4) have square-planar geometries and are assigned an
oxidation state of +3. Atoms Au(l) and Au(2) are assigned an oxidation state of +1. The
trigonal coordination for Au(2) is rare for this element. The largest angle is Se(2)-Au(2)-
Se(13) at 137.16 deg, which is closer to the ideal 120 deg than to 180 deg, and supports
the description of distorted trigonal planar geometry rather than a linear geometry with a

2+1 interaction. The only chalcogenide compound, that we are aware of, with an ideal

trigonal coordination for gold is AAuTe(A=Na,K)22 [Au-Te distance 2.682(1)A].

The most unique feature of the structure is the presence in it of all the known
coordination environments for Au.23 The repeating unit, described above, gives rise to an
infinite chain which propagates in a zig-zag fashion along the [110] direction (Figure 4-5).
In addition, the packing of these chains creates channels running parallel to the b-axis
where the cations are residing (Figure 4—4). The Au-Se distance for Au(l)-Se(l) is
2.402(2)A which compares very well with those found in KAuSe5,20a and CsAuSe320b all
featuring linearly coordinated Au(I). Au-Se distances for the square planar Au(3) and Au(4)

average at 2.47(2)A and they are also in excellent agreement with those found in

K3AuSe13,9 Na3AuSe3,10 and AAuSezlo (A=Na, K) all featuring square planar Au(III).

78
The distorted trigonal geometry of Au(2) involves two similar distances [Se(2) 2.494(3)A,

Se(13) 2.423(3)A] and a longer one [Se(5) 2.680(2)A]. The phosphorus-selenium
distances range from 2.120(6) to 2.258(6)A, with the non-coordinated selenium atoms
(e.g. Se(3), Se(4), Se(9) etc.) displaying the shorter ones. The phosphorus-phosphorus
bonds range from 2.219(8)A in P(5)-P(6) to 2.267(8)A in P(l)-P(2). There are two
coordination environments for rubidium cations. One out of the six crystallographically
independent cations is eight-coordinate [Rb-Se mean=3.6(1)A] and five are nine-coordinate

[Rb-Se mean=3.7(1)A]. Tables of selected distances and angles for szAuP28e6 are given

in Table 4-10.

79

 

 

 

. O O
."4" .'%.4 .r’4
f' O I‘ O I‘, O
1 1 15
11' 11' ‘11
O O O
1 O 1 O 1 C
“J; ‘6: “J\
. Se(2) . .
O ) O .
Se(l
0 «e: 0 e: P“) O ne‘ 0
O; ‘ Se(3) O) Se(4) O; ‘
AU (2 (‘1 (.1
1’ Se(5) 1’ Se(6) . A”
9" P(2) €:‘. 1 ta“.
Se(7') Se(7)
O 0 Se(8)
.
'5
.‘
\{l
‘ .- o
C
b;— > a

 

Figure 4-1: ORTEP representation and labeling of K3AuPZSeg in a diagonal view.

Cations have been omitted for clarity. (80% probability ellipsoids).

79

 

 

- - -
0's.» o'er. . :
a ' 0 9 a 9
l 1
b b 8
‘\ ' ‘\ ' K '
o "= c : 4*

 

 

O Se(2) o o
O 1) O .
Se(
0 «e: 0 192 P0) 0 12‘- O
O; ‘ * Se(3)‘ Se(4) ‘ O; ‘
AU (.2 (.1 (A)
15 ' JD Se(6) ' ,0
:5 56(5) P(2) rat. 1 :e‘
Se(7') 56(7)
O
.
0'3
."
~11
‘6
O
o‘-
C
11 g
b: Ar 8

 

 

Figure 4-1: ORTEP representation and labeling of K3AuP28e3 in a diagonal view.
Cations have been omitted for clarity. (80% probability ellipsoids).

80

$29.96 $338

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81

 

Figure 4-3: View of a single [AungSe6]2n- chain.

82

 

     
      
 

€‘ . ‘ “
~15 9 g 7!:- "
i-i-Q'e-{g‘c-mej-
iimfi'k’euh g o .1,
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“ -"- ’ "2. ,, . ~
. “ZEB'sifit’rgtt‘g9‘a Q.
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.555
1111
1L.
(:3
a? -
ah‘ -7 i 3‘.
.‘q‘l"? Q :2 1 1"".
c "8.0 ‘etwy‘fi __ .1.“ - '2‘“.
' 9.9113. 8’: fiPM-‘l'iimN'
—.

Figure 4-4: The unit cell of A2AuP2Se6 looking down the b-axis. The packing of the

chains in the unit cell forms channels where the A+ cations are residing
(open ellipses). In the infinite part of the structure, gold is shown as octant
shaded ellipses, selenium as open ellipses and phosphorus as crossed
ellipses with no shading.

83

to
i
o
o

0

Au(4)

i. 9) Se (3 1. 5489‘ l
. C'. . Au(21)8.(1() (1 S)‘ 313(2) “36(6
0 I Au(1). Au(3) Se(7)
a 9 fl
.1 Se(2). ”90 Se(12)
O a" 3(1) Au(2) . t‘. O Se(9)
P(3)
. Se(13) Se(11)
Se(15). P
(6) .s
. Se(17') Se(16)
Slde group (O (. Se (17)
g 88( (18)

 

Se(15’) side group

  

'1
e
9;
0
. o
0
to

chain direction

Figure 4-5: View showing a section of the chain in A2AuPZSe6 with labeling

Table 4-8. Selected Distances (A) and Angles (deg) for K3AuP28e3

Se(1)-P(1)
Se(2)-P( 1)
Se(3)-P( 1)
Se(4)-P( l)
Se(5)-P(2)
Se(6)-P(2)
Se(7)-P(2)
Se(8)-P(2)

Se( 1 )-Au-Se(7)
Se(4)-Se(5)-P(2)
Se(5)-Se(4)—P( 1 )

Se(1)-P(1)-Se(2)
Se( 1 )—P( 1 )-Se( 3)
Se( 1 )-P( 1)-Se(4)
Se(2)-P( 1 )-Se( 3)
Se(2)-P(1)-Se(4)
Se(3)-P( 1 )-Se(4)

2.242(9)
2.141(9)
2.143(9)
2.307(9)
2.295(9)
2.150(8)
2.235(9)
2.165(9)

178.4(1)
103.5(3)
104.8(3)

l 14.8(4)
1 13.0(4)
104.8(3)
1 15.4(4)
93.6(3)
1 13.2(4)

84

Au-Se( 1 )
Au-Se(7')

Se(4)-Se(5)

Au-Se(1)-P( 1 )

Se(5)-P(2)-Se(6)
Se(5)-P(2)-Se(7)
Se(5)-P(2)-Se(8)
Se(6)-P(2)-Se(7)
Se(6)-P(2)-Se(8)
Se(7)-P(2)-Se( 8)

2.419(4)
2.417(4)

2.342(6)

100.0(3)

1 13.5(4)
105.5(4)
94.8(3)
1 12.8(4)
1 15.9(4)
1 12.6(4)

85

Table 4-9. Selected Distances (A) and Angles (deg) for K2Au2P28e6

Se(1)-P 2.147(8) Au-Se(2) 2.405(2)
Se(2)-P 2.221(4)
P-P' 2.25(1) Au-Au' 3.697(3)
Se(2)-Au-Se(2'") 178.9(1) Au-Se(2)-P 98.2( 2)
Se(1)-P-Se(2) 1 16.2(2) Se(1)-P-P' 108.8(4)

Se(2)-P-Se(2') 1 10.5(3) Se(2)-P-P' 101.5(3)

86

Table 4-10. Selected Distances (A) and Angles (deg) for szAuP2$e6

Au(1)-Se( 1 )
Au(2)-Se(2)
Au(2)-Se(5)
Au(2)-Se(13)
Au(3)-Se(5)
Au(3)-Se(6)
Au(3)-Se(7)
Au(3)-Se(8)
Au(4)-Se(15)
Au(4)-Se(17)
Se( 1 )-P( 1)
Se(2)-P( l )
Se(3)-P( 1 )
P( 1 )-P(2)
P(3)-P(4)
P(5¥P(6)

2.402(2)
2.494(3)
2.680(2)
2.423(3)
2.489(2)
2.479(3)
2.455(2)
2.457(3)
2.461(2)
2.492(2)
2.220(6)
2.197(6)
2.132(6)
2.267(8)
2.256(8)
2.219(8)

Se(1)-Au(l)-Se(l )
Se(2)-Au(2)-Se(5)
Se(2)-Au(2)-Se( l3)
Se(5)-Au(2)-Se( 13)
Se(5)-Au(3)—Se(6)
Se(5)-Au(3)-Se(8)
Se(6)-Au(3)-Se(7)
Se(7)-Au(3)-Se(8)
Se(15)-Au(4)-Se(17)
Se(15)-Au(4)-Se(17')

180.0(0)
106.78(8)
137.16(8)
1 1469(8)
8618(7)
8660(7)
87.14(7)
100.07(8)
9888(7)
8 l . 12(7)

87

3.2. Synthesis, Spectroscopy and Thermal Analysis

The syntheses were the result of redox reactions in which the metal is oxidized by
polychalcogenide ions in the Ax[Psz] flux. The Aun+ centers are then coordinated by the

highly charged [Psz]n- ligands. The molten polychaleophosphate flux method is very

effective for crystal growth in this system. The isolation of pure crystalline products is
facilitated by the flux solubility in aqueous and organic solvents. Good control of the Lewis

basicity of the flux can be achieved by means of varying the starting composition. Species

of either P5+ or P4+ can be stabilized which results in compounds with different [Psz]n-

Hgands.

Our studies with quaternary chalcophosphates provide enough examples for the
construction of Table 4-11 in which we summarize under what conditions each species is
stabilized. It is evident that there are differences between thio- and seleno-phosphates and

we will discuss each case separately. According to the table the most decisive factor
controlling the production of P5+ or P4+ species in the Se flux is the A28e content. Using
high A28e content (basic conditions), exclusively species with P5+ are formed. Lowering
the A28e content (lowering the basicity), favors the stabilization of P4+ species, and in
particular the [P28e6]4- ligand. The only exception is Ti which provides species with P5+

even under low basicity conditions,7 which might be an effect of the highly acidic Ti4+

cation. The exact influence of each transition metal in the flux on the oxidation state of
phosphorus is not understood yet. Attempts to synthesize the hypothetical AAUIIIPZSC6
were not successful and instead the mixed valent A2AuPZSe6 or the Au+ compounds
A2Au2P28e6 were obtained. In the present work basic conditions stabilize the [P28e3]4-

ligand and less basic conditions the [P28e6]4‘.

88
For the thiophosphates, a wide range of conditions result in the formation of

exclusively P5+ species. Low P285 concentrations favored the [PS4]3- unit'while high
concentration of P285 favored the [P287]4- unit. A review of the literature revealed only a
few structurally characterized quaternary alkali compounds featuring the [P286]4- unit. Of
these compounds, KMP2S6 (M = Mn, Fe)24 was synthesized by direct combination and
Nao,16Bil_23P2S63 which was produced in a molten thiophosphate flux. In the latter case
the use of the less basic Na+ counterion may be important for the stabilization of P4+.
Structurally, the seleno- and thio-phosphates possess differences due mainly to the
presence of different ligands. Nevertheless, the [AuPS4]n2n- anion25 is similar to the
[AuP2Se3]n3n- anion in (I-III), in that two oxidatively coupled [PQ4]3- units give a
[P2Q3]4- group. Even in this case, though there are other essential chemical differences
such as the metal/phosphorus ratio. When the same ligands and the same countercation are
present it is possible to synthesize isostructural compounds. The case of KTiPSe57 and

KTiPSs,26 represents a rare example where isostructural analogs of both S and Se analogs
are known.

The optical absorption properties of were evaluated by examining the solid-state
UV/vis diffuse reflectance and/or single crystal optical transmission spectra of the materials
(see Table 4-12). The spectra confirm the semiconducting nature of the materials by
revealing the presence of sharp optical gaps. The A3AuPZSe3 (A: K, Rb, Cs) compounds
exhibit steep absorption edges from which the band-gap, Eg, can be assessed at 2.14 eV
(1), 2.22 eV (11), and 2.24 eV (111), respectively. The band-gaps of AzAu2P28e6 (A: K,
Rb) are 1.93 eV (IV) and 1.95 eV (V), respectively. The energy-gap increases slightly with
the larger alkali cation size, as expected. Representative spectra for (I) and (IV) are given in
Figure 4-6. The solid-state UV/vis diffuse reflectance spectra of AzAuP2Se6 show sharp

optical gaps in the range of 1.1-1.2 eV.

89
The far-IR and Raman data were in good agreement and the results are surmnarized

in Table 4-13. The far-IR spectra of (1-111) display absorptions at ~437 and ~447 cm-1
which can be assigned to PSe4 stretching modesl»6 but also three more absorptions at
~50], ~490 and 376 cm-1 which should be of diagnostic value in distinguishing the
[P28e3]4- ligand from the [PSe4]3-. The infrared spectra of (IV -V) display absorptions at
~477, ~434, ~421, ~288, ~237, and ~227 cm-l characteristic for the [P28e6]4-
group.1.4.5,9»12 All compounds (I-VI) possess weak absorptions below 200 cm-1 which
probably are due to Au-Se vibrations. For (VI) a splitting of the peaks can be observed

which corresponds to the differently coordinated [P2Se6]4- groups. In particular, the (504,
490 cm“) vibrations which can be attributed to PSe3 stretching modes have counterparts at
(422, 411 cm’l) as well. Similarly, the medium absorbance at ~300 cm‘I which was
ascribed to an out-of—phase PSe3 mode has been split to one at 304 cm‘l and one at 294

cm‘l. A tentative assignment of the lower energy peaks (422, 411, 294 cm‘l) can be made
to the first [P2Se6]4- group that connects Au(l), Au(2) and Au(3) since its higher
connectivity would reduce the energy of the PSe3 stretching modes. The higher energy
absorbances should contain the stretching modes for the rest two kinds of [P28e6]4- which
possess lower connectivity.

The Raman spectra of (I-V) display absorptions in the 224-500 cm-1 that are

tentatively assigned to P-Se and the absorptions below 200 cm-] are assigned to Au-Se

stretching vibrations.

Differential thermal analysis (DTA) data, see Figure 4-7, followed by careful XRD

analysis of the residues, show that (I-III) melt congruently, at 442, 483 and 478°C,
respectively. Differential thermal analysis (DTA) shows that KzAuP28e6 and szAuP28e6

melt at 457 0C and 474 0C respectively. An interesting feature of the DTA is that the

90
compounds give two exothermic peaks upon cooling. For example, KzAuPZSe6 gives two

exothermic peaks at 451 0C and 426 0C. Upon two more heating and cooling cycles the
peaks remained unchanged and examination of the ingot with x-ray powder diffraction and

EDS analysis did not indicate any decomposition. The DTA of (IV-V) show a single

endothermic peak ~5170C but two exothermic peaks at ~474 and ~4320C appear upon

cooling Figure 4-8A. On subsequent heating, a second endothermic peak is observed at
~4530C (Figure 4-8B) while the 5170C endothermic peak shifts to 5020C and the

exothermic peak at 474 shifts to 4530C. Four additional cycles did not alter the position of

the peaks but the relative intensity of the two exothermic peaks was reversed (In each cycle

the sample was isothermed for 2 hours at 580°C). The last DTA cycle is given in Figure 4-
8C. Examination of the residue by powder XRD revealed that most of the compound had

undergone a phase transformation to K2AuPZSe6 according to the self-redox reaction of

Scheme 3.

Scheme 3

3K2AU|2P2866 ——-—> K5AU'1_5AU"|1'5(P2895)3 + 3AUO

The latter is a mixed valence compound that contains both Au+ and Au3+. This indicates

that A2Au2P2Se6 is unstable with respect to disproportionation of the Au+ oxidation state.

Table 4-12 summarizes the optical and melting point data for all compounds.

91

Table 4-11. Synthetic conditions for the different [PyQZP' units. (M = metal, AzQ = alkali chalcogenide)

 

 

Reactant Ratio Pn+ / ligands Temp. (0C) References
M / P28e5 / A28e / Se
1 / 1-3/ 1-2/ 10 134+ / 1P236614‘ 410-510 1, 4, 5, 9, 12, present work
1 I 1.5-2 / 3-4/ 10 P5+ / [p334]3-, [PSe5]3', 440-450 6,8, present work
1P236814'
1 /2-3 / 2 / 10 P5+ / [P28e7]4-, 490 7
[P259914'
M/P235/A28/S
1 / 1.5-3 / 2-4 / 4-12 P5+ / [1334133 [1323714 400-500 2. 3, 25
1 / 3 / 2 / 4 P4+ / [P286]4- 400 3

Table 4-12. Optical Band Gaps, Colors and Melting Point Data

 

 

Formula Eg, eV Color mp, oC
K 3AuP28e8 2.14 Yellow-orange 442
Rb3AuP2Se3 2.22 Yellow 483
CS3AuP2Se8 2.24 Yellow 478
K2Au2P28e6 1.93 Red 517a
szAuszSe6 1.95 Red 519a
szAuPzSe6 1.20 Black 474

a = incongruent melting

92

Table 4-13. Infrared Data for (I), (IV) and (VI) and Raman Data (cm' 1) for (I), and (IV)

 

 

 

K3AuPzSeg (I) K2AU2P2$C6 (IV) szAuPzSe6 (V1)
IR Raman IR Raman IR
499 499 499 504
489 477 490
445 446 459
435 433 434 437

391 424 422

374 374 41 l
260 288 304

225 237 225 294

227 192 227

160 147 214

93

 

  
 

 

 

 

 

 

6 t t 1 1 1 T
E
.E 5 d1- «:1-
D K2A U2P28 66 r
.d .'
E E =1.93 9V I ~.
v 4 '1'- g —> 5 uni-
“:a-‘s :
8 3 __ :1 K3AuP2S 98 ..
c : Eg=2.14 eV
.9. ; .—
0 1
8 :
i 1 -- .' --
m l
e
O L P 1 -.i JI i i ii
0 ‘1 2 3 4 5 6 7
Energy (eV)
Figure 4-6: Solid-state optical absorption spectra of K3AuP28e3 (I) and KzAuzPZSe6

(1V)

94

 

 

 

 

 

100 5 5 L ‘ .

4170 4830
80 d T r

exo
60 - "
> lendo

1 40 - -
20 4 b
0 -1 ..

-20 i 1 w‘ i r
0 100 200 300 400 500

Temperature (°C)

Figure 4-7: Typical DTA diagram for the A3AuP2Se3 phases (A=Rb)

 

 

 

 

 

 

10 5 ,__¢ 4;_, L
O A
X
” 432
T 0‘ 474 ’
-1o« -
>~
l 20" h
o sol .
'o 517
A
g ( )
-40 : t i :
100 zoo 300 400 soo 500

Temperature (”C)

10 i 5 5

 

endo <—— HV ——-> exo

 

 

 

-40 . t ‘

A
I '

100 200 300 400 500 600
Temperature (‘0)

 

20 e a e s
453

 

.2o«

-30 -I

.‘0 -4

endo <———- “V ———> exo

 

 

 

~50 : 4 : t
100 200 300 400 500 600
Temperature (°C)

 

Figure 4-8: (A) DTA diagram for KzAuzP28e5 (first cycle) (B) Second DTA cycle of
KzAuszSe6, showing two phases. (C) Third DTA cycle of K2Au2P28e6

96

4. Conclusions

In summary, the first selenophosphate gold compounds have been prepared in molten
polyselenophosphate Ax[PySez] fluxes. The structural diversity displayed in
chalcophosphate flux grown compounds is astonishing and is due mainly to the variety of
possible [Psz]n- groups and the large diversity of binding modes of each [Psz]n- group.
The fluxes provide a convenient entry into the hitherto unknown Au chemistry and
preliminary results indicate that the elusive ternary Au/P/Q (Q = S, Se) compounds can also
be synthesized and structurally characterized.27 At a constant temperature, control of flux
composition and basicity is key in controlling which [Psz]n- ligands will appear in the
compounds. This enables some degree of control on the reaction outcome, in the sense that
one can construct structures with preselected ligands. The final structure type is still
difficult to predict. Nevertheless, there are significant chemical differences between
thiophosphate and selenophosphate chemistry, and so both types of species should be
explored to better comprehend this interesting area of chemistry.

AzAuPZSe6 is the first one so far that stabilizes in its structure all possible
coordination environments for gold. Its unexpected structural characteristics provide a
stimulating example of the rich chemistry that becomes accessible with the use of the flux

method in various metal systems.

10.

ll.

12.

13.
14.

15.
l6.

17.

97

References

(a) McCarthy, T. J.; Kanatzidis, M. G. Inorg. Chem. 1995, 34, 1257-1267. (b)
Sutorik, A.; Kanatzidis, M. G. Progr. Inorg. Chem. 1995, 43, 151-265.

McCarthy, T. J.; Hogan, T.; Kannewurf, C. R.; Kanatzidis, M. G. Chem. Mater.
1994, 6, 1072-1079.

McCarthy, T. J.; Kanatzidis, M. G. J. Alloys Comp. 1996, 236, 70-85.

McCarthy, T. J.; Kanatzidis, M. G. J. Chem. Soc. Chem. Commun. 1994, 1089-
1090.

McCarthy, T. J.; Kanatzidis,M. G. Chem. Mater. 1993, 5, 1061-1063.

Chondroudis, K.; McCarthy, T. J.; Kanatzidis, M.G. Inorg. Chem. 1996, 35,
840-844.

Chondroudis, K.; Kanatzidis, M.G. Inorg. Chem. 1995, 34, 5401-5402.

Chondroudis, K.; Kanatzidis, M.G. J. Chem. Soc. Chem. Commun. 1996, 1371-
1372.

Chondroudis, K.; Kanatzidis, M.G. C. R. Acad. Sci. Paris, Series B, 1996. 322,
887-894.

(a) Chen, J. H; Dorhout, P. K. Inorg. Chem. 1995, 34, 5705-5706. (b) Chen, J .
H; Dorhout, P. K. Ostenson, J. E. Inorg. Chem. 1996, 35, 5627-5633.

Patzmann, U.; Brockner, W.; Cyvin, B. N.; Cyvin, S. J. Raman Spectroscopy,
1986, 17, 257-261.

Chondroudis, K.; McCarthy, T. J.; Kanatzidis, M.G. Inorg. Chem. 1996, 35,
3451-3452.

CERIUSZ, Version 1.6, Molecular Simulations Inc., Cambridge, England, 1994.

McCarthy, T. J.; Ngeyi, S.-P.; Liao J.-H.; DeGroot, D.; Hogan, T.; Kannewurf,
C. R.; Kanatzidis, M.G. Chem. Mater. 1993, 5, 331-340.

Walker, N.; Stuart, D. Acta Cryst., 1983, A39, 158.

(a) Sheldrick, G. M., in Crystallographic Computing 3 ; Sheldrick, G. M., Kruger,
C., Doddard, R., Eds.; Oxford University Press: Oxford, England, 1985, p. 175.
(b) Gilmore G. J., Appl. Cryst. ; 1984, 17, 42-46.

Zhao, J. ;Pennington, W. T.; Kolis, J. W. J. Chem. Soc. Chem. Commun.
1992, 265-266.

18.

19.

20.

21.

22.
23.

24

25

26.
27.

98

Brec, R.; Ouvrard, G.; Evain, M.; Grenouilleau, P.; Rouxel, J. J. Solid State
Chem. 1983, 47, 174-184.

Brec, R.; Grenouilleau, P.; Evain, M.; Rouxel, J. Rev. Chim. Miner. 1983, 20,
295-304.

(a) Y. Park, M. G. Kanatzidis, Angew. Chem. Int. Ed. Engl. 1990, 29, 914-915.
(b) Y. Park, Ph.D. Dissertation, Michigan State University, E. Lansing, MI, 1991.

Muller, A.; Dornfeld, H.; Henkel, G.; Krebs, B.; Viegers, M. P. A. Angew.
Chem. Int. Ed. Engl. 1978, 17, 52.

Bronger, W.; Kathage, U. J. Alloys Comp. 1992, 184, 87-94.

There is a high pressure metastable phase of CsAuI3 which, at 6.8 GPa and at 167
0C, was reported to have a cubic perovskite structure. This would imply that the

AuII coordination geometry would be octahedral, however, no refinement of the
diffraction data (powder XRD data) has been carried out and the possibility of local
displacements of the gold centers from the ideal octahedral pockets has not been
unambiguously eliminated. The related x-ray isomorphous compound
CSAUQfiBI'Zfi , also studied with powder diffraction, has too many vacancies to
allow one to unequivocally establish the true local coordination of gold. A full
single crystal crystallographic refinement is needed to establish the gold
coordination in these materials. (a) Kojima, N.; Hasegawa, M.; Kitagawa, T.;
Shimomura, O. J. Am. Chem. Soc. 1994, 116, 11368-11374. (b) Kitagawa, T.;
Kojima, N.; Matsushita, N .; Ban, T.; Tsujikawa, I. J. Chem. Soc. Dalton Trans.
1991, 3115-3119.

(a) Menzel, F.; Brockner, W; Carrillo-Cabrera, W.; von Sehnering, H.G. Z.
Anorg. Allg. Chem. 1994, 620 , 1081-1086. (b) Carrillo-Cabrera, W.;
Sabmannshausen, J.; von Schnering, H.G.; Menzel, F.; Brockner, W. Z. Anorg.
Allg Chem. 1994, 620 , 489-494.

Chondroudis, K.; Hanko, J. A.; Kanatzidis, M.G. Inorg. Chem. 1997, 36, 2623-
2632.

Do, J.; Lee, K.; Yun, H. J. Solid State Chem. 1996 125 , 30-36.
Chondroudis, K.; Hanko, J .A.; Kanatzidis, M.G. Work in progress.

CHAPTER 5

Group-10 and 12 One-Dimensional Selenodiphosphates: A2MP2Se6 (A=K, Rb, Cs;
M=Pd, Zn, Cd, Hg) and the Novel, Tetranuclear, Cluster Anions [M4(Se2)2(PSe4)4]8-

(M=Cd, Hg) with a Stellane-like core

1. Introduction

Recently, there has been a resurgence of polychalcophosphate chemistry through
the use of melting fluxes and has led to many new ternary and quaternary chalcophosphate
compounds.1 The Ax[Psz] (Q = S, Se) fluxes provide various [Psz]n- anions which, in
the presence of metal ions, coordinate to give interesting new solid-state or molecular
materials. Many unusual compounds containing main group,2 transition metals,3

lanthanides and actinidesZC. 2f. 4 have been reported. We have now examined the reactivity
of group-10 and 12 metals in these melts and have already reported on the palladium
compounds A4Pd(PQ4)2 (A=K, Cs; Q=S, Se), CsloPd(PSe4)4, KPdPS4, and
KdeP286.3g Herein, we report the synthesis, structure, optical and thermal properties of
the one-dimensional selenodiphosphates CsdePZSe6 (1),3g K2ZnP28e6 (2), K2CdP28e6
(3), Rb2CdP28e6 (4), CsszPZSe6 (5), KzHgPZSe6 (6), and szHngSe6 (7 ) and of
the tetranuclear, stellane-like Rbng4(Se2)2(PSe4)4 (8) and RbgHg4(Se2)2(PSe4)4 (9)

complexes. Single-crystal X-ray diffraction analysis was performed for compounds (1),

(4), (6) and (9) representing the three different structure types.

99

100

2. Experimental Section

2.1. Reagents

The reagents mentioned in this study were used as obtained unless noted otherwise:
(i) Metals (99.99%) were acquired from Johnson Matthey/AESAR Group, Seabrook, NH;
(ii) red phosphorus powder, Morton Thiokol, Inc., -100 mesh, Danvers, MA. (iii) cesium
metal, analytical reagent, Johnson Matthey/AESAR Group, Seabrook, NH; (iv) rubidium
metal, analytical reagent, Johnson Matthey/AESAR Group, Seabrook, NH; (v) potassium
metal, analytical reagent, Aldrich Chemical Co., Milwaukee, Wi.; (vi) selenium powder,
99.5+% purity -100 mesh, Aldrich Chemical Co., Inc., Milwaukee, Wi.; (vii) N,N-
Dimethylforrnalide (DMF) reagent grade, EM Science, Inc., Gibbstown, NJ .; (viii)
diethyl ether, ACS anhydrous, EM Science, Inc., Gibbstown, NJ

2.2. Syntheses

AzQ (A=K, Rb, Cs; Q=S, Se) were prepared by reacting stoichiometric amounts

of the elements in liquid ammonia as described elsewhere.2

stes The amorphous phosphorus selenide glass "PZSes", was prepared by

heating a stoichiometric ratio of the elements as described elsewhere.2
Preparation of CsdeP28e6 (1). Method (A): A mixture of Pd (0.25

mmol), P28e5 (0.50 mmol), Cszse (0.75 mmol), and Se (2.50 mmol) was sealed under

vacuum in a Pyrex tube and heated to 490 0C for 4 d followed by cooling to 150 0C at 2 OC

101

h'l. Most of the excess CsxPySeZ flux was removed with degassed DMF. Following that,
the product was washed with ~2 ml of tri-n-butyl phosphine to remove residual elemental
Se. Further washing with anhydrous ether revealed black, irregular, rodlike crystals
(~60%) and residual flux in a form of gray powder (~40%). Method (B): Pure material

was obtained from a mixture of CsloPd(PSe4)4 (0.2 mmol), Pd (0.8 mmol), P (1.2 mmol)
and Se (2.8 mmol) that was sealed under vacuum in a Pyrex tube and heated to 480 0C for

4 d followed by cooling to 150 0C at 2 0C h]. Washings with DMF, tri-n-butyl phosphine,
and ether revealed analytically pure crystals of (I). The crystals are air- and water- stable.
Microprobe analysis with a scanning electron microscope (SEM), performed on a large
number of single crystals gave an average composition of Cs1_3PdP2.oSe5_9

Preparation of KZZnP28e5 (2). A mixture of Zn (0.25 mmol), P28e5 (0.75

mmol), Kzse (1.00 mmol), and Se (2.50 mmol) was sealed under vacuum in a Pyrex tube

and heated to 500 0C for 4 (1 followed by cooling to 150 0C at 2 OC h-l. Most of the excess
KxPySex flux was removed with degassed DMF. The product was then washed with ~2 ml
of tri-n-butyl to remove elemental Se. Further washing with anhydrous ether revealed an
intimate mixture of yellow microcrystals (~70%) and residual flux in a form of gray
powder (~30%). The crystals are air- and water- stable. Microprobe analysis with a
scanning electron microscope (SEM), performed on a large number of single crystals gave
an average composition of KZJZnPZJSesg.

