MN. m

twp-.0...
a...

- g h
2:9?
‘5'}.-
r

u ‘

' I ’ &

' 'Idi .
‘.‘."rx‘ .

v: *v m x...

“.3?“ ,: ,
.r:’ '
.

Sf

' },,:.v 3
m . , :.
'1’ l

I
i ‘
2:2:7533:
$

,.
; In 4-
a 53:5?“th . ..I.";!'

f X

1 ' : t
352%" ' ’ ' 1 .0 :J

- ‘ t 1:

'41

mN-fl- ...
)P"__V'I h‘
“0.3. .
III-twp «h
..-,

In “a?”

-.

u 1 w¢
nu“... ..

woo

Inn". .1.

~ m‘
an. ‘;
-... ‘
um“
>-

.,; ...‘;;-
..,u‘ -..‘.
11:3“:
;u;..,n
“aw:
W V..-
' O “out.
4'. 4
...q
n:u21‘
.n::1:.;¢

in

u
o
4....-.

9.
33:23}?
v _ ,. , ‘ ",5
1‘3?" V. f‘ ‘ :,~ 7" ‘ , I 3?.
' :74" z

n' “'u‘wz

' E ‘2!~
:g'.

-« ...‘
a- ."

 

Om'.

win-

..c:,
“VIO-

«-
'-‘ 1-,. .

,,_ .
.m.“ "l
t. u.—

«to.
v.» m»

;»

\~
Y;

my...“ .
- Inn- "

i 3:291"
in

.a

‘ r
“-u.
.. ,*

4- 9,. ,

3‘.”
.m.-;::
-..

.
C
3
2 r,
, ... ._. ‘
‘ 15' :z:.:.!‘
t ‘ "’\‘{'

~ u 3.3;!

.».r;*'r

Au“
n...5
v“...

 

». .-
run.

0
a“? . IV
';?§"‘g:“’fm
i) ‘. 5%]
id '1

.
'J v
“"'::r*

M
:55jEzl..

V:
' “,1”;
I

’2.”-
._ ,
1r 2

 

illllllllllllillillll’lllllilIlllllll‘lllllllllHIHIIJIHI

1293 01046 534 6

 

LIBRARY
Michigan State
University

 

 

 

This is to certify that the
dissertation entitled
Synthesis and Characterization of Novel Intercalation
Compounds of Molybdenum Trioxide and Molybdenum Disulfide
presented by

Rabindranath Bissessur

has been accepted towards fulfillment
of the requirements for

Doctor of Philosophy degree in Chemistry

I I V

Major professor

Date 4“? ’g/(?q:/

MS U i: an Affirmative Action/Equal Opportunity Institution 042771

 

 

A_V —’ fl“

PLACE Ii RETURN BOXtomnovoihb Mountain your record
TO AVOID FINES Mum on or baton date duo.

DATE DUE DATE DUE DATE DUE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

W1

 

0F
MOLWDI

SYNTHESIS AND CHARACTERIZATION
OF NOVEL INTERCALATION COMPOUNDS OF
MOLYBDENUM TRIOXIDE AND MOLYBDENUM DISULFIDE

by

Rabindranath Bissessur

AN ABSTRACT OF A DISSERTATION

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

DOCTOR OF PHILOSOPHY

Department of Chemistry

1994

PROFESSOR MERCOURI G. KANATZIDIS

OF M

Cond
ammmnh
amount of j
“P011 oxida
A). The ro
which is t
Thermopm
the intercaf

t”Import 01

Poly
“Hulose,
P01y(e1hyk
addiiion 0f
MOSZ- Thi:
POIymer Ci

0i theSe

ABSTRACT

SYNTHESIS AND CHARACTERIZATION
OF NOVEL INTERCALATION COMPOUNDS
OF MOLYBDENUM TRIOXIDE AND MOLYBDENUM DISULFIDE

BY

RABINDRANATH BISSESSUR

Conductive polyaniline has been intercalated into M003. This was
accomplished by first inserting aniline into M003 in the presence of a trace
amount of H20, forming (C5H5NH3+)xMoO3 (d-spacing: 20.1 A), which
upon oxidation with (NH4)28203 yielded (PANI)xMoO3 (d-spacing: 13.7
A). The room temperature conductivity of (PANI)xMoO3 is 0.003 S/cm
which is three orders of magnitude higher than its precursor phase.
Thermopower data show that (PANI)xMoO3 is a p-metal, suggesting that
the intercalated polymer is playing a more important role in the charge

transport of the composite material.

Polyaniline, poly(ethylene-oxide), poly(propylene glycol), methyl
cellulose, poly(ethylenimine), poly(vinylpyrrolidinone), Nylon-6 and
poly(ethylene) have been encapsulated into MoSz. This was achieved by
addition of the polymer solutions to aqueous suspensions of single layers of
M082. This causes flocculation during which the M082 layers sandwich the
polymer chains to give well-ordered single phase products. The d-spacings

of these intercalation compounds range from 10.3 A in

(polyethylei
compounds
6)3_6MoSz
Mmflm
putt clectr
pellets of (P
mmme
conducfiviq
MMMm
show :1 met
mmmm
isnot knom
mm<
&&Ra
M052. Tm
PIOpcny of
spacings d.-
Cluster,
[COMM]
of [C06Seg

“WNW
[Dz/8. nus

(polyethylene)3.oMoSz to 21.1 A in (PVP)0,75M082. The intercalation
compounds were found to be conductive with the exception of (Nylon-
6)3,6M082 and (polyethylene)3,oMoSz. The conductivity of the other
polymer-intercalated phases were in the range of 0.1- 0.0004 S/cm. Four-
probe electrical conductivity and thermopower measurements of pressed
pellets of (PANI)o,35M082, (PEI)0,33M082 and (PEO)1,0M082 show that
the charge transport in these materials is p-metallic. Below 9 K, the
conductivity and thermopower of (PANI)0,35M082 indicate a sudden
transition to the insulating state. (PEO)1.0M082 and (PEI)0.33M082 also
show a metal to insulator transition, at low temperatures. The metal to
insulator transition in these polymer/M082 nanocomposites is new, since it
is not known for either the polymers or MoSz.

Molecular clusters of the general formula, C06Q3(PR3)5, where Q =
S, Se, Te and R = ethyl, n-butyl and phenyl have been intercalated into
M082. This was accomplished by using the exfoliation and restacking
property of M082. The new inclusion solids have well-defined interlayer
spacings depending on the encapsulated cluster. For the C0683(PPh3)5
cluster, the interlayer spacing varies from 21.5 A in
[C0683(PPh3)3]o,093M082 to 10.9 A in [C0683]o,o3M082. The surface area
of [CosSe3(PEt3)y]o,06M082 was found to be 14.2 m2/g and upon removal
of the residual phosphine ligands the surface area value increased to 22.1

m2/g. This is the first example of a pillared sulfided layer.

Dedicated to Ramdass Bissessur
1906-1990

iv

First a
Mercouri Ka
throughout rr.
Professor Ha
Professor Jol
my graduate 1

Many i
Schindler for
0f the cobalt
for drawing l

lam g
and present, .
llSU a Very 1

Finally

Brothers and

ACKNOWLEDGMENTS

First and foremost I would like to thank my advisor, Professor
Mercouri Kanatzidis for all of his help, guidance and encouragement
throughout my entire graduate career at MSU. I would also like to thank
Professor Harry Eick for his helpful comments as a second reader and
Professor John McCracken and Professor Gary Blanchard for serving in
my graduate committee.

Many thanks go to Professor C. R. Kannewurf, D. DeGroot and J.
Schindler for charge transport measurements, Dr. W. Hirpo for synthesis
of the cobalt chalcogenide clusters, Dr. T. J. McCarthy and Dr. J .-H. Liao
for drawing ORTEP figures.

I am grateful to all the members of the Kanatzidis group, both past
and present, for their friendship and kindness. They have made my stay at
MSU a very pleasant one.

Finally, I would like to express my deepest gratitude to my Mother,
Brothers and Nephew Kailash for their love, support and understanding.

LIST OF
LIST OF
LIST OF
ABBREV]

CHAPTER
lntroductior
References.
CHAPTER
Iflttrcalative
alld ‘“003 I

of Aniline i

Abstract .....
2'1. Lilli 0dr

TABLE OF CONTENTS

Page
LIST OF TABLES ................................................................... ix
LIST OF FIGURES ................................................................. x
LIST OF SCHEMES ................................................................ xv
ABBREVIATIONS ................................................................. xvi
CHAPTER 1
Introduction ................................................................................ 1
References .................................................................................. 31
CHAPTER 2
Intercalative Nanocomposite between Polyaniline
and M003. Intercalation and Subsequent Oxidation
of Aniline into M003 ................................................................... 45
Abstract ..................................................................................... 46
2.1. Introduction ......................................................................... 47
2.2. Experimental Section ............................................................ 50
2.2.1. Reagents .......................................................................... 50
2.2.2. Synthesis of (C6H5NH3+)x(C5H5NH2)yMoO3 (I) ................. 50
2.2.3. Synthesis of (C6H5NH3+)X(C6H5NH2)yMoO3 (II) ................ 51
2.2.4. Oxidation of II with (NH4)28203:
Synthesis of (PANDxMoO3 (III) ....................................... 51
2.2.5. Extraction Experiment on I .............................................. 52
2.2.6. Extraction Experiment on II ............................................. 52
2.2.7. Extraction Experiment on (PANI)xMoO3 ........................... 53
2.2.8. Chemical Synthesis of Bulk PANI-HCI (Emeraldine Salt) ..... 53
2.2.9. Physicochemical Methods .................................................. 54

vi

2.3. Res
23.1. S
A

23.2. I
2.3.3.
23.4. 1
2.3.5. 5
3.4. Cor
Referenr

CHAPT

Encapsul
“Hal [0

Abstract
3-1. Lntr
3'2. Ex;
3.2.1. [
3.2.2. 1
3.2.3. 5
3.2.4. p
3.2.7.1,
3.2.3. Ir
3.2.9.1.
3.2.10.3
3-2.11.
3.2.13.

Page

2.3. Results and Discussions .......................................................... 58
2.3.1. Synthesis and Comparison of Two
Aniline Intercalation Compounds of M003 ......................... 58
2.3.2. Intralayer Polymerization of Anilinium in M003 ................ 78
2.3.3. Charge Transport Properties ............................................. 93
2.3.4. Spin Quantitation using EPR ............................................. 96
2.3.5. Solid State UV-vis/Near-IR Spectroscopy ........................... 97
2.4. Concluding Remarks ............................................................. 106
References .................................................................................. 108
CHAPTER 3
Encapsulation of Polymers into M082 and
Metal to Insulator Transition in Metastable M082 ........................... 115
Abstract ..................................................................................... 116
3.1. Introduction ......................................................................... 118
3.2. Experimental ........................................................................ 121
3.2.1. Reagents ........................................................................... 121
3.2.2. Synthesis of Neutral PANI ................................................ 121
3.2.3. Synthesis of LiM082 ......................................................... 122
3.2.4. Preparation of M082 Single Layers .................................... 123
3.2.5. Intercalation of Neutral PANI into M082 ........................... 123
3.2.6. Intercalation of Poly(ethylene-oxide) (PEO) into M082 ........ 124
3.2.7. Intercalation of Poly(propylene glycol) (PPG) into M082 ..... 124
3.2.8. Intercalation of Poly(vinylpyrrolidinone) (PVP) into M082.. 125
3.2.9. Intercalation of Methyl Cellulose (MCel) into M082 ............ 125
3.2.10. Intercalation of Poly(ethylenimine) (PEI) into M082 .......... 125
3.2.11. Intercalation of Nylon-6 into M082 .................................. 126
3.2.12. Intercalation of Poly(ethylene) into M082 ......................... 127
3.2.13. Preparation of Restacked M082 ........................................ 127

vii

3.3. physico
3.4. Results
3.4.1. T1161
3.41 Scan
3.43 Cha:
3.4.4. 8ch

UP
3.4.5. Sm“

3.4.6. Effec

Sam
3.4.7. MagI
3.5. Conclu:
References.

CHAPTER

htercalation
[Q = S, Se an

Formation of

Abstract .......
4.1. lutrodur
4.2. Experin

Page

3.3. Physicochemical Methods ...................................................... 128
3.4. Results and Discussion .......................................................... 129
3.4.1. Thermal Stabilities of Nanocomposites ............................... 147
3.4.2. Scanning Electron Microscopy (SEM) ................................ 151
3.4.3. Charge Transport Measurements ....................................... 163
3.4.4. Structural Transformation of M082 Layers
upon Intercalation ............................................................ 172
3.4.5. Structural Distortion in Oh-M082 ...................................... 198
3.4.6. Effect of Pressure on Conductivity of (Polymer)xMoS2
Samples ........................................................................... 201
3.4.7. Magnetic Susceptibility Measurements ................................ 203
3.5. Conclusions .......................................................................... 215
References .................................................................................. 217
CHAPTER 4.

Intercalation of the Cobalt Chalcogenide Clusters, C06Q3(PR3)6,
[Q = 8, Se and Te and R: Phenyl, n-Butyl and Ethyl] into M082.

Formation of Pillared Sulfided Layers ........................................... 223
Abstract ..................................................................................... 224
4.1. Introduction ......................................................................... 226
4.2. Experimental ........................................................................ 229
4.2.1. Reagents .......................................................................... 229
4.2.2. Physicochemical Methods .................................................. 229
4.2.3. Synthesis of Cluster Compounds ........................................ 231
4.2.4. Synthesis of Intercalation Compounds ................................ 231
4.3. Results and Discussion .......................................................... 232
4.3.1. Magnetic Susceptibility Measurements ................................ 245
4.3.2. Electrical Conductivity Data .............................................. 255
4.3.3. BET Surface Area Measurements ...................................... 258
4.4. Conclusions .......................................................................... 259
References .................................................................................. 260

viii

2.1. Summ
2.2. Summ;
3.1. Interca
3.2. Surnma
of p01)

3.3. Compar
nanocor

3.4. Showing
Heating

3.5. Summar
18513th

3.6. Summar
lPEOlll

3-7- Summar
31033 5)

18' Spins/rm
calculate
4-1- Summar
42' nletmal
'13- Summar
4'4- SL1mmar
45‘ Summar

2.1.
2.2.
3.1.
3.2.