Preparation of Kszste6 (3). A mixture of Cd (0.25 mmol), P28e5 (0.75
mmol), K28e (1.00 mmol), and Se (2.50 mmol) was prepared as above and heated with
the same heating profile. Isolation as in (2) revealed dark yellow, rod-like crystals that are
air- and water- stable (Yield ~65% based on Cd). Microprobe analysis gave an average
composition of K1,9CdP2.ZSe6_o.

Preparation of szCdPZSeg (4). A mixture of Cd (0.25 mmol), P28e5 (0.75

mmol), RbZSe (1.00 mmol), and Se (2.50 mmol) was prepared as above and heated with

102
the same heating profile. Isolation as in (2) revealed dark yellow, rod-like crystals (1-2

m) that are air- and water- stable (Yield ~75% based on Cd). Microprobe analysis gave an
average composition of Rb2.2CdP2_OSe6,1.

Preparation of CsszP2$e6 (5). A mixture of Cd (0.25 mmol), P28e5 (0.75
mmol), C528e (0.50 mmol), and Se (2.50 mmol) was prepared as above and heated with
the same heating profile. Isolation as in (2) revealed yellow, rod-like crystals that are air-
and water- stable (Yield ~69% based on Cd). Microprobe analysis gave an average
composition of CszoCsz. 1 Se5,9.

Preparation of K2HgP28e5 (6). A mixture of HgSe (0.25 mmol), P28e5
(0.75 mmol), K2Se (1.00 mmol), and Se (2.50 mmol) was prepared as above and heated
with the same heating profile. Isolation as in (2) revealed dark yellow, rod-like crystals
that are air- and water— stable (Yield ~79% based on Hg). Microprobe analysis gave an
average composition of K1.9HgP2.1Se5.3.

Preparation of RbZHngseg (7). A mixture of HgSe (0.25 mmol), P25e5
(0.75 mmol), szse (0.50 mmol), and Se (2.50 mmol) was prepared as above and heated
with the same heating profile. Isolation as in (2) revealed dark yellow, rod-like crystals
that are air- and water- stable (Yield ~74% based on Hg). Microprobe analysis gave an
average composition of Rb1.9HgP1,3Se6,o.

Preparation of Rbng4(Se2)2(PSe4)4 (8). Rbng4(Se2)2(PSe4)4 was

synthesized from a mixture of Cd (0.25 mmol), PZSe5 (0.50 mmol), szse (1.00 mmol),

and Se (2.50 mmol) heated to 550 0C for 4 d followed by cooling to 150 0C at 2 0C h-1.
Most of the excess bePySez flux was removed with degassed DMF. Following that, the
product was washed with ~2 ml of tri-n-butyl phosphine to remove residual Se. Further
washing with anhydrous ether revealed light yellow, needle-like crystals that are air-stable

but sensitive in H20. (Yield ~66% based on Cd). Microprobe analysis gave an average

103
composition of Rbg_0Cd4,0P4.4Se19.6. Cell data at 23cc ; a=b=17.564(3)A, c=7.275(2)A,

V=2244.3(8)A3.
Preparation of RbgHg4(Se2)2(PSe4)4 (9). RbgHg4(Se2)2(PSe4)4 was

synthesized from a mixture of HgSe (0.50 mmol), P28e5 (0.25 mmol), Rb28e (1.00
mmol), and Se (2.50 mmol) heated to 500 0C for 4 (1 followed by cooling to 150 0C at 2

oC h-l. Isolation as in (8) revealed light yellow, needle-like crystals that are air-stable but

sensitive in H20. (Yield ~78% based on Hg).

2.3. Physical Measurements

Powder X-ray Diflraction. Analyses were performed using a calibrated Rigaku-
Denki/RW400F2 (Rotaflex) rotating anode powder diffractometer controlled by an IBM

computer, operating at 45 kW 100 mA and with a lO/min scan rate, employing Ni-filtered

Cu radiation. Samples are ground to a fine powder and mounted by spreading the sample

onto a special etched-glass holder. Powder patterns were calculated with the CERIUSTM
molecular modeling program by Molecular Simulations Inc., St. John's Innovation Centre,
Cambridge, England. Calculated and observed XRD patterns are deposited with the
Supplementary Material.

Infrared spectroscopy. Infrared spectra, in the far-IR region (600-50 cm-l), were

recorded on a computer controlled Nicolet 750 Magna-IR Series II spectrophotometer

equipped with a TGS/PE detector and silicon beam splitter spectrophotometer in 4 cm-1
resolution. The samples were ground with dry CsI into a fine powder and pressed into
translucent pellets. For air sensitive compounds, samples were prepared in an N2 filled

glove box and pressed into a pellet immediately upon removal.

104
Solid state U V/Vis/Near IR spectroscopy. Optical diffuse reflectance

measurements were performed at room temperature using a Shimadzu UV-3101PC double
beam, double monochromator spectrophotometer. The instrument is equipped with
integrating sphere and controlled by a personal computer. BaSO4 was used as a 100%
reflectance standard for all materials. Samples are prepared by grinding them to a fine
powder and spreading them on a compacted surface of the powdered standard material,
preloaded into a sample holder. The reflectance versus wavelength data generated can be

used to estimate a material's band gap by converting reflectance to absorption data as

described earlier.5

Single crystal optical transmission. Room temperature single crystal optical
transmission spectra were obtained on a Hitachi U-6000 Microscopic FT
Spectrophotometer mounted on an Olympus BH2-UMA metallurgical microscope over a
range of 380 to 900 nm. Crystals lying on a glass slide were positioned over the light
source and the transmitted light was detected from above.

Diflerential thermal analysis (DTA). DTA experiments were performed as

described elsewhere.2 The residue of the DTA experiment was examined by X-ray powder
diffraction. To evaluate congruent melting we compared the X-ray powder diffraction
patterns before and after the DTA experiments, as well as monitored the
stability/reproducibility of the DTA diagrams upon cycling the above conditions at least two
times.

Semiquantitative microprobe analyses. The analyses were performed using a JEOL
JSM-6400V scanning electron microscope (SEM) equipped with a TN 5500 EDS detector.
Data acquisition was performed with an accelerating voltage of 20kV and a thirty second
accumulation time.

Single crystal X-ray crystallography. Intensity data for (4) and (6) were collected
using a Rigaku AFC6S four-circle automated diffractometer equipped with a graphite

crystal monochromator. An w-2q scan mode was used. Crystal stability was monitored

105
with three standard reflections whose intensities were checked every 150 reflections. No

crystal decay was detected in any of the compounds. A Siemens SMART Platform CCD
diffractometer was used to collect a hemisphere of data for (1) using 35 sec frames

(detector to crystal distance was 5 cm). The space groups were determined from systematic

absences and intensity statistics. For (1) an empirical absorption correction621 was applied
to the data. In this compound the presence of a structural disorder, along with the relatively
high thermal parameters of the atoms prompted us to search for a superstructure.
Investigations with long frame data collection on a SMART CCD diffractometer, and by
long exposure axial photographs on a Rigaku AFC6S four-circle diffractometer, did not
reveal any superstructure reflections. For (4) and (6) an empirical absorption correction
based on y scans was applied to all data during initial stages of refinement. An empirical

DIFABS correction was applied to (4) and (6) after full isotropic refinement as
recommendedfib A full anisotropic refinement was then performed. The structures were
solved by direct methods using SHELXS—86 software7a (for all compounds), and refined

with full matrix least squares techniques available in the TEXSAN software package.7b
Crystallographic information for the compounds are given in Table 5-1. The coordinates of
all atoms, average temperature factors, anisotropic displacement parameters and their

estimated standard deviations are given in Tables 5-2 to 5-9.

106

Table 5-1. Crystallographic data for CsdePZSe6, szCdP28e6, KzHngSe6, and RbgHg4(Se2)2(PSe4)4

 

 

Formula CsdeP28e6 szCdP25e6 KzHgP28e6 RbgHg4(Se2)2(PSe4)4
FW 907.92 819.05 814.49 3189.20
a, A 12.9750(4) 6.640(1) 13.031(2) 17.654 (2)
b, A 8.3282(2) 12.729(2) 7.308(2) 17.654 (2)
c, A 13.05680 ) 7.778(1) l4.l67(2) 7.226 (2)
or (deg) 90.0 90.0 90.0 90.0
[3 (deg) 102.940(2) 9824(1) 1 10.63( 1) 90.0
7 (deg) 90.0 90.0 90.0 90.0
2, V(A3) 4; 1375.07(5) 2; 650.6(2) 4; 1262.6(4) 2; 2253.6 (9)
2. (Mo Kat), A 0.71073 0.71069 0.71069 0.71069
space group C2/c (#15) P21/n (#14) P21/n (#14) P42/n (#86)
Dcalo g/cm3 4.385 4.180 4.285 4.699
11, cm-1 226.37 257.18 301.77 380.81
Temp (0C) - 141 26 23 26
Final R/Rw’a % 6.7/7.5 3.7/4.9 5.6/7.1 4.0/4.9
Total Data 3029 1307 3233 1874
Measured
Total Unique Data 1072 1201 3096 1850
(ave)
Data F02>30(F02) 650 583 2224 1254
No. of Variables 80 53 100 82

Crystal Dimen., 0.50 x 0.2] x 0.08

mm

0.70 x 0.28 x 0.22 0.56x0.32x0.10

are = £(lFol — men/21m, R,,. = {ZWUFOI - IFCI)2/2wlFol2 } 1/2.

0.40 x 0.06 x 0.06

107

Table 5-2. Positional parameters and Beqa for CsdePZSe6

 

 

Atom X Y Z B equ2
Cs 0.8679(1) 0.1740(2) 0.3662(1) 4.32(5)
Pd 1.0000 -0.5000 0.5000 502(8)

Se(1) 0.8888(2) -0.4697(3) 0.6276(2) 4.32(7)

Se(2) 1.1278(2) -0.0682(3) 0.3596(2) 395(7)

Se(3) 0.8763(2) 0.3134(4) 0.3882(2) 4.58(7)

p(1)b 0.912(2) -0.293(3) 0.226(2) 3.7(6)

P(2)b 1.031(2) -0.289(3) 0.338(2) 3.7(7)

p(3)b 1.028(2) 0.404(3) 0.715(2) 2.5(6)

P(4)b 1.026(2) -0. 182(3) 0.226(2) 2.5(6)

a B values for anisotropically refined atoms are given in the form of the isotropic
equivalent displacement parameter defined as Beq = (4/3)[aZB(1, l) + bZB(2, 2) + czB(3,
3) + ab(cosy)B(1,2) + ac(cosB)B(1,3) + bc(cosa)B(2, 3)]

b The occupancy factor of these atoms is 0.25 out of a maximum possible 1.00

Table 5-3. Anisotropic Displacement Parameters for Csdeste6

 

 

Atom U1 1 U22 U33 U12 U13 U23

C 8 0.058(1) 0.061(1) 0.045(1) -0.0165(9) 0.0129(9) -0.0102(8)

Pd 0.018(2) 0.054(2) 0.1 12(3) 0.003(1) 0.001(2) 0.043(2)
Se(1) 0.033(2) 0.050(2) 0.073(2) 0.013(1) -0.007( 1) 0.004(1)
Se(2) 0.058(2) 0.048(2) 0.038(2) -0.019(1) -0.001(1) -0.008( 1)
Se(3) 0.039(2) 0.075(2) 0.065(2) 0.008(2) 0.022(1) -0.013( 1)
P( l) 0.02(2) 006(2) 006(2) 001(1) 000(1) -0.01(2)
P(2) 004(2) 005(2) 005(2) -0.02(2) 002(2) -0.01(2)
P(3) 0.03(1) 004(1) 0.03( 1) 001(1) 001(1) 0.02( 1)
P(4) 001(2) 004(1) 005(2) 000(1) 000(1) -0.02( l)

108

Table 5-4. Positional parameters and Beq for szCdPZSe6

 

 

 

 

Atom X Y Z B eq A2

Cd 1/2 0 1/2 248(7)

Rb 0.2579(3) 0.1784(1) -0.021 1(2) 320(7)

Se(1) 0.2105(2) 0.1785(1) 0.4543(2) 2.16(7)

Se(2) 0.1916(2) -0.0701( 1 ) 0.2364(2) l.87(6)

Se(3) 0.2176(2) 0.4256(1) 0.7467(2) 203(7)

P 0.0237(5) 0.0404(3) 0.3753(5) 1.1(1)

Table 5-5. Anisotropic Displacement Parameters for szCdPZSe6
Atom U1 1 U22 U33 U12 U13 U23
Cd 0.0196(7) 0.047(1) 0.028(1) -0.0009(7) 0.0039(7) 0.0049(9)
Rb 0.049(1) 0.032(1) 0.038(1) -0.0153(8) -0.0030(8) 0.0049(8)
Se( 1) 0.0285(8) 0.01 18(8) 0.043(1) 0.0060(6) 0.0092(7) -0.0010(7)
Se(2) 0.0242(8) 0.029(1) 0.0193(9) 0.0014(6) 0.0074(6) -0.0097(7)
Se(3) 0.0238(8) 0.035(1) 0.0176(9) -0.0064(6) -0.0006(6) -0.0077(7)
P 0.017(2) 0.012(2) 0.013(2) 0.001(1) 0.005(1) 0.001(1)

109

Table 5-6. Positional parameters and Beq for KzHgPZSe6

 

 

 

 

Atom X Y Z B eq A2
Hg 0.74271(5) 0.10675(9) 0.97753(6) 2.14(3)
Se(1) 0.5991(1) 0.3313(2) 1.0002(1) 1.51(5)
Se(2) 0.6195(2) 0.01 14(2) 1.2039(1) 2.60(7)
Se(3) 0.6412(1) -0.2206(2) 0.9461(1) 1.74(6)
Se(4) 0.9084(1) 0.01 12(3) 1.1473(1) 224(6)
Se(5) 0.8421(1) 0.1884(2) 0.8511(1) l.87(6)
Se(6) 0.8865(1) -0.3021(2) 0.8955(2) 2.38(7)
K( 1) 0.6013(4) -0.0524(7) 0.7152(3) 3.9(2)
K(2) 1.1017(4) 0.0376(7) 1.3784(4) 4.1(2)
P( 1) 0.5192(3) 0.1120(5) 1.0592(3) 1.3(1)
P(2) 1.0389(3) 0.0360(5) 1.0829(3) 14( 1)
Table 5—7. Anisotropic Displacement Parameters for KzHgPZSeé
Atom U1 1 U22 U33 U 12 U13 U23
Hg 0.0245(3) 0.0274(3) 0.0308(5) 0.0006(2) 0.01 14(3) -0.0029(3)
Se( 1) 0.0232(7) 0.0142(6) 0.019(1) -0.0004(5) 0.0067(7) 0.0017(6)
Se(2) 0.041(1) 0.035(1) 0.01 1(1) 0.0044(8) -0.0058(8) 0.0047(8)
Se(3) 0.0260(8) 0.0162(7) 0.024(1) 0.0004(6) 0.0091(7) -0.0006(7)
Se(4) 0.0266(8) 0.051(1) 0.0084(9) 0.0014(7) 0.0069(7) -0.0015(8)
Se(5) 0.0256(8) 0.0268(8) 0.0164(9) 0.0023(6) 0.0046(7) 0.0078(7)
Se(6) 0.037(1) 0.0256(9) 0.026(1) -0.0053(7) 0.0091(8) -0.0100(8)
K( 1) 0.070(3) 0.056(3) 0.014(2) -0.026(2) 0.005( 2) -0.001(2)
K(2) 0.064(3) 0.055(3) 0.030(3) -0.004(2) 0.007(2) -0.008(2)
P( 1) 0.022(2) 0.014(2) 0.01 1(2) -0.002( 1) 0.004(2) -0.000(2)
P(2) 0.022(2) 0.024(2) 0.005(2) -0.000( 1) 0.003(2) -0.002(2)

Table 5-8. Positional parameters and Beq for RbgHg4(Se2)2(PSe4)4

110

 

 

Atom X Y Z B eq A2
Hg 0.62018(4) 0.68764(4) 0.2265(1) 2.12(3)
Rb(l) 0.5764(1) 0.6044(1) 0.2685(3) 270(9)
Rb(2) 0.6307(2) 0.3384(1) —0.2368(4) 4.6( 1)
Se(1) 0.3799(1) 0.6341(1) -0.2782(3) 2.9(1)
Se(2) 0.5178(1) 0.7706(1) 0.0333(3) 2.4(1)
Se(3) 0.7140(1) 0.4958(1) -0.0310(3) 2.4( 1)
Se(4) 0.5522(1) 0.5557(1) 0.2435(3) 215(8)
Se(5) 0.7395(1) 0.6824(1) -0.0122(3) 1.77(8)
P 0.3445(3) 0.5175(3) 0.2333(7) 1.6(2)

Table 5-9. Anisotropic Displacement Parameters for RbgHg4(Sc2)2(PSe4)4

 

 

Atom U1 1 U22 U33 U12 U13 U23
Hg 0.0262(4) 0.0256(4) 0.0288(5) 0.0000(3) 0.0007(4) -0.0028(4)
Rb( 1) 0.036(1) 0.037( 1) 0.030(1) -0.0028(8) -0.001(1) -0.000( 1)
Rb(2) 0.071 (2) 0.051(1) 0.053(2) -0.019( 1) -0.003(2) -0.0l 1(1)
Se( 1) 0.039(1) 0.023(1) 0.047(1) -0.0077(9) -0.003( 1) 0.004(1)
Se(2) 0.042( 1) 0.032(1) 0.019(1) 0.004(1) -0.000( 1) -0.005( 1)
Se(3) 0.034(1) 0.034(1) 0.024(1) -0.002(1) 0.009( 1) 0.000(1)
Se(4) 0.0202(9) 0.024(1) 0.037( 1) -0.0004(8) 0.001(1) -0.002( 1)
Se(5) 0.025(1) 0.026(1) 0.016(1) -0.0017(8) -0.0001(8) -0.0025(8)
P 0.022(2) 0.023(2) 0.016(3) -0.002(2) -0.001(2) 0.001(2)

111

3. Results and Discussion

3.1. Description of Structures

The compounds (1)-(7) belong to the A2MP2Q6 (A=K, Rb, Cs; M=Mn, Fe; Q=S,
Se) family of compounds that was observed during studies with the transition metals.3a. 3
In addition to this structure type, in this work, we encountered two new very closely
related types, namely that of CsdePzSe6 and KzHgP28e6.

Structure of Cs 2PdP 28 e6. (1) has the one-dimensional structure shown in
Figure 5-1A. The structure features the [P28e6]4- group which acts as bridging multidentate

ligand coordinating to the square planar Pd2+ atoms, utilizing four out of the six possible
coordination sites. The chains propagate in the [001] direction. The phosphorus positions
were found to be disordered inside the essentially fixed Se octahedral pocket adopting four
different orientations [P(l)-P(1), P(2)-P(2), P(3)-P(4) x 2], see Figure 5-lB. Each P-P
pair is oriented in such a way that a) it is perpendicular to opposite faces of the octahedron;
and b) the center of the Se octahedron is located in the middle of the P-P bonds. This
disorder most probably arises from the fact that there is no energetically favored orientation

for the P-P pairs, since the Se octahedron is close to ideal.

The staggered conformation of the ethane-like [P28e6]4- cause the neighboring square

planar Pd2+ atoms to rotate their plane in respect with each other. Nevertheless, the Pd

atoms are aligned parallel to the c-axis. The Pd-Se distances average at 2.466(7)A and they
are in good agreement with those found in other polyselenides with square planar Pd2+ like

CS4Pd(PSe4)2,3g CsloPd(PSe4)4,3g and K2[PdSe10].9 The P-P distances average at

2.212(5)A. The [PdPZSe6]n2"- chains are separated by nine-coordinate Cs+ ions [range of

112
Cs-Se distances, 3.590(2)-4.080(3)A; av 3.890A]. Selected bond distances and angles for

(l) are given in Table 5-10.
Structure of szCszseg. The compounds (2)-(S) have one-dimensional

chains propagating down the [100] direction, as shown in Figure 5-2. They also feature the
[P28e6]4- group which coordinates to the octahedral M2+ atoms. Zinc and cadmium adopt
octahedral coordination which is rare for these two elements,10 although octahedral
coordination is observed in the ternary M2P286 (M=Zn, Cd).11»12 Compounds (2)-(5)
are isostructural to A2MPZSe6 (A=K, Rb; M=Mn, Fe),3a which is closely related to the

TiI3 type (Ti216 by doubling the formula). The [MPZSe6]n2n- anion can be viewed as an

ordered substitution of the Ti atoms by M and P-P pairs, and of the I atoms by Se. Both the

M2+ ion and the P-P pairs reside in Se octahedra that share opposite faces. The M
octahedra are fully eclipsed when viewed along the chain axis, see Figure 5-3. For (4) the
Cd-Se distances average at 2.85(9)A with the axial Se(1) displaying the longer ones

[2.965(2)A]. The phosphorus-phosphorus distance is 2.257(7)A. The [CdPZSeann-

chains are separated by six-coordinate Rb+ ions [range of Rb-Se distances, 3.489(2)-
3.756(3)A; av 3.629A]. Selected bond distance and angles for (4) are given in Table 5-11.

Structure of KZHngseg. The Hg compounds (6) and (7) have a one-

dimensional structure which is shown in Figure 5-4. The structure contains the [PZSe6]4-

group which is bridging tetradentate as in (l). The major difference between this structure
and the structure of (2)-(5) is that the larger13 Hg2+ is tetrahedral. To accommodate that,

the [P28e6]4— adjusts both its denticity and its arrangement in the chain. Consequently, the

neighboring P—P pairs are tilted with respect to each other and are not parallel as in (2)-(5),
see Figure 5-5. The related compound Hg2P28e614 also features the [PzSe6l4- ligand and

tetrahedral Hg2+. It can be regarded as the parent compound of (6) and (7) since one can

113

envision "dismantling" the 2-D network of Hg2P28e6 by substituting one Hg2+ for two A+

ions, to obtain the 1-D chains of AzHgPZSeé, see Eq. 1.

_H92+
ngpzses ——> A2H9P2866
<2-D1 +2” <1-D>
Eq. 1

A single Hg2P28e6 layer is shown in Figure 5-6A. Removal of half of the Hg2+ cations

yields the [HgPZSe6]2- layer as shown in Figure 5-6B. To maintain electroneutrality, two
alkali metal ions must be introduced. This metal-deficient structure may very well be stable
with the proper counterion, but the lack of available space for a low energy packing
arrangement for the alkali metal atoms within the layer causes a structural change to a one-
dimensional structure. This generates more space for efficient packing of the alkali ions.

This effect can be understood in terms of the counterion effect which has been discussed

earlier.15
For (6) the Hg-Se distances average at 2.65(5)A which compare very well with those
of Hg2P28e6. The phosphorus-phosphorus distances average at 2.268(8)A. The

[HgPZSe6]n2n- chains are separated by the six-coordinate K(l) cation [range of K(l)-Se
distances, 3.352(5)-3.521(5)A; av 3.417A], and by the four-coordinate K(2) cation [range
of K(2)-Se distances, 3.360(6)-3.478(6)A; av 3.393A]. Selected bond distance and angles
for (6) are given in Table 5-12.

Structure of Rb3Hg4(Se2)2(PSe4)4. Compounds (8) and (9) are

isostructural. The single-crystal structure determination was performed on the Hg
compound. The discrete [Hg4(Se2)2(PSe4)4]8- anion is a tetranuclear complex, of
approximate D2d symmetry, containing the relatively rare [PSe4]3- ligand but also

diselenide 8e22- ligands in a novel cluster arrangement, see Figure 5-7. The most intriguing

114

feature of the molecule is its stellane-like, [Hg4(Se2)2]4+ core, composed of four Hg2+

ions and two Sezz- ligands. In this arrangement every 5e22- ligand coordinates to all four
metals and the two diselenides are perpendicular to each other, see Scheme 1A. The four

metal centers define a perfect 3.612(1) x 3.612(1)A square and the entire molecule resides

on a :1 crystallographic site. A similar cage structure, has been observed in the organic

molecule tricyclo[3.3.0.03.7]- octane,16,17 Scheme 13. Its projection is reminiscent of a

four pointed star and because of that is also known as stellane. b-tetra-arsenic tetrasulfide is

known to crystallize in discrete AS484 molecules with a similar cage structure,18 only in

this molecule the sulfur atoms occupy the four comers of the "star", Scheme 1C.

Scheme1

”A .f\..
<::\: / ./ fix: / s;<Asx >.
CCC\/ \S/

A. [M4(Se2)2]4+ B. Stellane c. B-AS4S4

\/M

The stereo view in Figure 5-8 can be useful in perceiving the cage core structure. This core
acting as a gigantic metal center is being coordinated by four [PSe4]3- ligands. Each
[PSe4]3- employs two of its four available donor sites to bind to two neighboring metal
atoms. In polyhedral terms, each [PSe4]3- tetrahedron shares two comers with the four
pointed [M4(Se2)2]4+ star giving rise to the [M4(PSe4)4(Se2)2]3- formula. Even though the

[PSe4]3- ligand is bidentate, its disposition is such that one of its non-coordinating Se

115
atoms interacts with the diselenide ligand (Figure 5-9), as evidenced by the Se(3)-Se(5)

distance of 3.327(3)A (Van der Waals radii sum is 3.8A).19 In support of this observation
the diselenide bond of 2.416(4)A for Se(5)-Se(5") is relatively long, for this coordination

mode, compared, for example, to [Hg7Se10]4-.20 where a similarly bound 8e22- ligand has

a 2.349(6)A bond length. This is consistent with partial electron transfer from the terminal

Se(3) atoms to the 6* orbital of the Se(5)-Se(5") ligand.

In (9) the Hg-Se distances average at 2.68(5)A which compare well with those of

[Hg7Se10]4-,20 and Hg2P28e621 Each cell contains two [Hg4(Se2)2(PSe4)4]8- molecules
which are separated by the nine-coordinate Rb(l) [range of Rb(1)-Se distances, 3.511(3)-
3.800(3)A; av. 3.661A], and by the six-coordinate Rb(2) cation [range of Rb(2)-Se
distances, 3.478(3)-3.786(3)A; av 3.644A]. Selected bond distance and angles are given in
Table 5-13.

Because a series of analogous compounds has been generated, it is useful at this
point, to draw some conclusions about the structural influence of the M2+ size on the
[P28e6]4- group. In A2MP28e6 (M = Mn, Fe, Pd, Cd, Hg), a comparison of the M2+ ionic
radius22 with the P-P distance in the [P2Se6]4- group, reveals a positive correlation
between the two, where the larger the metal the longer the P-P bond, see Figure 5-10. This

suggests that the [P28e6]4- can be viewed as a dimer of two PSe3 groups connected via a
relatively weak P-P bond. The latter can be easily stretched or shrunk, varying the Se-Se

"bite" size, so it can accommodate different sizes of metal ions. A similar trend is observed

for the [P286]4- group in the MPS3 phases.23

116

 

(A)
9 P 1' O
. .O - Se(3") (:l .0
e Se(1) :Se(1') . 0
Q n“ O . at" . ...-_ Q '. .u. \ . C .
o\ ’ .Se " Pd ' . ‘ M "I 9
(1)
. Se 3' ’Set3) “x s’9
e 9 0
Se(2). : 86(2) 9 .
Pit)
p
C

 

Figure 5-1: (A) An isolated [PdP25e6]n2n- chain with labeling. (B) The disorder of the
P atoms in the [P28e5]4- group. Bonds between P and Se atoms are omitted

for clarity

117

Se(1)
e " e " p e
" w”
i; 0 i: 0 9
e e P'
o o Se(3) o
a

Figure 5-2: ORTEP representation and labeling of a single [CdPZSe6]n2n' chain (70%

probability)

118

 

 

 

Figure 5-3: Projection of the [CdPZSe6]n2n- chain on the b—c plane

119

O

      

v
Se(3') P(1')

Se(2')

Figure 5-4: ORTEP representation and labeling of a single [HngSe6ln2n- chain (80%

probability)

120

 

 

 

 

 

 

 

of the [HgPZSC61n2n° chain on the b-c plane

Figure 5-5: Projection

121

E

' i
so:
(its;
5e",
as:

O

22‘:
I":
w

0
it:
it:

.‘. .9... .'..O..
a

*— .\'
z
'4‘?
(ED:
8

(8)..

$
4%
‘

~~s ~s
~§ . . . ‘Q . .
\“ \‘~
0 e ' 0 . O
. . s . . \ ‘.
‘s
“s e . 0 . o . 9 ;‘s
s O . O O
O
O o . O . Q
C
0 . . U
s
\ . . ~\
‘~ . . . . .“
\ C . . . .
O
O O .
O
. O
\~~. . . .
s‘ . .
o o . o o .
. O o . 9 O
~s‘ . . . . . .
s~ . . . . . .
O
O Q . O . o
O o O
U C
s“ .
. . . ‘s‘ . .

Figure 5-6: (A) A single Hg2P28e6 layer. (B) Removal of half of the Hg2+ ions
resulting in a hypothetical [HgP28e6]n2n- layer. Dashed lines highlight the
possibility of chain formation by breaking the corresponding Hg-Se bonds

122

 

Figure 5-7: ORTEP representation and labeling of a single [Hg4(Se2)2(PSe4)4]3-

molecule

123

 

Figure 5-8: Stereo view of a single [Hg4(Se2)2(PSe4)4]3- molecule

124

 

Figure 5-9: Perpendicular view of the same molecule. Dashed lines indicate Se-Se

interactions

125

P-P distance (A)

 

 

 

2-20 4. i i : i i i i
0.6 0.7 0.3 0.9 1

Ionic radius of M“

Figure 5-10: Diagram of the P-P distance versus M2+ ionic radius in AzMP28e6

Table 5-10. Selected Distances (A) and Angles (deg) for CsdePZSe6

126

Pd-Se(l) 2.449(3) (x2) Se(1)-Pd-Se(3') 9381(8)
Pd-Se(3) 2.464(3) (x2) Se(1)-Pd-Se(3") 86. 19(8)
Se(1)-Se(3") 3.357(4) (x2) Se(1)-Pd-Se( 1") 180.00
Se(1)-Se(3) 3.588(4) (x2)
P( l )-Se(av) 2.27(4) Pd-Se(1)—P( 1) 105.2(7)
P(2)-Se(av) 224(3) Pd-Se(3')-P( l ') l 10.8(6)
P(3)-Se(av) 2.23(4)
P(4)-Se(av) 2.28(4) Se(1)-P(1)-Se(2) 1 17.5(9)
Se(1)-P(l)-Se(3) 113.7(8)
P-P (av) 221(4) Se(2)-P(l)-Se(3) 117.9(9)
Se(1)-P(l)-P(1') 98.7(7)

a The estimated standard deviations in the mean bond lengths and the mean bond angles are calculated by the
equation 01 = {211011 — [)2/n(n —1)}1/2, where in is the length (or angle) of the nth bond, I the mean length
(or angle), and n the number of bonds.

Table 5-1 1. Selected Distances (A) and Angles (deg) for RDZCdPZSC6

Cd-Se( 1) 2.965(2) Se( 1 )-Cd-Se(2) 76.41(4)
Cd-Se(2) 2.827(2) Se(1)-Cd-Se(3) 8725(4)
Cd-Se(3) 2.772(2) Se(2)-Cd-Se( 3) 9060(4)
P-Se( 1) 2.188(4) Cd-Se( l )-P 75.5(1)
P-Se(2) 2.176(4) Cd-Se(2)-P 78.8(1)
P-Se(3) 2.176(4) Cd-Se(3)-P 98.8(1)
P-P 2.257(7) Se(1)-P-Se(2) 1 104(2)
Se(1)-P-Se(3) 115.1(2)

Se(2)-P-Se(3) l 14.3(2)

Se(1)-P-P'

105.5(2)

Table 5-12. Selected Distances (A) and Angles (deg) for KzHgP25e6

Hg-Se( l )
Hg-Se(3)
Hg-Se(4)
Hg-Se(5)

P(1)-Se( l )
P(1)-Se(2)
P( l )-Se(3)
P(2)-Se(4)
P(2)-Se(5)
P(2)-Se(6)

P(l )-P( 1)
P(2)-P(2)

2.592(2)
2.694(2)
2.697(2)
2.622(2)

2.228(4)
2.137(5)
2.212(4)
2.202(4)
2.223(4)
2.148(4)

2.269(8)
2.268(8)

127

Se(1)-Hg-Se(3)
Se(1)-Hg-Se(4)
Se(1)-Hg-Se(5)
Se(3)-Hg-Se(4)
Se(3)-Hg-Se(5)

Hg-Se( 1 )-P( l)
Hg-Se(3)-P( 1)
Hg-Se(4)-P(2)
Hg-Se(5)-P(2)

Se(1)-P(1)-Se(2)
Se(1)-P(l)-Se(3)
Se(2)-P( l )-Se(3)
Se(4)-P(2)-Se(5)
Se(4)-P(2)-Se(6)
Se(5)-P(2)-Se(6)
Se( 1 )-P( l )-P( 1')
Se(3)-P( 1')-P( 1)
Se(4)-P(2)-P(2')
Se(5)-P(2')-P(2)

104.40(5)
l 1608(6)
l 1949(6)
9631(6)

l 14.91 (6)

92.5(1)
95.2(1)
95.9(1)
89.1(1)

113.5(2)
106.8(2)
114.0(2)
106.9(2)
113.1(2)
113.2(2)
104.6(3)
105.9(2)
106.3(2)
104.8(2)

128

Table 5-13. Selected Distances (A) and Angles (deg) for RbgHg4(Se2)2(PSe4)4

fig-Se(2)
Hg-Se(4)
Hg-Se(5)
Hg-Se(5')
P-Se( l)
P—Se(2)
P-Se(3)
P-Se(4)
Se(5)-Se(5")
Se(3)-Se(5)

2.713(2)
2.623(2)
2.669(2)
2.725(2)
2.175(5)
2.221(5)
2.184(5)
2.237(5)
2.416(4)
3.327(3)

Se(2)-Hg-Se(4)
Se(2)-Hg-Se(5)
Se(2)-Hg-Se(5')
Se(4)-Hg-Se(5)
Se(4)-Hg-Se(5')
Se(5)-Hg-Se(5')
Hg-Se(2)-P
Hg-Se(4)-P‘
Hg-Se(5)-Hg"'
Hg-Se(5')-Se(5")
Se( l)-P-Se(2)
Se(1)-P-Se(3)
Se(1)-P-Se(4)
Se(2)-P-Se(3)
Se(2)-P-Se(4)

1 01 .44( 7)
1 1433(6)
101.98(7)
125.45(7)
l 1070(6)
100.84(8)
96.5( 1)
97.9(1)
8407(6)
109.43(7)
108.7(2)
l 1 1.6(2)
107.9(2)
1 109(2)
107.0(2)

129

3.2. Synthesis, Spectroscopy and Thermal Analysis

The new compounds were obtained by the oxidative dissolution of the appropriate
metal in a polyselenophosphate flux. The metal cations are coordinated in situ by the
highly charged [PySez]n- ligands present in the flux. For the same AZMPZSe6 formula, we
observe three different but closely related structure types which result from the different
coordination requirements and/or preferences of the metal ions. The relatively Se-rich
conditions used in the syntheses yielded compounds with the [P2Se6]4- ligand which
contains P4+. If higher basicity conditions are employed (by increasing the A28e content)

compounds with P5+ atoms, i.e. with the [PSe4]3- ligand are formed.3d-g This is now a

general theme in this chemistry. 2f. 3b» 4b Such conditions were employed for the synthesis
of the molecular compounds (8) and (9).

All compounds are wide gap semiconductors as determined with optical absorption
spectroscopy, see Figure 5-11. The band-gaps, Eg, are given in Table 5-14. Data for (2)
are not reliable because of the presence of impurities.

The transparent well formed crystals of (4) were suitable for single crystal optical
transmission measurements. This served two purposes. First, to evaluate the nature of the
bandgap in the A2CdP2$e6 phases and second, to provide an estimation of the agreement
between the Eg values obtained from powder (reflectance) and single crystal (transmission)
data. The spectrum from a single crystal of (4), converted to absorption data, is shown in

Figure 5-12A. The absorption edge is much steeper than that from the diffuse reflectance
spectrum but gives a very similar band-gap (Eg = 2.66 eV). The absorption”2 vs energy
plot (Figure 5-12B) is very nearly linear (R = 0.99), while the plot of absorption2 vs

energy (Figure 5-12C) deviates significantly from linearity (R =093). This suggests24 that
(4) has an indirect bandgap.

130
Rb8M4(PSe4)4(Se2)2 (M=Cd, Hg) are insoluble in DMF and acetonitrile but

soluble in a solution of crown ether, 18-crown-6, in DMF. The solution is greenish-brown
and stable, according to UV/vis, for up to 2-3 days. The DMF/ complexant solution gives a
different spectrum from the solid material with one medium absorption at ~585 nm (2.12
eV) and a shoulder at ~400 nm (3.10 eV), suggesting that the cluster undergoes
rearrangement in solution.

The far-IR spectra of (1) display three strong absorptions at ca. 490, 442 and 306
cm-1. (2)-(7) have nearly identical spectra, displaying three strong absorptions at ca. 475,
465 and 304 cm-1. The vibrations at ca. 490, 475, 465, and 442 cm-1 can be assigned to
PSe3 stretching modes and the ones at ca. 304 and 306 cm-1 to the out-of-phase
translational PSe3 mode.3a All compounds possess weak absorptions below 200‘ cm-1
which probably are due to M-Se vibrations.3 The far-LR. spectra of (8) and (9) display
three strong absorptions at ~46l, ~434 and ~417 cm-l. These vibrations can be assigned to

PSe4 stretching modes and are of diagnostic value in distinguishing this selenophosphate

ligand from others.2f.3a
Differential thermal analysis (DTA) measurements followed by XRD analysis of the

residues, suggest that (2)-(7) melt congruently (see Table 5-14), while (1), (8) and (9)
melts incongruently yielding binary M/Se phases and amorphous AxPySeZ.

131

 

 

 

alS Absorption Coeff. (arb. units)

 

Energy (eV)

Figure 5-11: Optical absorption spectra of szCdPZSe6 (solid line) and of szHgPZSe6

(dotted line).

132
(A) 2 1'-

Absorption

0.5"-

 

0 T I r

1.5 2 2.5

A l 4'
3

Energy (eV)

(B) 1.1 ~-

09 ‘-

08 "r

Absorption"2

0.7 T

 

 

l l l l 1 l 4]
0.6 r fi I T I I I

2.64 2.66 2.68 2.7 2.72 2.74 2.76 2.78 2.8
Energy (eV)

.1».

Absorption2

 

 

0 1 l l 1 l l l l
T I I I I I I I

2.64 2.66 2.68 2.7 2.72 2.74 2.76 2.76 2.8
Energy (eV)

Figure 5-12: (A) Single crystal optical transmission spectrum of converted to absorption

data. (B) The region close to the absorption edge is plotted for
absorption 1/7- vs energy. (C) The same region is plotted for absorption2 vs

energy

133

Table 5-14. Optical Band Gaps and Melting Point Data

 

 

Formula Eg, eV mp, oC
CsdePzSe6 1.60 615i
K2CdP2$e6 2.58 640
Rb2CdP28e6 2.58 (2.66)! 720
CSZCdPZSe6 2.63 773
K2HgP2$e6 2.25 541

szHngSe6 2.32 578
Rbng4(Sez)2(PSe4)4 2.57 456i
RbgHg4(Se2)2(PSe4)4 2.32 416i

1 = incongruent melting

t = from single crystal transmission data

134

4. Conclusions

The synthesis of new members of the AzMP28e6 family has been accomplished with
the use of polyselenophosphate Ax[PySez] fluxes. This general family seems to be very
stable, and so far, compounds with this formula have been synthesized from Groups 7, 8,
10 and 11. Given that some sulfide members also exist (e.g. KZMP286; M=Mn, Fe)8 the
size of the A2MP2Q6 family could approach that of the ternary M2P2Q6. The observed P-P
bond elasticity according to metal ion size provides additional flexibility for these structures
to form. It would be interesting to see if members of this family with appropriate alkali ions
are soluble in polar solvents.25 The extremely high charge of the [M4(Se2)2(PSe4)4]3- unit
would make its synthesis through conventional "wet" chemistry very difficult, perhaps
prohibitive. This accentuates the value of the flux technique in stabilizing highly charged
molecular entities. The novelty of the compositional and structural features of the
[M4(Se2)2(PSe4)4]3- cluster, provides a stimulating example of the new chemistry that
becomes accessible and suggests that the molten alkali polychalcogenide approach has not

yet been fully exploited.

10.

ll.
12.
13.

135

References

M. G. Kanatzidis, Curr. Opinion Solid State and Mater. Sci. 2, 139, (1997).

(a) T. J. McCarthy, M. G. Kanatzidis, Chem. Mater. 5, 1061, (1993). (b) T. J.
McCarthy, M. G. Kanatzidis, J. Chem. Soc., Chem. Commun. 1089, (1994). (c)
T. J. McCarthy, T. Hogan, C. R. Kannewurf, M. G. Kanatzidis, Chem. Mater. 6,
1072, (1994) (d) T. J. McCarthy, M. G. Kanatzidis, J. Alloys Comp. 236, 70,
(1996). (e) K. Chondroudis, M. G. Kanatzidis, Materials Research Society, Fall
1996 Meeting, Boston, MA. (f) K. Chondroudis, T. J. McCarthy, M. G.
Kanatzidis, Inorg. Chem. 35, 840, (1996). (g) K. Chondroudis, M. G.
Kanatzidis, J. Chem. Soc., Chem. Commun. 1371, (1996).

(a) T. J. McCarthy, M. G. Kanatzidis, Inorg. Chem. 34, 1257, (1995). (b) K.
Chondroudis, M. G. Kanatzidis, Inorg. Chem. 34, 5401, (1995). (c) K.
Chondroudis, T. J. McCarthy, M. G. Kanatzidis, Inorg. Chem. 35, 3451, (1996).
(d) K. Chondroudis, M. G. Kanatzidis, J. Chem. Soc., Chem. Commun. 401,
(1997). (e) K. Chondroudis, M. G. Kanatzidis, Angew. Chem. 36, 1324, (1997).
(f) K. Chondroudis, J. A. Hanko, M. G. Kanatzidis, Inorg. Chem. 36, 2623,
(1997). (g) K. Chondroudis, M. G. Kanatzidis, J. Sayettat, S. Jobic, R. Brec,
Inorg. Chem. In Press.

(a) K. Chondroudis, M. G. Kanatzidis, C. R. Acad. Sci. Paris, Series B, 322,
887, (1996). (b) K. Chondroudis, M. G. Kanatzidis, J. Am. Chem. Soc. 119,
2574, (1997).

T. J. McCarthy, S.-P. Ngeyi, J.-H. Liao, D. DeGroot, T. Hogan, C. R.
Kannewurf, M. G. Kanatzidis, Chem. Mater. 5, 331, (1993).

(a) R. H. Blessing, Acta Cryst. A51, 33, (1995). (b) N. Walker, D. Stuart, Acta
Cryst. A39, 158, (1983).

(a) G. M. Sheldrick, " Crystallographic Computing 3 " G. M. Sheldrick, C.
Kruger, R. Doddard, p. 175, Oxford University Press: Oxford, England, 1985. (b)
G. J. Gilmore, Appl. Cryst. 17, 42, (1984).

(a) F. Menzel, W. Brockner, W. Carrillo-Cabrera, J. Sabmannhausen, Z. Anorg.
Allg. Chem. 620, 1081, (1994). (b) W. Carrillo-Cabrera, J. Sabmannhausen, H.
G. Sehnering, F. Menzel, W. Brockner, Z. Anorg. Allg. Chem. 620, 489,
(1994).

K. -W. Kim, M. G. Kanatzidis, J. Am. Chem. Soc. 114, 4878, (1992).

F. A. Cotton, G. Wilkinson, Advanced Inorganic Chemistry; Wiley J. and Sons:
New York, 1988.

E. Prouzet, G. Ouvrard, R. Brec, Mat. Res. Bull. 21, 195, (1986).
G. Ouvrard, R. Bree, J. Rouxel, Mat. Res. Bull. 20, 1181, (1985).
R. D. Shannon, Acta Crystallogr. A32, 751, (1976).

14.

15.
i 16.
17.
18.
19.
20.
21.

22.

23.
24.

25.

136

M. Z. Jandali, G. Eulenberger, H. Hahn, Z. Anorg. Allg. Chem. 447, 105,
(1978).

M. G. Kanatzidis, Phosphorus, Sulfur, Silicon 93-94, 159, (1994).

P. K. Freeman, V. N. M. Rao, G. E. Bigam, Chem. Commun. 21, 511, (1965).
J. L. Adcock, H. Zhang, J. Org. Chem. 61, 1975, (1996).

E. J. Porter, G. M. Sheldrick, J. Chem. Soc., Dalton Trans. 1347, (1972).

A. Bondi, J. Phys. Chem. 68, 441, (1964).

K-W. Kim, M.G. Kanatzidis, Inorg. Chem. 30, 1966, (1991).

M. Z. Jandali, G. Eulenberger, H. Hahn, Z. Anorg. Allg. Chem. 1978, 447, 105.

The revised effective ionic radii for halides and chalcogenides by Shannon13 were
used. For Fe2+ and Mn2+ high spin configuration was assumed based on the
magnetic measurements performed for AzMPzSe6.3a

R. Bree, G. Ouvrard, J. Rouxel, Mat. Res. Bull. 20, 1257, (1985).

J. I. Pankove, Optical Processes in Semiconductors; Dover Publications: New
York, 1971; pp 34-42.

K. Chondroudis, M. G. Kanatzidis, J. Sayettat, S. Jobic, R. Bree, Work in
Progress.

CHAPTER 6

K41n2(PSe5)2(PZSe6) and Rb3Sn(PSe5)(PZSe6): One-Dimensional Compounds with

Mixed Selenophosphate Anions. Isolation of [Sn(PSe5)3]5-, and [Sn28e4(PSe5)2]6~, the

First Discrete Complexes from Molten Alkali Metal Polyselenophosphate Fluxes

1. Introduction

Our extensive work with the polychalcophosphate fluxes has yielded many novel
quaternary thiophosphate and selenophosphate compounds.l Many unusual compounds
containing main group,2 transition metals,3 lanthanides and actinidesZe. 2f. 4 have been
reported. The basic building elements in these compounds are the negatively charged
[Psz]n- (Q=S, Se) chalcophosphate units which bind to the metal ions, in an astonishing
number of ways, forming extended covalent framework structures. The frameworks then
incorporate alkali metal countercations according to their charge balancing needs. The great
number of different [PyQZPI- building blocks along with their impressive bonding
versatility creates many possibilities for new structure types and compositions most of
which unanticipated. The other important building block, the metal ion, plays also an

important role in the stabilization of a specific structure but this role is not fully understood

yet. For example, in K3RuPsSe10 we observe a protagonistic role of the metal (Ru) in
determining ligand formation and selection according to its coordination chemistry needs.36

To access molecular compounds a high concentration of [Psz]"' ligands is necessary

which can be achieved by increasing the basicity of the flux.
137

138
Herein we report the synthesis, structural characterization, optical and thermal

properties of the solid-state selenophosphate compounds, K41n2(PSCS)2(PQSC6) and
Rb3Sn(PSe5)(PZSe6) and of the molecular compounds AsSn(PSe5)3 (A=K, Rb), and
A6SHQSC4(PSBS)2 (A=Rb, Cs). It is noteworthy, that access to these molecular compounds

is more convenient through the flux method than using "wet" chemistry, because of the

difficulty of stabilizing the highly charged [Psz]““ species in solution. Furthermore, the

complexes themselves are very highly charged (5- and 6-) and their stabilization through

conventional synthesis would be troublesome.

139

2. Experimental Section

2.1. Reagents

The reagents mentioned in this study were used as obtained unless noted otherwise
: (i) red phosphorus powder, Morton Thiokol, Inc., -100 mesh, Danvers, MA. (ii)
rubidium/cesium metal, analytical reagent, Johnson Matthey/AESAR Group, Seabrook,
NH; (iii) potassium metal, analytical reagent, Aldrich Chemical Co, Milwaukee, Wi.; (iv)
selenium powder, 99.5+% purity -100 mesh, Aldrich Chemical Co., Milwaukee, Wi.; (v)
N,N-Dimethylformamide (DMF) reagent grade, EM Science, Inc., Gibbstown, NJ .; (vi)
diethyl ether, ACS anhydrous, EM Science, Inc., Gibbstown, NJ.

2.2. Syntheses

Azse (A=K, Rb, Cs; Q=S, Se) were prepared by reacting stoichiometric amounts

of the elements in liquid ammonia as described elsewhere.2

PZSes The amorphous phosphorus selenide glass "P2Se5", was prepared by
heating a stoichiometric ratio of the elements as described elsewhere.2

Preparation of K4In2(PSe5)2(P28e6) (I). A mixture of In (0.25 mmol),
PZSe5 (0.5 mmol), KzSe (0.5 mmol), and Se (2.5 mmol) was sealed under vacuum in a
Pyrex tube and heated to 4800C for 3d followed by cooling to 150°C at 40C h-l. The
excess KxPySeZ flux was removed by washing with DMF under N2 atmosphere. The

product was then washed with tri-n-butylphosphine to remove residual elemental Se and

then ether to reveal analytically pure brick-red, needles (77% yield based on In). The

140

crystals are air- and water-stable. Microprobe analysis carried out on several randomly
selected crystals gave an average composition of K1_7InP1_9Se3_2.

Preparation of Rb3Sn(PSe5)(P28e6) (II). A mixture of Sn (0.3 mmol),
P28e5 (0.3 mmol), Rb2Se (0.3 mmol), and Se (2.0 mmol) was sealed under vacuum in a
Pyrex tube and heated to 4950C for 4d followed by cooling to 150°C at 40C h-l. The flux
was removed as above to reveal a mixture of black plates of Rb3Sn(PSe5)(PzSe6) (70%)
and black irregular crystals of Rb4Sn5(P2Se6)3Se2 (30%).26 The plate crystals were
manually separated and they are air- and water-stable. Microprobe analysis gave an average
composition of Rb2,3SnP2,7Se11I3.

Preparation of A 58n(PSe5)3 (III). (A) A58n(PSe5)3 (A=K, Rb) were

synthesized from a mixture of Sn (0.3 mmol), P2865(0.6 mmol), A28e (0.90 mmol), and
Se (3 mmol) that was sealed under vacuum in a Pyrex tube and heated to 440 0C for 4 (1

followed by cooling to 150 0C at 4 OC h‘l. The excess AxPySez flux was removed with
DMF to reveal black platelike crystals (80% yield based on Sn). The crystals are air- and

water- sensitive.

(B) B-RbSSn(PSe5)3 at 23 0C, a=13.566(3)A, b=16.244(4)A, c=7.303(2)A,
0t=102.04(2)0, B=94.22(2)°, y=76.91(2)0, V=1532.6(6)A3, Z=2, Dc = 3.951 g cm‘3,
space group PT (no. 2). The crystals are also black, platelike and air sensitive. Data were

also collected in this unit cell. The solution of the structure illustrated that in this unit cell
the same molecular unit is present. Both crystalline forms have the same infrared spectra
and DTA response.

Preparation of A68n28e4(PSe5)2 (IV). A63n2$e4(PSe5)2 (A=Rb, Cs) were

synthesized from a mixture of Sn (0.3 mmol), P28e5(0.45 mmol), A2Se (1.20 mmol), and

141

Se (3 mmol) by heating at 495°C for 4 d and isolated as above to reveal orange rodlike

crystals (89% yield based on Sn). The crystals are air- and water- sensitive.

2.3. Physical Measurements

Powder X-ray Dijfraction (XRD). Analyses were performed using a calibrated
Rigaku-Denki/RW4OOF2 (Rotaflex) rotating anode powder diffractometer controlled by an

IBM computer, operating at 45 kW 100 mA and with a lO/min scan rate, employing Ni-
filtered Cu radiation. Powder patterns were calculated with the CERIUS2 software.l3

Infrared Spectroscopy. Infrared spectra, in the far-IR region (600-50 cm-l), were

recorded on a computer controlled N icolet 750 Magna-IR Series II spectrophotometer

equipped with a TGS/PE detector and silicon beam splitter in 4 cm-1 resolution. The
samples were ground with dry CsI into a fine powder and pressed into translucent pellets.
Solid State U V/Vis Spectroscopy. Optical diffuse reflectance measurements were
performed at room temperature using a Shimadzu UV-3101PC double beam, double
monochromator spectrophotometer. The instrument is equipped with integrating sphere and
controlled by a personal computer. BaSO4 was used as a 100% reflectance standard for all
materials. Samples are prepared by grinding them to a fine powder and spreading them on a
compacted surface of the powdered standard material, preloaded into a sample holder. The

reflectance versus wavelength data generated can be used to estimate a material's band gap

by converting reflectance to absorption data as described earlier.6

Differential Thermal Analysis (DTA). DTA experiments were performed on a
computer-controlled Shimadzu DTA-50 thermal analyzer. Typically, a sample (~ 25 mg) of
ground crystalline material was sealed in quartz ampoules under vacuum. A quartz ampoule

of equal mass filled with A1203 was sealed and placed on the reference side of the detector.

The samples were heated to the desired temperature at 10 0C/min, then isothermed for 10

142

minutes and finally cooled to 50 0C at the same rate. Residues of the DT A experiments
were examined by X-ray powder diffraction. To evaluate congruent melting we compared
the X-ray powder diffraction patterns before and after the DTA experiments. The
stability/reproducibility of the samples were monitored by running multiple heating/cooling
cycles.

Semiquantitative Microprobe Analyses. The analyses were performed using a
JEOL JSM-6400V scanning electron microscope (SEM) equipped with a TN 5500 EDS
detector. Data acquisition was performed with an accelerating voltage of 20kV and thirty
seconds accumulation time.

Single Crystal X-ray Crystallography. Intensity data for (ID-(IV) were collected
using a Rigaku AFC6S four-circle automated diffractometer equipped with a graphite
crystal monochromator. Crystal stability was monitored with three standard reflections

whose intensities were checked every 150 reflections, and no crystal decay was detected.

An empirical absorption correction based on I]! scans was applied to all data during initial

stages of refinement. An empirical DIFABS correction was applied after full isotropic

refinement as recommended,7 after which full anisotropic refinement was performed. A

Siemens SMART Platform CCD diffractometer was used to collect data for (I). An

empirical absorption correction3 was applied to the data. The space groups were determined
from systematic absences and intensity statistics. To check for the correct enantiomorph for
(I) we refined the Flack parameter which yielded the value of 0.0. Attempts at the other

two possible space groups C 2/c and C2 were unsuccessful. The structures were solved by
direct methods using SHELXS-86 software93 and full-matrix least squares refinement was

performed using the TEXSAN software package.9b Crystallographic information for the
compounds are given in Table 6-1. The coordinates of all atoms, average temperature
factors, anisotropic displacement parameters and their estimated standard deviations are

given in Tables 6-2 to 6-9.

143

Table 6-1. Crystallographic data for K4In2(PSe5)2(PZSe6), Rb3Sn(PSe5)(P2Se6), Rb5Sn(PSe5)3, and

 

 

C36Sn23e4(PSe5)2
Formula K4In2P43616 Rb3SnP3Se] 1 Rb5SnP3Sel5 C56Sn2P2$el4
FW 1773.29 1336.57 1823.35 2202.20
a, A 1 1.1564(1) 14.013(2) 11.745(3) 9.899(1)
b, A 22.877l(1) 7.3436(8) l9.230(5) 12.416(2)
c, A 12.6525(2) 21.983(4) 7.278(3) 7.497(1)
or (deg) 90.00 90.00 9997(3) 9162(1)
B (deg) 109.039( 1) 106.61 (1) 107.03(2) 1 1019(1)
7 (deg) 90.00 90.00 87. 16(2) 79.94(1)
Z, V(A3) 4; 3052.60(5) 4; 2167.7(6) 2; 1548.1(9) 1; 851.0(2)
A (Mo Kor), A 0.71073 0.71069 0.71069 0.71069
space group Cc (#9) P21/a (#14) PT (#2) PT (#2)
Dcalc~ g/cm3 3.858 4.095 3.932 4.297
11. cm'1 213.44 261.92 261.85 226.73
Temp (0C) 20 23 26 25
Final R/wa‘ % 4.1/4.4 3.5/4.4 4.1/5.2 3.2/4.1
Total Data 13355 3485 4271 3171
Measured
Total Unique Data 5357 3305 4028 2979
(ave)

Data F02>30(F02) 2190 1993 2853 2033
No. of Variables 235 163 217 110
Crystal Dimen., 0.50 x 0.15 x 0.15 0.28 x 0.12 x 0.04 0.28 x 0.12 x 0.04 0.39 x 0.14 x 0.11

mm

are = 2(IFOI - Inn/21m, Rw = {ZWUFOI - IFCI)2/ZWIF012} 1/2.