3.3.

3.4.

3.5.

3.6.

3.7.

3.8.

4.1.
4.2.
4.3.
4.4.
4.5.

LIST OF TABLES

Page
Summary of EPR data ........................................................... 77
Summary of GPC results ....................................................... 82
Intercalation compounds prepared by Frindt et a1 ..................... 133
Summary of results obtained from the encapsulation
of polymers in M082 ............................................................. 146
Comparison of thermal stability of polymer/M082
nanocomposites with their respective bulk polymers ................. 150
Showing Tc(Max, 0C) for various M082 systems.
Heating rate was kept fixed at 5 oC/min ................................... 183
Summary of results obtained from kinetic studies on
restacked M082 ..................................................................... 188
Summary of results obtained from kinetic studies on
(PEO)1.0M082 ...................................................................... 191
Summary of activation parameters measured for various
M082 systems ........................................................................ 193
Spins/mol values of various (polymer)xM082 samples
calculated from field dependent magnetization curves ............... 214
Summary of UV-visible results on cluster compounds .............. 234
Thermal stability of cobalt clusters ......................................... 235
Summary of intercalation compounds prepared ........................ 241
Summary of magnetic susceptibility data ................................. 254
Summary of thermal stability and conductivity data .................. 257

ix

1.1. Structu

1.4. Structu
15. Moleca
1.6. Inner c
21. XRD o:

22.1-HR o
2.3. T611 01
2.4. SEM rt
35. TGA of
3.6. PITR of
(PAM);
2.7. EPR 0ft
((1) Extra
and (e) 1
2A FUR of
lb) Extr
2-9. Calibrati
Who
1 (b) Ext:
‘11-ng13
by USing
slithesi;
112- GPC of
by using
(PANI)XI
2.13.8131“ m;

2
;14.SEM m-

”15' SEM mil

LIST OF FIGURES

Page

1.1. Structure of a-M003, a parallel view of the layers ................... 15
1.2. A perpendicular view of the M003 layers ............................... 16
1.3. Structure of 2H-M082; a parallel view of the layers .................. 18
1.4. Structure of 2H-M082; a perpendicular view of the layers ......... 19
1.5. Molecular structure of C068e3(PEt3)6 ..................................... 29
1.6. Inner core of C06Se3(PEt3)6 .................................................. 30
2.1. XRD of (a) I, (b) II and (c) (PANI)xMoO3 ............................. 59
2.2. FTIR of I ............................................................................. 61
2.3. TGA of I under oxygen flow ................................................. 63
2.4. SEM micrographs of I .......................................................... 66
2.5. TGA of II under oxygen flow ................................................ 68
2.6. FI‘IR of (a) II, (b) (PANI)xMoO3, (c) Extracted PANI from

(PANI)xMoO3 and (d) Chemically synthesized bulk PANI ......... 70

2.7. EPR of (a) H, (b) Extracted product from 11, (c) (PANDXMoOg
(d) Extracted PANI from (PANI)XM003

and (e) Chemically synthesized bulk PANI .............................. 72
2.8. FTIR of (a) Extracted product from I and
(b) Extracted product from II ................................................ 73
2.9. Calibration curve for determining MW of extracted
products from II and I ......................................................... 74
2.10. GPC of (a) Extracted product from 11 and
(b) Extracted product from I ................................................ 75

2.11. FTIR spectrum of (a) (PANI)xMoO3 synthesized
by using 10 equiv. of (NH4)28208 and (b) (PANDXM003
synthesized by using 4 equiv. of (NH4)28203 .......................... 80
2.12. GPC of (a) PANI extracted from (PANDXM003, synthesized
by using 10 equiv. of (NH4)28203 and (b) PANI extracted from
(PANI)xMoO3, synthesized by using 4 equiv. of (NH4)28203.. 81

2.13. SEM micrographs of pristine M003 ...................................... 86
2.14. SEM micrographs of II ....................................................... 87
2.15. SEM micrographs of (PANI)xMoO3 ..................................... 88

2.16. SEM
217. Calib
PANI

of (N1

2.18. GPC l
by us

2.19. Varial
(a) (P

2.20. Varial
on pr:

2.21. Solid 5
33304

2.22. Solid 3
of l. B
2.23. Solid 3
(a) usin
224. Solid st
Ba304
125. Solid sr
BaSO4
216.301id gt
PANI fr
and (b)

Page

2.16. SEM micrographs of PANI-HCI ........................................... 89

2.17. Calibration curve used in determining MW of extracted
PANI from (PANI)XM003, synthesized by using 2 equiv.

of (NH4)S203 ...................................................................... 91
2.18. GPC of extracted PANI from (PANI)xMoO3, synthesized
by using 2 equiv. of (NH4)S203 .......................................... 92
2.19. Variable temperature conductivity data on pressed pellets of
(a) (PANI)XM003 (b) II ................................................ 94
2.20. Variable temperature thermoelectric power data
on pressed pellet of (PANDXMoOg ........................................ 95
2.21. Solid state UV-Visible/Near-IR spectrum of II.
BaSO4 was used as reference ................................................ 100
2.22. Solid state UV-Visible/Near-IR spectrum
of I. BaSO4 was used as reference ......................................... 101

2.23. Solid state UV-Visible/Near-IR spectrum of (PANI)xMoO3,
(a) using CdS as reference and (b) using BaSO4 as reference... 102

2.24. Solid state UV-Visible/Near-IR spectrum of bulk PANIoHCl.

BaSO4 was used as reference ................................................ 103
2.25. Solid state UV-Visible/Near-IR spectrum of M003.
8380.; was used as reference ................................................ 104

2.26. Solid state UV—Visible/Near-IR spectrum of extracted
PANI from (PANI)xMoO3, (a) using CdS as reference

and (b) using Ba804 as reference .......................................... 105

3.1. XRD of (a) pristine M082 and (b) LiMoS2 .............................. 130
3.2. XRD of (PANI)0_35M082 ...................................................... 137
3.3. XRD of restacked M082 ........................................................ 140
3.4. XRD of (a) (PEO)1.0M082 (MW 100,000), (b) (PEO)1.0M082

(MW 5,000,000) and (C) (PPG)0.5M032 .................................. 143
3.5. XRD of (a) (PVP)0.76M082, (b) (MCe1)0.26M082

and (C) (PEI)0.33MOSZ ........................................................... 144
3.6. XRD of (a) (Nylon-6)3.6M082 and

(b) (polyethylene)3.0M082 ...................................................... 145

3.7. TGA of (a) bulk PEG and (b) (PEO)M082 under oxygen flow.. 148

xi

3.8. TGA o
3.9 SEM r
3.110 SEM
311. SEM
3.12. SEM
3.13 SEM
3.14 SEM
3.15 SEM
3.16. SEM
3.17 SEM
3.118. SEM:
3.11.9 (a )V’a
(PANI,
data 0
33.3301 V31
of (PE(
data of

Page

3.8. TGA of (a) bulk PEG and (b) (PEO)MoS2 under nitrogen flow 149

3.9. SEM micrographs of pristine M082 ........................................ 153
3.10. SEM micrographs of restacked M082 .................................... 154
3.11. SEM micrographs of (PANI)0.35M082 .................................. 155
3.12. SEM micrographs of (PEO)1.0M082 ..................................... 156
3.13. SEM micrographs of (PPG)0.5M082 ..................................... 157
3.14. SEM micrographs of (PVP)0.76M082 .................................... 158
3.15. SEM micrographs of (MCe1)0.26M082 .................................. 159
3.16. SEM micrographs of (PEI)0.33MoS2 ..................................... 160
3.17. SEM micrographs of (Nylon-6)3.6M082 ................................ 161
3.18. SEM micrographs of (polyethylene)3.0M082 .......................... 162

3.19. (a) Variable temperature electrical conductivity data of
(PANI)Q35M082 and (b) Variable temperature thermopower
data Of (PANI)0.35MOSZ ...................................................... 164
3.20. (a) Variable temperature electrical conductivity data
of (PEO)1.0M082 and (b) Variable temperature thermopower

data of (PEO)1.0M082 ......................................................... 167
3.21. Variable temperature conductivity data of (PEI)0.83M082 ....... 168
3.22. Variable temperature conductivity data of restacked M082 ...... 169

3.23. Variable temperature thermopower data of restacked M082... 170
3.24. Comparison of qualitative band diagram of (A) 2H-M082

with that of metastable lT-M082 (B) ..................................... 175
3.25. Structure of lT-M082, looking parallel to the layers ............... 176
3.26. Structure of lT-MoSZ, looking perpendicular to the layers ...... 177
3.27. DSC of restacked M082 ....................................................... 179
3.28. Plot of xm versus temperature for (a) restacked M082

and (b) heated restacked M082 under vacuum at 185 0C .......... 180
3.29. Plot of d-spacing as a function of Tc(Max.) ........................... 184
3.30. DSC of restacked M082 at heating rates of (a) 5 (b) 10 (c) 15

(d) 20 and (e) 25 0C/min ...................................................... 187
3.31. Arrhenius plot for restacked M082 ....................................... 189
3.32. DSC of (PEO)M082 at heating rates of (a) 5 (b) 10 (c) 15

(d) 20 and (e) 25 0C/min ....................................................... 190
3.33. Arrhenius plot for (PEO)1.0M082 ........................................ 192
3.34. DSC of bulk PEO ................................................................ 195
3.35. DSC of (Nylon-6)3.6M082 ................................................... 196

xii

3.36. DSC
3.37. Plot 0:

as a it
was 1

3.38. Magnr
(b) (P1
3.39. Magn:
(b) (P‘
3.40. Magnr
(b) (P1

Page

3.36. DSC of (polyethylene)3.oM082 ............................................. 197
3.37. Plot of resistance of a (PEO)1.oMoS2 sample
as a function of applied pressure. The resistance

was measured by the four-probe method ................................ 202

3.38. Magnetization of (a) (PANI)0.35M082

(b) (PEO)1.0M082 as a function of field in gauss .................... 205
3.39. Magnetization of (a) (PPG)0.5M082 and

(b) (PVP)0.75MoS2 as a function of field in gauss ................... 206
3.40. Magnetization of (a) (MCel)o.26M082 and

(b) (PEI)0.33M082 as a function of field in gauss .................... 207
3.41. (a) Plot of xm versus temperature for (PANI)0.35M082

(b) Plot of xm‘l versus temperature ..................................... 208
3.42. (3) Plot of xm versus temperature for (a) (PEO)1.0M082 and

(b) the corresponding xm-l versus temperature plot ............... 209
3.43. (a) xm versus temperature plot for (PPG)0.5M082 and

(b) the corresponding xm'l versus temperature plot ............... 210
3.44. (a) Plot of am versus temperature for (PVP)0_76M082 and

(b) the corresponding xm-l versus temperature plot ............... 211
3.45. (a) xm versus temperature plot for (MCe1)0.26M082 and

(b) the corresponding xm-l versus temperature plot ............... 212
3.46. (a) xm versus temperature plot for (PEI)O.33M082 and (b)

the corresponding xm'l versus temperature plot .................... 213

4.1. UV-Visible spectrum of (a) C0683(PPh3)6, (b) C0683(PBu3)5,
(c) C068e3(PBu3)5, (d) C06Te3(PEt3)6, (e) C06Te3(PBu3)6

and (f) C06Seg(PEt3)6 ............................................................ 233

4.2. TGA of (a) CO6Seg(PBU3)6, (b) C06Seg(PEt3)6 and
(C) CO6T63(PBU3)6 ............................................................... 236

4.3. TGA of (a) C06Teg(PEt3)6, (b) C0683(PBU3)6 and
(C) C06Sg(PPh3)6 ................................................................. 237

4.4. XRD of pyrolysed products of (a) C068e3(PBu3)6,
(b) CO6Te3(PBU3)6 and (C) C0633(PBU3)6 ................................ 238

4.5. XRD of (a) [C0683(PPh3)3]0,093M082
(b) [C0688(PPh3)4]o.046M082 (C) [C06T68]o.03M082
(d) [C06Teg]o,02MoS2 (e) [C06Te3(PBU3)5]0,047M082 ............... 244

xiii

4.6.1021 of (a
(b) [C0638
and (d) [C

4.1. 1m versus
Inset crap

4.8. 1m versus
Inset grap

4.9. 1m versus
Inset grap'

4.10. In versu

Inset gra

4.11. In vcrsu

Inset gra;
4.12.1“, versu.
Inset gra]
313. in versu
“‘56! gm]
“4- Qualitatis
(b) MOSg

Page

4.6. TGA of (a) [C0638(PPh3)3]o.093M082.
(b) [C0688(PPh3)4]o.046M082. (C) [C06TC8IO.O3M032.

and (d) [C05363(PEI3)6]0.023M082 .......................................... 246
4.7. xm versus temperature plot for [C0583(PPh3)3]o,093M082.
Inset graph shows xm'l versus temperature .............................. 247
4.8. xm versus temperature plot for [C0683(PPh3)4]o,o46M082.
Inset graph shows xm'l versus temperature .............................. 248
4.9. xm versus temperature plot for C0683(PPh3)5.
Inset graph shows xm-l -versus temperature ............................. 249
4.10. xm versus temperature plot for C05Te3(PEt3)6.
Inset graph shows xm'l versus temperature ............................ 250
4.11. xm versus temperature plot for [C06Te3(PBu3)5]o,o47M082.
Inset graph shows xm'l versus temperature ............................ 251
4.12. xm versus temperature plot for [C068e3(PEt3)6]o,o31M082.
Inset graph shows xm-l versus temperature ............................ 252
4.13. Xm versus temperature plot for [C0583(PBu3)5]o,059M082.
Inset graph shows Xm'l versus temperature ........................... 253
4.14. Qualitative band diagrams of (a) 2H-M082 and
(b) M082 in the octahedral modification ................................ 256

xiv

1.1. Insertion r
12 Formation

ofpynd
13. Example 0

1.4. Example 0
21. Proposed a

12. Pinposed n
aniline am

23. Proposed 2
14. Orientation
3.1. Proposed n
of single 1;

3.1 Inclusion o:
33- Representat
0f (PAM)C

14' EmaPSulati
singlet;

5- RCiaich 31;
39 339128 leadir
3-i- Splitting Of
and the dxzd

in Oh-MoS‘

i- Intercalatio.