144

Table 6-2. Positional parameters and cha for K41n2(PSe5)2(PZSe6)

 

 

Atom X Y Z B equZ
In(1) 0.3819(2) 0.11792(6) 0.6830(1) l.76(3)
In(2) 0.7462(2) 0.12163(5) 0.6906(1) l.63(3)
K(l) 0.8435(5) 0.1993(2) 0.3490(4) 3.9(1)
K(2) 0.8152(4) 0.0615(2) 0.0701(4) 3.1(1)
K(3) 0.4083(4) 0.1972(2) 0.3234(4) 3.3(1)
K(4) 0.2044(4) 0.0550(2) 1.0171(4) 3.3( 1)
P( 1) 0.0874(4) 0.1626(2) 0.7426(4) l . 19(9)
P( 2) 0.0469(4) 0.0827(2) 0.6333(4) 1.22(9)
P(3) 0.5613(5) 0.2657(2) 0.6709(4) 1.58( 10)
P(4) 0.5737(5) -0.0254(2) 0.7058(4) 1 .66( 10)
Se(1) 0.2852(2) 0.151 12(8) 0.8486(2) l.62(4)
Se(2) 0.9671(2) 0.15123(8) 0.8525(2) l.63(4)
Se(3) 0.0466(2) 0.23919(7) 0.6406(2) 200(4)
Se(4) 0.0877(2) 0.00594(8) 0.7349(2) 198(4)
Se(5) 0.8423(2) 0.09023(8) 0.5293(2) 157(4)
Se(6) 0.1547(2) 009720(8) 0.5185(2) 1.71(4)
Se(7) 0.3669(2) 0.231 19(8) 0.5961(2) 215(4)
Se(8) 1.0715(2) 0.14018(8) 1.1880(2) 238(4)
Se(9) 0.6975(2) 0.23106(8) 0.5960(2) 207(4)

Se( 10) 0.6240(2) 0.24433(8) 0.8539(2) 191(4)

Se(l 1) 0.6200(2) 0.14238(8) 0.8443(2) 1.57(4)

Se(12) 0.5081(2) 0.09500(8) 0.5301(2) 155(4)

Se( 1 3) 0.5146(2) -0.00709(8) 0.5202(2) 1.157(4)

Se(14) 0.4094(2) 0.00407(8) 0.7548(2) 1.86(4)

Se(15) 0.58010(2) 0.1 1975(8) 0.1986(2) 2.57(4)

Se(16) 0.7599(2) 0.01333(8) 0.7878(2) 185(4)

3 B values for anisotropically refined atoms are given in the form of the isotropic
equivalent displacement parameter defined as Beq = (4/3)[azB( 1, 1) + b7-B(2, 2) + czB(3,
3) + ab(cosy)B(1,2) + ac(cosB)B(1,3) + bc(cosot)B(2, 3)]

Table 6-3. Anisotropic Displacement Parameters for K41n2(PSe5)2(PZSc6)

145

 

 

Atom U1 1 U22 U33 U12 U13 U23
In(1) 0.0175(6) 0.0171(7) 0.0314(8) -0.0008(5) 0.0068(6) -0.0016(6)
In(2) 0.0194(7) 0.0154(7) 0.0257(7) -0.0009(5) 0.0057(6) -0.0023(6)
K(l) 0.056(3) 0.035(3) 0.058(3) -0.008(2) 0.020(3) 0.013(3)
K(2) 0.032(2) 0.035(3) 0.050(3) -0.005(2) 0.01 1(2) 0.010(2)
K(3) 0.043(3) 0.031(3) 0.052(3) 0.01 1(2) 0.015(2) 0.013(2)
K(4) 0.048(3) 0.036(3) 0.045(3) 0.010(2) 0.018(2) 0.014(2)
P( 1) 0.016(2) 0.007(2) 0.020( 3) -0.001(2) 0.002(2) 0.000(2)
P(2) 0.016(2) 0.007(2) 0.021 (3) 0.001(2) 0.003(2) -0.001(2)
P(3) 0.018(2) 0.015(2) 0.021 (3) -0.001(2) -0.001(2) 0.001(2)
P(4) 0.026(2) 0.013(2) 0.024(3) 0.001(2) 0.008(2) 0.002(2)
Se(1) 0.0169(9) 0.021(1) 0.022(1) -0.0008(7) 0.0032(8) -0.0041(8)
Se(2) 0.0200(9) 0.020(1) 0.021(1) 0.0001(7) 0.0053(8) -0.0006(8)
Se(3) 0.030(1) 0.0090(9) 0.037( 1) 0.0013(8) 0.0108(9) 0.0026(9)
Se(4) 0.027(1) 0.0107(9) 0.035(1) 0.0009(8) 0.0072(9) 0.0008(9)
Se(5) 0.0177(9) 0.018(1) 0.021(1) -0.0010(7) 0.0016(8) -0.001 1(9)
Se(6) 0.0219(9) 0.021(1) 0.022(1) -0.0006(7) 0.0077(8) -0.0021(9)
Se(7) 0.0202(9) 0.025(1) 0.026(1) -0.0045(8) 0.0054(8) 0.004(1)
Se(8) 0040( 1) 0.0105(9) 0.037( 1) -0.0012(9) 0.0088(9) 0.004(1)
Se(9) 0.031(1) 0.01 8( 1) 0.032(1) 0.0061(8) 0.0143(9) 0.0050(9)
Se( 10) 0.0285(9) 0.01 8( 1) 0.019(1) -00003( 8) -0.0009(8) -0.0045(9)
Se( 1 1) 0.0214(9) 0.0175(9) 0.01 8( 1) 0.0016(8) 0.0026(7) 0.0028(9)
Se( 12) 0.0231(9) 0.016(1) 0.017(1) 0.0008(7) 0.0024(7) 0.0010(9)
Se( 1 3) 0.0280(9) 0.0138(9) 0.0197(9) 0.0005(8) 0.0049(8) -0.0019(9)
Se( 14) 0.0263(9) 0.021(1) 0.024(1) 0.0028(8) 0.0092(8) 0.0049(9)
Se(15) 0.041(1) 0.0107(8) 0.046(1) 0.0016(8) 0.0139(9) -0.0021(9)
Se(16) 0.022(1) 0.018(1) 0.025(1) -0.0007(7) 0.0014(8) 0.0062(9)

146

Table 6-4. Positional parameters and Beq for Rb3Sn(PSe5)(P2Se6)

 

 

Atom X Y Z B eq A2
Sn 0.22167(6) 0.6390(1) 0.27946(5) 152(4)
Rb(l) 0.3880(1) 0.6712(2) 0.51 104(9) 307(7)
Rb(2) 0.0128(1) 1.1318(2) 0.2296(1) 332(8)
Rb(3) 0.3451(1) 0.9667(3) 0.07028(9) 379(8)
Se( 1) 0.2390(1) 0.3466(2) 0.2 1 400( 8) 206(6)
Se(2) 0.3268(1) 0.4647(2) 0.08140(9) 301(8)
Se(3) 0.0768(1) 1.2698(2) 0.05704(9) 3.29(8)
Se(4) 0.1 152(1) 0.7123(2) 0.10986(8) 232(6)
Se(5) 0.2259(1) 0.8773(2) 0.19115(8) 234(7)
Se(6) 0.2040( 1) 0.8801(2) 0.36949(8) 1.89(6)
Se(7) 0.2036(1) 0.4001(2) 0.37357(8) 1.82(6)
Se(8) 0.1 178(1) 0.6527(2) 0.49267(7) 2.14(6)
Se(9) 0.0144(1) 0.6328(2) 0.23323(7) 1.89(6)
Se( 10) 0.4180(1) 0.6054(2) 0.34440( 8) 191(6)
Se(l 1) 0.4011(1) 1.1083(2) 0.34219(8) 248(7)
P( 1) 0.1941(3) 0.4382(5) 0.1124(2) 2.0(2)
P(2) 0.1280(2) 0.6433(5) 0.3977(2) 1.5(1)
P(3) 0.0210(2) 0.6274(5) 0.3260(2) 15(1)

ll:

Table 6-5. Anisotropic Displacement Parameters for Rb3Sn(PSeS)(P2Se6)

147

 

 

Atom U1 1 U22 U33 U12 U13 U23
Sn 0.0189(5) 0.0206(5) 0.0187(6) -0.0013(4) 0.0061(4) -0.0021(5)
Rb( 1) 0.0331(9) 0.038(1) 0.047(1) 0.0016(7) 0.0147(8) -0.006( 1)
Rb(2) 0.039(1) 0.033(1) 0.054(1) -0.0027(7) 0.0127(8) 0.002( 1)
Rb(3) 0.060(1) 0.052(1) 0.031(1) -0.006( 1) 0.0128(9) -0.002( 1)
Se(1) 0.0366(9) 0.0209(8) 0.019( 1) 0.0042(6) 0.0049(7) 0.0008(8)
Se(2) 0.034(1) 0.049(1) 0.037( 1) 0.0034(8) 0.0184(8) 0.002(1)
Se(3) 0.043(1) 0.043(1) 0.031(1) -0.0126(8) -0.0009(8) ~0.009( 1)
Se(4) 0.0297(8) 0.0320(9) 0.024(1) 0.0070(7) 0.0044(7) 0.0020(8)
Se(5) 0.039(1) 0.021 1( 8) 0.031(1) -0.0045(7) 0.0137(8) 0.0014(8)
Se(6) 0.0252(8) 0.0205(8) 0.027(1) -0.0045(6) 0.0085(7) -0.0040(7)
Se(7) 0.0237(8) 0.0212(8) 0.025(1) 0.0045(6) 0.0090(7) 0.0045(7)
Se(8) 0.0278(8) 0.036(1) 0.01 8( 1) 0.0020(7) 0.0062(7) -0.0018(8)
Se(9) 0.0195(8) 0.033(1) 0.018(1) 0.0007(6) 0.0033(6) -0.001 1(8)
Se(10) 0.0182(7) 0.023 1(8) 0.029(1) -0.0035(6) 0.0030(7) 0.0042(8)
Se(] 1) 0.0312(9) 0.0251(9) 0.041(1) 0.0104(7) 0.0145(8) 0.0065(8)
P( 1) 0.027(2) 0.028(2) 0.023(2) 0.001(2) 0.006(2) -0.003(2)
P(2) 0.0 1 8( 2) 0.020(2) 0.017(2) -0.002(2) 0.004(2) -0.003(2)
P(3) 0.015(2) 0.021(2) 0.020(2) 0.001(2) 0.006(2) 0.000(2)

148

Table 6-6. Positional parameters and Beq for Rb5Sn(PSe5)3

 

 

Atom X Y Z Beq A2
Sn 0.9008(1) 0.74193(6) 0.1701(1) l.80(5)
Rb(l) 0.4027(2) 0.8811(1) 0.9454(3) 3.68(8)
Rb(2) 1.3874(2) 0.6296(1) 0.0016(3) 400(9)
Rb(3) 0.6487(2) 0.7534(1) 0.5852(2) 322(8)
Rb(4) 1.1456(2) 0.5441(1) 0.3286(3) 316(8)
Rb(5) 0.1361(2) 0.9631(1) 1.3023(3) 3.74(9)
Se( 1) 0.9919(2) 0.8345(1) 0.4903(2) 279(8)
Se(2) 1.1505(2) 0.7640(1) 0.6307(2) 290(8)
Se(3) 1.3578(2) 0.8401(1) 0.4091(3) 356(9)
Se(4) 1.3776(2) 0.6642(1) 0.5220(3) 3.48(9)
Se(5) 1.1268(2) 0.7116(1) 0.1282(2) 285(8)
Se(6) 0.8408(2) 0.6397(1) -0. 1406(2) 246(7)
Se(7) 0.6810(2) 0.6008(1) -0.0591(2) 257(7)
Se(8) 0.6224(2) 0.5523(1) 0.3356(3) 305(8)
Se(9) 0.8703(2) 0.4664(1) 0.1810(3) 292(8)
Se(10) 0.9002(2) 0.6483(1) 0.4132(2) 234(7)
Se(] 1) 0.6639(2) 0.7712(1) 0.1229(2) 233(7)
Se(12) 0.7056(2) 0.8907(1) 0.2601(2) 257(7)
Se( 1 3) 0.6254(2) 0.9408(1) -0.2306(3) 304(8)
Se(14) 0.8547(2) 1.0261(1) 0.1893(3) 284(8)
Se( 15) 0.8979(2) 0.8467(1) -0.0509(2) 246(7)
P( 1) 1.2606(4) 0.7484(3) 0.4141(6) 2.2(2)
P(2) 0.7735(5) 0.5628(2) 0.2310(6) 2.2(2)
P(3) 0.7697(4) 0.9281(2) 0.0266(6) 2.3(2)

149

Table 6-7. Anisotropic Displacement Parameters for Rb5Sn(PSe5)3

 

 

Atom U1 1 U22 U33 U12 U13 U23
Sn 0.0245(7) 0.0210(7) 0.0229(6) 0.0007(6) 0.0075(5) 0.0024(5)
Rb( 1) 0.036(1) 0.047(1) 0.054(1) 0.006(1) 0.010(1) 0.009( 1)
Rb(2) 0.034(1) 0.069(2) 0.049(1) 0.002( 1) 0.010(1) 0.014(1)
Rb(3) 0.044(1) 0.046(1) 0.031(1) 0000( 1) 0.007(1) 0.0070(8)
Rb(4) 0.040( 1) 0.037( 1) 0.043(1) -0.002( 1) 0.012(1) 0.0056(8)
Rb(5) 0.038(1) 0.060(1) 0.047(1) 0.001(1) 0.012(1) 0.019(1)
Se( 1) 0.042(1) 0.031(1) 0.031(1) -0.003( 1) 0.014(1) -0.0079(8)
Se(2) 0.036(1) 0.047(1) 0.026(1) -0009( 1) 0.0065(9) 0.0050(8)
Se(3) 0.038(1) 0.042(1) 0.057(1) -0009( l) 0.01 1(1) 0.014( 1)
Se(4) 0.034(1) 0.044(1) 0.052(1) 0.004(1) 0.003(1) 0.019( 1)
Se(5) 0.028(1) 0.050(1) 0.028(1) 0.006(1) 0.0085(9) -0.0028(8)
Se(6) 0.045(1) 0.024(1) 0.027(1) -0004( 1) 0.0167(9) -0.0012(7)
Se(7) 0.031(1) 0.036(1) 0.029(1) -0.002( 1) 0.0045(9) 0.0096(8)
Se(8) 0.032(1) 0.048(1) 0.042(1) 0.000( 1) 0.016(1) 0.013(1)
Se(9) 0.039(1) 0.026(1) 0.047(1) 0.004(1) 0.015(1) 0.0023(8)
Se( 10) 0.039(1) 0.026(1) 0.0231(9) -0.004(1) 0.0062(8) 0.0048(7)
Se( 1 1) 0.028(1) 0.030(1) 0.034(1) 0.0015(9) 0.0120(9) 0.0086(8)
Se(12) 0.041(1) 0.030(1) 0.030(1) 0.006( 1) 0.017(1) 0.0040(8)
Se(13) 0.035(1) 0.042(1) 0.034(1) -0004( 1) 0.001(1) 0.0085(9)
Se(14) 0.037(1) 0.024(1) 0.040( 1) -0.002( 1) 0.005(1) -0.0013(8)
Se( 15) 0.040(1) 0.026(1) 0.034(1) 0.002( 1) 0.020(1) 0.0065(8)
P( 1) 0.017(3) 0.035(3) 0.031(3) -0.001(2) 0.003(2) 0.005(2)
P( 2) 0.035(3) 0.023(3) 0.028(2) 0.004(2) 0.013(2) 0.007(2)
P(3) 0.035(3) 0.022(3) 0.028(2) -0.001(2) 0.009(2) 0.002(2)

Table 6-8. Positional parameters and Beq for C56$n2$e4(PSe5)2

150

 

 

 

 

Atom X Y Z B eq A2

Cs( 1) 0.6192(1) 0.40160(8) 0.3304(1) 291(4)

Cs(2) 0.6889(1) 0.02224(7) 0.3732(1) 263(4)

Cs( 3) 0.9692(1) 0.80100(8) -0.0578( 1) 3. 18(4)

S n 0.9220(1) 0.63475(7) 0.4053(1) 2.41 (4)

Se( 1) 0.9041(2) 0.5276(1) 0.6791(2) 279(6)

Se(2) 1.0185(1) 0.8050(1 ) 0.4696(2) 259(6)

Se(3) 0.7301(1) 0.6253(1) 0.0727(2) 226(6)

Se(4) 0.4248(1) 0.2047(1) -0.0282(2) 2.20(6)

Se(5) 0.6705(2) 0.3591(1) 0.8571(2) 258(6)

Se(6) 0.6948(2) 0.0596(1) 0.8667(2) 2.65(6)

Se(7) 0.4036(2) 0.2370(1) 0.4908(2) 291(6)

P 0.5586(3) 0.2208(3) 0.7813(5) 1.7(1)

Table 6-9. Anisotropic Displacement Parameters for C865n2Se4(PSe5)2
Atom U1 1 U22 U33 U 12 U13 U23
Cs( 1) 0.0351(5) 0.0395(5) 0.0354(5) -0.0092(4) 0.0098(4) 0.0014(4)
Cs( 2) 0.0360(5) 0.0305(5) 0.0337(5) -0.0039(4) 0.0132(4) -0.0018(4)
Cs( 3) 0.0360(5) 0.0459(6) 0.0413(6) -0.0054(4) 0.0173(4) -0.0013(4)
S n 0.0351(5) 0.0234(5) 0.0286(5) 0.0084(4) 0.0037(4) 0.0021(4)
Se(1) 0.0455(9) 0.0281(8) 0.0353(8) -0.0041(6) 0.0188(7) -0.0008(6)
Se(2) 0.0319(8) 0.0269(8) 0.04 1 9( 8) -0.0105(6) 0.0134(6) -0.0047(6)
Se(3) 0.0260(7) 0.0307(7) 0.0290(7) 0.0037(6) 0.0101(6) -0.0077(6)
Se(4) 0.0281(7) 0.0283(8) 0.0285(7) -0.0028(6) 0.0123(6) 0.0029(6)
Se(5) 0.0322(8) 0.0264(7) 0.0399(8) -0.0073(6) 0.0123(6) -0.0023(6)
Se(6) 0.0352(8) 0.0257(7) 0.0375(8) 0.0046(6) 0.0145(6) 0.0010(6)
Se(7) 0.0358(8) 0.0435(9) 0.0281(8) -0.0096(7) 0.0055(6) 0.0035(6)
P 0.022(2) 0.021(2) 0.023(2) -0.002( 1) 0.010(1) 0.000(1)

151

3. Results and Discussion

3.1. Description of Structures

Structure of K4In2(PSe5)2(ste6) (I). The structure of (I) is shown
in Figure 6-1. The compound has one—dimensional infinite chains of
[In2(PSe5)2(PZSe6)]n4n- which contain In2(PSe5)2 dimers. Each dimer is formed by two
edge-sharing InSe6 octahedra that are bridged via tridentate [PSe5]3- ligands, Figure 6-2.
Every [PSe5]3- ligand employs two monoselenides to coordinate to the In atoms [e. g.
Se(7), Se(9)] and one Se atom from the diselenide "arm" that is shared by both In atoms
[c.g. Se(11)]. Two such ligands cap the dimer from above and below yielding an In-In
distance of 4.036(2)A. The dimers are then linked along the a-axis by tetradentate [P28e6]4r
ligands to form the chain. The [PZSe6J4- unit adopts the staggered conformation and
employs two Se atoms from each P [e. g. Se(1), Se(2) from P(1)] to bridge the neighboring
dimers, while the third Se is non-coordinating. A similar chain structure exists in KzMP287
(M=V, Cr) which contain [M2(PS4)2(P2S6)]n4n- chains.10 In these chains M2(PS4)2
dimers are linked by tetradentate [P286]4- ligands which are in a different coordination
mode than those of K41n2(PSe5)2(P2S66). For comparison, the repeating units of the

K41n2(PSe5)2(P2Se6) and K2MP257 are shown in Scheme 1A and 18 respectively.

152

 

 

 

Se 3
l l
Se/S; Sle ie 8/ §\5
a
SS ’PN S I
‘5 IASGM... «939 39%. Ski «‘9 4"... I S”.- P
In "111"“ In M7... . \ ’8‘
se/ ‘SIe’ \Se\P/Se( S, l‘S/RES’ Ii" (M
a 8
Se 5
8 Se ‘ 3
Se 9',
(A) (3)

Scheme 1
In K41n2(PSe5)2(P2866), there are two sets of In-Se distances; the first set of long

distances averages at 2.80(2)A and the second set of short distances averages at 2.74(2)A.
Similar distances have been observed in In4(PzSe6)3.11 The [In2(PSe5)2(PzSe6)]n4n-

chains are separated by K+ ions that are located in four different sites. K(l) is coordinated
by seven Se atoms [range of K(l)-Se distances, 3.367(6)-3.769(7)A; av. 3.552A], K(2) is
eight-coordinate [3.295(6)-3.744(7)A; av. 3.502A], K(3) is eight-coordinate [3.366(6)-
3.815(6)A; av. 3.546A], and K(4) is also eight-coordinate [3.384(6)-3.685(6)A; av.
3.538A]. Selected distances and angles for K41n2(PSe5)2(P2$e(,) are given in Table 6-10.

Structure of Rb3Sn(PSe5)(P28e6) (II). The structure of (II) is shown
in Figure 6-3. The compound features one-dimensional [Sn(PSe5)(PzSe6)]n3n- infinite

chains, which consist of Sn(PSe5) units stacked parallel to the a-axis. The [PSe5]3- ligands

are bidentate and use one monoselenide and the diselenide "arm" to chelate to an octahedral

Sn atom. The tetradentate [P28e6]4- unit plays a bridging role as in the indium compound.
It uses three Se atoms to cap a triangular face of one octahedron [e.g. Se(6), Se(7) and
Se(9)] and employs another Se [e.g. Se(10)] to share a comer with a neighboring
octahedron, Figure 6-4. There are two sets of Sn-Se distances; the first set of long

distances is between Sn and Se(6), Se(7), Se(9), Se(10) with an average distance of

153
2.75(4)A and the second set of short distances is between Sn and Se(1) and Se(5) with an

average distance of 2.631(5)A. The same Sn coordination has been observed in the
molecular compounds A5Sn(PSe5)3 (A=K, Rb)28 with average Sn-Se distances of
2.76(2)A and 2.66(1)A (for long and short set respectively). The [Sn(PSe5)(P2Se6)]n3n-

chains are separated by Rb+ ions that are located in three different sites. Rb(l) is
coordinated by eight Se atoms [range of Rb(1)-Se distances, 3.537(2)-3.881(2)A; av.
3.710A], and one P atom at 3.785(4)A, Rb(2) is eight-coordinate [3.613(3)-3.800(2)A;
av. 3.699A], and Rb(3) is eight-coordinate [3.511(3)-3.864(2)A; av. 3.694A]. Selected
distances and angles for Rb3Sn(PSe5)(PZSe6) are given in Table 6-11.

Comparison of Structures. The most important difference between (I)
and (II) is the oxidation state of the metal center. In the [Sn(PSe5)(PZSe6)]n3n- chain we
find one [PSe5]3- and one [P28e6]4- equivalents per Sn4+ metal center. On the other hand,
the [In2(PSe5)2(PZSe6)]n4n- chain contains one [PSe5]3- and half [P28e6]4- equivalents per
metal center for the lower charged In3+. The rare [PSe5]3- ligand can be derived from the
tetrahedral [PSe4]3- by substitution of an 8622- ion for a monoselenide. Known examples
of compounds containing this group include [PPh4]2[Fe2(CO)4(PSe5)2],12 (III) and (IV)

all of which contain finite molecular anions. In the present study, the [PSe5]3- unit, with a

different coordination mode in each case, is not involved in the chain propagation in both
compounds. The torsion angle around the Se-Se bond in the [PSe5]3- unit is quite different
between the two compounds. For example for P(3)-Se(10)-Se(11)-In(2) is 47.0(0)0
whereas for P(1)-Se(4)-Se(5)-Sn is 58.6(1)0 [A torsion angle of 63.3(1)0 has been

observed for A58n(PSe5)3 (A=K, Rb)Zg]. The [P2Se6]4- unit is tetradentate in both

frameworks but it adopts a different coordination mode in each case. Interestingly, in both

compounds the [P2Se6]4' unit is bridging the fragments to built the one-dimensional

154

structure. The larger ionic radius of the six-coordinate In3+ (0.80A)13 compared to six-

coordinate Sn4+ (0.69A)l3 does not appear to have any significant effect other than the

longer In-Se distances.
Structure of ASSn(PSe5)3 (III). Compounds A5Sn(PSe5)3 (A=K, Rb)

form in a basic polyselenophosphate flux. In the rubidium salt two different crystalline

forms, or- and B-, were observed. The latter is formed at a reaction temperature 20 0C

higher than the former. The molecular anion in A5Sn(PSe5)3 contain the rare [PSe5]3' ion
as a chelating unit, see Figure 6-5. The [PSe5]3‘ ligand can be derived from the tetrahedral
[PSe4]3‘ group by a substitution of a Sezz' ion for a monoselenide. The only other known
example of a compound featuring this ligand is [PPh4]2[Fe2(CO)4(PSe5)2]l4 in which

[PSe5]3‘ acts as a tridentate ligand. In A58n(PSe5)3, three such ligands chelate to a Sn(IV)
atom, each employing the diselenide "arm" and one of the remaining monoselenides. In this
way, three five-membered rings are formed [e.g. Sn-Se(1)-Se(2)-P(1)-Se(5)] with the tin
in a slightly distorted octahedral environment. There are two sets of Sn-Se distances; the
first set of long distances is between Sn and Se(5), Se(10), Se(] 1), Se(15) with an average

distance of 2.76(2)A and the second set of short distances is between Sn and Se(1) and
Se(6) with an average distance of 2.66(1)A. [Sn(PSe5)3]5' bares a resemblance to

[Sn(Se4)3]2‘t15 in which three Se42' bidentate ligands, coordinate to a tin atom forming

three five-membered rings, two of which adopt a puckered and one an envelope

conformation. In [Sn(PSe5)3]5' two rings (both crystalline forms) have an envelope

conformation, and one ring adopts the puckered conformation. The complex is expected to

be optically active, but since every unit cell contains both A and A enantiomorphs, the
compound is racemate (In Figure 6-5 the A enantiomorph is given). The non-planarity of

the rings introduces dissymetry and the actual conformation of the complex is AAAS (or

155
A551), similar to that of a-[Pt(Se4)3]2',16 whereas [Sn(Se4)3]2‘,15 crystallizes as the A155

conformer. The P-Se distances range from 2.157(6) to 2.299(5)A, with the non-
coordinated selenium atoms [e.g. Se(3), Se(4), etc.] displaying the shorter ones, and
compare well with those found in P/Se compounds. There are two six-coordinate rubidium
cations [Rb-Se mean=3.6(1)A], one seven-coordinate [Rb-Se mean=3.6(1)A], and two
eight-coordinate [Rb-Se mean=3.6(1)A]. Selected distances and angles for Rb58n(PSe5)3

are given in Table 6-12.

Structure of A68n28e4(PSe5)2 (IV). The molecular anion in (IV) is shown

in Figure 6-6. The structure consists of a centrosymmetric [Sn(ttz-Se)(Se)]2 dimeric core in
which two 112 Se2' ions bridge two adjacent tin atoms. This core is further coordinated to

two (PSe5)3' ligands by either side. In this case, however, the ligand is monodentate and
uses only the diselenide "arm" to coordinate. This is a unique coordination mode and
further illustrates the many different bonding modes that the [Psz]“' ligands can exhibit.
- The coordination geometry around tin is tetrahedral and the Sn-Se distances range from
2.438(2)A to 2.626(2)A, in good agreement with [Sn2Se6]4‘-17 in which tin features a
tetrahedral coordination. The P—Se distances range from 2.162(4) to 2.291(4)A, and in this
case every (PSe5)3‘ group displays three shorter distances since it is monodentate. There
are two eight-coordinate cesium cations [Cs-Se mean=3.77(7)A], and one six-coordinate
[Cs-Se mean=3.76(9)A]. Selected bond distances and angles for Cs6SnZSe4(PSe5)2 are

given in Table 6-13.

 

 

 

 

Figure 6-1: Unit cell of K41n2(PSe5)2(PzSe6) viewed down the a-axis. In the infinite
part of the structure, indium is shown as octant shaded ellipses, selenium as

open ellipses, and phosphorus as crossed ellipses. The K+ ions located
between the chains are shown as open ellipses

157

 

 

Figure 6-2: An isolated [ln2(PSe5)2(PzSe6)]n4n- chain with labeling

158

 

 

 

 

Figure 6-3: Unit cell of Rb3Sn(PSe5)(P28e6) viewed down the b-axis. In the infinite
part of the structure, tin is shown as octant shaded ellipses, selenium as

open ellipses, and phosphorus as crossed ellipses. The Rb+ ions located
between the chains are shown as open ellipses

   
 
  

362

‘9
. P]. . Sed

  
   

C 895
Set 0 . seg

3" P3
. k 2:"r Q
8910' U . .1:

w 8911
Se? P2

O
898

Sea .

   

 
   

 

159

  
   
  

  
    
    
 

 

  
 
   

       

5; ’ 9: e .<: o

 

Figure 6-4: An isolated [Sn(PSe5)(P28e6)]n3n- chain with labeling

160

S 14
Se(13) P e( )

 

 

 

 

 

 

P(3)
© Se(15)
Se(12)
Se(1)
Se(l 1Q Sn &
Se(6) %
Se(2) (2?
Se(7) Se(IO)
P(2)
Se(9)
Se(8)

Figure 6-5: ORTEP representation and labeling scheme of the structure of the

[Sn(PSe5)3]5' anion ( A315 enantiomorph )

161

:25 -cfifiomn—vvommcfl 05 .8 9.2256. 05 he 982.8. wE—ofi— Ea 53356.23. mmhmo

((3

3% 6mm

«
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.‘, . \

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1
AMVom a! Avvom

es 8:5

162

Table 6-10. Selected Distances (A) and Angles (deg) for K41n2(PSe5)2(PZSe6)

In(1)-Se(1) 2.757(3) P(3)-Se(7) 2.209(6) Se(7)-In( 1 )-Se( 1) 93.18(8)
In(1)-Se(6) 2.746(3) P(3)-Se(8) 2.164(6) Se(7)-In( l )-Se(6) 8655(8)
In(1)-Se(7) 2.799(3) P(3)-Se(9) 2.184(7) Se(7)-In(1)-Se( 1 1) 9125(8)
In(1)-Se(] 1) 2.828(3) P(3)-Se(10) 2.243(6) Se(7)-In(l)-Se(12) 83.12(8)
In(1)-Se(12) 2.789(3) P(4)-Se( l 3) 2.262(6) Se(7)-In(1)-Se( 14) 174.48( 10)
In(1)-Se(14) 2.742(3) P(4)-Se(14) 2.223(6) Se(9)—In(2)-Se(1 l) 9451(8)
In(2)-Se(2) 2.726(3) P(4)-Se( 15) 2. 162(6) Se(9)-In(2)-Se(12) 8298(8)
In(2)-Se(5) 2.695(3) P(4)-Se( 16) 2. 184(6) Se(9)-In(2)-Se( 16) 171 57(9)
In(2)-Se(9) 2.75 1 (3) Se(9}In(2)-Se(2') 9590(8)
In(2)-Se(l 1) 2.789(3) Se(10)-Se( 1 1) 2.335(3) Se(9)-In(2)-Se(5') 8909(8)
In(2)-Se(12) 2.835(3) Se(12)-Se( l 3) 2.341(3)
In(2)-Se(16) 2.748(3) Se(1)-P( l )-Se(2) 107.1(2)
Se(1)-P(1)—Se(3) 1 16.2(2)
P(l)-Se(l) 2.192(6) P(1)-P(2) 2.247(7) Se(1)-P(1)-P(2) 103.8(2)
P( l )-Se(2) 2.241(6) Se(7)-P(3)Se(8) 1 14.2(3)
P(1)-Se(3) 2. 134(6) In(1)-In(2) 4.036(2) Se(7)-P(3)-Se(9) 1 14.2(3)
P(2)-Se(4) 2. 136(6) Se(7)-P(3)-Se( 10) 107.3(3)
P(2)-Se(5) 2.239(5)
P(2)-Se(6) 2. 193(6) P( 1 )-Se( 1 )-In( 1) 97.7(2)
In(1)-Se(7)-P(3) 103.8(2)
P(3)-Se(10)-Se(l 1) 99.8(2)
Se(10)-Se(1 l)-In(1) 103.47( 10)
In(1)-Se(l l)—In(2) 91 .86(8)
P(3)-Se(10)-Se(1 1)—In( 1) 47.7(2)
P(3)-Se(10)-Se(1 1)-In(2) 47.0(2)

a The estimated standard deviations in the mean bond lengths and the mean bond angles are calculated by the
equation 01 2 {Swan - [)2/n(n — 1)}1/2, where 1,, is the length (or angle) of the nth bond, 1 the mean length
(or angle), and n the number of bonds.

163

Table 6-1 1. Selected Distances (A) and Angles (deg) for Rb3Sn(PSe5)(P2Se6)

Sn-Se( 1)
Sn-Se(5)
Sn-Se(6)
Sn-Se(7)
Sn-Se(9)
Sn-Se( 10')

P(1)-Se(1)
P(1)-Se(2)
P(1)-Se(3)
P( l )-Se(4)

P(2)-Se(6)
P(2)-Se(7)
P(2)-Se(8)
P(3)-Se(9)
P(3)-Se(10)
P(3)-Se(] l )

Se(4)-Se(5)

P(2)-P(3)

2.634(2)
2.627(2)
2.719(2)
2.779(2)
2.790(2)
2.724(2)

2.244(5)
2.163(4)
2.137(4)
2.290(5)

2.218(4)
2.216(4)
2.135(4)
2.232(4)
2.224(4)
2.131(4)

2.341(2)

2.231(5)

Se(5)-Sn-Se( l)
Se(5)-Sn-Se(6)
Se(5)-Sn-Se(7)
Se(5)-Sn-Se(9)
Se(5)-Sn-Se(10')

Se(1)-P(1)-Se(2)
Se(1)-P(1 )-Se(3)
Se( 1)-P( 1 )-Se(4)
Se(6)-P(2)-Se(7)
Se(6)-P(2)-Se(8)
Se(6)-P(2)-P(3)

Sn-Se( 1 )-P( 1)
Sn-Se(5)-Se(4)
Sn-Se(6)-P(2)
Sn-Se(9)-P(3)
P(3)-Se(10)-Sn'

P( l )-Se(4)-Se(5)-Sn

9655(6)
9748(6)
175.51(6)
8902(5)
102.4 1 ( 6)

108.6(2)
110.1(2)
106.4(2)
105.4(1)
114.8(2)
105.7(2)

104.9(1)
9398(7)
81 .0( 1)
98.5(1)
102.0(1)

58.6(1)

Sn-Se(l )

Sn-Se(5)

Sn-Se(6)
Sn-Se(10)
Sn-Se(l l)
Sn-Se(15)
Se(1)-Se(2)
Se(6)-Se(7)

Se(11)-Se(l2)

Se(2)—P( 1)
Se(3)-P( 1)
Se(4)-P(1)
Se(5)-P( 1)
Se(7)-P(2)
Se(8)-P(2)
Se(9)-P(2)
Se(10)-P(2)
Se(12)-P(3)
Se(13)-P(3)
Se(14)-P(3)
Se(15)-P(3)

2.653(2)
2.782(3)
2.673(2)
2.736(2)
2.743(2)
2.781(3)
2.338(3)
2.319(3)
2.354(3)
2.289(6)
2.160(6)
2.170(5)
2.233(4)
2.299(5)
2.157(6)
2.160(5)
2.237(5)
2.281(6)
2.166(5)
2.161(5)
2.235(5)

164

Table 6-12. Selected Distances (A) and Angles (deg) for RbsSn(PSe5)3

Se(1)-Sn-Se(5)
Se(1)-Sn-Se(6)
Se( 1 )-Sn-Se( 10)
Se(1)-Sn-Se(1 l)
Se(1)-Sn-Se(15)
Se(5)-Sn-Se(6)
Se(5)-Sn-Se( 10)
Se(5)-Sn-Se(1 1)
Se(5)-Sn-Se(15)
Se(6)-Sn-Se( 10)
Se(6)-Sn-Se(l 1)
Se(6)-Sn-Se(15)
Se(10)-Sn-Se(l 1)
Se(10)-Sn-Se(15)
Se(l l)-Sn-Se(15)
Se(1)-Se(2)-P(l)
Se(6)-Se(7)-P(2)
Se(] 1 )-Se(12)-P(3)
Sn-Se( 1 )-Se(2)-P( 1)
Sn-Se(6)-Se(7)-P(2)
Sn-Se(1 1)-Se(12)-P(3)

9072(7)
171 .49(8)
8648(7)
98.75(7)
8910(7)
8155(7)
9783(7)
167.13(7)
8494(8)
9106(7)
8945(7)
93.7l(7)
91 .48(8)
l74.80(7)
8650(7)
103.5(1)
102.0(2)
100.8(1)
63.0( 1)
-63.3( 1)
67.8(1)

Sn-Se(1 )
Sn-Se( 1')
Sn-Se(2)
Sn-Se(3)

Se(3)-Se(4)

Se(4)-P
Se(5)-P
Se(6)-P
Se(7)-P

Sn-Sn

2.550(2)
2.626(2)
2.438(2)
2.575(2)
2.340(2)
2.291(4)
2.162(4)
2.183(4)
2.179(4)
3.543(2)

165

Se(1)-Sn-Se(l')
Se(1)-Sn-Se(2)
Se( 1 ')-Sn-Se(2)
Se(1)-Sn-Se(3)
Se( l')-Sn-Se(3)
Se(2)-Sn-Se(3)
Sn-Se( 1 )-Sn'
Sn-Se(3)-Se(4)
Se(3)-Se(4)-P
P-Se(3)-Se(4)—Sn

Table 6-13. Selected Distances (A) and Angles (deg) for Cs6Sn2Se4(PSe5)2

9362(6)
l 19.18(6)
l 1430(6)
1 1792(6)
89. 17(5)
1 1544(6)
8638(6)
103.80(6)
103.1(1)
74.8(1)

166

3.2. Synthesis, Spectroscopy and Thermal Analysis

The syntheses of these compounds involve a redox reaction in which the metals are
oxidized by polyselenide ions in the AleySez] flux. The Sn4+ or In3+ centers are then
coordinated by the highly charged [PySez]n- ligands. Good control of the Lewis basicity of
the flux can be achieved by means of varying the starting composition.3f In the case of (I)-
(II) the flux was relatively less basic (Lewis) such as to obtain compounds with the
[P2866]4- unit which contains P4+. Instead, both compounds posses [P28e6]4- and
[PSe5]3- containing P4+ and P5+ respectively, indicating the presence of a complicated
Lewis acid-base equilibria.

The optical absorption properties of the compounds were evaluated by examining
the solid-state UV/vis diffuse reflectance spectra of the materials, Figure 6—7. The spectra
suggest that the compounds are semiconductors by revealing the presence of sharp optical
gaps. From these spectra the band-gap, Eg, can be assessed at 2.11 eV for
K41n2(PSe5)2(PZSe6) and at 1.51 eV for Rb3Sn(PSe5)(P25e6). The spectra of the
molecular compounds (III) and (IV) show also sharp optical gaps, where for
Rb5Sn(PSe5)3, Eg, is 1.61 eV, while for Cs6SnZSe4(PSe5)2 is 2.09 eV.

Both (III) and (IV) are insoluble in DMF and acetonitrile, but very soluble in a
solution of crown ether, 18C6, in DMF. They are also soluble, to a lesser degree, in a
solution of the same crown ether in acetonitrile. The solutions are dark-green in color, and
they are stable, by UV/vis, out to 3-4 days. The DMF and CH3CN/complexant solution
gave similar UV/vis spectra. For Rb58n(PSe5)3 one strong absorption at ~340 nm (3.65
eV)[in DMF], ~333 nm (3.72 eV)[in CH3CN], and for Cs6SnZSe4(PSe5)2 one strong
absorption at ~398 nm (3.12 eV)[in DMF], ~390 nm (3.18 eV)[in CH3CN].

The far-IR spectrum of K41n2(PSe5)2(P28e6) displays absorptions at ca. 486, 469,
451, 427, 304, 225, 184, 150 and 135 cm-1 whereas Rb3Sn(PSe5)(PZSe6) displays
absorptions at ca. 516, 490, 458, 452, 420, 389, 299, 225, 203, 186, 166, and 144 cm-1.

167

The absorptions above 200 cm-1 are assigned to P-Se vibrations of the [P2866]4- and
[PSe5]3- units with the characteristic Se-Se vibration appearing at ca. 225 cm-Lth 3a The
absorptions below 200 cm-1 are probably due to M-Se vibrations (M=In, Sn).2,3 The I .R.
spectrum of [Sn(PSe5)3]5' display absorptions at ~490, ~477, ~436, ~402, ~212, and
~177 cm'l, while [Sn28e4(PSe5)2]6' at ~550, ~475, ~379, ~350, ~267, ~240, ~198,
~183, and ~l42 cm’l. The absorptions at ~267, and ~240 cm‘1 are attributed to Se-Se
stretching vibrations,15 those at ~198, ~183, ~177, ~l42 cm“ to Sn-Se vibrations},3 and
those at higher energies are due to P-Se vibrations. The Raman spectra of [Sn(PSe5)3]5'
display absorptions at ~480, ~437, ~387, ~282, ~264, «224 and ~160 cm'l, while
[Sn23e4(PSe5)2]6' at ~473, ~379, ~354, ~263, ~227, ~195, ~159, and ~143 cm'l.
Differential thermal analysis (DTA) data, followed by careful XRD analysis of the
residues, show that Rb3Sn(PSe5)(P2Se6) melts incongruently at 4260C yielding mainly
SnSez. Compounds Rb58n(PSe5)3 and Cs6Sn28e4(PSe5)2 melt congruently at 406 and
456°C respectively. The DTA of K41n2(PSe5)2(P2Se6) displays more interesting behavior.
The first cycle (Figure 6-8A) shows a single endothermic peak at ca. 4200C but no
exothermic peaks appear upon cooling. Examination of the residue with XRD analysis
reveals only the presence of IngSe3. On subsequent heating, an exothermic peak is
observed at ca. 3000C (Figure 6-8B) indicating crystallization. Further heating results in
the same endothermic peak at ca. 4180C. If the heating in the above experiment is
terminated at 350°C, the XRD pattern of the residue matches that of the
K41n2(PSe5)2(P28e6). We attribute this behavior to a phase transformation of
K41n2(PSe5)2(P28e6) to In2Se3 and an amorphous glass of nominal composition

"K4P4Se13" at 4200C, according to the reaction of Eq. [1]:

Eq. [1]

420°C
K4'nz(P595)2(P2396) ——> |n2893 + "K4P4Sets"

168

Upon reheating, In23e3 and ”K4P4Se13" recombine, exothermically, to form the
starting compound K41n2(PSe5)2(P28e6) at 3000C. The decomposition of selenophosphate
frameworks to simpler binary compounds and amorphous glass has been observed in other
compounds before,3b. 36» 41) but this is the first case that we observe a reversibility of the

decomposition reaction upon reheating the decomposed byproducts. It is noteworthy, that

(Ph4P)[In(Se6)2] displays a similar thermal behavior. 18

169

 

 

 

 

3.0
if)
0
O 2.0-
05
D . §.0--...
s. :
U) .' 7“
O I
_1 I
t
I
I
I
1.0 . r‘ .

 

 

Energy (eV)

Figure 6-7: Solid-state optical absorption spectra of K4In2(PSe5)2(PZSe6) (dashed line)
and Rb3Sn(PSe5)(PZSe6) (solid line)

170

 

 

0
-3o
1
420°C exo
11V 0
endo
/ '
-30 300°C
41 8°C
-60

 

 

 

100 200 300 400 500 600

Temperature (°C)

Figure 6-8: DTA diagram for K41n2(PSe5)2(PZSe6) (A) First cycle, (B) second cycle

171

4. Conclusions

One of the appealing features of the chalcophosphate flux method is the possibility to
obtain different [Psz]n- groups to coexist in the same compound. In this type of chemistry
the metal is given the freedom to choose its own ligands which are suitable for lattice
construction. Although we have developed a working knowledge as to which type of.
[Psz]n- groups (i.e. P4+ or P5+) are likely to be stable in certain flux compositions, the
prediction of the exact ligands, especially when two different ones are involved in the same
compound, is very difficult. It is hoped that further work, in progress, will shed some light
on the role of the metal center in the complex acid-base equilibria of these reactions. In
addition, the first molecular, selenophosphate tin compounds with the unusual [PSe5]3‘
ligand have been prepared in molten polyselenophosphate Ax[PySez] fluxes. One of them,
Rb58n(PSe5)3, crystallizes in two forms, and access to each form can be very easily
achieved by slight adjustment of the synthesis temperature. These compounds maybe

useful as starting materials or building blocks for further solution or solid-state chemistry.

10.
11.

12.
13.
14.

15.
16.
17.
18.

172

References

M. G. Kanatzidis, Curr. Opinion Solid State and Mater. Sci. 2, 139, (1997).

(a) T. J. McCarthy, M. G. Kanatzidis, Chem. Mater. 5, 1061, (1993). (b) T. J.
McCarthy, M. G. Kanatzidis, J. Chem. Soc., Chem. Commun. 1089, (1994). (c)
T. J. McCarthy, T. Hogan, C. R. Kannewurf, M. G. Kanatzidis, Chem. Mater. 6,
1072, (1994) (d) T. J. McCarthy, M. G. Kanatzidis, J. Alloys Comp. 236, 70,
(1996) (e) K. Chondroudis, M. G. Kanatzidis, Materials Research Society, Fall
1996 Meeting, Boston, MA. (1) K. Chondroudis, T. J. McCarthy, M. G.
Kanatzidis, Inorg. Chem. 35, 840, (1996).

(a) T. J. McCarthy, M. G. Kanatzidis, Inorg. Chem. 34, 1257, (1995). (b) K.
Chondroudis, M. G. Kanatzidis, Inorg. Chem. 34, 5401, (1995). (c) K.
Chondroudis, T. J. McCarthy, M. G. Kanatzidis, Inorg. Chem. 35, 3451, (1996).
(d) K. Chondroudis, M. G. Kanatzidis, J. Chem. Soc., Chem. Commun. 401,
(1997). (e) K. Chondroudis, M. G. Kanatzidis, Angew. Chem. 36, 1324, (1997).

K. Chondroudis, M. G. Kanatzidis, J. Am. Chem. Soc. 119, 2574, (1997).

CERIUSZ, Version 1.6, Molecular Simulations Inc., Cambridge, England, 1994.

T. J. McCarthy, S.-P. Ngeyi, J.-H. Liao, D. DeGroot, T. Hogan, C. R.
Kannewurf, M. G. Kanatzidis, Chem. Mater. 5, 331, (1993).

N. Walker, D. Stuart, Acta Cryst. A39, 158, (1983).
R. H. Blessing, Acta Cryst. A51, 33, (1995).

(a) G. M. Sheldrick, " Crystallographic Computing 3 ", Oxford University Press:
Oxford, England, 1985. (b) G. J. Gilmore, Appl. Cryst. 17, 42, (1984).

W. Tremel, H. Kleinke, C. Reisner, J. Alloys Comp. 219, 73, (1995).

(a) R. Diehl, C. D. Carpentier, Acta Cryst. B34, 1097, (1978). (b) A. Katty, S.
Soled, A. Wold, Mater. Res. Bull. 12, 663, (1977).

J. Zhao, J. W. Kolis, J. Chem. Soc., Chem. Commun. 265, (1992).
R. D. Shannon, Acta Crystallogr. A32, 751, (1976).

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

S. P. Huang ; S. Dhingra ; M. G. Kanatzidis, Polyhedron , 1990, 9, 1389-1395.
J. M. McConnachie ; M. A. Ansari ; J. A. Ibers, Inorg. Chem, 1993, 32, 3250.
W. S. Sheldrick ; H. G. Braunbeck, Z. Naturfon, 1989, 44b, 851.

S. Dhingra, M. G. Kanatzidis, Science, 258, 1769, (1992).

CHAPTER 7

New Lanthanide Polychalcophosphates. Synthesis and Characterization of the molecular

Rb9C6(PSe4)4, l-D A3MP2863, and the 2-D A2MP2867 (A = Rb, CS; M = Ce, Gd)

1. Introduction

The application of the polychalcophosphate fluxes to the synthesis of new

chalcophosphates is contributing significantly to the development of this class of
compoundsl-5 The in situ fusion of AzQ/P2Q5/Q (A=Alkali metal, Q=S, Se) forms highly

reactive [Psz]n- species solubilized in an excess of polychalcogenide flux. These species
in the presence of metal ions, coordinate and become the building blocks of new polymeric
structures. The variation of the flux composition provides a way of controlling the reaction

outcome in the sense that we can select species with either P4+ (usually [P28e6]4-) or

P5+.3f By increasing the Lewis basicity of the flux, (i.e. increase of the AzQ

concentration), we demonstrated that access to molecular compounds is feasible, provided

of course a sufficient concentration of [Psz]n- ligands is present.2b. 3b Application of this
technique to the lanthanides yielded the first molecular lanthanide selenophosphate, namely
Rb9Ce(PSe4)4 (I) and herein, we report the synthesis, structure, optical, magnetic and
thermal properties of this novel complex. Given the oxophilicity of cerium and the
extremely high negative charge of this complex, it is unlikely that it could be prepared via a
solution route. Its very preparation underscores the synthetic power of these chalcogen-

based fluxes.

173

174
By utilizing the ability of our method to control the flux composition and affect the

presence of the various [Psz]n‘ units in the final product,3f we also synthesized the solid-
state one-dimensional A3MPZSe8 (II, III), and the two-dimensional A2MP2Se7 (IV, V)
(A = Rb, Cs; M = Ce, Gd) and here we report their synthesis, structural characterization,

optical and thermal properties.

2. Experimental Section
2.1. Reagents

The reagents mentioned in this study were used as obtained unless noted otherwise
: The reagents mentioned in this study were used as obtained unless noted otherwise : (i)
Ce and Gd metal (99.99%) were acquired from Johnson Matthey/AESAR Group,
Seabrook, NH. (ii) red phosphorus powder, Morton Thiokol, Inc., -100 mesh, Danvers,
MA. (iii) rubidium and cesium metal, analytical reagents, Johnson Matthey/AESAR Group,
Seabrook, NH. (iv) selenium powder, 99.5+% purity, -100 mesh, Aldrich Chemical Co.,
Inc., Milwaukee, Wi. (v) N,N-Dimethylformamide (DMF) reagent grade, EM Science,
Inc., Gibbstown, NJ. (vi) diethyl ether, ACS anhydrous, EM Science, Inc., Gibbstown,
NJ.

2.2. Syntheses.

A28e (A=K, Rb, Cs; Q=S, Se) were prepared by reacting stoichiometric amounts

of the elements in liquid ammonia as described elsewhere.33

175
P28e5 The amorphous phosphorus selenide glass "P28e5", was prepared by

heating a stoichiometric ratio of the elements as described elsewherefiwl
Preparation of Rb9Ce(PSe4)4 (I). (A) Single crystals of Rb9Ce(PSe4)4 were
synthesized from a mixture of Ce (0.30 mmol), P28e5 (0.60 mmol), Rb28e (1.50 mmol),

and Se (3.00 mmol) heated to 510 0C for 4 d followed by cooling to 50 0C at 3 0C h-l. The

excess bePySez flux was removed with degassed DMF. The product was then washed

with ca. 2 ml of tri-n-butyl phosphine to remove SeO. Washing with ether revealed a
mixture of orange rod-like crystals of Rb9Ce(PSe4)4 (70%), and red crystals of Rb4PZSe9
(30%).3b The crystals of Rb9Ce(PSe4)4 decompose on exposure to air (2-3 h) and water (1
min). (B) Pure material was synthesized from a mixture of Ce (0.30 mmol), P (1.20
mmol), Rb2Se (1.35 mmol), and Se (3.45 mmol) heated to 620 0C for 2 (1 followed by
cooling to 150 0C at 24 OC h-l. Washings with DMF and ether revealed pure orange
microcrystals of Rb9Ce(PSe4)4 (84%). Microprobe analysis gave a composition of
Rb9.1Cel.0P4.3Sei6.4-

Preparation of Rb3CePZSe3 (II). (A) Single crystals of (II) were synthesized

from a mixture of Ce (0.6 mmol), P28e5 (0.6 mmol), RbQSe (1.2 mmol), and Se (3.0
mmol) that was sealed under vacuum in a Pyrex tube and heated to 5000C for 4d followed

by cooling to 150°C at 30C h-l. The excess bePySeZ flux was removed by washing with
DMF to reveal a mixture of red polyhedral plates of Rb3CePZSeg (60%) and orange rod-
like crystals of Rb9Ce(PSe4)4 (40%). The Rb3CeP2$e3 crystals decompose on exposure to

air (2-3 h) and water (1 min). (B) Pure material was synthesized from a mixture of Ce
(0.40 mmol), P (0.80 mmol), szSe (0.60 mmol), and Se (2.60 mmol) heated to 570 0C

for 2 d followed by cooling to 150 0C at 24 0C h-1. Small amounts of bePySeZ flux and

Rb9Ce(PSe4)4 were removed by washing the material with a mixture of DMF/1120 (30:1)

176

for two minutes. Further washing with ether revealed pure red-orange microcrystals of
Rb3CePZSeg (86%). Microprobe analysis gave a composition of Rb3,2Ce1 _0P2.25e7.9.
Preparation of CS3GdPZSe3 (III). A mixture of Gd (0.40 mmol), P (0.80

mmol), C528e (0.60 mmol), and Se (2.60 mmol) was heated to 570 0C for 2 (1 followed by

cooling to 150 0C at 24 0C h]. Small amounts of CsxPySeZ flux were removed by washing
the material with a mixture of DMF/HzO (30:1) for two minutes. Further washing with
ether revealed pure yellow microcrystals of CS3GdP28e3 (84%). The crystals decompose
on exposure to air (2-3 h) and water (1 min). Microprobe analysis gave a composition of
C82.8Gd1.0P2.1368.1-

Preparation of szCePZSe7 (IV). A mixture of Ce (0.40 mmol), P (0.80

mmol), szse (0.40 mmol), and Se (2.40 mmol) was heated to 650 0C for 2 (1 followed

by cooling to 150 0C at 25 0C h-l. Small amounts of bePySez flux were removed by
washing with DMF. Further washing with ether revealed pure red microcrystals of
szCePZSe7 (81%). The crystals decompose on exposure to air (3-5 h) and water (3 min).
Microprobe analysis gave a composition of Rb1,9Ce1_oP2,3Se7,3.

Preparation of CszGdPZSe7 (V). (A) Single crystals of (V) were synthesized

from a mixture of Gd (0.6 mmol), P2Se5 (0.6 mmol), C828e (0.6 mmol), and Se (3.0
mmol) that was sealed under vacuum in a Pyrex tube and heated to 5150C for 4d followed

by cooling to 1500C at 30C h-l. Most of the CsxPySez flux was removed by washing with
DMF to reveal a mixture of small orange plates of CszGdPZSe7 (40%) and black powder
of residual flux (60%). The CszGdPZSe7 crystals decompose on exposure to air (3-5 h)

and water (3 min). (B) Pure material was synthesized from a mixture of Gd (0.40 mmol),
P (0.80 mmol), C828e (0.40 mmol), and Se (2.40 mmol) heated to 650 0C for 2 (1

followed by cooling to 150 0C at 24 0C h-l. Small amounts of CsxPySez flux were

removed by washing with DMF. Further washing with ether revealed pure red-orange

177
microcrystals of CszGdP2$e7 (87%). Microprobe analysis gave a composition of

C81.8Gd1.0P2.1367.3-

2.3. Physical Measurements

Powder X-ray Dijfraction (XRD). Analyses were performed using a calibrated
Rigaku-Denki/RW400F2 (Rotaflex) rotating anode powder diffractometer controlled by an

IBM computer, operating at 45 kV/ 100 mA and with a 10/min scan rate, employing Ni-
filtered Cu radiation. Powder patterns were calculated with the CERIUS2 software.6

Infrared Spectroscopy. Infrared spectra, in the far-IR region (600-50 cm-l), were

recorded on a computer controlled Nicolet 750 Magna-IR Series II spectrophotometer

equipped with a TGS/PE detector and silicon beam splitter in 4 cm-1 resolution. The
samples were ground with dry CsI into a fine powder and pressed into translucent pellets.
Solid State U V/Vis Spectroscopy. Optical diffuse reflectance measurements were
performed at room temperature using a Shimadzu UV-3101PC double beam, double
monochromator spectrophotometer. The instrument is equipped with integrating sphere
and controlled by a personal computer. BaSO4 was used as a 100% reflectance standard for
all materials. Samples were prepared by grinding them to a fine powder and spreading them
on a compacted surface of the powdered standard material, preloaded into a sample holder.

The reflectance versus wavelength data generated can be used to estimate a material's band

gap by converting reflectance to absorption data as described earlier.7
Single crystal optical transmission spectroscopy. Room temperature single crystal
Optical transmission spectra were obtained on a Hitachi U-6000 Microscopic FT

Spectrophotometer mounted on an Olympus BH2-UMA metallurgical microscope over a

178
range of 380 to 900 nm. Crystals lying on a glass slide were positioned over the light

source and the transmitted light was detected from above. .

Differential Thermal Analysis (DTA). DTA experiments were performed on a
computer-controlled Shimadzu DTA-50 thermal analyzer. Typically, a sample (~ 25 mg) of
ground crystalline material was sealed in quartz ampoules under vacuum. A quartz ampoule

of equal mass filled with A1203 was sealed and placed on the reference side of the detector.
The samples were heated to the desired temperature at 10 0C/min, then isothermed for 10

minutes and finally cooled to 50 0C at the same rate. Residues of the DT A experiments
were examined by X-ray powder diffraction. To evaluate congruent melting we compared
the X-ray powder diffraction patterns before and after the DTA experiments. The
stability/reproducibility of the samples were monitored by running multiple heating/cooling
cycles.

Semiquantitative Microprobe Analyses. The analyses were performed using a
JEOL JSM-6400V scanning electron microscope (SEM) equipped with a TN 5500 EDS
detector. Data acquisition was performed with an accelerating voltage of 20kV and thirty
seconds accumulation time.

Magnetic Susceptibility Measurements. The magnetic response of the compounds
was measured over the range of 5-300K using a MPMS Quantum Design SQUID
magnetometer. Samples were ground to a fine powder to minimize possible anisotropic
effects, and loaded into PVC containers. Corrections for the diamagnetism of the PVC
sample container were made by measuring the magnetic response of the empty container
under identical conditions. Corrections for core atom diamagnetism were also applied.

Single Crystal X-ray Crystallography. A Siemens SMART Platform CCD

diffractometer was used to collect data from a crystal of (II). An empirical absorption

correction3 was applied to the data. Intensity data for (I) and (IV) were collected using a

Rigaku AFC6S four-circle automated diffractometer equipped with a graphite crystal

179

monochromator. An empirical absorption correction based on t}! scans was applied during

initial stages of refinement. The space groups were determined from systematic absences

and intensity. No crystal decay was detected in any of the compounds. The structures were

solved by direct methods using SHELXS-86 software93 (for all compounds), and full

matrix least squares refinement was performed using the TEXSAN software package.9b
Crystallographic information for the compounds are given in Table 7-1. The

coordinates of all atoms, average temperature factors, anisotropic displacement parameters

and their estimated standard deviations are given in Tables 7-2 to 7-7.

180

Table 7-1. Crystallographic data for Rb9Ce(PSe4)4, Rb3Cesteg. and CszGszSe7

 

 

Formula Rb9Ce(PSe4)4 Rb3CeP28e3 CszGdP2$e7
FW 2296.58 1090. 15 1037.73
a, A 21.446(5) 9.6013(2) 10.137(2)
b, A 10.575(5) 18.06040) 7.212(1)
c, A 18.784(4) 10.09310) 20.299(2)
ot (deg) 90.00 90.00 90.00
[3 (deg) 1 1594(2) 90.619( 1) 98.230)
7 (deg) 90.00 90.00 90.00
2, V(A31 4; 3831(2) 4; 1750.07(3) 4; 1468.8(4)
11(Mo 1(a), A 0.71069 0.71069 0.71069
space group C2/c P21/c (#14) P21/n (#14)
peak, g/cm3 3.980 4.137 4.692
p, cm.1 274.78 276.66 269.36
Temp (0C) 23 -100 25
Final R/wa! % 4.4/5.5 3.0/3.3 3.1/2.6
Total Data 2764 8932 2993
Measured
Total Unique Data 2677 3086 2824
(ave)
Data F02>30(F02) 1592 2465 1737
No. of Variables 137 128 110

Crystal Dimen..
mm

are = 201701 - Inn/215,1. RW = {£w(IF0| - IFC|)2/ZWIF0|2}1/2.

0.56 x 0.17 x 0.17

0.28 x 0.25 x 0.18

0.39 x 0.20 x 0.14

181

Table 7-2. Positional parameters and Beqa for Rb9Ce(PSe4)4

 

 

Atom X Y Z Bequz
Ce 1/2 0.2468(2) 1/4 1.38(7)
Rb( 1) 0.4146(1) 0.5109(2) 0.0180(1) 2.6(1)
Rb(2) 0.2671(1) 0.7410(3) 0.1309(2) 3.8(1)
Rb(3) 0.5854(1) -0.01 12(2) 0.1035(1) 2.6(1)
Rb(4) 0.2538(1) 0.2418(2) 0.1293(1) 3.0(1)
Rb(5) 1/2 0.7460(3) 1/4 1.1(1)
Se(1) 0.4261(1) 0.1744(2) 0.0673(1) 2.1(1)
Se(2) 0.3933(1) 0.0197(3) 0.2096(1) 25( 1)
Se(3) 0.2387( 1) 0.4901 (2) —00029( 1) 249(9)
Se(4) 0.4179(1) 0.8367(2) 0.0585(2) 2.6(1)
Se(5) 0.4274(1) 0.3209(2) 0.3598(1) 2.1(1)
Se(6) 0.3930(1) 0.4734(2) 0.1836(1) 2.2(1)
Se(7) 0.2617(1) 0.4846(2) 0.2587(1) 2.21 (9)
Se(8) 0.4178(1) 0.6586(2) 0.3588(1) 2.2(1)
P( 1) 0.3721(2) 0.0066(5) 0.0831(3) 1.4(2)
P(2) 0.3720(2) 0.4874(5) 0.2889(3) 1.2(2)

a B values for anisotropically refined atoms are given in the form of the isotropic equivalent displacement
parameter defined as Beq = (4/3)[aZB(1, 1) + bZB(2, 2) + czB(3, 3) + ab(cosy)B( 1 ,2) + ac(cos13)B(l,3) +

bc(cos0t)B(2, 3)]

182

Table 7-3. Anisotropic Displacement Parameters for Rb9Ce(PSe4)4

 

 

Atom U1 1 U22 U33 U12 U13 U23
Ce 0.0157(9) 0.014(1) 0.021(1) 0 0.0071(8) 0
Rb( 1) 0.036(1) 0.038(1) 0.030(1) -0.001(1) 0.01 8( 1) 0.000( 1)
Rb(2) 0.069(2) 0.032(1) 0.050(2) 0.008(1) 0.032(2) 0.006(1)
Rb(3) 0.035(1) 0.038(1) 0.025(1) 0.002( 1) 0.012(1) 0000( 1)
Rb(4) 0.047(1) 0.028(1) 0.045(2) -0.005(1) 0.025(1) -0.008(1)
Rb(5) 0.016( 1) 0.014(1) 0.01 1(2) 0 0.003(1) 0
Se(1) 0.035(1) 0.022(1) 0.023( 1) -0.002( 1) 0.014(1) 0.001(1)
Se(2) 0.019(1) 0.061(2) 0.017(1) -0.005( 1) 0.007(1) -0.002(1)
Se(3) 0.015( 1) 0.045(1) 0.024(1) -0.002( 1) -0.001(1) -0.005(1)
Se(4) 0.042(2) 0.024(1) 0.037(2) -0.001( 1) 0.022(1) -0.009(1)
Se(5) 0.039(1) 0.018(1) 0.025(1) 0.005(1) 0.015(1) 0.006(1)
Se(6) 0.018(1) 0.049(2) 0.018(1) 0.008(1) 0.008( 1) 0.002( 1)
Se(7) 0.014(1) 0.034(1) 0.038(1) -0.001(1 ) 0.013(1) -0.004(1)
Se(8) 0.035(1) 0.018(1) 0.029(2) -0.003(1) 0.013(1) -0.007(1)
P( 1) 0.015(3) 0.022( 3) 0.014(3) -0.000(2) 0.004(2) -0.002(3)
P(2) 0.01 1(3) 0.018(3) 0.016(3) -0.003(2) 0.005(2) -0.004(3)

183

Table 7-4. Positional parameters and ng for Rb3CeP2$e8

 

 

 

 