LIST OF SCHEMES

Page
1.1. Insertion of lithium ions into Ti82 layers ................................. 3
1.2. Formation of the intercalation compound
of pyridine into M003 ........................................................... 4
1.3. Example of an acid/base type of intercalation reaction .............. 5
1.4. Example of an ion-exchange intercalation reaction ................... 6
2.1. Proposed arrangement of an aniline/anilinium pair in I ............ 60
2.2. Proposed reaction pathway showing insertion of
aniline and anilinium into M003 ............................................. 64
2.3. Proposed arrangement of anilinium in II ................................ 67
2.4. Orientation of polyaniline chains inside M003 layers ................ 85
3.1. Proposed mechanistic pathway showing formation
of single layers of M082 ......................................................... 132

3.2. Inclusion of ferrocene into M082 by using a two-phase system.. 135
3.3. Representation of the lamellar arrangement

of (PANI)0.35M082 ............................................................... 138

3.4. Encapsulation of polymer into M082 by using the
single-layer technique ........................................................... 141
3.5. Relative stability of various M082 phases ................................. 174
3.6. Steps leading to the formation of Sch'dllhom’s lT-M082 ........... 182

3.7. Splitting of the dxz.y 2,xy,22 band due to structural distortion

and the dx2-y2, xy band due to the Peierls type distortion
in Oh-MoS2 .......................................................................... 200

4.1. Intercalation of C0683(PPh3)6 into M082 ................................ 240

XV

ABBREVIATIONS

DSC: Differential Scanning Calorimetry
FTIR: Fourier transform infra-red
EDS: Energy Dispersive Spectroscopy
EPR: Electron Paramagnetic Resonance
GPC: Gel Permeation Chromatography
SEM: Scanning Electron Microscopy
TGA: Thermogravimetric analysis
XRD: X-ray Diffraction

PANI: Polyaniline

PEO: Poly(ethylene-oxide)

PEI: Poly(ethylenimine)

PPG: Poly(propylene glycol)

PVP: Poly(vinylpyrrolidinone)

MCel: methyl cellulose

NMP: N-methylpyrrolidinone
Mn: Number average molecular weight

Mw: Weight average molecular weight

xvi

Chapter 1

Introduction

The

some extra 11
leap year. It
species into 1
hosts are ma
usage of the
to three dime
such as (Mo;
such as C60
retention in 1
reversibility I
For example.
SPace of laye
reiffl'l‘Ed 10 as
The fit:

who successi
Pioneering m
until 1960's. -
"W and re.
35 electrode.
COlltluctors ['
c0“Pounds Q.
leads to their

forces in inte.

The term intercalation literally refers to the act of inserting
some extra interval of time into the calendar, such as February 29 in a
leap year. In chemistry it connotes the reversible insertion of guest
species into lamellar host structures where the structural integrity of the
hosts are maintained [1]. However, in today's chemical literature the
usage of the term 'intercalation' is rather loose. The term is also applied
to three dimensional solids such as zeolites [2], one dimensional chains
such as (M03Se3')n [3] and very recently to zero dimensional materials
such as C60 [4]. The term is also adopted for cases where complete
retention in structural features of the hosts are not preserved [5]. The
reversibility of the insertion reaction is no longer a prerequisite either.
For example, the introduction of conductive polypyrrole in the gallery
space of layered FeOCl [6], which is an irreversible process, has been
referred to as an intercalation reaction.

The first intercalation reaction was reported in 1841 by Schauffaiitl
who successfully intercalated sulfate ions into graphite [7]. Since this
pioneering work, the infatuation with intercalation chemistry did not start
until 1960's. The synthesis and study of intercalation compounds are both
useful and rewarding. Intercalated phases have potential applications such
as electrodes in high-energy density batteries [8], low dimensional
conductors [9] and catalytic materials [10]. In general, intercalation
compounds can be classified according to the type of driving forces that
leads to their formation. There are four most common types of driving
forces in intercalation chemistry and these are (a) redox (b) coordination
(c) acid-base (d) ion-exchange.

In a redox-type of intercalation chemistry, electrons are transferred

from the guest species to the layered host. For this reaction to take place,

the guest
molecule
must be 1
example

LiliSz [I

(a) n-BuI

Bu

Scheme i

In this re
the T133
the nIfgat

ln
Vacant 5i
Could be
dimming
fuming-
M003 c
0th6dr
into Sing
hOSI‘ the
"Cited C

Clearly it

the guest and the host must be electronically compatible. The guest
molecule must be reducing enough to donate electrons to the host which
must be a strong enough oxidant to accept the transferred electrons. An
example of such a reaction is the reaction of n-BuLi with Ti82 to form
LiTi82 [11].

 

 

 

 

(a) n-BuLi + Ti82 ------- > LiTi82 + 1/ZBu-Bu
[ T182 1 [ '1'182 ]
Butt" + ------- -> 11* w Li“
i 1132 l I Tl52 I

 

 

 

Scheme 1.1. Insertion of lithium ions into Ti82 layers.

In this reaction the BuLi (for simplicity is viewed as BU'Li'I') [12], reduces
the Ti82 layers and Li ions insert in the van der Waals gap to counteract
the negative charge on the layers.

In a coordination type of intercalation reaction, the layers have
vacant sites, usually low coodination number of the metal atoms, which
could be a consequence of the intercalation reaction itself. Electron-
donating atoms could therefore coordinate to those empty vacant sites,
forming bonds. An example is the intercalation of pyridine into M003 [13],
M003 consists of 7.0 A thick double layers of edge- and comer-sharing
octahedra. Upon intercalation with pyridine, the bilayer of M003 splits
into single layers and as a result of this structural transformation of the
host, the pyridine molecules are now capable of bonding to the newly
created coordinatively unsaturated molybdenum atoms. This example also

clearly illustrates the non-topotactic nature of the reaction.

(b) Pyrid

 

 

(b) Pyridine + M003
T
N
_i/ .L./_._i../_
/ I i /|
/N /N

/ /

\N I \N I
_i../__._J./_ i.<__i.4_
/L L L /l

 

O

/

Scheme 1.2. Formation of the intercalation compound of pyridine into

M003. (From reference 13).

In an acid/base type of intercalation reaction, the hosts usually have
protons which are part of the crystal lattice. The hosts are therefore

capable of acting as Bronsted acids when treated with bases such as amines.

The reactio

the acid/has

(c) xC3H7i\'

NVH'

The reaction of n-propyl amine with VOHPO4-5H20 [14] clearly illustrates

the acid/base interaction as the vital driving force.

(0) xC3H7NH2 + VOHPO4-5H20 --------- > VOHPO4-5H2O-xC3H7N H2

33.3

H‘n’HHgHV

 

/\/NH2+

 

 

Scheme 1.3. Example of an acid/base type of intercalation reaction. (From

reference 14).

Ion—e
types. In th;
usually neg
ions, locatec
with other c;
invennicull

[15].

 

 

Scheme 1.4.

Potentially,
intercalation
since these n
examples. T}
chemjsuy.
Since I
imercait'iiion }
I“ 1987. Ma
conduqiVe pt
reaction. At f
I'Ould be kine
[be driving f

“M 01
nlCh IS belim

Ion-exchange intercalation chemistry is the most pervasive of all
types. In this type of insertion chemistry, the layers of the host which are
usually negatively charged are counterbalanced with positively charged
ions, located in the gallery spaces. The interlayer cations can be exchanged
with other cations. An example is the exchange of the monovalent cation M
in vermicullite clay, Mx(Mg)3[(Alei4-x)O10](OH)2, with NH4+ cations
[15].

 

 

 

 

 

 

 

 

I vermicullite clay ] 2NH4+ [ vermicullite clay ]
W M” * NH 4+ NH 4+ + 2M+
[ vermicullite clay ] I vermicullite clay j

 

Scheme 1.4. Example of an ion-exchange intercalation reaction.

Potentially, layered hosts which have undergone redox or acid/base
intercalation chemistry are susceptible to ion-exchange insertion reactions
since these reactions lead to intralamellar cations as shown in the above
examples. This, therefore vastly opens up the realm of intercalation
chemistry.

Since the first report of Schaufftaiil and until the mid 1980's,
intercalation has been involved exclusively with small molecules. However
in 1987, Marks and Kanatzidis reported the insertion polypyrrole, a
conductive polymer, into layered FeOCl [6]. This is a truly remarkable
reaction. At first sight, one would predict that this intercalation reaction
would be kinetically slow. However, the feasibility of this reaction lies in
the driving force. The FeOCl is a highly oxidizing agent, the potential of
which is believed to be similar to that of FeCl3 which is about 1.1 V [16].

The FeOl
the layen
intercalat
reaction I
have been
polyfurar
polythiop‘
V2056“:
these inter
Inte
materials a
rapid pace
lal’fimd m;
of underg(
lWatcher:
Peri-0mm
mOHOmerS
resulting t
Successful
[0 abSOrb
inIErCalatiO
p0Liberia
Anot;
ZeOlite Y “

The FeOCl oxidizes the pyrrole monomer, which oxidatively inserts into
the layered host as the polymer. This reaction is referred as an in-situ
intercalation/polymerization reaction. The exact mechanism of how this
reaction works is not fully understood. Since, other conductive polymers
have been encapsulated into FeOCl such as polyaniline, polythiophenc and
polyfuran [17]. The prototype conductive polymers, polyaniline,
polythiophenc and polypyrrole have also been introduced into layered
V205-nH2O xerogels [18]. V2O5onH2O is a very highly oxidizing host and
these intercalation reactions work in a similar manner as in FeOCl.

Interest in the encapsulation of conductive polymers in layered
materials and other structurally restricted environments keeps growing at a
rapid pace. However, there is a lack of highly oxidizing hosts. Not all
layered materials or other structurally confined environments are capable
of undergoing in-situ intercalation/polymerization reactions. Therefore,
researchers working in this area have to resort to alternative methods of
performing the inclusion reactions. One logical approach is to insert the
monomers into the constrained environments and then polymerize the
resulting templates with external sources. Several groups have been
successful in exploiting this technique. For instance, Inoue et a1. were able
to absorb aniline monomers into montmorillonite clays. The resulting
intercalation compounds were then used as electrodes to electrochemically
polymerize the encapsulated aniline to polyaniline [19].

Another example is where, Bein et al. treated the protonated form of
zeolite Y with aniline monomers. An acid/base intercalation reaction took
place, yielding anilinium inside the zeolite pores. The resulting template

gave intrazeolitic conductive polyaniline chains upon treatment with

(NH4)28203. These encapsulated polymer chains have been referred to as
"molecular wires" [ 20].

In our laboratory we were able to insert aniline into layered uranium
phosphate and then used molecular oxygen at relatively high temperature to
polymerize the trapped monomers [21].

Another method for inserting conductive polymer chains in confined
environments is to first insert the oxidant and then treat the resulting
materials with the monomer molecules. This technique has been applied by
Giannelis et a1. They have been able to incorporate highly oxidizing Cu2+
in the gallery space of mica which upon treatment with aniline yielded
polyaniline inside the clay layers [22]. This technique was also employed by
Bein and coworkers. They first introduced Fe3+ or Cu2+ ions inside zeolite
pores which upon treatment with pyrrole and thiophene molecules gave the
respective polymers trapped in the pores [23].

An entirely different approach was employed by Nazar et al. They
were able to insert conductive poly(p-phenylene vinylene) (PPV) into
M003 in a series of steps [24]. Mixed alkali hydrated bronzes of M003,
NaxLiy(H20)zMoO3 were first cation exchanged with the PPV precursor,
poly(p-xylylene-or-dimethylsulfonium chloride). The resulting polymer-
intercalated phase was then heated under vacuum to give (PPV)xMoO3.

There has also been a considerable amount of interest with the
insertion of saturated polymers into constrained environments. For
instance, Okada et al. at Toyota in Japan, have prepared hybrid materials
consisting of clays (5% by wt) and Nylon-6 and other plastics [25] and
these were shown to exhibit extraordinary mechanical and thermal
properties far better than those obtained by a mere physical mixture of the

two components or from the fairly robust plastics themselves. These

materials a
phases are
found appli
Since thi
organic/inc
There are 5
this area. 15
zeolites. Th
followed b
structures [2
Recei
insertion of
[27]. The r
materials its
used especiz
known to be
known that .
Possesses in
range 10-6 t
solid elect”)
Because of
materials in 1
Has; amOU
transport in
continue“,
crown‘elher

materials are referred as "nanocomposites" since the organic and inorganic
phases are intimately mixed at the molecular level. They have already
found applications in the construction of automobile parts such as bumpers.
Since this amazing discovery, the field of hybrid saturated
organic/inorganic polymeric materials has been growing very rapidly.
There are several groups in the whole world actively pursuing research in
this area. Bein et al. have been able to incorporate polyacrylonitrile into
zeolites. This was achieved by first diffusing the monomer into the pores
followed by heat treatment to induce polymerization within the pore
structures [26].