Atom X Y Z Beq A2
Ce 0.72784(5) 0.51301(2) 0.02630(5) 091(1)
Rb( 1) 0.7631(1) 0.46475(5) 0.48286(9) 1.68(2)
Rb(2) 0.6097(1) 0.79445(5) 0.1332(1) 234(2)
Rb(3) 0.0975(1) 0.71053(5) 0.1415(1) 375(3)
Se(1) 1.0396(1) 052276(4) 017836(9) 1.1 1(2)
Se(2) 1.1719(1) 0.34340(4) 0.09120(8) 132(2)
Se(3) 1.0733(1) 037553(5) 0.42713(8) 135(2)
Se(4) 0.8120(1) 0.37049(5) 0.16763(9) 152(2)
Se(5) 0.5557(1) 051539(5) -025420(8) 1.4 l (2)
Se(6) 0.3824(1) 0.68264(5) 0.35582(9) l.45(2)
Se(7) 0.4677(1) 0.62157(5) 0.02460(8) 1 . 15(2)
Se(8) 0.7233(1) 0.61369(5) 0.27239(8) l.29(2)
P( 1) 0.9728(2) 0.5979(1) 0.2221(2) 090(4)
P(2) 0.4982(2) 0.6032(1) 0.2403(2) 082(4)
Table 7-5. Anisotropic Displacement Parameters for Rb3CeP28e3
Atom U1 1 U22 U33 U 12 U13 U23
Ce 0.0137(3) 0.0042(2) 0.0166(3) 0.0008(2) 0.0058(2) 0.0007(2)
Rb( 1) 0.0227(5) 0.0174(5) 0.0237(5) 0.0002(4) 0.0035(4) 0.0018(4)
Rb(2) 0.0281(6) 0.0164(5) 0.0441(6) 0.0083(4) 0.0158(5) 0.0039(4)
Rb(3) 0.0735(9) 0.0124(5) 0.0556(7) 0.01 1 1(5) 0.0430(7) 0.01 19(5)
Se(1) 0.0167(5) 0.0043(4) 0.0210(5) 0.0008(4) 0.0026(4) 0.0010(3)
Se(2) 0.0242(5) 0.0056(4) 0.0205(5) 0.0031(4) 0.0009(4) 0.0010(4)
Se(3) 0.0207(5) 0.0156(5) 0.0150(5) 0.0004(4) 0.0054(4) 0.0032(4)
Se(4) 0.0144(5) 0.0095(5) 0.0337(5) 0.0029(4) 0.01 12(4) 0.0051(4)
Se(5) 0.0281(6) 0.0057(4) 0.0196(5) 0.0005(4) 0.0068(4) 0.0010(4)
Se(6) 0.0223(5) 0.01 10(5) 0.0216(5) 0.0037(4) 0.0008(4) 0.0057(4)
Se(7) 0.0148(5) 0.0151(5) 0.0137(4) 0.0043(4) 0.0054(4) 0.0033(4)
Se(8) 0.0129(5) 0.0202(5) 0.0160(5) 0.0019(4) 0.0054(4) 0.0002(4)
P( 1) 0.011(1) 0.006(1) 0.017(1) 0.001(1) 0.005(1) 0.0000(9)
P(2) 0.012(1) 0.007(1) 0.012(1) 0.001(1) 0.001(1) 0.0013(9)

184

Table 7-6. Positional parameters and Beq for CszGdP28e7

 

 

 

 

Atom X Y Z B eq A2
Gd 0.19034(5) 0.02248(8) 0.84834(2) 1.15(1)
Cs(l) -035622(7) 0.0006(1) 0.79778(4) 267(2)
Cs(2) 0.26145(7) 0.4983(1) 1.02675(4) 232(2)
Se( 1) 0.3082(1) 0.0839(2) 0.72420(5) 151(2)
Se(2) 0.0722(1) 0.2560(2) 0.59694(6) l.43(2)
Se(3) 0.1044(1) 0.2367(2) 0.60355(6) 159(2)
Se(4) -0.02913(9) 0.0016(2) 0.73524(5) l.65(2)
Se(5) -00069( 1) 0.2402(2) 0.89686(6) l.48(2)
Se(6) -0.0150( 1) 0.2504(2) 0.89924(6) 1.60(3)
Se(7) 0.2642(1) 0.0053(2) l .01924(5) 1.79(2)
P( 1) 0.3852(2) 0.4828(4) 0.8364(1) 1 . 17(5)
P(2) 0.0668(2) 0.0005(5) 1.0485(1) l.19(5)
Table 7-7. Anisotropic Displacement Parameters for CszGdPZSe7
Atom U1 1 U22 U33 U12 U13 U23
Gd 0.0125(3) 0.0174(3) 0.0139(3) 0.0002(3) 0.0016(2) 0.0001(3)
Cs( 1) 0.0221(4) 0.0404(5) 0.0388(4) 0.0013(4) 0.0039(3) 0.0049(5)
Cs(2) 0.0296(4) 0.0247(4) 0.0362(4) 0.0012(4) 0.0121(3) 0.0019(4)
Se(1) 0.01 13(5) 0.0284(7) 0.0162(6) 0.0027(5) 0.0033(4) 0.0031(5)
Se(2) 0.0177(6) 0.0196(6) 0.0152(6) 0.0010(5) 0.0043(5) 0.0041(5)
Se(3) 0.0238(6) 0.0176(6) 0.0166(7) 0.0035(5) 0.0049(5) 0.0035(5)
Se(4) 0.0135(5) 0.0336(7) 0.0161(5) 0.0018(6) 0.0029(4) 0.0024(6)
Se(5) 0.0229(6) 0.0194(6) 0.0150(7) 0.0026(5) 0.0064(5) 0.0020(5)
Se(6) 0.0229(7) 0.0166(6) 0.0225(7) 0.0033(6) 0.0072(5) 0.0035(5)
Se(7) 0.0139(5) 0.0269(6) 0.0279(6) 0.0004(6) 0.0052(5) 0.0013(6)
P(l) 0.016(1) 0.017(1) 0.012(1) 0.002(1) 0.002(1) 0.001(1)
P(2) 0.014(1) 0.017(1) 0.015(1) 0.000(1) 0.002(1) 0.000(1)

185

3. Results and Discussion

3.1. Description of Structures

Structure of Rb9Ce(PSe4)4 (I). The discrete [Ce(PSe4)4]9- anion features a

trivalent cerium center coordinated by four chelating [PSe4]3- tetrahedra, Figure 7-1. The

eight donor Se atoms around the Ce adopt a triangulated dodecahedral geometry, see
Scheme 1, with a pseudo D2d symmetry. The Ce center is situated on a 2-fold axis.

According to the notation of Hoard & Silverton, chelation is along the mmmm

dodecahedral edges and thus the complex belongs to the Id (DZd-ZZm) sub-class of

M(X2)4 stereoisomers.10 Eight-coordinate Ce3+ has been observed in CePS411 and

KCeSe412 but in both cases the metal is in a square antiprismatic environment.

SGS-A a 881 "A

 

 

a SSS-A
Set -A

Scheme 1

186
In Rb9Ce(PSe4)4 the four-membered P-Se-Ce-Se rings which form by the chelation

of the [PSe4]3- ligands are not significantly strained probably due to the relatively large

ionic radius of the Ce3+ center (1.143A).13 The degree of strain in a chelating ligand is

often expressed in terms of the bite distance, i.e. the separation of the two donor atoms in a
chelate ring. For comparison, we can consider the complex [Pd(PSe4)2]4- which contains
bidentate [PSe4]3- ligands and significantly strained four-membered P-Se-Pd-Se rings.14 In
[Ce(PSe4)4]9-, the "bite" distance [Se(1)-Se(2)] for the P(l) group is 3.457(3)A and for the
P(2) group [Se(5)-Se(6)] is 3.459(3)A, whereas the corresponding one for [Pd(PSe4)2]4-
is 3.305(4)A [the Se-Se distance for an uncoordinated [PSe4]3- unit is 3.562(7)A].10 The
Se-P-Se angle is 102.7(2)o for the P(l) group [Se(1)-P(l)-Se(2)] and 1026(2)0 for the
Se(5)-P(2)-Se(6), whereas the corresponding angle for [Pd(PSe4)2]4- is 94.1(2)o [the
corresponding angle for an uncoordinated [PSe4]3- unit is 107.6(3)0].

The unit cell, see Figure 7-2, contains four [Ce(PSe4)4]9- molecules which when
viewed down the b-axis are remarkably well ordered, stacking in an eclipsed fashion.
These anions are separated by the eight-coordinate Rb(l), Rb(3) and Rb(5) [range of Rb-
Se distances, 3354(3)-3.740(3)A; av. 3.543A], by the seven-coordinate Rb(4) cation
[range of Rb(4)-Se distances, 3.467(3)-3.884(3)A; av. 3.590A] and by the six-coordinate
Rb(2) cation [range of Rb(2)-Se distances, 3.520(3)-3.833(3)A; av. 3.660A]. Selected
bond distances and angles for (I) are given in Table 7-8.

Structure of Rb3CeP28es (II). Rb3CePZSeg (II) and CS3GdPZSe3 (III) are
isostructural, but since the single-crystal structure determination was performed on (II),

the discussion will refer mainly to this compound. A more descriptive formula for (11) is
Rb+3Ce3+(PSe4)3-2. The structure contains infinite [Ce(PSe4)2]n3n- chains separated by
Rb+ cations which propagate along the [l 0 0] direction, Figure 7-3. The chains consist of

Ce3+ cations linked by tridentate [PSe4]3- ligands, Figure 7-4A. Each Ce atom is

187
coordinated by four such ligands to yield a coordination polyhedron of a bicapped trigonal

prism, Figure 7-4B. Each [PSe4]3- ligand coordinates to two neighboring Ce centers, by
utilizing one Se atom for every Ce, whereas a third Se atom is coordinated to both Ce
centers. This structural motif has been observed in other chalcophosphates such as
KTiPSe5,3b and KZMP2S7 (M=V, Cr). 15 The Ce polyhedra share edges along the direction
of the chain, in such a way that there is an alternating short-long-short Ce-Ce distance in
the chain. For example, the Ce-Ce’ distance is 5.280(1)A, whereas the Ce-Ce” one is
4.426(1)A. The Ce-Se distances average at 3.15(4)A and compare very well with those
found in (I). The longest Ce-Se distances are exhibited by the capping Se atoms [Se(l’),
Se(5)], Figure 7-4B. The P-Se distances range from 2.164(2) to 2.227(2)A with the
terminal selenium atoms displaying the shorter distances. The chains are separated by Rb+
ions that are located in three different sites. Rb(l) is coordinated by eight Se atoms [range
of Rb(l)-Se distances, 3.403(l)-3.898(1)A; av. 3.568A], Rb(2) is also eight-coordinate
[3.438(1)-3.978(1)A; av. 3.654A], and Rb(3) is six-coordinate [3.457(1)-3.609(1)A; av.
3.529A]. Tables of selected distances and angles for Rb3CePZSe3 are given in Table 7-9.
Structure of CszGdP28e7 (V). szCeP28e7 (IV) and CszGdP28e7 (V) are
isostructural, but since the single-crystal structure determination was performed on (V),
the discussion will refer mainly to this compound. A more descriptive formula for (V) is
Cs+4Gd3+2(PSe4)3-2(P28e6)4-. The [Gd2(PSe4)2(P2Se6)]n4n- layers propagate along the
[1 0 1] direction and they are separated by Cs+ cations, Figure 7-5. The compound is

mixed ligand containing both [PSe4]3- and [P2Se6]4- units. The layers consist of infinite

[Gd(PSe4)]x “chains” that propagate along the [010] direction. These “chains” are then
interstiched in two dimensions by hexadentate [P2Se6]4- units which coordinate to two

neighboring Gd3+ centers, Figure 7-6A. There is a crystallographic center of symmetry

located in the center of every P—P bond. Each tetradentate [PSe4]3- unit bridges three Gd3+

188
centers and every Gd3+ center is coordinated by three [PSe4]3- units. The Gd3+
coordination is completed by one [P28e6]4- unit yielding a square antiprismatic
environment for the metal, Figure 7-6B. The Gd-Se distances average at 3.07(2)A slightly

shorter than Ce-Se as expected for the smaller Gd ion.13 The P-Se distances range from

2.167(3) to 2.214(4)A. The P-P bond is 2.224(7)A. The layers are separated by Cs+ ions
that are located in two different sites. Cs(l) is coordinated by seven Se atoms [range of
Cs(1)-Se distances, 3.565(2)-3.921(2)A; av. 3.751A], and Cs(2) is ten-coordinate
[3.559(2)-3.982(2)A; av. 3.747A]. Tables of selected distances and angles for
CszGdP28e7 are given in Table 7-10.

(D;
Se(4)

189

Se(3) Se(7)
a; (9
3P0) P(2)

(1e) Se(5) f,

(N

S 2 S 6 v

e( 0\611 et) Se(8)

. Ce

Se(2') 1.91 1' Se(6') a)
,. Se(1') Se(5) :9

n.1,
1!

Figure 7-1: A single [Ce(PSe4)4]9- molecule with labeling (ORTEP view, 70%

ellipsoids)

190

 

The unit cell of Rb9Ce(PSe4)4 looking down the b-axis

 

 

Figure 7-2:

191

 

 

 

 

 

 

 

Figure 7-3: ORTEP representation of Rb3CePzSe3 as viewed down the a-axis (70%
ellipsoids). In the infinite part of the structure Ce is shown as octant shaped
ellipses, selenium as open ellipses and phosphorus as crossed ellipses with
no shading. Rb cations between the chains are shown as open ellipses

192

 

 

 

Figure 7-4: (A) View of a single [CeP28e3]n3n- chain with labeling. (B) Bicapped

trigonal prismatic environment around Ce3+

193

 

 

 

Figure 7-5: ORTEP representation of CszGdP28e7 as viewed down the b-axis. (80%
ellipsoids). In the infinite part of the structure Gd is shown as octant shaped
ellipses, selenium as Open ellipses and phosphorus as crossed ellipses with
no shading. Cs cations between the layers are shown as open ellipses

194

 

 

 

 

 

 

 

Figure 7-6: (A) Perpendicular view (along [1 0 1]) of a [GszSe7]n2"- layer with

labeling. (B) Square antiprismatic environment around Gd3+.

Table 7-8. Selected Distances (A) and Angles (deg) for Rb9Ce(PSe4)4

195

Se(1)-Ce-Se(2) 6594(6) Ce-Se (av.) 3.175(4)
Se(1)-Ce-Se(5) l 27.23( 6) P( 1 )-Se( 1) 2.209(6)
Se(1)-Ce-Se(6) 7987(6) P( 1 )-Se( 2) 2.219(6)
Se(1)-Ce-Se(2') 9245(7) P(1)-Se(3) 2.188(5)
Se(1)-Ce-Se(6') 12268(6) P(1)—Se(4) 2.192(6)
Ce-Se( l )-P( 1) 953(2)
Ce-Se(2)-P( l) 95.3(2)
Se(1)-P(1)-Se(2) 102.7(2)
Se(1)-P(l)-Se(3) 111.7(3)
Se(1)-P(1)-Se(4) 108.7(2)
Se(3)-P(1)-Se(4) 108.6(2)

a The estimated standard deviations in the mean bond lengths and the mean bond angles are calculated by the
equation 0'1 = (2,,(ln — [)2/n(n — 1)}1/2, where in is the length (or angle) of the nth bond, 1 the mean length
(or angle), and n the number of bonds.

Table 7-9. Selected Distances (A) and Angles (deg) for Rb3CeP28eg

Ce-Se( l)
Ce-Se(l ’)
Ce-Se( 2)
Ce-Se(4')
Ce-Se(5)
Ce-Se(7)
Ce-Se(7’)
Ce-Se(8’)
Ce-Ce’
Ce-Ce’ ’

Se(1)-Ce-Se( l ’)
Se( 1 )-Ce-Se(2)
Se(1)-Ce-Se(4’)
Se( 1 )-Ce-Se(5)
Se( 1 )—Ce-Se(7)
Se( 1 )-Ce-Se(7’)
Se(l ’)-Ce-Se(5)
Se(1)-Se(] ‘)-Se(2)
Se(1)-Se(4’)—Se(7)
Se( 1 )-Se(2)-Se(7’)
Se( 1 )-Se(2)-Se( 8’)
Se(2)-Se(7’ )-Se(7)

3.126(1)
3.354(1)
3.014(1)
3.048(1)
3.263(1)
3.111(1)
3.175(1)
3.079(1)
5.280(1)
4.426(1)

7090(3)
71 .60(3)
8697(3)
7777(3)
9941(3)
133.75(3)
l46.89(3)
5370(2)
7700(3)
104.85(3)
9845(3)
9009(3)

196

P( 1 )-Se( 1 )
P( l )-Se(2)
P( 1)-Se(3)
P( 1 )-Se(4)
P(2)-Se(5)
P(2)-Se(6)
P(2)-Se(7)
P(2)-Se(8)

Ce-Se(1)-P( 1)
Ce-Se(2)-P( 1)
Ce-Se(5)-P(2)
Ce-Se(7)-P(2)
Ce-Se(1)-Ce’
Ce-Se(7)-Ce’ ’

Se(1)-P(l )-Se(2)
Se(1)-P(l)-Se(3)
Se(1)-P( 1 )-Se(4)
Se(5)-P(2)-Se(6)
Se(5)-P(2)-Se(7)
Se(5)-P(2)-Se(8)

2.227(2)
2.200(2)
2.165(2)
2.207(2)
2.208(2)
2.164(2)
2.218(2)
2.190(2)

8823(7)
91 .61(6)
9280(6)
9078(6)
109.10(3)
8953(3)

108.5(1)
113.31(9)
104.82(9)
119.1(1)
100.32(9)
107.8(1)

Table 7- 10. Selected Distances (A) and Angles (deg) for CszGszSe7

Gd-Se( 1 )
Gd-Se( 1 ’)
Gd-Se(2')
Gd-Se(3’)
Gd-Se(4)
Gd-Se(5)
Gd-Se(6)
Gd-Se(7‘)

Se( 1 )«Gd-Se( 1 ')
Se( 1 )—Gd-Se(2’)
Se( 1)-Gd-Se(3’)
Se(1)-Gd-Se(4)
Se( 1)-Gd-Se(5)
Se(1)—Gd-Se(6)
Se(1)-Gd-Se(7')
Se(1)-Se(4)-Se(5)
Se(3’)-Se(1)—Se(4)
Se(1)—Se(1’)-Se(6)
Se(1)—Se(3’)-Se(2')
Se(1’)«Se(6)-Se(7’)
Se(6)-Se(7')-Sc(2’)

3.038(1)
3.199(2)
2.969(2)
2.991(2)
2.965(2)
3.020(2)
2.953(2)
3.445(2)

7928(3)
9299(4)
7606(4)
7155(4)
1 18.01(5)
144.25(5)
140.51(4)
9241(5)
9586(5)
9596(4)
7227(5)
9802(5)
7424(5)

197

P( 1 )—Se( 1 )
P(1)-Se(2)
P( l )-Se(3)
P(1)-Se(4)
P(2)-Se(5)
P(2)-Se(6)
P(2)-Se(7)
P(2)-P(2’)

Gd-Se(1)—P(l)
Gd-Se(4)-P( 1)
Gd-Se(5)—P(2)
Gd-Se(6)-P(2)

Gd-Se(l )-Gd’

Se(1)-P(1)—Se(2)
Se(1)—P(l)—Se(3)
Se(1)-P(l)-Se(4)
Se(5)-P(2)-Se(6)
Se(5)-P(2)Se(7)
Se(5)-P(2)-P(2’)

2.214(4)
2.194(4)
2.194(4)
2.205(3)
2.187(4)
2.199(4)
2.167(3)
2.224(7)

8908(9)
91.1(1)
85.1(1)
86.6(1)

129.35(6)

104.6(2)
117.3(2)
105.2(1)
107.6(1)
117.4(2)
105.9(3)

198
3.2. Synthesis, Spectroscopy and Thermal Analysis

The syntheses of these compounds involves a redox reaction in which oxidation of
the metals occurs by polyselenide ions in the An[PySez] flux. The M3+ centers are then
coordinated by the highly charged [PySez]n- ligands. Good control of the Lewis basicity of
the flux can be achieved by means of varying the starting composition.3f In the case of (I-

III) the basic flux was chosen such as to obtain compounds with the [PSe4]3- unit (P5+).
The successful synthesis of (I-III) validated this approach and in addition the use of high
basicity yielded the molecular complex (I). For (IV,V) the relatively less basic flux was

such as to obtain compounds with the [P28e6]4- unit (P4+). Instead, (IV,V) possess

[P28e6]4- and [PSe4]3‘ containing P4+ and P5+ respectively, indicating the presence of a
complicated Lewis acid-base equilibria. All compounds can be synthesized by direct
elemental synthesis indicating some thermodynamic stability of the products. This approach
yields pure materials but in the form of microcrystalline powder. The exploratory value of
the flux method and the ability to produce good quality single crystals is even in this case
indispensable.

To place (I-V) in a greater context, it is useful to consider them as members of a

series with the general formula (A4P28e6)1(A3PSe4)n[LnPSe4]m. The 3-D LnPSe4 (l = O, n

= 0, m = 1) would be the parent member of the series. Interestingly, only the sulfur analog
of this compound has been reported.16.17 One can envision "dismantling" the 3-D network
of LnPSe4 by introducing one [PSe4]3- unit per formula, to obtain the 1-D A3Ln(PSe4)2 (l
= O, n = 1, m = 1) (II,III). To maintain electroneutrality, of course, for every [PSe4]3-

unit that is introduced, three A+ cations should follow. Addition of 2 more equivalents of
A3PSe4 yields the molecular A9Ln(PSe4)4 (l = 0, n = 3, m =1) (1). The 2-D
A4Ln2(PSe4)2(PZSe6) (l = 1, n = 0, m = 2) (IV,V) belong to the same family, and can be

199
generated by introduction of an equivalent of A4P2$e6 to the parent LnPSe4. This is

illustrated in Scheme 2:

Scheme 2

1/2 A4Ln2(PSe4)2(PZSe6)

1/2 A4P2896[

A3PSG4
LnPSe4 = A3Ln(PSe4)2

 

2 A3PSe4
. 3 A3PSe4
------------------- '> AgLn(PSe4)4

Interestingly, when Ln is divalent (e.g. Eu2+ ) a similar family exists with the general
formula (A3PSe4)n[Ln3(PSe4)2]m and presently, the 2—D KEuPSe4 (n = 1, m = 1),26 and

the 1-D K4Eu(PSe4)2 (n = 4, m = 1)2c have been already prepared.

The solid-state UV/vis diffuse reflectance spectra of the compounds reveal sharp
optical absorptions consistent with semiconductors, see Table 7-11 and Figure 7-7. The
estimated band-gaps, Eg, are 2.26 eV for (1) (single crystal transmission data), 2.03 eV
for (11), 2.21 eV for (111), 2.00 eV for (IV), and 2.19 eV for (V). The values are
identical, within the experimental error, for the solid-state Ce compounds (11) and (IV)
and for the Gd compounds (III) and (V). It appears therefore that, in this case, the metal
center plays the most important role in determining the band-gap rather than the structural
framework.

Rb9Ce(PSe4)4 is insoluble in dimethylformamide (DMF) and acetonitrile but
soluble in a solution of the crown ether, 18-crown-6, in dmf forming a greenish-brown

solution. The latter gives a different spectrum from the solid material with one medium

200
absorption at ca. 639 nm (1.94 eV) and a strong one at ca. 445 nm (2.79 eV), suggesting

that the molecule undergoes rearrangement in solution. The absorption at 639 nm is

reminiscent of that observed in solution of Sex2-.13 To stabilize the intact complex not only
a solubilizing agent such as a crown ether or cryptand is needed but an appropriate less
polar solvent as well.

The far-LR. spectrum of (I) displays three strong absorptions assigned to PSe4
stretching modes at ca. 455, ca. 448 (terminal P-Se) and ca. 436 cm.1 wridging P-
Se).2€.3d.4b Weak absorptions at ca. 166 and ca. 155 cm-1 can be assigned to Ce—Se
vibrations.2-4 The far-IR spectra of (II,III) display absorptions at ca. 476, 464 and 442
cm-1 also assigned to [PSe4]3- stretching modes and two more absorptions at ca. 180 and
163 cm-1 assigned to M-Se vibrations, Figure 7-8A. The infrared spectra of (IV,V)
display absorptions at ca. 488, 457, 447, 435, 300, 237, and 227 cm-1, Figure 7-88. The
ones at ca. 457, 300, 237 and 227 cm-1 are characteristic for the [P28e6]4- group,2a.3a.3c

whereas the rest are due to the [PSe4]3-. Absorptions at ca. 186, 165, 142, and 134 cm-1

are due to M-Se vibrations.

Differential thermal analysis (DTA) data followed by careful XRD analysis of the
residues, show that (II-V) melt congruently in the 683-8080C range, whereas (I) melts

incongruently at 7410C, see Table 7-11.
The magnetic susceptibility of (I) was measured from 5 to 300 K at 2000 G. The

compound is paramagnetic, obeying Curie-Weiss law in the range 60-300 K, with a 9 of -
18 K. In this temperature range the calculated “eff is 2.36 BM, very close to that of the free

Ce3+ ion (2.54 BM). At temperatures below 60K, the curve deviates negatively from a

straight line extrapolated from the higher temperature data. Similar deviations have been

reported for other Ce3+ compounds and have been attributed to crystal-field splitting of the

201

cation's 2F5/2 ground state.12.19 The magnetic susceptibility of (II-V) was measured as a

function of temperature (5-3OOK), Figure 7-9. All four compounds are paramagnetic,

conforming to Curie law. The ueff values calculated from the slope of the straight line of the
llx-T data are 2.69, 8.05, 2.43, and 7.96 for (II-V) respectively. These values are

consistent for Ce3+ (f l) and Gd3+ (f7) configurations.

202

 

 

 

 

 

 

 

 

 

 

1 2 : . : .1 l
1.0- .
0.8- -
U) 0.6- -
B
0.4- -
0.2- ‘ .
0-0 i r 'r : r .
1 2 3 4 5 6 7
eV
(B)
6.0 l : : a i
5.0. -
4.0- .
Q 3.0- -
as
2.0- _
1d) -
0-0~ i i 4 : 4'
1 2 3 4 5 6 7
eV

Figure 7-7: Solid-state optical absorption spectra of (A) Rb3CeP28e3 (II) and (B)
CszGdPZSe-I (V)

203

(A)

 

 

80 i i 1 l
70" I-
a)
8 60- .
as
E
E 50- -
(D
c
g 40- -
'—
o\° 30.. ..
20' I
: l J l

 

 

t I I
600 500 400 300 200 100
Wavenumbers (cm'l)

 

(B) 70 l l 1 l

 

 

 

 

 

 

60" I-
8
c 50- -
£9
"E. 40. .-
‘3
9 30- -
1-
°\o 20- -
10- -
o ; . .

r 1 i
600 500 400 300 200 100
Wavenumbers (cm")

Figure 7-8: Far-IR spectra of (A) Rb3CeP28eg (II) and (B) CszGdP28e7 (V)

204

 

 

 

 

 

(A)

0.14 L 350

0.12- --300
c 0.1- «250
g o.oe~ -2oo x
“E, 0.06- 4-150 i
Z 0.04- «100
9 0.02- 0..., «so

0 i. oi. o z o .iLL-O

o 50 100 150 200 250 300
Temp (K)

 

Q X (emu/mol)

 

 

 

 

o 50 100 150 200 250 300
Temp (K)

Figure 7-9: Plot of the magnetic susceptibility x and llx vs. temperature for (A)
Rb3CeP2$eg (II) and (B) CszGszSe7 (V).

205

Table 7-1 1. Optical Band Gaps. Colors. Melting Points and ueff Data

 

 

Formula Eg, eV Color mp, 0C ueff, BM
Rb3CeP2$e3 2.03 red 717 2.69
CS3GdP28e3 2.21 orange 683 8.05
szCePzSe7 2.00 red 808 2.43
CszGszSe7 2. l9 orange 747 7.96
Rb9CeP4Se 1 6 2.26 orange 741i 2.36

l = incongruent melting

206

4. Conclusions

Successful synthesis of three new structure types of rare-earth selenophosphates was
achieved. The new members display an interesting structural diversity due mainly to the
variety of [Psz]n- groups and the large variety of binding modes of each [Psz]n- group.
Along with the known ternary compounds they belong to a family with the general formula
(A4P2Se6)1(A3PSe4)n[LnPSe4]m. Control of flux composition and basicity is key in
controlling which [Psz]n- ligands will appear in the compounds. It would be interesting to
test if missing members of this family [for example the probably molecular A6Ln(PSe4)3 (l
= 0, n = 2, m = 1)], could be synthesized by direct synthesis using as a guide their
predicted formula. The high oxophilicity of the rare-earth metals discourages or even
precludes the use of solvents containing oxygen for the synthesis of molecules with highly
charged chalcogen-based ligands. The extremely high charge of [Ce(PSe4)4]9- would most
probably make its synthesis through conventional "wet" chemistry prohibitive. That its
synthesis is achieved through the chalcophosphate fluxes is significant and points to an
alternative, oxygen-free route to molecular rare-earth selenophosphates. Preliminary
experiments point to a very intriguing prospect of using such molecular compounds as

starting materials for synthetic reaction chemistry.l4

10.
11.
12.
13.
14.
15.
16.
17.
18.

19.

207

References

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

(a) K. Chondroudis, T. J. McCarthy and M. G. Kanatzidis, Inorg. Chem. 1996,
35, 840. (b) K. Chondroudis, and M. G. Kanatzidis, J. Chem. Soc., Chem.
Commun. 1996, 1371.

(a) K. Chondroudis, T. J. McCarthy and M. G. Kanatzidis, Inorg. Chem. 1996,
35, 3451. (b) K. Chondroudis, and M. G. Kanatzidis, J. Chem. Soc., Chem.
Commun. 1997, 401.

K. Chondroudis, and M. G. Kanatzidis, J. Am. Chem. Soc. 1997, 119, 2574.

(a) J. H. Chen, P. K. Dorhout, Inorg. Chem. 1995, 34, 5705. (b) J. H. Chen, P.
K. Dorhout, J. E. Ostenson, Inorg. Chem. 1996, 35, 5627.

CERIUSZ, Version 1.6, Molecular Simulations Inc., Cambridge, England, 1994.

T. J. McCarthy, S.-P. Ngeyi, J.-H. Liao, D. DeGroot, T. Hogan, C. R.
Kannewurf, M. G. Kanatzidis, Chem. Mater. 1993, 5, 331.

Blessing, R. H. Acta Crystallogr. 1995, A51, 33.

(a) Sheldrick, G. M., in Crystallographic Computing 3 ; Oxford University Press:
Oxford, England, 1985, p 175. (b) Gilmore G. J., Appl. Cryst. 1984, 17, 42.

J. L. Hoard, J. V. Silverton, Inorg. Chem. 1963, 2, 235.

V.V Yampol'Skaya, V.V. Serebrennikov, Russ. J. Inorg. Chem. 1972, 17, 1771.
A. C. Sutorik, M. G. Kanatzidis, Angew. Chem.,Int. Ed. Engl. 1992, 31, 1594.
R. D. Shannon, Acta Crystallogr. 1976, A32, 751.

K. Chondroudis, M. G. Kanatzidis, S. Jobic, R. Brec, Inorg. Chem. In Press.
Tremel, W.; Kleinke, H.; Derstroff, V.; J. Alloys Comp. 1995, 219, 73.