Recently, there has been a tremendous amount of interest in the
insertion of poly(ethylene-oxide), PEO into 2-dimensional (2-D) materials
[27]. The motivation behind such work is the realization of cathode
materials for application in high energy and power density batteries, to be
used especially for electric vehicle propulsion. 2-D materials are already
known to be good candidates for rechargeable cathodes [28] and it is well-
known that PEO when complexed with ionic salts, especially lithium salts
possesses ionic conductivity similar to that of dilute ionic solutions in the
range 10'6 to 10'1 S/cm [29]. PEO complexed with salts are referred as
solid electrolytes due to movement of the ions within the polymer chains.
Because of this very important observation the application of these
materials in solid state batteries was quickly realized [30]. There is actually
a vast amount of research aimed at elucidating the mechanisms of ion
transport in these materials [31]. Because these materials are ion-
conductors, it would be very interesting to look at the intercalation of
crown-ether type of materials into layered structures. The resulting

intercalation compounds could be coupled with lithium electrochemically,

litre
the
the

10

giving rise to solid state batteries. Solid state batteries are more desirable
than conventional batteries such as the lead-acid battery, in that they last
longer (possess longer shelf-lives) and, in principle, they do not leak. In the
past, polymeric solid electrolytes such as PEO have been intimately mixed
with layered materials such as Ta82 [32]. It was found that the diffusion of
lithium from the anode to the cathode layered material is torturous because
of the high activation energy of the process. However, PEO inserted in a
layered cathode, would facilitate lithium movement from the solid
electrolyte to the cathode because of the lowered activation energy of the
process. With these objectives in mind several groups in the world have
been actively pursuing research in this domain.

The first intercalation of PEO in a layered material was reported by
Ruiz-Hitzky et al. The intercalation was performed in layered silicates [33].
The driving force of this intercalation reaction is complexation of the
polymer with the interlayer alkali ion. The same group also reported the
intercalation of PEO into V2Os-nH2O xerogels using a similar technique
[34]. The xerogels were first reduced by Lil, forming the lithiated
LixV205.nH2O phase which upon treatment with a PEO solution leads to
encapsulation of the polymer.

Kanatzidis et a1. [35] were able to insert PEO into V2Os~nH2O
through an entirely different approach. Since both the PEO and layered
V205-nH2O are soluble in water, mixing solutions of the two and pouring
the resulting mixture on a flat glass substrate, followed by evaporation of
the solvent leads to the formation of (PEO)XV205.

Clement et al. were also able to insert PEO inside the layered MnPS3
[36]. MnPS3 is best viewed as the salt of the thi0phosphate anion,
2Mn2+(P2S6)4', the 2Mn2+ cations being part of the lattice. The intralayer

canor
exmo
ions

haah
msuh
luau
tothe
sauce

report

adnes
new v
oxidiz
and 1
avaha
mmhh
be We
meant
wuh(]
hand a
binge
Such

p0blet
POIyeyp
Thh “g
with ii]:
Sandy-t

11

cations can potentially be exchanged by other cations. Clement et al.
exploited that unique property by exchanging part of the Mn2+ with K+
ions. It is interesting to note that the K+ ions are arranged in the van der
Waals gap of the host, as evidenced from the interlayer expansion of the
resulting K2x(H20)yMn1-xPS3 phase. PEO has an affinity for K+ ions.
Treatment of K2x(H20)yMn1-xP83 with a solution of PEO in MEOH leads
to the incorporation of PEO inside the van der Waals gap of the layered
structure. However, complete characterization of this material was not
reported.

To expand the scope of organic/inorganic polymeric materials
achieved via the technique of intercalation, we are interested in devising
new ways of inserting polymers, both saturated and conjugated in non-
oxidizing layered hosts. Two layered hosts chosen for this thesis are M003
and M082 because they are both highly crystalline and are readily
available. M082 occurs naturally as its mineral molybdenite [37] and is
readily converted to M003 upon heating in an atmosphere of oxygen [38].
We were able to insert polyaniline into M003 in two reaction steps. First,
the aniline monomer was inserted into M003. The latter was then oxidized
with (NH4)28203 to yield polyaniline inside the M003 layers. On the other
hand a wide range of polymers were inserted into M082. These polymers
range from the conjugated polymer, polyaniline, to saturated polymers
such as poly(ethylene-oxide), poly(vinylpyrrolidinone),
poly(ethylenimine), poly(propylene glycol), methyl cellulose, Nylon-6 and
polyethylene. The polymers were directly inserted into the M082 layers.
This was achieved by exfoliating M082 into single layers [39] and mixing
with the polymer solutions. This causes flocculation where the M082 layers

sandwich the polymer chains. This exfoliation/restacking technique was

also
into
P9P
chos
C061
wor‘l
IllCSt
coba
hydr
pilla

12

also exploited to include a variety of molecular cobalt chalcogenide clusters
into M082. The cobalt clusters are structurally well-characterized clusters

prepared by Hong et al. [40] and Steigerwald et al. [41]. The clusters we
chose as intercalants are C0583(PPh3)6, CoeTe3(PBu3)5, C0583(PBu3)6
C058c3(PBu3)5, C068e3(PEt3)6 and C06Te3(PEt3)6. The idea behind this
work is to "pillar" M082 with these clusters in order to tailor micro and/or

mesoporous materials. We chose cobalt clusters as our intercalants since

cobalt species have already been used as promoters for M082 as far as
hydrodesulfurization (HDS) is concerned [42]. The other incentive is that
pillared sulfided layers, as opposed to pillared clays [43] and oxides [44],
are virtually unknown in the literature.

DESCRIPTION OF LAYERED MATERIALS
I. M003

The structure of M003 is shown in Figures 1.1 and 1.2. The
structure is described as a layered structure in which each layer is built up
of M006 octahedra at two levels connected in the c direction by common
edges and corners so as to form zig-zag rows and in the a direction
perpendicular to this by common comers only. The interlayer spacing of
M003 is 6.93 A. The layers stack in an ABA fashion, with two layers per
unit cell. The material crystallizes in an orthorhombic lattice, space group
anm, with unit cell dimensions, a= 3.9628 A, b= 13.855 A and 0: 3.6964
A. Tire crystal structure of M003 was determined in 1931 by Brakken [45]
and independently by Wooster [46]. The results obtained by these two

invesdgz
blocks (
demons!
2.010 2.
Wooster
rather a;
and Ma
electron
features
reported
disrortic
What w;
Pm’ious
Kihlboré
strum"E
In recer
1936‘ M
[491.171
dfinensh
M003

Wiened

l3

investigators are quite consistent. Both authors pointed out that the building
blocks of the layers, i.e, the M005 octahedra are rather distorted as
demonstrated by the divergence of the Mo-O distances. These range from
2.0 to 2.5 A according to Brakken and from 1.90 to 2.34 A according to
Wooster. In these early structure elucidations, the distances given are
rather approximate. The structure was later reinvestigated by Anderson
and Magnéli using Fourier methods [47]. They found maxima in the
electron density maps close to the assumed positions and the principal
features of the structures were accordingly confirmed. The Mo-O distances
reported by these authors range from 1.8 to 2.35 A, indicating that the
distortion of the octahedral coordination is even more pronounced than
what was previously assumed. Due to the uncertainties in the work of
previous investigators, the crystal structure of M003 was redeterrnined by
Kihlborg in 1963 by using the method of least square refinements [48]. The
structure of M003 is unique since it is not shared by any other compounds.
In recent years, two new M003 phases were reported. For instance, in
1986, McCarron 111, reported the synthesis of a metastable phase of M003
[49]. The structure of this new phase is related to W03, which adopts a 3-
dirnensional ReO3 type structure. This metastable phase is referred to as B-
M003 and the thermodynamically more stable (Kihlborg's M003) is
referred to as or-MoO3. B-MoO3 was prepared by the thermal treatment of
spray-dried powders of aqueous molybdic acid solutions at 300 0C under
an oxygen atmosphere. DSC experiment showed that B-MoO3 converts to
a-MoO3 at 450 0C by observation of an exothermic peak at that
temperature. B-MoO3 undergoes intercalation chemistry with lithium and
hydrogen. The crystal structure of B-MoO3 has been accurately determined
by neutron diffraction [49].

1
high pi
MoO3
[1. Mo
51003
SUUCtU
HOWCV
an imp
a-Mo(
it is m
more i
MOD 3
chemis

aMo(

14

In 1991, McCarron III and Calabresse reported the synthesis of a
high pressure phase of M003 [50]. This phase was obtained by treating a-
MoO3 at high temperature and high presssure and is referred to as M003-
II. M003-II is actually a more condensed form of a-MoO3. The density of
M003-II is 4.75 g/cm3 whereas that of a-MoO3 is 4.71 g/cm3. The
structure of M003-II is layered and is quite similar to that of a-MoO3.
However, in M003-II, the layers stack in an AAA fashion which results in
an improved packing efficiency for the layers of M003-II versus those in
or-MoO3. No intercalation chemistry has been reported for M003-II, since
it is metastable at ambient pressure and converts to the thermodynamically
more stable a-phase rapidly at temperatures above 200 0C. However, 0:-
MoO3 enjoys a wide range of redox intercalation and ion-insertion
chemistry [51]. In this work, all intercalation chemistry were performed on

a-MoO3 and this layered material is going to be referred simply as M003.

b

‘

 

15

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 1.1. Structure of a-MoO3 , a parallel view of the layers.

16

 

Figure 1.2. A perpendicular view of the M003 layers.

ll.h

main

thttt

used

lubri

densi

by l
phot.
l98l
SU‘UC
authi
Shou

layer

17

II. M082

M082 is a material of paramount technological importance. It is the
main constituent of the hydrodesulfurization (HDS) catalyst used in
petroleum industry. The efficiency of MoSz as an HDS catalyst is as high as
that of RuSz, the best known catalyst for HDS [52]. However, Ru82 is not
used commercially as an HDS catalyst since it is very expensive and has to
be made synthetically. Similar to graphite, M082 is being used as a solid
lubricant [53]. It is also a potential candidate as cathodes in high energy
density lithium batteries [54].

The crystal structure of M082 was first determined quite accurately
by Dickinson and Pauling in 1923, by means of spectral and Laue
photographs and, with the aid of space group theory [55]. In the 1970's and
1980's, several research groups have accurately elucidated the crystal
structure of M082 with modem X-ray techniques and the results from these
authors are very consistent with each other [56]. The structure of M082 is
shown in Figures 1.3 and 1.4. MoSz possesses a layered structure with 2
layers per unit cell which stack in an hexagonal symmetry. As such, this
polytype of M082 is denoted as 2H-MoSz to distinguish it from the less
common, 3R polytype which has three layers per unit cell stacked in a
rhombohedral symmetry [57]. In this work, 2H-MoSz is also going to be
referred to as D3h—M082, from point group considerations, since each Mo

atom is coordinated to 6 S atoms in a trigonal prismatic fashion.

l8

 

 

.a 0o 9 Q g.

 

 

 

 

1 O) O 0 (I
0 0 0 (O (a
/
'\ "\ ’5' ’x5 . ./
\ . W ..
.' O a 96 '\

 

 

 

Figure 1.3. Structure of 2H-MoSz; a parallel view of the layers.

.9?

F.
lgure 1

19

 

Figure 1.4. Structure of 2H-MoSz; a perpendicular view of the layers.

Guest
l. Pol

l
polyme
the focr
over 5l
behind
applies.
electroc
[61] an
hand, [i
materia
for mgr
later to
Green a
the line
the firs
early d;
that the
70's‘ J
underst
Were (it
and 0th

P
elecll’ic

20

Guest Species

I. Polyaniline

Polyaniline is one of the prototype electronically conductive
polymers that is being increasingly studied and, in recent years, has been
the focus of a considerable amount of scientific interest [58]. To date, well
over 500 publications and patents have been recorded. The motivation
behind the study of polyaniline lies in its wide range of potential
applications such as electrodes in rechargeable batteries [59],
electrochromic display devices [60], microelectronic devices and sensors
[61] and a plethora of other anticipitated applications [62]. On the other
hand, the starting material, aniline, is cheap and polyaniline is a very stable
material. However, polyaniline is not a novel material. It has been known
for more than 150 years. It was first made by Runge in 1834 [63] and years
later to follow by Lightfoot [64], Coquillon [65], Forpelstroeder [66],
Green and Woodhead [67] and many others [68]. These authors referred to
the uncharacterized oxidized products as 'aniline blacks'. Fritzsche made
the first attempt to characterize the so-called 'aniline blacks' [69]. In the
early days PANI suffered from a great deal of controversy due to the fact
that the material was poorly understood. However, in the 1960's and early
70's, Jozefowicz et a1. made an outstanding contribution to the
understanding of PANI [70]. In the 1980's, a tremendous amount of work
were done by Bard et al. [71], Genies et a1. [72], MacDiarmid et al. [73]
and others.

Polyaniline is unique among the conductive polymers in that its

electrical properties could be reversibly controlled by changing its

 

0.1
Sll

[hl

re]

pc

C0

ell

P0

iUS

21

oxidation state and degree of protonation [74]. Even though the actual
structure of polyaniline is not known, it is believed that in the base form

the polymer can be described by the general formula,

H H } . .
c ta (1 d
@—< HWY 0 C -y x on rnrng re uce

repeat units, 03—0—55— , and oxidized repeat units,
W. When O<y<l the polymer is

poly(paraphenyleneamineimine) in which the oxidation of the polymer

continuously increases with decreasing value of y. The fully reduced

. H
poly(paraphenyleneamine), {Q4892- , also known as
X

leucoemeraldine, corresponds to a value of y=1. The fully oxidized,

poly(paraphenyleneimine), also named

pemigraniline corresponds to a value of y=0. The 50 % oxidized

poly(paraphenyleneamineimine),

H H
kO—N—‘Q‘VWI , commonly named as
X

emeraldine, corresponds to a value of y = 0.5. Each oxidation state of the
polymer, as described above, is shown in its base form, each of which can
in principle be converted into the acid form (protonated, salt form). For

instance, the emeraldine base can be converted reversibly to its salt form

22

by treatment with acid. The emeraldine salt form of the polymer is the
form which is conductive.