Rolland, B.; Colombet, P. Eur. J. Solid State Inorg. Chem. 1990, 27, 715.
Wibbelmann, C.; Bronckner, W.; Schafer, H. Z. Naturforsch. 1984, 39a, 190.
(a) K. W. Sharp, W. H. Koehler, Inorg. Chem. 1977, 16, 2528. (b) L. D.
Schultz, W. H. Koehler, Inorg. Chem. 1987, 26, 1989. (c) P. Dubois, J. P.
Lelieur, G. Lepoutre, Inorg. Chem. 1988, 27, 1883.

(a) H. Lueken, W. Bruggemann, W. Bronger, J. Fleischhauer, J. Less-Common

Met. 1979, 65, 79. (b) M. Duczmal, L. Pawlak, J. Magn. Mater. 1988, 76-77,
195.

CHAPTER 8

Synthesis and Characterization of KZUP3Seg; the First Actinide Selenophosphate.

Stabilization of U5+ in Rb4U4P4Se26; an Actinide Compound with a Mixed

Selenophosphate / Polyselenide and Ion-Exchange Properties

1. Introduction

The advancement of the polychalcophosphate flux technique in recent years has
resulted in many novel quaternary thiophosphate and selenophosphate compounds.l To
form these fluxes we fuse in situ AzQx, and P2Q5 (Q=S, Se), which produces various
[Psz]“' ligands (Q=S, Se). In the presence of metal ions, these highly anionic ligands
bind in an astounding number of ways to the metals forming new materials.1 The variation
of the flux composition stabilizes different ligands such as [PQ4]3', [PSe5]3', [P2Q6]4', and
[P2Q7]4‘,1‘12 which become the building blocks of various polymeric solid-state or even
molecular structures.8 This chemistry gave rise to several unusual compounds such as
ABiPZS7 (A=K,Rb),2 A3M(PS4)2 (A=Rb, Cs; M=Sb, Bi),3 C33Bi2(PS4)3,3
Na0_16BiL23PZS6,3 A2MPZSe6 (A=K, Rb; M=Mn, Fe),l A2M2P28e6 (A=K, Cs; M=Cu,
Ag),l KMPZSe6 (M=Sb, Bi),4 C53M4(P28e6)5 (M=Sb, Bi),5 APbPSe4,6 A4M(PSe4)2
(A=Rb, Cs; M=Pb, Eu),6 Rb4Ti2(P23e9)2(PZSe7),7 KTiPSe5,7 A58n(PSe5)3 (A=K,
Rb),8 A6SnZSe4(PSe5)2 (A=Rb, Cs),8 AzAuPZSe6 (A=K, Rb),9 A3AuP28eg (A=K, Rb,
Cs),10 A2Au2P2Se6 (A=K, Rb),10 AzAuPS4 (A = K, Rb, Cs),10 and AAuPZS7 (A = K,
Rb).10 Extension of this chemistry to lanthanides and actinides yielded the first lanthanide
selenophosphate K4Eu(PSe4)2.6 The K(RE)PZSe(, (RE=Y, La, Ce, Pr, Gd) series has

208

209

been also reported recently.12 We have now examined the reactivity of actinides such as
uranium in these melts and here we report the synthesis, structure and optical, thermal and
magnetic properties of the first selenophosphate quaternary actinides; the two-dimensional

KQUP3Se9 (I) and the novel three-dimensional, ion-exchange material Rb4U4P4Se26 (II),
containing the rare U5+ ion. Pentavalent uranium [U5+] compounds are relatively scarce
because of the strong tendency of U5+ to disproportionate to U4+ and U6+. Therefore, they
are of fundamental importance since U5+ has the simplest Sf-electron configuration

[Rn]5f1, and are useful in understanding the behavior of the f electrons of actinide-ions.

2. Experimental Section

2.1 . Syntheses

Preparation of KZUP3Se9 (I). K2UP3Se9 was synthesized from a mixture of

U (0.3 mmol), PZSe5(O.9 mmol), Kzse (0.60), and Se (3 mmol) that was sealed under

vacuum in a Pyrex tube and heated to 495 0C for 4 (1 followed by cooling to 200 0C at 3 0C
h‘l. The excess KxPySez flux was removed with DMF to reveal black, shiny, irregular

plates (83% yield based on U). The crystals appear air- and water- stable.

Preparation of Rb4U4P4Se26 (II). Rb4U4P4Se26 was synthesized from a

mixture of U (0.60 mmol), PZSe5(O.3 mmol), RbZSe (0.60 mmol), and Se (6 mmol) that

was sealed under vacuum in a Pyrex tube and heated to 500 0C for 4 (1 followed by cooling

to 50 0C at -2 oC h'l. The excess bePySeZ flux was removed with DMF under N2

210
atmosphere. The product was then washed with tri-n-butyl phosphine and ether. Metallic

gray, irregular, rodlike crystals were obtained (81% yield based on U). The crystals appear

air- and water- stable.

2.2. X-ray Crystallography

A Siemens SMART Platform CCD diffractometer was used to collect data from a

crystal of (II). Lorentz polarization effects correction and an empirical absorption

correction13a were applied to the data. A Rigaku AFC6S diffractometer equipped with a
graphite crystal monochromator was used to collect data from (I). A DIFABS correction

was applied to the isotropically refined data of (I). The structures were solved with

SHELXS-8613b and refined by full-matrix least squares techniques of the TEXSAN13c
package of crystallographic programs. The space groups were determined from systematic
absences and intensity. No crystal decay was detected.

Complete data collection parameters, details of the structure solution and
refinements for all compounds are given in Table 8-1. The coordinates of all atoms,
average temperature factors, anisotropic displacement parameters and their estimated

standard deviations are given in Tables 8-2 to 8-5.

211

Table 8-1. Crystallographic data for K2UP3Se9, and Rb4U4P4Se26

 

 

Formula KZUP3Se9 Rb4U4P4Se26
FW 1 l 19.79 3470.84
a, A 10.407(3) 1 1.9779(1)
b, A 16.491(7) 14.4874(1)
c, A 10.143(3) 27. 1377(2)
11 (deg) 107.51(3) 90.00
[3 (deg) 91 .74(2) 90.00
7 (deg) 9028(3) 90.00
2, V(A3) 4; 1659(1) 4; 4709.l7(5)
2. (Mo 1(a), A 0.71069 0.71073
space group PT (#2) Pbca (#61)
peak, g/cm3 4.483 4.895
p, cm-1 312.52 380.63
Temp (0C) - 120 23
Final Rlwai % 5.2/6.5 4.7/5.7
Total Data 4635 2 1432
Measured
Total Unique Data 4337 4150
(ave)
Data F02>3o(F02) 3587 2211
No. of Variables 271 172

Crystal Dimen.,
mm

0.39 x 0.34 x 0.22 0.22 x 0.01 x 0.01

are = 2(IFOI - chl)/ZIF0|, R.;. = {XWUFOI - IFC|)2/ZWIF0|2}1/2.

212

Table 8-2. Positional parameters and Beqa for K2UP3Se9

 

 

Atom X Y Z BequZ
U( 1) 0.78020( 8) 0.16846(6) 0.22230( 8) 071(3)
U(2) 0.72235(8) 0.22327(6) 0.80589(8) 063(3)

Se( 1) 0.7423(2) 00 1 58( 2) 0.0096(2) 090(8)
Se(2) 1.01 11(2) 0.0671(2) 0.2754(2) 088(8)
Se(3) 0.9324(2) 0.1484(1) -0.0338( 2) 078(8)
Se(4) 0.9479(2) 0.3149(2) 0.3499(2) 1.08(9)
Se(5) 0.8748(2) 0.1715(2) 0.5345(2) 1 . 17(9)
Se(6) 1.2055(2) 0.2746(2) 0.5758(2) l.6( 1)
Se(7) 0.9820(2) 0.31 15(2) 0.8756(2) 1 . 19(9)
Se(8) 0.9822(2) 0.5001(2) 0.2510(3) 1.8(1)
Se(9) 0.7222(2) 0.3751(2) 0.7094(2) 1.26(9)

Se(10) 0.7302(2) 0.0326(2) 0.6427(2) 1.1 1(9)

Se(] 1) 0.6180(2) 0.0359(2) 0.2933(2) 1.00(9)

Se(12) 0.4898(2) 0.1748(2) 0.6224(2) 084(8)

Se(13) 0.5835(2) 0.2809(2) 0.3736(2) 098(8)

Se(14) 0.7706(2) 0.3260(2) 0.1073(2) 088(8)

Se(15) 0.5319(2) 0.4800(2) 0.2841(2) 1 .5(1)

Se(16) 0.7391(2) -0.2779(2) -0. 1082(2) 1.6( 1)

Se(17) 0.5591(2) 0.1483(2) -0.0071(2) 084(8)

Se(18) 0.4938(2) 0.3341(2) 0.8873(2) 1.3( 1)
K( 1) 0.7600(6) 0.5487(4) 0.5523(6) 2.7(3)
K(2) 0.6699(5) -0.1502(4) -0.2965(5) 1.6(2)
K(3) 0.2469(6) 0.4664(4) 0.9717(6) 2.7(2)
K(4) 1.1861(6) 0.1333(5) 0.7513(7) 3.2(3)
P( 1) 0.9233(5) 0.0086(4) -0.0733(6) 0.7(2)
P(2) 1.0027(5) 0.2822(4) 0.5381(6) 08(2)
P(3) 0.9333(6) 0.3778(4) 0.7235(6) 1.1(2)
P(4) 0.5719(5) 0.0536(4) 0.5103(6) 0.8(2)
P(5) 0.5857(6) 0.3491(4) 0.2193(6) 1.0(2)
P(6) 0.4560(5) 0.2735(4) 1.0478(6) 1.0(2)

a 8 values for anisotropically refined atoms are given in the form of the isotropic equivalent displacement
parameter defined as Beq = (4/3)[a23(1, 1) + b28(2, 2) + c23(3, 3) + ab(cosy)B(1,2) + ac(cosB)B(l,3) +

bc(cosot)B(2, 3)]

213

Table 8-3. Anisotropic Displacement Parameters for KzUP3Se9

 

 

Atom U1 1 U22 U33 U12 U13 U23
U( 1) 0.0097(5) 0.0076(5) 0.0099(5) 0.0007(4) 0.0005(4) 0.0027(4)
U(2) 0.0093(5) 0.0072(5) 0.0074(4) 0.0002(4) -0.0010(4) 0.0024(4)
Se(1) 0.011(1) 0.009(1) 0.013(1) -0.001(1) 0.003(1) 0.002(1)
Se(2) 0.0 I 4(1) 0.008(1) 0.009(1) 0.002(1) -0.000( 1) -0.002( 1)
Se(3) 0.013(1) 0.004(1) 0.014(1) 0.002( 1) 0.001(1) 0.004(1)
Se(4) 0.017(1) 0.011(1) 0.014(1) -0.004(1) -0.003(1) 0.006(1)
Se(5) 0.018(1) 0.008(1) 0.015(1) -0.004( 1) 0.008(1) -0.003(1)
Se(6) 0.010(1) 0.031(2) 0.024(1) 0.001(1) -0.000(1) 0.013(1)
Se(7) 0.016(1) 0.017(1) 0.014(1) -0.003(1) -0.001(1) 0.008(1)
Se(8) 0.030(1) 0.008(1) 0.029(1) —0.006( 1) -0.002( 1) 0.005(1)
Se(9) 0.015(1) 0.013(1) 0.022(1) 0.004(1) 0.001(1) 0.007( 1)

Se( 10) 0.012(1) 0.013(1) 0.020(1) -0.002( 1) -0.004( 1) 0.009( 1)

Se(l 1) 0.016( 1) 0.013(1) 0.008(1) -0.005(1) 0.001(1) 0.003(1)

Se(12) 0.010(1) 0.008( 1) 0.013(1) 0.001(1) -0.001(1) 0.002(1)

Se(13) 0.014(1) 0.014(1) 0.010(1) 0.001(1) 0.000(1) 0.004(1)

Se(14) 0.012(1) 0.009(1) 0.010(1) -0.002(1) 0.000(1) -0.000( 1)

Se(15) 0.028(1) 0.007(1) 0.022(1) 0.008(1) 0.005(1) 0.001 ( 1)

Se(16) 0.010(1) 0.024(2) 0.026(1) 0.002( 1) 0.002(1) 0.009(1)

Se(17) 0.01 1(1) 0.006(1) 0.013(1) -0.001(1) -0.000(1) 0.002(1)

Se(18) 0.021(1) 0.017(2) 0.013(1) 0.007(1) 0.004(1) 0.006(1)
K( 1) 0.031(3) 0.041(4) 0.035(3) -0.007(3) -0.006(3) 0.021(3)
K(2) 0.027(3) 0.014(3) 0.022( 3) -0.002(3) -0.001(2) 0.006(3)
K(3) 0.034(3) 0.027(4) 0.037(4) 0.01 1(3) -0.001(3) 0.005(3)
K(4) 0.042(4) 0.040(4) 0.054(4) 0.022(3) 0.028(3) 0.035(4)
P( 1) 0.011(3) 0.002( 3) 0.012(3) 0.002(3) 0.001(2) 0.002(3)
P(2) 0.014(3) 0.005(3) 0.008(3) 0.000(3) 0.000(2) -0.001(3)
P(3) 0.014(3) 0.010(4) 0.015(3) -0.001(3) 0.001(3) 0.003(3)
P(4) 0.008(3) 0.010(4) 0.015(3) -0.001(3) -0.001(2) 0.009(3)
P(5) 0.013(3) 0.01 1(4) 0.010(3) -0.002(3) 0.002(3) -0.003(3)
P(6) 0.008(3) 0.016(4) 0.013(3) 0.001(3) -0.001(3) 0.000(3)

214

Table 8-4. Positional parameters and Beq for Rb4U4P4Se26

 

 

Atom X Y Z Beq A2
U( l) 0.21504(9) 0.48257(6) 0.33046(4) 075(2)
U(2) 0.2148900) 0.25584(6) 0.41904(4) 081(2)

Rb( 1) 0.3380(4) 0.3039(3) 0.6803(2) 7.4(2)

Rb(2) 0.3042(5) 0.5299(3) 0.5562(2) 7.2(2)
Se(1) 0.0401(2) 0.3763(2) 0.4710(1) 1.12(6)
Se( 2) 0.3240(2) 0.6708(2) 0.3219(1) 1.05(7)
Se(3) 0.2778(3) 0.4758(2) 0.2240(1) l.62(7)
Se(4) 0.0363(2) 0.6049(2) 0.2923(1) 1.49(7)
Se(5) 0.0282(2) 0.3680(2) 0.3744(1) 1.30(6)
Se(6) 0.1669(2) 0.5710(2) 0.4261(1) 1. 18(7)
Se(7) 0.0373(2) 0.7693(2) 0.4297(1) 1.33(6)
Se(8) 0.3155(2) 0.2908(2) 0.3237(1) 1.01(6)
Se(9) 0.4643(2) 0.4879(2) 0.3251(1) l.32(7)

Se( 10) 0.3056(2) 0.4503(2) 0.4289(1) 1.10(7)

Se(] 1) 0.4692(2) 0.6317(2) 0.4491(1) 1.69(7)

Se(12) 0.2305(3) 0.7537(2) 0.5273(1) 1.37(7)

Se(13) 0.5500(2) 0.1425(2) 0.7228(1) 1 . 16(7)
P(1) 0.5517(6) 0.7448(4) 0.4892(3) 1.0(2)
P(2) 0.4546(6) 0.4866(5) 0.2429(3) 1.1(2)

215

Table 8-5. Anisotropic Displacement Parameters for Rb4U4P4SCZ6

 

 

Atom U1 1 U22 U33 U12 U13 U23
U( 1) 0.0105(6) 0.0122(5) 0.0060(7) 0.0002(5) 0.0007(5) 0.0002(5)
U(2) 0.01 1 1(6) 0.0125(6) 0.0071(7) 0.0000(4) 0.0009(6) -0.0002(4)

Rb(l) 0.096(4) 0.060(3) 0.123(5) 0.033(3) -0.056(3) -0.044(3)

Rb(2) 0.126(5) 0.065(3) 0.082(5) 0.046(3) 0.036(3) 0.031(3)
Se(1) 0.018(2) 0.015(1) 0.009(2) -0.002( 1) 0.005(1) -0.001( 1)
Se( 2) 0.017(2) 0.014(1) 0.008(2) -0.002( 1) 0.004(1) -0.002(1)
Se(3) 0.01 1(2) 0.039(2) 0.01 1(2) -0.002( 1) 0.002(2) 0.003(2)
Se(4) 0.017(2) 0.015(1) 0.024(2) 0.001(1) -0.005(1) -0.002(1)
Se(5) 0.010(1) 0.017(1) 0.023(2) 0.001( 1) 0.000( 1) -0.001(1)
Se(6) 0.017(2) 0.014(1) 0.013(2) -0.004( 1) 0.004(1) -0.001(1)
Se(7) 0.0 1 6( 2) 0.024( 1) 0.01 1(2) 0.000( 1) -0002( 1) 0.002(1)
Se(8) 0.016(2) 0.013(2) 0.010(2) 0.001(1) 0.002( 1) -0.001(1)
Se(9) 0.013(2) 0.025(2) 0.012(2) 0.000(1) 0.000(1) -0.001( 1)

Se( 10) 0.016(2) 0.013(1) 0.012(2) -0.003( 1) -0.001(1) -0.001(1)

Se(11) 0.019(2) 0.019(1) 0.026(2) 0.003(1) -0.01 1(1) -0.008( 1)

Se(12) 0.015(2) 0.031(2) 0.007(2) 0.002(1) -0.001 ( 1) -0.002( 1)

Se( 13) 0.016(2) 0.016(1) 0.012(2) -0.002( 1) 0.005(1) -0.002(1)
P( 1) 0.013(4) 0.016(4) 0.010(5) 0.002(3) -0.005(4) 0.002(3)
P(2) 0.014(4) 0.015(4) 0.013(5) 0.003(3) -0.003(4) 0.002(3)

216

3. Description of Structures

Structure of K2UP3Se9 (I). K2UP3Se9 is formally a U4+ compound and

has a complicated layered structure. The layers run perpendicular to the crystallographic b-

axis, see Figure 8-1. The compound contains only [P28e6]4' anions and so a more

descriptive formula, which provides the formal oxidation states would be

K+4U4+2[P25e6]4'3. There are two crystallographically independent uranium atoms, both
displaying, tricapped trigonal prism (TTP), geometry. For U(l) the prism positions are
occupied by Se(2'), Se(3), Se(4), Se(ll), Se(13), Se(17), and the capping positions by
Se(1), Se(5), Se(l4), see Scheme 1. For U(2) the prism positions are occupied by Se(3),
Se(l4), Se(17), Se(5'), Se(9'), Se(12"), and the capping positions by Se(7'), Se(10"),
Se(18).

 

Scheme 1

Every U atom in the structure is coordinated to four [P2Se6]4‘ ligands. To our
knowledge is the first time this coordination geometry has been observed for uranium

chalcogenides. The closest relevant compound to the one reported here is UP286 in which

the U atoms are eight-coordinate with a dodecahedral geometry.14 Known uranium

217
chalcogenides exhibit bicapped trigonal prismatic geometry as in, UMS3 (M=V, Cr, Co,

Ni),15 and U2MS5 (M=Co, Fe).16

The coordination polyhedron around each metal atom is actually a triangular
decatetrahedron. Two such decatetrahedra share a triangular face [via atoms Se(3), Se(14)
and Se(17)] to form “dimers” of (U28e14) with a U-U distance of 4.601(2)A, Figure 8—2.
These U “dimers” then join by sharing a Se atom [Se(15)], forming chains of (U28e14)x as

illustrated in Scheme 2.

face
shafing

corner
shafing

 

Scheme 2

The complicated intralayer structure is formed by the side-by-side arrangement of the
(U28e14)x chains which propagate along the [001] direction to form what are essentially
“pleated” layers, see Figure 8-3. The chains are then cross—linked in two dimensions by
[PZSe6]4‘ ligands. The [P28e6]4' anions engage in three different binding modes, as

illustrated in Scheme 3.

218

U\
Se Se
Se\ s“ /,,
/ . \ ./ \
U /

 

 

I II III

Scheme 3

Binding modes I and II use all available coordination sites (6 Se), to engage four U atoms.

They cross-link two adjacent columns and are the units which create the two-dimensionality

of the compound. In binding mode III the [P2Se6]4' ligands use only four selenium atoms
each to bind to two metal centers and are the connective units stitching the (U28e14) dimers
into a chain. Their different binding modes can also be seen in Figures 8-1 and 8-3, where
the (U28e14) chains run perpendicular to the ab-crystallographic plane, the type—I groups
are located at the comers of the unit cell and the type-II groups halfway along the a-axis.
The U-Se distances range from 2.914(3) to 3.273(3)A, with the capping selenium atoms

located, on average, farther from the metal. The distances compare very well with those

found in K4USeg.17 The phosphorus-selenium distances range from 2.132(7) to
2.257(7)A, with the non-coordinated selenium atoms (e. g. Se(6), Se(8) etc.) displaying the
shorter ones. The phosphorus-phosphorus bonds range from 2.203(8)A in P(2)-P(3) to
2.27(1)A in P(4)-P(4'). The layers are separated by potassium cations which are located in
four different sites and their coordination environment is irregular. K(l) is coordinated by
eight Se atoms [range of K(1)-Se distances, 3.471(7)-3.782(7)A; av. 3.638A], K(2) is
also eight-coordinate [3.266(6)-3.564(6)A; av. 3.396A], K(3) is six-coordinate [3.340(7)-

219
3.766(7)A; av. 3.567A], and K(4) is seven-coordinate [3.340(7)-3.744(8)A; av. 3.525131].

Selected distances and angles for (I) are given in Table 8-6.

Structure of Rb4U4P4Se26 (II). Rb4U4P4Se26 has a three-dimensional
framework with pentavalent U centers. It contains [PSe4]3‘, Sez', (Se2)2' anions and so it

could be described as Rb4+U45+(PSe4)43‘(Se)22‘(Se2)42‘. The most unusual feature of the
structure is the presence of pentavalent U. Some notable, structurally characterized,
examples with U5+ include UC15,18 Ph4AsUC16,l8 UC15-Ph3PO,18 U(OR)5,l8 and
Ba(UO3)2.18 In Rb4U4P4Se26 every U5+ atom is coordinated to two [PSe4]3', three 8e22'

, and one SeZ' ligands. The structure, contains two crystallographically independent
uranium atoms, both displaying, tricapped trigonal prismatic (TTP) geometry, see Scheme

4.

 

Scheme 4

This coordination is unusual for uranium chalcogenides and it has been observed only
for (1). Two U 'ITPs share a triangular face [via atoms Se(1), Se(2), Se(3)] to form
"dimers" of (U28e14) with a U-U distance of 4.071 (2)A; see Figure 8-4. These "dimers"
then join by sharing edges [Se(4), Se(5)], forming chains of (U28e14)x that propagate

along the [100] direction. The intricate three dimensional structure is formed by the side-

220
by—side arrangement of these chains cross-linked at four sides by [PSe4]3‘ ligands, as can
be seen at the [010] view in Figure 8-5. The Sezz‘ ligands [e.g. Se(3)-Se(4), Se(1)-(Se5')]
have an average distance of 2.412(2)A and play an important role in the structure since they
bridge the "dimers" leading to the formation of the chains. It is interesting that the
compound shares many structural features with (I). Both structures are formed by

interstitched (U28e14)x chains, despite the fact that they contain different selenophosphates

([P2Se6]4' versus [PSe4]3‘), and different oxidation states of U (U4+ versus U5+). The
(U28e14)x chains are made by face sharing U ”dimers" in both compounds but in (I) the

U-U distance is 0.530(2)A longer. On the other hand, the "dimers" join by sharing comers
in (I) whereas in (II) they share edges. Other interesting features of the structure include

the presence of interconnected channels that run both in [100] and [010] directions and

where the Rb+ counterions reside, see Figure 8-5 and 8-6. The largest size channels have a

rectangular cross-section with dimensions 6.95A x 5.3413. and run in the [010] direction.
The Rb+ size (1.52A)19 is relatively small for the cavity it occupies and both

crystallographically independent Rb+ cations seem to "rattle" trying to occupy more cavity
space, as indicated by their anisotropic displacement parameters. This suggests possible
ion-exchange properties for this material, which we have tested. The Rb+ cations exchange
readily with other smaller cations such as Li+. The extent of ion-exchange exceeds 90%.
The valency of U atoms in chalcogenide compounds can be postulated by

considering the mean U-Q (Q=S, Se) distances in the structure.20 The values for

Rb4U4P4Se26 (2.9921) and KZUP3Se9 (3.06A) are consistent with U5+ and 04+
respectively. There are two, crystallographically independent, five-coordinate, Rb cations

with an average Rb-Se distance of 3.692A. Selected distances and angles for (11) are given

in Table 8-7.

221

4. Physical Measurements

Diffuse reflectance Mid-LR. spectroscopy of (1) reveals two well defined peaks

one at ~3725 cm”1 (0.46 eV) and one at ~5856 cm‘1 (0.72 eV) which are too broad to be

associated with vibrational transitions in the compound. They are thought to have an

electronic origin associated with the f orbital manifold and the f2 configuration of W”. In

comparison, (II) has a peak at ~3900 cm‘I (0.48 eV) which is thought to be associated

with the f 1 configuration of U5+.

The vibrational modes of the [P2Se6]4' group for (I) appear at ~516, ~496, ~485,
~472, ~446, ~436, ~290, ~190, ~180, and ~164 cm‘l. Whereas similar absorptions have

been observed in other compounds with the [P28e6]4' group, a splitting of the peaks is

observed here caused by the different types of selenophosphate groups and their
coordination. The vibrational modes of the [PSe4]3' group for (II) appear at ~453, ~444,
~416, ~278 and ~270 cm‘l.

(I) melts congruently at 573 0C. (II) melts incongruently at 597°C yielding

amorphous bePySeZ glasses and a mixture of binary USex phases, and it is tempting to

attribute this instability on melting to the tendency of U5+ to disproportionate.
The magnetic susceptibility of (I) was measured as a function of temperature (5-

300 K). Above 100 K we observe strong paramagnetic behavior, conforming to Curie-

Weiss law. The [Jeff calculated from the slope of the straight line in the data in this
temperature region is 3.72 113, consistent with an f2 configuration. Below 100 K

antiferromagnetic order sets in similar to that observed in K4USe3 (3.82 [113) for which the

222

antiferromagnetic transition is at approximately 90 K.17 The magnetic susceptibility of (II)

was also measured under the same conditions. Above 70 K Curie-Weiss law is observed

with a 0 of -42.6 K. This compares to the value of -43.75 K for KzUP3Se9. The “eff
calculated from the slope of the straight line in the data 1.85 llB, is consistent with an f1

configuration.18»2' Below 70 K weak antiferromagnetic ordering sets in.

223

 

The unit cell of K2UP3Se9 looking down the c-axis. The arrows indicate the boundaries between two layers since the

Figure 8-1:

overlapping selenium atoms from the two layers conceal them

224

O

   

  
  

O P O
S I
1 P(4") “5 )
Se 10" .
Se(12") ( ) P(2)
Se(9')
O'TQC Se(3)
[1(7) (3) \
~ ~ . Se(7')
3608)?) S (1) P\(l) Se(l')
6 KJ 56(3')
S (17
Se(16) P(6) . e ). /Se(3)
/(\\)Se(l4) P(1')
U(l)
, Se(15) \C)Se(2')
Se(lO) C)
O Se(12) (ls/ Se(ll) OSe(4)
/O Se(13)
Se(lO)
-\0)
Se( 1 1') Se(9) O 86(8)
Se(7)

Figure 8-2: ORTEP representation and labeling scheme of the U2Se14 dimer showing

the disposition of the [P2Se6]4- ligands around it

225

was 520 2: :33 33> 5383..
85-56808 5&8 2 :oEmé Sam—-3 a E v8.2a 88:0 05 a6

EoEomcata 0293.35 of .3 258 a 52m -vfiGomNmVNE 0:0

3 econ ad a: 28 dd

 

 

(U

”Tw aha—mi

226

   

<— Edge sharing

 

Figure 8-4: (A) Polyhedral representation of a (U2Se14)x chain in the [100] direction.
(B) The "dimer" in the chain with labeling of atoms, including the side

[PSe4]3‘ groups

227

 

 

The tunnel framework of Rb4U4P4Se26 looking down the b—axis. Cations have been omitted for clarity

Figure 8-5:

228

 

Figure 8-6: Polyhedral representation down the [100] direction showing the smaller

tunnels

229

Table 8-6. Selected Distances (A) and Angles (deg) for K2UP3Se9

U(1)«Se( l )
U(1)-Se(2')
U( l )-Se(3)
U( l )-Se(4)
U(1)—Se(5)
U( l )-Se(1 l)
U(1)-Se( 13)
U( 1 )-Se( 14)
U( l )~Se( 17)
U(1)-Se( 18)

Se( 1 )-U( 1 )-Se( 2')
Se(1)-U(1)-Se(3)
Se(1)-U( l)—Se(4)
Se(1)-U(1)-Se(5)
Se(1)-U(1)«Se(1l)
Se(1)-U( l )-Se(13)
Se(1)-U(l)-Se(14)
Se(1)-U(1)—Se(17)
Se(2')-U(1)-Se(3)
Se(2')-U( l )-Se(5)
Se(2')—U(1 )-Se( 1 3)
Se(2')-U( 1 )-Se( 14)
Se(5)—U( l )-Se(l l)
Se(5)U(1)—Se(l3)
Se(5)-U( 1 )—Se( 1 4)
Se(5)-U( 1 )—Se( 1 7)
Se(11)—U(l)-Se(l3)
Se(11)-U(l)-Se(14)
Se(l l)~U(1)—Se( l 7)
Se(12)-U(2)~Se( 14)

3.168(3)
3.060(3)
3.017(2)
2.914(3)
3.273(3)
3.021(3)
2.915(3)
3.153(3)
3.165(3)
2.989(3)

7459(7)
6859(7)

148.930)

1 1467(7)
5947(6)
127.90(7)
l 1832(7)
6409(7)
7819(7)
5784(6)
l40.05(7)
129.71(7)
7397(7)
82.23(7)
126.14(7)
150.37(6)
8196(7)
144.11(7)
81 .70(7)
134.39(7)

U(2)-Se(3)
U(2)-Se(5)
U(2)-Se(7')
U(2)—Se(9')
U(2)-Se(10")
U(2)-Se(12")
U(2)-Se(14)
U(2)—Se(17)

Se(3)-U(2)-Se(5)
Se(3).U(2)-Se(7)
Se(3)-U(2)~Se(9)
Se(3)-U(2)-Se( 10)
Se(3)U(2)-Se(14)
Se(3)-U(2)-Se(18)
Se(5)—U(2)-Se(7)
Se(5)—U(2)Se(9)
Se(5)-U(2)-Se(10)
Se(7)-U(2)-Se( 10)
Se(7)-U(2)-Se(12)
Se(7)-U(2)-Se( 14)
Se(7)-U(2)-Se(17)
Se(9)-U(2)-Se(10)
Se(9)-U(2)-Se(12)
Se(9)-U(2)Se(14)
Se( 10)-U(2)-Se(12)
Se( 10)-U(2)-Se(14)
Se(10)—U(2)-Se( 1 8)

3.157(3)
3.1 13(2)
3.024(3)
2.950(3)
3.085(3)
2.962(3)
3.042(3)
3.098(3)

9254(7)
6097(7)
132.04(7)
7553(7)
65.1 1(7)
135.00(7)
7345(7)
74.8 1(7)
6238(7)
l 1508(7)
150.58(7)
64.25(7)
127.53(7)
130.69(7)
8379(7)
9349(8)
7026(7)
134.59(7)
2880(8)

U( 1 )-U(2)
U( l)-Se(1 )
U(1)-Se(2)
U( l )Se(3)
U( l )Se(4)
U( l )-Se(5)
U( l )-Se(6)
U( l )—Se(7')
U( l )vSe(8')
U( 1 )—Se(9)
Se(1)-Se(5')
Se(3)-Se(4)

4.071(1)
3.033(3)
3.033(3)
2.920(2)
2.952(3)
3.032(3)
2.966(3)
2.986(3)
2.990(3)
3.046(3)
2.41 1(4)
2.413(4)

230

Table 8-7. Selected Distances (A) and Angles (deg) for Rb4U4P4Se26

Se( 1)-U( l)-Se(2)
Se(1)-U(l )-Se(3)
Se( 1)-U(1 )-Se(4)
Se(l )-U( l )-Se(5)
Se( 1 )-U( 1)-Se(6)
Se(1)—U(1)Se(7')
Se(1)«U(l)—Se(8')
Se( l)-U(1 )-Se(9)
Se( 1 )—U(2)-Se(2)
Se(1)-U(2)Se(3)
Se( 1 )-U(2)Se(4')
Se( 1)-U(2)-Se(5')
Se(1)—U(2).Se( 10)
Se(1)-U(2)—Se(l 1')
Se( 1 )-U(2)-Se( 12')
Se(1)—U(2)-Se(13)
U( 1 )—Se( 1 )-U(2)
U(l)-Se(2)—U(2)
U(1)-Se(3)—U(2)
U( l )-Se(3)-Se(4)
U(2)-Se(5')-Se( l)

7932(7)
76. 1 8( 8)
121.86(9)
130.43(8)
144.36(9)
7915(8)
6796(7)
71 59(7)
9254(7)
6097(7)
132.04(7)
7553(7)
65.1 1(7)
135.00(7)
7345(7)
7481(7)
8665(7)
8459(7)
8629(8)
66.4(1)
6456(9)

231

5. Conclusions

In conclusion, the first quaternary selenophosphate actinides have been prepared in
molten polyselenophosphate Ax[PySez] flux. The two-dimensional K2UP3Se9 contains the
very stable [P28e6]4‘ unit which displays a remarkably multifunctional chemical and
structural behavior. The three-dimensional Rb4U4P4Se26, possesses a intriguing three-
dimensional framework structure and U5+ centers. The stabilization of U5+ in a
magnetically, and optically "inert" Rb-PSe4/Sex matrix provides an interesting and
unequivocal example of an air stable f 1 actinide for magnetic and spectroscopic studies.
Thanks to the Ax[Psz] fluxes the chemistry of the various [Pny]"' units can be readily
probed and exploited to construct solid state chalcogenophospates with a higher lever of
structural complexity than has been possible before. Further work is under way to see if
other U5+ or mixed valent U‘l’tlU5+ compounds can be stabilized from a chalcophosphate

flux.

10.
11.

12.
13.

14.
15.
16.
17.
18.
19.
20.
21.

232

References

(a) T. J. McCarthy, M. G. Kanatzidis, Inorg. Chem. 1995, 34, 1257-1267. (b)
Sutorik, A.; Kanatzidis, M. G. Progr. Inorg. Chem 1995, 43, 151-265.

T. J. McCarthy, T. Hogan, C. R. Kannewurf, M. G. Kanatzidis, Chem. Mater.
1994, 6, 1072-1079.

McCarthy, T. J.; Kanatzidis, M. G. J. Alloys Comp. 1996, 236, 70—85.

McCarthy, T. J.; Kanatzidis, M. G. J. Chem. Soc. Chem. Commun. 1994, 1089-
1090.

T. J. McCarthy, M. G. Kanatzidis, Chem. Mater. 1993, 5, 1061-1063.

Chondroudis, K.; McCarthy, T. J.; Kanatzidis, M.G. Inorg. Chem. 1996, 35 ,
840-844.

Chondroudis, K.; Kanatzidis, M.G. Inorg. Chem. 1995, 34, 5401-5402.
Chondroudis, K.; Kanatzidis, M.G. J. Chem. Soc. Comm. 1996, 1371-1372.

Chondroudis, K.; McCarthy, T. J.; Kanatzidis, M.G. Inorg. Chem. 1996, 35,
3451-3452.

Chondroudis, K.; Hanko, A. J .; Kanatzidis, M.G. Submitted for publication.

Chondroudis, K.; Kanatzidis, M. G. C. R. Acad. Sci. Paris, B, 1996, 322, 887-
894.

Chen, J. H; Dorhout, P. K. Ostenson, J. E. Inorg. Chem. 1996, 35, 5627-5633.
a) R. H. Blessing, Acta Cryst. 1995, A51, 33-38. b) G. M. Sheldrick, In
Crystallographic Computing 3; Oxford University Press: Oxford, England, 1985,
p. 175-189. c) TEXSAN: Single Crystal Structure Analysis Software (1981 &
1992). Molecular Structure Corporation, The Woodlands, TX 77381.

Junghwan, D.; Jungwook, K.; Sangmoo, L.; Hoseop, Y. Bull. Korean Chem.
Soc., 1993, 14(6), 678—681.

Noel, H.; Padiou, J.; Prigent, J. C. R. Acad. Sci. Ser. C, 1975, 280, 123-126.
Noel, H. C. R. Acad. Sci. Ser. C, 1974, 279, 513-515.

Sutorik, A.; Kanatzidis, M. G. J. Am. Chem. Soc. 1991, 113, 7754-7755.
Selbin, J.; Ortego, J. D. Chem. Rev. 1969, 69, 657-671.

Shannon, R. D. Acta Crystallogr. 1976, A32, 751-767.

Noel, H. J. Solid State Chem. 1984, 52, 203-210.

Freeman, A. J.; Keller, C. Handbook on the Physics and Chemistry of the
Actinides; New York, 1991; Vol. 6, pp 337-366.

CHAPTER 9

Rb4Sn2Ag4(PZSe6)3: First Example of a Quintenary Selenophosphate and an Unusual Sn--

Ag s2-d10 Interaction

1. Introduction

In order to study the class of chalcophosphate compounds, we have developed the
molten polychalcophosphate flux technique, the advantages of which are now well
documented}-4 Many unusual compounds containing main group,2 transition metals,3
lanthanides and actinidesze~ 4’ 5 have been reported which demonstrably attest to the broad
synthetic scope of this technique. The next question to be asked is how to access
increasingly complex multinary phases, particularly those with more than one kind of metal
in the framework, which are likely to feature new and novel characteristics. The flux
method is well suited for such exploratory work because it could allow a complex reaction
system to equilibrate at relatively low temperature, favoring kinetically stable phases. This
twist for complexity would test the limits of the flux method in terms of its ability to deliver
higher order multinary compounds, since the potential problem of phase separation has to
be overcome. Both tin and silver have displayed a very fertile structural chemistry yielding
several interesting compounds.1v 2f. 33 Our attempts to introduce the two metals into one

compound yielded the first quintemary selenophosphate, namely Rb4Sn2Ag4P68etg.

233

234
2. Experimental Section

2.1. Syntheses

Preparation of Rb4Sn2Ag4(PZSe6)3. Rb4Sn2Ag4(P28e6)3 was synthesized
from a mixture of Sn (0.60 mmol), Ag (0.30 mmol), P28e5 (0.60 mmol), szSe (0.30
mmol), and Se (3.00 mmol) which was sealed under vacuum in a Pyrex tube and heated to

5150C for 4 (1, followed by cooling to 1500c at 4 oc h-l. The excess bePySez flux was
removed with degassed DMF. The product was then washed with ~2 ml of tri-n-butyl to

remove elemental Se. Further washing with anhydrous ether revealed an intimate mixture

of black hexagonal crystals of AgzsnPgseg (~50%),7 and red irregular shaped crystals of
Rb4Sn2Ag4(PzSe6)3 (~50%). The latter are air- and water-stable. Semiquantitative
microprobe analysis on single crystals gave Rb3,7Sn2,oAg3_3P5,1Se17,5 (average on four

data acquisitions).

2.2. X-ray Crystallography

A Rigaku AFC6S diffractometer equipped with a graphite crystal monochromator,
was used to collect data. The structure was solved with SHELXS-866a and refined by full-
matrix least squares techniques of the TEXSANGb package of crystallographic programs.
An empirical absorption correction based on y scans was applied to the data, followed by a
DIFABS correction to the isotropically refined data as recommended.8 Complete data
collection parameters, details of the structure solution and refinements are given in Table 9-
1. The coordinates of all atoms, average temperature factors, anisotropic displacement

parameters and their estimated standard deviations are given in Tables 9-2 and 9-3.

235

Table 9-1. Crystallographic data for Rb4Sn2Ag4P6Se13

 

 

Formula Rb4Sn2Ag4P6Se13
FW 2617.85
a, A 11.189(2)
b, A 7.688(2)
c, A 21.850(3)
11 (deg) 90.00
B (deg) 9431(1)
7 (deg) 90.00
2, V(A3) 2; 1874.2(5)
2t (Mo 1(01), A 0.71069
space group P21/n (#14)

Dealer g/cm3

11, cm-1
Temp (0C)
Final R/Rw,a %

Total Data
Measured

Total Unique Data
(ave)

Data F02>30(F02)
No. of Variables

Crystal Dimen.,
mm

4.639

262.50
-125
4.1/3.8

3774

3579

1930

154
0.28 x 0.17 x 0.02

air = 2(le - ch|)/ZIFOI, R.;. = {ZWUFOI — IFC|)2/ZWIF0|2}1/2.

236

Table 9-2. Positional parameters and Beqa for Rb4Sn2Ag4P6Se13

 

 

Atom X Y Z B equZ
Sn 081995(9) -00567( 1) 0.1 1359(4) 080(2)
Ag( 1) 0.6962(1) 0.2171(2) 025155(8) 425(4)
Ag(2) 0.5816(1) -0.0734(2) 015298(5) 135(2)
P( 1) 1.0549(4) -0.3859(5) 0.1570(2) 066(7)
P( 2) 0.9456(4) 0.3745(5) 0.1764(2) 064(7)
P(3) 0.4455(4) 0.1 191(5) 0.0094(2) 064(8)
Rb( 1) 0.2451(1) -0.4350(2) 0.32330(6) 1.25(3)
Rb(2) 0.7454(1) 0.4327(2) 000414(6) 1.31(3)
Se( 1) 1.2358(1) -0.4680(2) 015154(6) 106(3)
Se( 2) 0.9706( 1) -0.2875(2) 0.06705(6) 077(3)
Se(3) 04746( 1 ) 0.3060(2) 0.27246(6) 103(3)
Se(4) 0.4791(1) -0.2397(2) 0.23 840(6) 087(3)
Se(5) 0.7561(1) 0.4548(2) 017566(6) 085(3)
Se(6) 0.9766(1) 0.2071(2) 0.09601 (6) 074(3)
Se(7) 0.5089(1) 0.2206(2) 009905(6) 095(3)
Se(8) 0.5340(1) -0.3066(2) 0.06314(6) 089(3)
Se(9) 0.7436(1) -0.0229(2) -001049(6) 088(3)

a 3 values for anisotropically refined atoms are given in the form of the isotropic

equivalent displacement parameter defined as Beq = (4/3)[a28(1, 1) + b23(2, 2) + c280,

3) + ab(cosy)B(1,2) + ac(cosB)B(l,3) + bc(cosa)B(2, 3)]

Table 9-3. Anisotropic Displacement Parameters for Rb4Sn2Ag4POSe13

237

 

 

Atom U1 1 U22 U33 U12 U13 U23
Sn 0.0093(5) 0.0093(5) 0.01 17(5) 0.0004(5) 0.0014(4) -0.0015(4)
Ag( 1) 0.0222(8) 0.064(1) 0.077(1) 0.0088(9) 0.0174(8) 0.059(1)
Ag(2) 0.0216(7) 0.0204(7) 0.0094(5) 0.0002(7) 0.0019(5) 0.0034(5)
Rb( 1) 0.0127(8) 0.0196(8) 0.0150(7) -0.0013(8) -00002(6) -0.0005(6)
Rb(2) 0.0165(8) 0.0176(8) 0.0150(7) 0.0007(8) . -0.0027(6) -0.0018(7)
Se(1) 0.0081(8) 0.0161(9) 0.0158(7) 0.0017(8) -0.0001(6) 0.0016(6)
Se(2) 0.0128(8) 0.0088(8) 0.0072(7) 0.0001 (8) -0.0012(6) 0.0006(6)
Se(3) 0.0166(9) 0.0097(9) 0.0129(7) 0.0036(8) 0.0026(7) 0.0056(6)
Se(4) 0.0173(9) 0.0082(8) 0.0073(7) -0.0007(7) 0.0003(6) 0.0003(5)
Se(5) 0.0085(8) 0.0105(8) 0.0131(7) -0.0005(8) -0.0001(6) 0.0026(6)
Se(6) 0.0121(9) 0.0078(8) 0.0086(7) -0.0020(8) 0.0019(6) -0.0032(6)
Se(7) 0.0177(9) 0.0106(8) 0.0073(7) 0.0000(8) -0.0026(6) -0.0014(6)
Se(8) 0.0150(9) 00085( 8) 0.0103(7) -0.0009(8) -0.0005(6) 0.0043(6)
Se(9) 0.0085(8) 0.0164(9) 0.0086(7) -0.0005(8) 0.0001(6) 0.001 1(6)
P( l) 0.01 1(2) 0.004(2) 0.011(1) 0.001(2) 0.002( 1) 0.002( 1)
P(2) 0.012(2) 0.006(2) 0.007(2) 0.004(2) 0.001(2) 0.001 ( 1)
P(3) 0.008(2) 0.008(2) 0.007( 1) -0.001(2) -0.001(1) 0.001(1)

238

3. Description of Structure

Structure of Rb4Sn2Ag4(PZSe6)3. Rb4Sn2Ag4P68e13 is an unusual two-
dimensional compound with formally Sn2+ and Ag+ atoms held together by [P2Se6]4-
units. The [SnzAg4(PzSe6)3]n4n- layers are separated by seven-coordinate Rb+ cations
[range of Rb-Se distances, 3.425(3)-3.845(3)A; av. 3.624A], see Figure 9-1. The layers

form a perforated network which contains rings made of 8 [P28e6]4- groups, 12 Ag, and 6
Sn atoms (ring dimensions: 9.0 x 3.8 A), Figure 9-2. These layers stagger by being offset
along the [1 0 1] direction by a 1/2 translation and consequently the rings do not form
channels. Each layer consists of [SnzAg4(PZSe6)2]x "chains" which propagate along the [0
1 0] direction, Figure 9-2. These "chains" contain infinite zig-zag (AgSe3)x strands which

consist of comer sharing Ag(l) trigonal planes. The (AgSe3)x fragments are capped by
pentadentate [PZSe6]4- groups [P(1)-P(2)] which are also coordinated to the four coordinate
Ag(2)+ and Sn2+ cations to form the [SnzAg4(P28e6)2]x "chains", Figure 9-3. These

"chains" are then connected along the [0 0 1] direction by bridging [P28e6]4' groups [P(3)-
P'(3)] to form the layer, Figure 9-2.

The most unique feature of the structure is the presence of Sn2+-Ag+ interactions

involving Sn and Ag(2) [2.866(2)A], Scheme 1. Both atoms are closed-shell ions yielding

a s2-d10 interaction9 (van der Waals radii sum is 3.90A).

 

Scheme 1

The coordination geometry around Sn looks like trigonal pyramidal with an empty axial
position. Assuming that the lone pair is stereochemically active, then it would occupy the

empty axial position to form a trigonal bipyramid (tpb). pr geometry has been observed for
several four-coordinate Sn2+ compounds. 10 On the other hand, the lone pair could also be

used as a donor to Ag, as is the case for SnCl3- in compounds with a Sn-M bond. 11 The
bonding nature of this interaction is also supported from the following observations: a) The
Sn-Ag bond [2.866(2)A] is only slightly longer than the Sn-Se bonds [av. 2.74(4)A]; b) the
coordination of Ag(2) significantly deviates from trigonal planar geometry and it can better

described as tetrahedral with a comer occupied by Sn. To our knowledge, there are no other
compounds with a Sn-Ag interaction. In fact sZ-dlo interactions are rare with those observed
in AuTl[Ph2P(CH2)S]2,12t13 and Ausz[Ph2P(CH2)S]4,13 being exemplary. These
interactions have been attributed to relativistic effects.12,13

Atom Ag(l) is in a trigonal planar coordination and has a relatively high thermal
parameter. This is a common feature in silver-containing and other d10 selenophosphates

and has been attributed to anharrnonic thermal vibrations of these atoms.3as 14-18 The Ag-

Se distances for Ag(l) average at 2.61(3)A in excellent agreement with those found in

CszAgzPZSe6 [2.59(5)A],3a also featuring trigonal planar Ag+. For Ag(2) the Ag-Se

240
distances average at 2.64(4)A, in excellent agreement with those of K3Ag3P3Se9

[2.69(7)A],3a which features tetrahedral Ag+. The Sn-Se distances average at 2.74(5)A,

slightly longer than those observed for [Sn2Se4(PSe5)2]6-.2f and [SnzSe6]4-,19 which
contain tetrahedral Sn. The phosphorus-selenium distances range from 2.132(6) to
2.247(6)A, with the non-coordinated selenium atoms [Se(1)] displaying the shorter ones.

Selected distances and angles are given in Table 9—4.

4. Physical Measurements

Single crystal optical transmission spectroscopy shows a sharp optical gap Eg, of 2.15 eV.
The infrared spectrum displays absorptions at ca. 500, 474, 462, 439, 430, 298, 190, 175

and ~166 cm-l. The vibrations at ca. 500, 474 and 462 cm-1 can be attributed to PSe3
stretching modes whereas the one at 298 cm-1 can be ascribed to an out-of-phase PSe3

mode.3a.3c The absorptions below 200 cm-1 are most probably due to M-Se vibrations.3

Differential thermal analysis (DTA) shows that Rb4Sn2Ag4P68e13 melts congruently at ca.

568 oC.

241

 

 

 

 

 

 

 

 

Figure 9-1: ORTEP representation of the unit cell of Rb4Sn2Ag4P6Selg viewed down

the b-axis. Rb+ cations have been omitted for clarity. Tin and silver atoms
are shown as octant shaped ellipses, selenium as open ellipses and
phosphorus as crossed ellipses with no shading (90% thermal ellipsoids)

242

mafia-u. ”S
9% .m
d 2 m
8m... mo

'ngle [SnzAg4P58e13]n4n- layer showing the rings

Figure 9-2: View perpendicular to a s1

(stick model)

243

  
       

' ¢ ' \.~
?glI>\;,“ Sea
<— 9’ \ ‘P\ , ’/

Figure 9-3: View showing a section of the layer with labeling. Solid arrows indicate

connectivity to the rest of the layer

Table 9-4. Selected Distances (A) and Angles (deg) for Rb4Sn2Ag4P68e13

Sn-Se(2)
Sn-Se (av.)
Ag( 1 )-Se (av.)
Ag(2)-Se (av.)
P( 1 )-Se( 1)
P( l )-Se(2)
P(1)-Se(3)
P(1)-P(2)
P(3)-P(3)

2.866(2)
274(5)
261(3)
264(4)

2.132(6)

2.247(6)

2.176(6)

2.269(7)
2.26( 1)

244

Se(2)-Sn-Se(6)
Se(2)-Sn-Se(9)
Se(2)-Sn-Ag(2’)
Se(3)-Ag( 1 )-Se(5)
Se(3)-Ag( l )-Se(5')
Se(4)-Ag(2)-Se(7')
Se(4)-Ag(2)-Se(8')
Se(4)-Ag(2)-Sn'
Se(1)-P(1)-Se(2)
Se(1)-P(l)-Se(3)
Se(1)-P(1)-P(2)
P( l )-Se(2)-Sn
P(lrSeOrAgU)
P(2}Se(4)-Ag(2)
P(3)-Se(8)-Ag(2')
P(3)-Se(9)-Sn

9055(7)
81 .35(7)
l34.87(9)
104.29(9)
102.7(1)
127.0(1)
9704(9)
135.09(9)
1 129(2)
1 15.8(3)
107.3(3)
97.2(1)
98.1(2)
104.7(2)
93.7(2)
100.3(1)

245

5. Conclusions

The synthesis of the first quintenary selenophosphate has been achieved in a
polyselenophosphate Ax[PySez] flux. As the level of complexity in a flux reaction system
goes up, by introducing different kinds of metals, the risk of phase separation and
formation of mixtures also increases. The successful outcome reported here maybe due to
various factors, the most intriguing one being the ability of Sn and Ag to associate via 52-
d10 bonding. This apparently is enough to hold these two elements in the same crystalline
lattice and avoid the alternative of forming a mixture of Rb/Sn/P/Se and Rb/Ag/P/Se
phases. The unexpected observation of this interaction suggests that new chemistry can be

learned by exploring selenophosphate compounds with more complex compositions.

(1)
(2)

(3)

(4)

(5)

(6)

(7)
(8)
(9)
(10)

(11)

(12)

(13)

(14)

246

References
Kanatzidis, M. G. Curr. Opinion Solid State and Mater. Sci. 1997, 2, 139.

(a) McCarthy, T. J.; Kanatzidis, M. G. Chem. Mater. 1993, 5, 1061. (b)
McCarthy, T. J.; Kanatzidis, M. G. J. Chem. Soc., Chem. Commun. 1994,
1089. (c) McCarthy, T. J.; Hogan, T.; Kannewurf C. R.; Kanatzidis, M. G.
Chem. Mater. 1994, 6, 1072. (d) McCarthy, T. J.; Kanatzidis, M. G. J. Alloys
Comp. 1996, 236, 70. (e) Chondroudis, K.; McCarthy, T. J.; Kanatzidis, M. G.
Inorg. Chem. 1996, 35, 840 (f) Chondroudis, K.; Kanatzidis, M. G. J. Chem.
Soc., Chem. Commun. 1996, 1371.

(a) McCarthy, T. J.; Kanatzidis, M. G. Inorg. Chem. 1995, 34, 1257. (b)
Chondroudis, K.; Kanatzidis, M. G. Inorg. Chem. 1995, 34, 5401. (c)
Chondroudis, K.; McCarthy, T. J.; Kanatzidis, M. G. Inorg. Chem. 1996, 35,
3451. (d) Chondroudis, K.; Kanatzidis, M. G. J. Chem. Soc., Chem. Commun.
1997, 401. (e) Chondroudis, K.; Kanatzidis, M. G. Angew. Chem. Int. Ed. Engl.
1997, 36, 1324. (f) Chondroudis, K.; Hanko, J. A.; Kanatzidis, M. G. Inorg.
Chem. 1997, 36, 2623. (g) Chondroudis, K.; Kanatzidis, M. G.; Sayettat J.;
Jobic S.; Brec, R. Inorg. Chem. In Press.

(a) Chondroudis, K.; Kanatzidis, M. G. C. R. Acad. Sci. Paris, Series B, 1996,
322, 887. (b) Chondroudis, K.; Kanatzidis, M. G. J. Am. Chem. Soc. 1997,
119, 2574.

(a) Chen, J. H; Dorhout, P. K. Inorg. Chem. 1995, 34, 5705. (b) Chen, J. H;
Dorhout, P. K. Ostenson, J. E. Inorg. Chem. 1996, 35, 5627.

(a) Sheldrick, G. M. In Crystallographic Computing 3; Sheldrick, G. M.; Kruger,
C., Doddard R. EDS.; Oxford University Press: Oxford, England, 1985; pp. 175-
189. (b) TEXSAN: Single Crystal Structure Analysis Software, Version 5.0;
Molecular Structure Corp; The Woodlands, TX 77381, 1981.

Chondroudis, K.; Kanatzidis, M. G. Manuscript in preparation.

Walker, N.; Stuart, D. Acta Crystallogr., 1983, A39, 158.

Pyykko, P. Chem. Rev. 1997, 5, 597.

Cotton, F. A.; Wilkinson, G. Advanced Inorganic Chemistry; John Wiley & Sons:
New York, 1988; pp. 271-297.

Greenwood, W. W.; Eamshaw, A. Chemistry of the Elements; Pergamon Press:
Oxford, England, 1993; pp. 454-458.

Wang, S.; Fackler, J. P. Jr.; King, C.; Wang, J. C. J. Am. Chem. Soc. 1988,
110, 3308.

Wang, S.; Garzon, G.; King, C.; Wang, J. C.; Fackler, J. P. Jr. Inorg. Chem.
1989, 28, 4623.

Lee, S.; Colombet, P.; Ouvrard, G.; Brec, R. Inorg. Chem. 1988, 27, 1291.

(15)
(16)
(17)
(18)

(19)

247
Lee, S.; Colombet, P.; Ouvrard, G.; Brec, R. Mater. Res. Bull. 1986, 21, 917.

Ouvrard, G.; Bree, R. Mater. Res. Bull. 1988, 23, 1199.
Pfeiff, R.; Kniep, R. J. Alloys Compd. 1992, 184, 111.

Gaudin, B.; Fischer, L.; Boucher, F.; Evain, M.; Petricek, V. Acta Crystallogr.,
1997, BS3, 67.

Sheldrick, W. S.; Braunbeck, H. G. Z. Naturforsch. 1989, 44, 851.

CONCLUSIONS-OUTLOOK

The chalcophosphate chemistry had attracted a lot of research interest in the 70's
and 80's. The direct synthesis approach yielded numerous ternary compounds and many of
them exhibited new structure types. However, when almost every element on the periodic
table was studied, the interest in this area gradually faded and the remaining research was
focused on optimizing properties of known phases with potential technological interest. But
even so, many metal systems still exist that have not been well studied and characterized.
These metals are primarily located in the middle of the periodic table including groups 6-9.
Metals such as Mo, W, Tc, Re, Ru, Os, Rh, and Ir have yet to display any member of the
chalcophosphate family. This is mostly due to the chemical nature of these metals rather
than insufficient exploratory research. In particular, many of these metals are very difficult
to oxidize so that they can participate in compound formation. In addition, the binary MSex
phases can act as thermodynamic “traps” in the these experimental conditions.

The emergence of flux synthetic techniques and particularly of the molten Ax[Psz]
fluxes presents the greatest opportunity to expand the chalcophosphate class of compounds
in a systematic way. Therefore, it has revived this area of research which is currently very
active. Many novel, quaternary compounds are being synthesized that cover the whole
spectrum of structural dimensionalities (from one-dimensional to three-dimensional), and
occasionally new ternary compounds, which evaded detection via the direct synthesis
approach, also appear. The accumulation of new structure types provides a lot of structural

information that can help us get a better insight into this chemistry. This in turn would

248

249

provide the basis of designing compounds with predetermined structural fragments and
allow the stabilization of interesting materials via rational synthesis. Any metal of the
periodic table can now be studied provided the appropriate synthetic conditions are
employed. Traditionally noble metals such as Au, and Ru cannot "resist" the highly reactive
flux conditions and succumb by producing new compounds with unexpected structures.
The fluxes provide an excellent tool to study these metal systems but for the rest of the
periodic table the future is also great.

By varying the Lewis basicity and stabilizing different [Psz]“‘ building blocks,
endless possibilities for new structural types arise. In addition, the employment of low-
interrnediate temperatures allows the stabilization of metastable phases which are otherwise
inaccessible.

The bonding versatility of the [Psz]"' ligands might prove useful in the synthesis
of open-framework structures, if one could employ large countercations that would act as
templates. If the structure determining parameters are well optimized they could lead to
microporous materials which could feature novel properties, both catalytic and electronic.

The discovery that even molecular compounds can be conveniently synthesized at
very basic conditions is also appealing. The high negative charge of these molecular entities
would make their synthesis through conventional "wet" chemistry very difficult perhaps
prohibitive. These compounds maybe useful as starting materials or building blocks for
further solution or solid-state chemistry.

Access to increasingly complex, multinary phases, which are likely to feature new
and novel characteristics appears feasible. The flux method seems well suited for such
exploratory work because it could allow a complex reaction system to equilibrate at
relatively low temperature, favoring kinetically stable phases. In Chapter 9, convenient
entry into the hitherto unknown quintenary chemistry was demonstrated, opening new

opportunities to expand the chalcophosphate family of compounds. The unexpected

250

observation of a Sn-Ag interaction in Rb4Sn2Ag4(PZSe6)3 suggests that new chemistry can
be learned by exploring chalcophosphate compounds with more complex compositions.

Eventhough, the success of the method is a fact and we have already gained some
experimental control over it, a number of important parameters are still unknown. In
particular, the actual nature of the flux during the molten state can now only be speculated,
based on the structure of the final compounds, and therefore needs further elucidation. For
example, the kind of [PyQZP' ligands, the existence of intermediates, and their distribution
in the molten state along with the role of the metal in this equilibria are some of the factors
that need to be examined. Such studies should be performed in situ and cover a wide range
of compositions and temperatures. Bulk probing techniques such as in situ Raman
spectroscopy and diffraction using X-ray or synchrotron radiation hold great promise.
Currently, the most attractive technique appears to be 31P and 77Se solid-state NMR, and
preliminary experiments suggest that they can shed some light on the different species that
exist in the chalcophosphates.

The term chalcophosphates includes, of course, tellurium as a chalcogenide, as
well. Therefore, for the chalcophosphate chemistry to be complete one would expect the
existence of [PyTez]"' units. A review of the literature, however, does not provide any
examples of compounds containing bonds between phosphorus and tellurium. This appears
to be a limiting factor in the synthesis of [PyTezP‘ units. On the other hand, one could
envision quaternary A/M/P/I‘e (A=alkali cation; M=metal) phases that feature bonding

between the metal center the phosphorus and the tellurium but not direct P-Te bonds.