PANI can be made chemically or electrochemically. However, it is
worth noting that other methods for the formation of polyaniline exist. For
instance, Millard [75] and Shen [76] are responsible for the development of
a gas—phase plasma technique for the polymerization of aniline and its
substituted derivatives. The main advantage of this method is that it does
not require the use of solvents or oxidizing agents. Consequently, the
resulting product is very clean since it does not necessitate separation from
by-products. The polymer is also obtained in the undoped state and the
supporting material does not have to be conductive. However, the technique
requires the use of very high energy which leads to polymer degradation.

MacDiarmid et al. [77] have been able to vapor-deposit PANI onto
quartz by heating neutral emeraldine at 350 0C. The resulting products
were found to contain shorter chain lengths but were found to be less
contaminated by oxygen.

Polyaniline has been inserted into the gallery space of layered
materials such as V205-nH20 [18a], FeOCl [17b], uranyl phosphate [21]
and clays [19, 22].

23

II. Poly(ethylene-oxide) (PEG) and Poly(ethylenimine) (PEI)
{CHZCH209H {CHZCHzNfi

PEO is an ionically conductive polymer when it is complexed with
ionic salts, particularly, lithium salts. Basically, it can be regarded as a
'solvent' capable of dissolving ionic salts. The first measurements of the
ionic conductivity in PEO-salt complexes were carried out by Wright et al.
in the 1970's [78]. However, it was Armand who first came to the
realization that these materials could be used as electrolytes in the
development of solid-state batteries [79]. Hence, these polymeric materials
have often been referred to as solid electrolytes, in analogy to the already
well-known classical solid electrolyte materials such as PbF2, AgI,
Ag2HgI4 and B-alumina [80].

PEG is a semicrystalline material with about 60 % of the bulk being
crystalline at room temperature and the remainder is present as an
amorphous elastomeric phase. It is the crystalline portion of the polymer
that possesses low ionic conductivity. Ions move easier in the amorphous
part the polymer. Intercalation of PEO has been reported in layered hosts
such as silicates [33], V205-nH20 [34, 35], MnPS3 [36] and montmorillonite
clays [27b].

Poly(ethylenimine) (PEI) is structurally closely related to PEO.
Therefore any differences in the behavior of the two polymers is due to the
difference between the oxygen atom and the nitrogen atom. Linear PEI is
highly crystalline and suffers the same complications as PEO as far as
being a good host for polymer electrolyte formation [78]. The branched

commercial grades of PEI are amorphous and are therefore superior to the

24

its crystalline counterpart [81]. Contrary to PEO, the intercalation
chemistry of PEI in layered structures has not been exploited.

III. Poly(propylene-oxide) (PPO), Poly(propylene glycol)
(PPG)

i‘

{CHrc—o
CH3

1'1

PPO that are available commercially lack in stereoregularity and as
such are amorphous. This may seem as an asset, but the presence of cross-
linking agents in the commercial materials has posed a major problem in
the fundamental studies of PPO. However, an enormous amount of
exploratory work has been done on the ionic conductivities of PPO-salt
complexes [82]. Interestingly enough, when amorphous PPO is complexed
with LiBF4 to give PPO-(LiBF4)o,13 , the conductivity is found to be very
low ca. 10'8 S/cm, the same as that of PEO-(LiBF4)o,13 [83]. Steric
hindrance of the methyl group on the PPO chain is believed to be the cause

of low conductivity despite the fact that the polymer is amorphous.
Intercalation of PPO has been achieved in layered V205-nH20 [34, 84].

25

IV. Poly(vinylpyrrolidinone) (PVP)

-(-cH—CH2-}n
. o

PVP is a very important commercial polymer with a wide range of
uses. By far, the most important applications of PVP are in
pharmaceuticals and cosmetics. For instance, it is used on a very large scale
as a blood plasma expander or substitute and as an antiseptic for cuts and
bruises when it is complexed with iodine.

In the field of polymeric solid electrolytes, PVP gives rise to very
low conductivity of the resulting PVP/salt complexes, even when the salts
used are lithium salts, e.g LiSO3CF3 [85]. However, it was found that the
ionic conductivity of the PVP-LiSO3CF3 can be increased to a fairly high
value of 5 x 10'5 S/cm when it is plasticized with poly(ethylene glycol)
(PEG) [86]. The low glass transition temperature (Tg) of the solid
complex, PVP-PEG-LiSO3CF3 (-55 0C) is responsible for the high ionic
conductivity observed. The solid electrolyte, PVP-LiSO3CF3 itself has a
high Tg of 180 oC. So far, encapsulation of PVP has been reported only in
layered V205~nH20 [84].

26

V. Methyl Cellulose

ocrr3

 

CHZOCH3

The structure of methyl cellulose suggests that it should be a very
good candidate for complexation with ionic salts. Unfortunately, no report
is available in the literature regarding that matter. Methyl cellulose is a
derivative of cellulose, which is structurally very similar to glucose.
Cellulose is found widely in nature [87]. It is the major component of the
cell wall in plants which averages about 50 % in a typical wood. Cellulose

is actually the most abundant organic compound on earth. Encapsulation of

methyl cellulose has been reported only in V205-nH20 [84].
VI. Nylon-6 (poly(caprolactam))

{ii-(crifigco);

Nylon was the first synthetic fiber invented by Du Pont Chemical
Company [88]. Depending on the number of methylene groups, in principle

27

a homologous series of polyamides could be synthesized. Nylon-6 is the
most common of all the polyamides. It possesses exceptional mechanical
and thermal properties and has found a wide range of applications
particularly in textiles, cosmetic products, airplane tire cords etc.
Intercalation of Nylon-6 into layered clays has been reported by Okada et
al. [25].

VII. Poly(ethylene)
{CHI— CH2)!-1

Poly(ethylene) is the most common plastics encountered by people in
their everyday life. Poly(ethylene) possesses strong mechanical strength
and has very good thermal properties. Consequently, the polymer has
found uses in the manufacture of bottles, drums, pipes, conduit, sheet, film,
wire and cable insulation [89]. No intercalation compound of

poly(ethylene) exists.

VIII. Molecular Clusters of the General Type C05Q3(PR3)5 [Q2
S, Se, Te and R = phenyl, n-butyl and ethyl]

The clusters C0683(PPh3)6, Co6Teg(PBU3)6, CosSg(PBu3)6,
CosSe3(PBu3)6, Co6Se3(PEt3)6 and Co6Te3(PEt3)6 are isostructural. The
six cobalt atoms form a slightly distorted octahedron. The eight C03 faces

of the octahedral C06 core are capped by chalcogen atoms. In addition,

pr

[ht

[ht

28

each cobalt atom is terminally bonded to phosphine ligands. Figure 1.5
shows the molecular structure of CoaSe3(PEt3)5 and Figure 1.6 the inner
core of the cluster.

So far there has only been one report where a cluster molecule has
been inserted in a sulfided layered material. In 1986, Nazar and Jacobson
were able to intercalate Fe683(PEt3)62+ into TaSz, by exchanging the
sodium ions in Nao,33TaSz [90]. The driving force for this work was to
"pillar" the TaSz layers with the cluster molecule in order to develop
porous materials similar to zeolitic phases. Pillaring of a layered structure
offers the advantage over zeolites in that the pore size could be controlled
by tailoring the amount of the pillaring agent to that of the layered host.
This was first demonstrated with layered clays where it was shown that
pore size larger than faujastic zeolites could be realized by using the

pillaring phenomenon [91].

A detailed description of the layered host materials and intercalant
molecules, ranging from polymers to molecular clusters has been
presented. Interesting and intriguing properties have been obtained from
the intercalation compounds synthesized. For instance, the conformation of
the intercalated polyaniline in (PANI)xMoO3, has been directly probed by
spectroscopic means (chapter 2). The exfoliation and restacking properties
of MoSz have been exploited to produce polymer/M082 nanocomposites
with high electronic conductivity and interesting magnetic properties
(chapter 3). The exfoliation and restacking property of M082 has also been
capitalized to encapsulate molecular clusters in M082. Pillared layered
structures have been obtained as shown by BET surface area measurements

(chapter 4).

29

 

Figure 1.5. Molecular structure of C068e3(PEt3)6.

3O

 

49A

  

69/

Figure 1.6. Inner core of Co6Se3(PEt3)6.

   

31

REFERENCES

[l] Whittingham, M. S.; Jacobson, A. J In Intercalation Chemistry,

Materials Science Series, Academic Press, 1982.

[2] (a) Quig, A.; Rees, L. V. C. J. Chem. Soc. Faraday I 1976, 12, 771-
790. (b) Wolf, F.; Danes, F.; Pilchowski, Adv. Chem. Ser. 1971,1112,
229-237.

[3] (a) Vassiliou, J. K.; Ziebarth, R. P.; DiSalvo, F. J. Chem. Mater. 1990,
2, 738-741. (b) DiSalvo, F. J. Science 1990, 241, 649-655.

[4] (a) Holczer, K.; Klein, 0.; Griiner, G.; Thompson, J. D.; Diederich, F.;
Whetten, R. L. Phys. Rev. Lett. 1991, 61, 271-274. (b) Holczer, K.; Klein,
0.; Huang, S-M.; Kaner, R. B.; Fu, K-J.; Whetten, R. L.; Diederich, F.
Science 1991, 212, 1154-1156.

[5] Johnson, J. W.; Jacobson, A. J.; Rich, S. M.; Brody, J. F. Revue de
Chimie Minerale 1982, 12, 420-431.

[6] Kanatzidis, M. G.; Tonge, L. M.; Marks, T. J. .I. Am. Chem. Soc.
1987. .1122, 3797-3799.

[7] Schauffaiitl, P. J. Prakt. Chem. 1841, 2], 155.

32

[8] (a) Gore, J. 8.; Walk, C. R. U.S. Patent 3, 929,504, 1975. (b)
Merriman, M. R.; Vezzoli, G. C. Mater. Res. Bull. 1979, 11, 77-84 (c)
Whittingham, M. S. Mat. Res. Bull. 1978, 13, 959-965. ((1) Whittingham,
M. S. J. Chem. Soc. Chem. Commun. 1974, 328-329. (e) Matsuda, Y.;
Morita, M.; Takata, K-I. J. Electrochem. Soc. 1984, 131, 1991-1995. (f)
Vaccaro, A. J .; Palanisamy, T.; Kerr, R. L.; Maloy, J. T. 1982, 129, 677-
681. (g) Caja, J.; Kaner, R. B.; MacDiarmid, A. G. J. Electrochem. Soc.
1984, 131, 2744-2750. (h) Whittingham, M. S. Science 1976, 122, 1126-
1127. (i) Whittingham, M. S. Ann. Chim. Fr. 1982, 1, 204-214.

[9] (a) Gamble, F. R.; DiSalvo, F. J .; Klemm, R. A.; Geballe, T. H. Science
1970, 168,, 568. (b) Gamble, F. R.; Osiecki, J. H.; Cias, M.; Pisharody, R.;
DiSalvo, F. J.; Geballe, T. H. Science 1971, 114, 493-497. (c) Averill, B.
A.; Kauzlarich, S. M. Mol. Cryst. Liq. Cryst. 1984, LQZ, 55-64. ((1)
Rouxel, J.; Meerschaut, A.; Gressier, P. Synth. Met. 1989, 3_4_, 597-607.

[10] (a) Boersma, M. A. M. Catal. Rev. 1974, m, 243-280. (b) Pinnavaia,
T. J.; Farzanch, F.; Inorg. Chem. 1983, 22, 2216-2220. (c) Figueras, F.
Catal. Rev. 1988, 39, 457-499. ((1) Wang, M. C. Clays & Clay Minerals
1991, 32, 202-210.

[11] (a) Whittingham, M. 8.; Gamble, F. R. Mat. Res. Bull. 1975, LQ, 363-
372. (b) Silbemagel, B. G.; Whittingham, M. S. J. Chem. Phys. 1976, 65,

3670-3673.

[12] Dines, M. Mat. Res. Bull. 1975, m, 287-292.

33

[13] Johnson, J. W.; Jacobson, A. J.; Rich, S. M.; Brody, J. F. J. Am.
Chem. Soc. 1981, 103, 5246-5247.

[14] Guliants, V. V.; Benziger, J. B.; Sundaresan, S. Chem. Mater. 1994,
Q9 353'356.

[15] Barrer, R. M., Zeolites and Clay Minerals as Sorbents and Molecular

Sieves , Academic Press, New York, 1978.

[16] Meyer, H.; Weiss, A.; Besenhard, J. 0. Mat. Res. Bull. 1978, 13, 913-
920.

[17] (a) Kanatzidis, M. G.; Marcy, H. O.; McCarthy, W. J.; Kannewurf, C.
R.; Marks, T. J. Solid State Ionics 1989, 32133, 594-608. (b) Kanatzidis,
M. G.; Wu, C-G.; Marcy, H. O.; DeGroot, D. C.; Kannewurf, C. R.;
Kostikas, A.; Papaefthymiou, V. Adv. Mater. 1990, _2_, 364-366. (c) Wu,
C-G.; Marcy, H. O.; DeGroot, D. C.; Kannewurf, C. R.; Schindler, J. L.;
Leang, W. Y.; Benz, M.; LeGoff, E.; Kanatzidis, M. G. Synth. Met. 1991,
M3, 693-698.

[18] (a) Kanatzidis, M. G.; Wu, C-G.; Marcy, H. O.; Kannewurf, C. R.; J.
Am. Chem. Soc. 1989, lfl, 4139-4141. (b) Wu, C-G.; Kanatzidis, M. G.;
Marcy, H. O.; Degroot, D. C.; Kannewurf, C. R. Polym. Mater. Sci. Eng.
l989,6_l_, 969-973. (c) Wu, C-G.; Kanatzidis, M. G.; Marcy, H. O.;
Degroot, D. C.; Kannewurf, C. R. NATO Advanced Study Institute; Lower
Dimensional Systems and Molecular Devices; Metzger, R. M., (Ed.),
Plenum Press, New York, 1991; pp 427-434. ((1) Kanatzidis, M. G.; Wu,

v.

I
.l

PFO

34

C-G.; Marcy, H. 0.; Degroot, D. C.; Kannewurf, C. R. Chem. Mater.
1990, 2, 222-224.

[19] Inoue, H.; Yoneyama, H. J. Electroanal. Chem. 1987, 233, 291-294.

[20] (a) Bein, T.; Enzel, P. Synth. Met. 1989, 22, El63-El68. (b) Enzel,
P.; Bein, T. J. Phys. Chem. 1989, 23, 6270-6272.

[21] Liu, Y.-J.; Kanatzidis, M. G.; Inorg. Chem. 1993, fl, 2989-2991.

[22] (a) Mehrotra, V.; Giannelis, E. P. Mat. Res. Soc. Symp. Proc. 1990,
111,, 39-44. (b) Mehrotra, V.; Giannelis, E. P. Solid State Commun. 1991,
11, 155-158. (c) Mehrotra, V.; Giannelis, E. P. Solid State Ionics 1992,
31,, 115-122. ((1) Vaia, R. A.; Ishii, H.; Giannelis, E. P. Chem. Mater.
1993, 3, 1694-1696.

[23] (a) Enzel, P.; Bein, T. J. Chem. Soc., Chem. Commun. 1989, 1326-
1327. (b) Bein, T.; Enzel, P. Angew. Chem. Int. Ed. Engl. 1989,23,
1692-1694.

[24] Nazar, L. F.; Zhang, Z.; Zinkweg, D. J. Am. Chem. Soc. 1992, 1L4,
6239-6240.

[25] (a) Okada, A.; Kawasumi, M.; Kurauchi, T.; Kamigaito, O. Polymer
Prepr. Am. Chem. Soc., Div. Polym., 1987,23, No. 2, 447. (b)
Fukushima, Y.; Inagaki, S. J. Inclusion Phenom. 1987, 3, 473-482. (c)
Okada, A.; Kawasumi, M.; Usuki, A.; Kojima, Y.; Kurauchi, T.;

35

Kamigaito, 0. Mat. Res. Soc. Symp. Proc. 1990, 111, 45-50. (d) Okada,
A.; Kawakado, M. Japanese Patent Application No. Sho 60 [1985]-217396.

[26] Enzel, P.; Bein, T. Chem. Mater. 1992, 3, 819-824.

[27] (a) Bissessur, R.; Kanatzidis, M. G.; Schindler, J. L.; Kannewurf, C.
R. J. Chem. Soc. Chem. Commun. 1993, 1582-1585. (b) Lerner, M. M.;
Wu, J.; Chem. Mater. 1993, 3, 835-838. (c) Aranda, P.; Ruiz-Huzky, E.
Chem. Mater. 1992, 3, 1395-1403. (d) Ruiz-Hitzky, E.; Jimenez, R.;
Casal, B.; Manriquez, V.; Santa Ana, A.; Gonzalez, G. Adv. Mater. 1993,
5, 738-741. (e) Lemmon, J. P.; Lerner, M. M. Chem. Mater. 1994, 3,
207-210.

[28] (a) Murphy, D. W.; Christian, P. A.; Science 1979, 223, 651-656. (b)
Whittingham, M. S. J. Electrochem. Soc. 1976, .123, 315-320. (c)
Whittingham, M. S. Prog. Solid State Chem. 1978, _12, 41-99.

[29] (a) Armand, M.; Solid State Ionics 1983, 2Ll_0, 745-754. (b) Armand,
M. Adv. Mater. 1990, 2, 278-286. (c) Armand, M. B.; Chabagno, J.-M.;
Duclot, M. In Fast Ion Transport in Solids. Electrodes and Electrolytes,
Vashishta, P.; Mundy, J. N.; Shenoy, G. K. (Eds.), Elsevier, New York,
1979.

[30] (a) Gauthier, M.; Fauteux, D.; Vassort, G.; Bélanger, A.; Duval, M.;
Ricoux, P.; Chabagno, J. M.; Muller, D.; Rigaud, P.; Armand, M. B.;
Deroo, D.; J. Electrochem. Soc. 1985, 132, 1333-1340. (b) Hunter, C. C.;
Sinclair, D. C.; West, R.; Hooper, A. J. Power Sources 1988, _2_4_, 157.

36

[31] Ratner, M. A.; Shriver, D. F. Chem. Rev. 1988, 38, 109-124.

[32] (a) Harris, K. D. M.; Rogers, M. D.; Vincent, C. A. Solid State Ionics
1986, 13112, 833. (b) Steele, B. C. H. In Transport-Structure Relations in
Fast Ion and Mixed Conductors (Proceedings of the RISO International
Symposium on Metallurgy and Materials Science); Paulsen, F. W.,
Andersen, N. H., Clausen, K., Skaarup, S.; Sorensen, D. T., (Eds.),
Roskilde, 1985.

[33] Ruiz-Hitzky, E.; Aranda, P. Adv. Mater. 1990, 2, 545-547.

[34] Ruiz-Hitzky, E.; Aranda, P.; Casal, B. J. Mater. Chem. 1992, 2, 581-
582.

[35] Liu, Y.-J.; DeGroot, D. C.; Schindler, J. L.; Kannewurf, C. R.;
Kanatzidis, M. G. Chem. Mater. 1991, 3, 992-994.

[36] Lagadic, I.; Léaustic, A.; Clement, R. J. Chem. Soc. Chem. Commun.
1992, 1396-1397.

[37] Greenwood N. N.; Eamshaw, A. Chemistry of The Elements,
Pergarnon Press, New York, 1984.

[38] (a) Cotton, F. A.; Wilkinson, G. Advanced Inorganic Chemistry, A
Comprehensive Text, 4th Edition, Wiley-Interscience, 1990. (b)
Divigalpitiya, W. M. R.; Frindt, R. R; Morrison, R. F. Thin Solid Films
1990, 188, 173-179.

37

[39] Divigalpitiya, W. M. R.; Frindt, R. R; Morrison, S. R. Appl. Surf.
Sci. 1991, 48142, 572-575.

[40] (a) Hong, M.; Huang, 2.; Lei, X.; Wei, G.; Kang, B.; Liu, H. 1989,
Inorg. Chim. Acta 1989, 132, 1-2. (b) Hong, M.; Huang, 2.; Lei, X.;
Wei, G.; Kang, B.; Liu, H. Polyhedron 1991, 12, 927-934.

[41] (a) Steigerwald, M. L.; Siegrist, T.; Stuczynski, S. M. Inorg. Chem.
1991, 30, 4940-4945. (b) Stuczynski, S. M.; Kwon, Y.-U.; Steigerwald,
M. L. J. Organomet. Chem. 1993, £2, 167-172.

[42] Prins Roel In Characterization of Catalytic Materials, Wachs, I. E.
(Ed.), Butterworth-Heinemann, 1992.

[43] (a) Pillared Layered Structures: Current Trends and Applications;
Mitchell, 1. V., (Ed.); Elsevier, New York, 1990. (b) Figueras, F. Catal.
Rev. 1988, 32, 457-499. (c) Vaughan, D. E. W. In Perspective, in
Molecular Sieve Science, Flank, W. H., Whyte, T. E., (Eds.), American
Chemical Society: Washington, D. C., 1988, p 308.

[44] Nazar, L. F.; Yin, X. T.; Zinkweg, D.; Zhang, Z.; Liblong, S. Mat.
Res. Soc. Symp. Proc. 1991, 212, 417-422.

[45] Briikken, V. H., Z. Krist. 1931, E, 484-488.

[46] Wooster, N. Z. Krist. 1931, LO, 504-512.

[47} .

HSIQ

H911

5011
1214

151] 1
1992
Bud.
0. .11
hon
thl
M. L.
Com.
Bunn
dppl
1norg

GOpa.

52]]

38

[47] Anderson, G.; Magnéli, A. Acta Chem. Scand. 1950, A, 793-797.
[48] Kihlborg, L. Arkiv Kemi 1963, 21, 357-364.
[49] McCarron III, E. M. J. Chem. Soc. Chem. Commun. 1986, 336-338.

[50] McCarron III, E. M.; Calabresse, J. C. J. Solid State Chem. 1991, 21,
121-125.

[51] (a) Lerf, A., Lalik, E.; Kolodziejski, W.; Klinowski, J. J. Phys. Chem.
1992, 26, 7389-7393. (b) Thomas, D. M.; McCarron III, E. M.; Mat. Res.
Bull. 1986, 21, 945-960. (c) Schollhom, R.; Kuhlmann, R.; Besenhard, J.
0. Mat. Res. Bull. 1976, 11, 83-90. ((1) Schollhom, R.; Schulte-Nolle, T.;
Steinhoff, G. J. Less Common Met. 1980, 11, 71-78. (e) Dickens P. G.,
Hibble S. J. Solid State Ionics 1986, 21, 69-73. (f) Chatakondu, K.; Green,
M. L. H.; Qin, J.; Thompson, M. E.; Wiseman, P. J. J. Chem. Soc. Chem.
Commun. 1988, 223-225. (g) Green, M. L. H.; Qin, J.; O'Hare, D.;
Bunting, H. E.; Thompson, M. E.; Marder, S. R.; Chatakondu, K. Pure &
Appl. Chem. 1989, fl(5), 817-822. (h) Kanatzidis, M. G.; Marks, T. J.
Inorg. Chem. 1987,E_, 783-784. (i) Ganguli, A. K.; Ganapathi, L.;
Gopalakrishnan, Rao, C. N. R. J. Solid State Chem. 1988, 14, 228-231.

[52] Pecoraro, T. A.; Chianelli, R. R. J. Mol. Cat. 1981, 61, 430-445.

Z561
Scht
407.

Pu]

[53]

Abal
Skim

39

[53] (a) Fleischauer, P. D. Thin Solids Films 1987, 153, 309-322. (b)
Hinokuma, K.; Sakamaki, K; Fujishima, A. Bull. Chem. Soc. Jpn. 1990,
63, 2713-2715.

[54] (a) Tributsch, H. Faraday Discuss. Chem. Soc. 1980, 1Q, 190-205.
(b) Julien, C.; Saikh, S. I.; Nazri, G. A. Mater. Sci. Eng. 1992, B13, 73-
77.

[55] Dickinson, R. G.; Pauling, L. J. Am. Chem. Soc. 1923,13, 1466-
1474.

[56] (3) Murray, R.; Evans, B. L. J. Appl. Cryst. 1979, _l_2, 312-315. (b)
Schonfeld, 8.; Huang, J. J.; Moss, S. C. Acta Cryst., Section B 1983, 404-
407. (c) Kalikhman, Inorg. Mater. 1983, 12, 957-962.

[57] Bromley, R. A.; Murray, R. B.; Yoffe, A. D. J. Phys. C: Solid State
Phys. 1972, 3, 759-778.

[58] (a) Srinivasan, S.; Pramanik, P. Synth. Met. 1994, 63, 199-204. (b)
Abalyaeva, V. V.; Kogan, I. L. Synth. Met. l994,_6_3_, 109-113. (c)
Skinner, N. G.; Hall, E. A. H. Synth. Met. 1994, _63, 133-145. ((1) Amano,
K.; Ishikawa, H; Kobayashi, A.; Satoh, M.; Hasegawa, E. Synth. Met.
1994, Q, 229-232. (e) Long, S. M.; Cromack, K. R.; Epstein, A. J.; Sun,
Y.; MacDiarmid, A. G. Synth. Met. 1994, Q, 287-289. (f) Skotheim, T.
A. (Ed.) In Handbook of Conductive Polymers, Marcel Dekker, New
York, Vol. 1, 2, 1986.

1591
2496

Crys

W
D. N
Rico
Chac

1631

here

1631
1991]

40

[59] Stilwell, D. E.; Park, S.-M. J. Electrochem. Soc. 1988, 133, 2491-
2496.

[60] MacDiarmid, A. G.; Mu, S. L.; Somasiri, N. L. D.; Wu, W. Mol.
Cryst. Liq. Cryst. 1986, 121, 187-190.

[61] (a) Tirnoeeva, O. N.; Lubentsov, B. Z.; Sudakova, Y. Z.; Cheryshov,
D. N.; Khidekel, M. L. Synth. Met. 1991, 46, 111-116. (b) Paul, E. W.;
Ricco, A. J.; Wrighton, M. S.; J. Phys. Chem. 1985, 82, 1441-1447. (c)

Chao, S.; Wrighton, M. S. J. Am. Chem. Soc. 1987, 1132, 6627-6631.

[62] Miller, J. S. Adv. Mater. 1993,_3, No. 7/8 587-589 and references

therein.

[63] Genies, E. M.; Boyle, A.; Lapowski, M.; Tsintavis, C. Synth. Met.
1990, 36, 139-182.

[64] Lightfoot, Br. Patent, 1863, 151.

[65] Coquillon, Compt. Rend. 1875, 32, 408.

[66] Forpelstroeder, Compt. Rend. 1876, 82, 331.

[67] Green, A. G.; Woodhead, A. E. J. Chem. Soc. 1910, 21, 2388-2403.

[68] (a) Yasui, T.; Bull. Chem. Soc. Jpn. 1935, 12, 305-311. (b) Datta, R.
L.; Sen, J. N. J. Am. Chem. Soc. 1917, 32(1), 747-750.

41

[69] Fritzsche, J. J. Prakt. Chem. 1940, 29, 453.

[70] (a) Doriomedoff, M.; Hautiére-Cristofini, F.; de Surville, R.;
Jozefowicz, M.; Yu, L-T.; Buvet, R. J. Chim. Phys. Physico Chim. Biol.
1971, 68,, 1055-1069. (b) Yu, L-T.; Petit, J.; Jozefowicz, M.; Belorgey,
G.; Buvet, R. C. R. Acad. Sci. Ser. C. 1965, 26Q, 5026.

[71] Carlin, C. M.; Kepley, L. J .; Bard, A. J. J. Electrochem. Soc. 1985,
1.12. 353-359.

[72] (a) Geniés, E. M.; Tsintavis, C. J. Electroanal. Chem. 1985, 123, 109-
128. (b) Geniés, E. M.; Syed, A. A.; Tsintavis, C. Mol. Cryst. Liq. Cryst.
1985, 121, 181-186. (c) Geniés, E. M.; Lapkowski, M. Synth. Met. 1988,
23, 61-68. ((1) Travers, J. P.; Chroboczek, J.; Devreux, F.; Genoud, F.;
Nechtschein, M.; Syed, A.; Genies, E. M.; Tsintavis, C. Mol. Cryst. Liq.
Cryst. 1985, 121, 195-199.

[73] (a) MacDiarmid, A. G.; Chiang, J.-C.; Halpem, M.; Huang, W.-S.;
Mu, S.-L.; Somasiri, N. L. D.; Wu, W.; Yaniger, S. 1. Mol. Cryst. Liq.
Cryst. 1985, 121, 173-180. (b) MacDiarmid, A. G.; Mu, S.-L.; Somasiri,
N. L. D.; Wu, W. Mol. Cryst. Liq. Cryst. 1985, 121, 187-190. (c)
Salaneck, W. R.; Liedberg, B.; Inganas, O.; Erlandsson, R.; Lundstrom, I.;
MacDiarmid, A. G.; Halpem, M.; Somasiri, N. L. D. Mol. Cryst. Liq.
Cryst. 1985, 121, 191-194.

42

[74] MacDiarmid, A. G.; Somasiri, N. L. D.; Salaneck, W. R.;
Lundstroem, 1.; Liedberg, B.; Hassan, M. A.; Erlandsson, R.; Konrasson,
P.; Springer Series in Solid State Science Vol. 63, Springer, Berlin, 1985,
p.218.

[75] Millard, M. Synthesis of Organic Polymer Films in Plasmas,
Hollahan, J. R.; and Bell, A. T. (Eds.); Techniques and Applications of
Plasma Chemistry, Wiley, New York, 1974, Chapter 5.

[76] Shen, M. Plasma Chemistry of Polymers, Marcel Dekker, New York,
1976.

[77] Uvdal, K.; Logdlund, M.; Dannetun, P.; Bertilsson, L.; Stafstrom, S.;
Salaneck, W. R.; MacDiarmid, A. G.; Ray, A.; Scherr, E. M.; Hjertberg,
T.; Epstein, A. J. Synth. Met. 1989, 22, E451-E456.

[78] (a) Fenton, B. E.; Parker, J. M.; Wright, P. V. Polymer, 1973, 14;,
589. (b) Wright, P. V.; Brit. Polym. J. 1975, 1, 319-327.

[79] (a) Armand, M. B.; Chabagno, J. M.; Duclot, M. J. Second
International Conference on Solid Electrolytes, 1978, St. Andrews, paper
6.5.

[80] Shriver, D. F.; Farrington, G. C. Chem. Eng. News 1985, 63(22), 42-
57.

43

[81] (a) Chiang, C. K.; Davis, G. T.; Harding, C. A.; Takahashi, T.
Macromolecules 1985, 1_8_, 825-827. (b) Harris, C. S.; Shriver, D. F.;
Ratner, M. A. Macromolecules 1986, Q, 987-989. (c) Harris, C. S.;
Ratner, M. A.; Shriver, D. F. Macromolecules 1987, 22, 1778-1781.

[82] (a) Watanabe, M.; Ogata, N. In Polymer Electrolytes Reviews;
Elsevier: London, 1987. (b) Armand, M. B. Solid State Ionics 1983, 2110,
745.

[83] Abraham, K. M. In Applications of Electroactive Polymers, Scrosati,
B. (Ed.), Chapman and Hall, 1993.

[84] Liu, Y.- J.; DeGroot, D. C.; Schindler, J. L.; Kannewurf, C. R.;
Kanatzidis, M. G. Adv. Mater. 1993, 5(5), 369-372.

[85] Polak, A. J. In Conductive Polymers and Plastics, Margolis, J. M.
(Ed.), Chapman and Hall, 1989.

[86] Blonsky, P. M.; Clancy, S.; Hardy, L. C.; Harris, C. S.; Spindler, R.;
Shriver, D. F. Poly. Mater. Sci. Eng. 1985, 33, 736.

[87] Ott, E.; Spurlin, H. M.; Griffin, M. W. (Eds.) , Cellulose and

Cellulose Derivatives, 2nd Edition, Wiley-Interscience, New York, 1954.

[88] Hounshell, D. A.; Smith, Jr., J. K. Invention and Technology. Fall
1988, 40-55.

44

[89] Stevens, M. P. Polymer Chemistry, An Introduction. 2nd Edition,
Oxford University Press, 1989.

[90] Nazar, L. F.; Jacobson, A. J. J. Chem. Soc., Chem. Commun. 1986,
570-571.

[91] Pinnavaia, T. 1. Science 1983, 222, 365-371.

lntt
lntt

45

Chapter 2

Intercalative Nanocomposite between Polyaniline and M003.

Intercalation and Subsequent Oxidation of Aniline into M003.

46

Abstract

Two aniline-M003 intercalation compounds referred to as I and II were

synthesized hydrothermally in Pyrex-sealed ampoules at 185 0C. Both
compounds contain the same maximum loading of aniline/anilinium, i.e
(Ani)o,4MoO3, but they are structurally distinct as evidenced from their X-
ray powder diffraction and other spectroscopic properties. In compound I
the intercalants are thought to be arranged as monolayers with their
aromatic rings perpendicular to the M003 slabs (d-spacing = 13.3 A)
whereas in 11 they are predominantly oriented in a bilayer fashion (d-
spacing = 20.1 A). Compound I is pale-blue in color whereas compound II
is dark-blue. Compound I was found to be resistant towards oxidation with
a variety of oxidizing agents, while oxidation of II with (NH4)28203 was
facile yielding (PANI)xMoO3 (III). The d-spacing of III is 13.7 A and is

consistent with a monolayer of the polymer chains in the inorganic host.
The room temperature conductivity of (PANI)xMoO3 is 0.003 S/cm which

is three orders of magnitude higher than that of its precursor phase (CRT =
2 x 10'6 S/cm). The molecular weight (MW) of the intercalated polyaniline
was found to be dependent on the number of equivalents of (NH4)28203
used. Large quantities of the oxidant favor shorter polyaniline chains
whereas small amounts of oxidant yielded higher MW of the polymer.
Solid state UV-visible/Near-IR spectroscopy showed that the polyaniline
chains are stretch-aligned in the layered structure and this is the first report
showing the conformation of a conjugated polymer in a constrained

environment.

vie
cor
her
5111
the

Sin

Spa!
Wor

the

Poly
Capa

113m

47

2.1. Introduction

M003 is an interesting compound with a unique layered structure
consisting of 7.0 A thick double layers of edge- and comer-sharing
octahedra [1]. It is an important component of many industrial catalysts [2].
The intercalation chemistry of MoO3 has been explored to an appreciable
extent in recent years [3], owing to its high crystallinity, its potential
applications in lithium high-energy-density batteries [4] and electrochromic
devices [5]. However, of particular interest lately has been the intercalation
of conductive polymers in this layered system [6, 7]. Conductive polymers
[8] such as polyaniline, polythiophenes, polypyrrole, poly(p-phenylene
vinylene) continue to attract a considerable amount of interest and
excitement in the scientific community, both from a fundamental point of
view as well as for the wide range of anticipated applications [9]. However,
conductive polymers are amorphous in nature and as such real structure
determination of these materials is terribly hindered. The lack of structural
studies on electronically conductive polymers inhibits the development of a
theoretical understanding of charge transport processes in these materials.
Single crystals of conductive polymers are not available and intercalation
of these materials into the gallery regions of layered solids or the channel
spaces of microporous materials is a major driving force in this line of
work, since it may provide an excellent means of at least partially orienting

the polymer chains.

The pioneering work regarding the intercalation of conductive
polymers made use of highly oxidizing, semiconducting hosts which are
capable of accepting and dispersing the negative charges (electrons)

transferred from the monomers (reducing agents). Such reactions are

48

referred as redox intercalative polymerization (RIP), i.e the monomers

oxidatively insert inside the hosts and polymerize. To date, only three hosts
capable of performing RIP are known, namely FeOCl, V205-nH20 and

VOPO4-2H20. For instance, intercalation of pyrrole, aniline and

bithiophene have been successfully achieved in FeOCl [10] and VZOS-nHZO
[11], and 3-methyl pyrrole into VOPO4.2H20 [12].

However, with M003 or most other layered systems RIP is not

applicable because inadequate oxidizing ability hampers the intercalation
process. Even if its oxidizing power is high, an insulating host would not
be able to distribute the charges through its structure rendering redox

intercalation polymerization (RIP) very difficult if not impossible.

Indeed, intercalation of conductive polymers into M003 proved to be

a challenging task, in view of the fact that the layered material is poorly
oxidizing and is an insulator. Therefore, alternative routes or intercalation

techniques had to be employed [6, 7].

Our attempt to insert polyaniline (PANI) into M003 in a one step
fashion via RIP failed. However, we were able to insert aniline inside
M003 under varied reaction conditions yielding two distinct (Ani)xMoO3
phases, I and II. Compound II yields (PANI)xMoO3 upon treatment with

(NH4)2S203. This particular technique of inserting monomers in

constrained environments followed by oxidation of the resulting templates
has been applied in other cases as well. Examples include the acidic form of
zeolite Y which was first loaded with aniline, then oxidized with

(NH4)28208 [13], the electropolymerization of aniline absorbed into a

montmorillonite clay electrode [14], the intercalation compounds of aniline

49

into hydrogen uranyl phosphate and V205.nH20 polymerized by molecular
oxygen [15, 16].

This work describes, in detail, the insertion of polyaniline into
M003. The materials reported were characterized by a variety of
experimental techniques such as X-ray diffraction, electron microscopy,
optical and infra-red spectroscopy, thermal gravimetric analysis, electron
paramagnetic resonance, gel permeation chromatography and charge
transport measurements. Related to this work is a previous report by
Nazar et a1. regarding the insertion of conductive poly(p-phenylene
vinylene), (PPV), into M003 [6]. This was achieved in a series of steps.
Mixed alkali hydrated bronzes of MoO3 were first cation exchanged with

the PPV precursor, poly(p-xylylene-a-dimethylsulfonium chloride),
followed by heat treatment to yield (PPV)xMoO3.

A previous report by Schollhom et al. describes the insertion of
aniline in M003, by using an entirely different method. First, the proton
bronze of M003, Ho,5MoO3, was synthesized by the reduction of M003 in
aqueous acids [17]. H0,5MoO3, which can be regarded as a solid acid,
yielded the intercalated phase, (C6H5NH3+)xMoO3 (d-spacing = 19.6 A)
upon treatment with aniline [3f]. However, this intercalation compound was
poorly characterized. Our initial goal was to oxidatively insert aniline into
M003, by reacting the two reagents in a Pyrex-sealed ampoules at high
temperature. However, this process did not form any intercalated
polyaniline into M003, but rather two intercalation compounds of aniline

were obtained. These intercalation compounds of aniline were
characterized in details as well as (PANI)xMoO3 obtained.

50

2.2. Experimental Section

2.2.1. Reagents: M003 was purchased from Johnson Matthey Company

in the form of powder and was used without any further purification.
Aniline was purified by drying over CaH2 followed by distillation under

vacuum.

2.2.2. Synthesis 0f (C6H5NH3+)X(C6H5NH2)’,MOO3 (I)

A large Pyrex ampoule containing M003 (1.98 g, 13.75 mmol),
freshly distilled aniline (5.11 g, 54.95 mmol) and H20 (0.2 g, 11.11 mmol)

was sealed under vacuum from a Schlenk-line. The tube was introduced in
a furnace at 185 0C and the reaction was allowed to carry out for 3 days.
The reaction tube was opened and the product isolated in air. It was washed
profusely with chloroform by using suction from a water-aspirator. It was
then allowed to dry under suction before drying under dynamic vacuum.
The material obtained is pale-blue in color and analyzes for
(C6H5NH3+)X(C6H5NH2)yMoO3, where (x + y = 0.4) from elemental
analysis and TGA under oxygen flow. Found % C: 15.55; % H: 1.60; % N:
3.00; % M003 by difference: 79.85. Calculated % C: 15.86; % H: 1.76; %
N: 3.08; % M003 by difference: 79.30.

51

2.2.3. Synthesis of (C6H5NH3+)X(C6H5NH2)yMoO3 (II)

A large Pyrex tube containing M003 (1.98 g, 13.75 mmol), freshly
distilled aniline (5.11 g, 54.95 mmol) and H20 (0.005 g, 0.28 mmol) was

sealed under vacuum. The tube was then loaded in a furnace at 185 0C for
20 days. The dark-blue product obtained was isolated in the same manner
described in 2.2.2 and analyzes for (C6H5NH3+)X(C6H5NH2)yMoO3,
where (x + y = 0.4) from elemental analysis and TGA under oxygen flow.
Found % C: 15.59; % H: 1.67; % N: 2.93; % M003 by difference: 79.81.
Calculated % C: 15.86; % H: 1.76; % N: 3.08; % M003 by difference:

79.30.

2.2.4. Oxidation of II with (NH4)2S208:Synthesis of
(PANI)xMoO3, (III)

An amount of II (0.26 g, 1.43 mmol) was suspended in 5 ml of
distilled water which was precooled in ice. (NH4)ZSZOS (0.65 g, 2.9 mmol)

was dissolved in 10 m1 of distilled water which was also precooled in ice.
The cold (NH4)28208 solution was added dropwisely to the cold aqueous
suspension of II and the reaction mixture was allowed to warm to room
temperature. It was then stirred at room temperature for ca. 75 minutes.
The black precipitate formed was filtered off by using suction from a
water aspirator. It was washed copiously with distilled water followed by

washing with ethanol and ether. It was allowed to dry under suction

52

followed by drying under dynamic vacuum. The black product analyzes for
(PANI)0.7MoO3 from elemental analysis and TGA under oxygen flow.

Found % C: 24.50; % H: 1.92; % N: 4.82; % M003 by difference: 68.76.
Calculated % C: 24.27; % H: 1.69; % N: 4.72; % MoO3 by difference:
69.32.

2.2.5. Extraction Experiment on I

To 2.37 g of I was added 100 m1 of an aqueous solution of 1M
NH4OH and the reaction mixture was allowed to stir at room temperature
for 15 hours. A very small amount of a black product was collected which
was washed thoroughly with distilled water. The extracted product was
allowed to dry under suction followed by drying under vacuum.
Percentage of black product extracted was ca. 0.03%, based on the total
weight of 1.

2.2.6. Extraction Experiment on II

To 2.12 g of II in a 125 ml Erlenmeyer flask was added 110 ml of a

1M aqueous solution of NH4OH. The reaction mixture was allowed to stir
at room temperature for 40 hours. A black precipitate was collected by
filtration. It was washed thoroughly with distilled water and then dried

Under suction before drying under vacuum. Percentage by weight of black

53

product recovered was ca. 7%, based on the total weight of the intercalated

compound.

2.2.7. Extraction Experiment on (PANI)xMoO3

To 0.085 g of (PANI)xMoO3 was added 5 ml of a 2% aqueous

solution of NaOH. The reaction mixture was allowed to stir at room
temperature for 1 hour. The black precipitate was obtained by filtration
and washed with 1M HCl. The product was then allowed to equilibrate in
1M HCl for 4 hours and collected. It was then dried under suction followed

by drying in a vacuum oven at room temperature.

2.2.8. Chemical Synthesis of Bulk PANI'HCI (Emeraldine Salt)

(NH4)28208 (5.8 g, 25.4 mmol) was dissolved in 100 ml of 1M HCl

which has been precooled at ice-temperature. Aniline (10 ml, 109 mmol)
was dissolved in 150 ml of 1M HCl which has also been precooled at ice-
temperature. The (NH4)2S208 solution was added dropwise, over a period
of 5 minutes to the aniline solution, with constant stirring. The resulting
mixture was allowed to stir in an ice-bath for 2.5 hours during which time
the temperature remained below 5 0C. The black precipitate formed was
collected by filtration and was washed repeatedly with 1M HCl. A
minimum of 300 ml of 1M HCl was used. The product was allowed to dry

54

under suction before drying under dynamic vacuum at 80 oC. FTIR of the
product confirmed it to be the emeraldine salt. (PANI-HS04 was prepared

in the same manner but instead of 1M HCl, 1M H2804 was used).

2.2.9. Physicochemical Methods.

X-ray Powder Diffraction Measurements. (XRD) Patterns were
recorded on a Rigaku X-ray diffractomcter using Cu-Ka radiation
(1:1.5418 A). Samples were run as pressed pellets using a scan rate of
0.05 deg/min.

Infra-red Spectroscopy. Spectra were recorded in the Mid-IR range
(4000-310 cm'l) on a Nicolet 740 FTIR Spectrometer. Samples were run
as pressed KBr pellets.

Thermogravimetric Measurements. Samples were run on a Shimazdu
TG 50 instrument using oxygen flow and a heating rate of 1°C/min.

Samples were dried under vacuum for 2 days prior to run.

Conductivity and Thermopower Measurements. Direct-current
electrical conductivity and thermopower measurements were made on

pelletized samples. Conductivity measurements were performed in the

55

usual four-probe geometry with 60 mm and 25 mm gold wires used for the
current and voltage electrodes, respectively. Measurement of the pellet
cross-sectional area and voltage probe separation were made with a
calibrated binocular microscope. Conductivity data were obtained with the
computer-automated system as described elsewhere [18]. Thermoelectric
power measurements were made by using a slow ac technique [19] which
requires the production of a slowly varying periodic temperature gradient
across the samples and the measurement of the resulting sample voltage.
Samples were suspended between quartz block heaters by 60 mm gold
wires thermally grounded to the block with GE 7031 varnish. The gold
wires were used to support and conduct heat to the sample as well as to
measure the voltage across the sample resulting from the applied
temperature gradient. The magnitude of the applied temperature gradient
was generally 1.0 K. Smaller temperature gradients gave essentially the
same results but with somewhat lower sensitivity. In both measurements,
the gold contacts were held in place on the sample with conductive gold
paste. Mounted samples were placed under vacuum (10'3 Torr) and heated
to 320 K for 2-4 hr to cure the gold contacts. For a variable-temperature
run, data (conductivity or thermopower) were acquired during sample
warming. The average temperature drift rate during an experiment was
kept below 0.3 K/min. Multiple variable-temperature runs were carried out
for each sample to ensure reproducibility and stability. At a given

temperature reproducibility was within 5%.

Scanning Electron Microscopy (SEM) and Energy Dispersive
Spectroscopy (EDS). SEM micrographs were taken on a JOEL-JSM-

351

Ira

exp

KV

tim

alu:

ace

Ele

lie.

will

All

(18)

For

day

i=2
con

one
KC}

11101

ltpr

pacl

11118

ind

56

35C scanning electron microscope. Energy Dispersive Spectroscopy was
run on a JOEL-JSM-35C scanning electron microscope equipped with a
Tracor Northern TN 55000 X-ray microanalysis attachment. Typical
experimental conditions for EDS are as follows: Accelerating Voltage, 20
KV; Detector window, Berryllium; Take-off angle, 27 deg.; Accumulation
time, 60 seconds. For both SEM and EDS, samples were glued on
aluminum stubs with conductive carbon paint in order to dissipate

accumulated charges.

Electron Paramagnetic Resonance Spectroscopy.

Measurements were carried out on a Bruker ER 200 D machine, equipped
with a TE cavity. A 100 kHz field modulation was used in all experiments.
All spectra were recorded at room temperature at a power of 2.08 mW (20
dB) by using a scan range of 400 gauss and a field modulation of 20 gauss.
For spin quantitation the same conditions were used except the field
modulation was reduced to 12.5 gauss and all samples were run the same
day. 2, 2-phenyl-1-picrylhydrazyl (DPPH, Aldrich 99% reagent grade,
g=2.0036) was used as the standard for the determination of absolute spin
concentration on the assumption that it exhibited a signal resulting from
one spin per molecule. The DPPH was intimately mixed with recrystallized
KCl to achieve a concentration of 1% by weight. This concentration
represents the spin concentration present in our samples. Samples were
packed in quartz tubes to a length of approximately 0.4 cm. The sample
mass was measured to an accuracy of 0.0005 mg. The sample was centered

in the TB cavity. Small sample size and careful positioning ensured that the

insu
mea

first

8011
refit
UV-
insti
PC.
p101
finer

1611c

ism

57

instrument response was a function of the entire sample for each sample
measured. Spin quantitation was performed by double integration of the

first-derivative EPR spectrum.

Gel-Permeation Chromatography.

Molecular weight measurements were performed using a Shimazdu LC-
10A HPLC system coupled to a GPC column PLgel 5 11 mix which was
held at 75 0C. The eluent NMP contained 0.5 wt % LiCl to avoid
agglomeration of PANI [20]. The elution rate was 0.2 ml/min. Calibration
was performed on a series on polystyrene samples of known molecular

weights.

Solid-State UV/Vis Near-IR Spectroscopy. Optical diffuse
reflectance measurements were made at room temperature with a Shimazdu
UV-3101PC double-beam, double-monochromator spectrophotometer. The
instrument was equipped with an integrating sphere and controlled by a
PC. The digitized spectra were processed using the Kaleidagraph software
program. BaSO4 powder or CdS powder was used as reference at all
energies (100% reflectance). Absorption data were calculated from the

reflectance data using the Kubelka-Munk function:
a/S = (1-R)2/2R ---------- Equation 1

R is the reflectance at a given wavelength, or is the absorption coefficient, S

is the scattering coefficient. The scattering coefficient has been shown to

58

be practically wavelength independent for particle larger than 5 mm [21],

which is smaller than the particle size of the samples used in this thesis.

Elemental analyses. Analyses were done at Oneida Laboratories in
Oneida, New York.

2.3. Results and Discussion

2.3.1. Synthesis and Comparison of Two Aniline Intercalation

Compounds of M003

The reaction of M003 with aniline and H20 in a 1.2 : 5 : 1 ratio in a

vacuum-sealed Pyrex ampoule at 185 0C for 3 days afforded l, a pale blue
material. Washing the product with an organic solvent such as chloroform
was essential to remove excess aniline used and low molecular weight,
soluble forms of polyaniline which do not intercalate inside the layered
host. The filtrate was purplish which is the characteristic color of
oligomeric, soluble forms of polyaniline [22] and this is indicative of the

redox nature of the reaction.

XRD shows that the interlayer spacing of I is 13.3 A (Figure 2.1a).
The interlayer spacing of pristine M003 is 7.0 A. Therefore, the M003

layers have expanded by 6.3 A in order to accomodate the monomers
which must lie with their phenyl rings perpendicular to the M003 sheets as

shown in Scheme 2.1. Similar structural models have been proposed for

other intercalates consisting of aromatic rings. e.g,

59

;

i (a) i
I

g , l

 

 

 

5. 10. 15. 20. 25. 30. 35. 40. 45. 50. 55. 50.
IGK‘I.)

(b)

 

 

 

5. :0. 15. 20. 25. 30. 35. 40. 45. so. 55. 60.
ledll)

i (C)

 

 

 

Figure 2.1. XRD of (a) I, (b) 11 and (c) (PANI)XM003.

6O

(pyridine)x(pyridinium)yTaS2 (x + y = 0.5) [23], (PANI)O.44V205 [11a]
and (polypyrrole)o.23Fe0Cl [10a,b,c].

Infra-red spectroscopy (Figure 2.2) of I reveals vibrations from
aniline and anilinium. In particular, two fairly high intensity peaks are
observed at 2606 cm‘1 and 2566 cm'l. These are assigned to hydrogen
bonds between nitrogen atoms of aniline and hydrogen atoms of anilinium
(Scheme 2.1), suggesting the presence of an aniline/anilinium pair. Similar
types of stretches for systems involving hydrogen bonding, e.g, pyridine
and pyridinium intercalated in TaSz, the trimethylammonium-
trimethylamine complex cation and many others are well-documented in
the literature [23, 24].

 

 

 

 

 

Scheme 2.1. Proposed arrangement of an aniline/anilinium pair in I.

Elemental analysis cannot distinguish between aniline and anilinium.
However, the ratio of aniline to anilinium can be accurately determined

from TGA under oxygen flow (Figure 2.3). The first step, A, in the

6 l

'05
3:-

 

2 TERMS"! TTflNCE
3‘!

23

 

 

12

 

 

 

 

1. 3500 sfeo 2770 2500 1550 t§§0 1130 Tea éro
unvmn

Figure 2.2. FI‘IR of I.

thermog
loss of 2

Fl'IRst

(C6H51
(2011111101

correst
1NH4+)r

T
the tran.
excess (
negative
the 11081
in Sche;
that 011
has bee:
down n
has bee
and am
Apparel
spews i
has be:
Comple
been an
of anili

crrrficull

62

thennogram corresponds to the loss of aniline followed by step B which is
loss of anilinium to yield the stable M003 phase as verified from XRD and

FTIR spectroscopy. Therefore, a more accurate representation of I is

(C6H5NH3+)0.26(C6H5NH2)0_13MOO3. This type 0f TGA analysis 18
commonly used to accurately determine the amount of protonated and

corresponding unprotonated species in layered hosts, e.g
(NH4+)X(NH3)yTiS2 [25].

The reaction of aniline with M003 in the presence of water involves
the transfer of electrons. It is believed that M003 oxidizes part of the large
excess of aniline to soluble polyaniline oligomers. In order to balance the
negative charge on the M003 layers, a certain amount of aniline inserts in
the host as anilinium (aniline molecules pick up protons released as shown
in Scheme 2.2). The water acts as a source of OH‘ ions. Here, it appears
that OH' behaves as a reducing agent, assisting in the reduction of M003. It
has been found that decreasing the amount of water in this reaction slows
down the intercalation process (vide-infra). Indeed, the presence of water
has been known to speed up the insertion of Lewis bases such as pyridine
and aniline in other layered systems such as TaSz [23] and MnPS3 [26].
Apparently, the same effect is observed in our system. Addition of water
speeds up the insertion of aniline into M003, where complete intercalation
has been observed in a relatively short period of time, i.e. 3 days.
Complete intercalation has even been observed in one day, but 3 days has
been the usual reaction time employed. We also found that the intercalation

of aniline into M003 under strictly anhydrous conditions is extremely

difficult. The presence of water favors the intercalation of aniline and

‘70 Wt

11

11

(O

63

 

 

 

 

 

 

105 1411111rrlrrrrlrlrrlrrrllerr1rlrr
100'“ '— -
A
95" _
is 90— -

B
85" t“
80- M93 1 -
75 rrtrfrtttfrrttlltrrlrrtrlrtrr'rrt
0 100 200 300 400 500 600 700
Temperature(°C)

Figure 2.3. TGA of I under oxygen flow.

64

AGO—2 25 535:5 95 05:5 Lo :oEumE wEBozm $353 .8382 3885 .N.~ Seesaw

:
a; YQ: :1. YO.
:\+ I
swivel. 11 .= .
=
e 4
-nnOo—Z +.:~ + +21? [nOOE +

I
/ O

+ IIIZ x ”m new
Ah.

I

N no.
=VZIO N m
_. O

n no.
I _ m

65

in this way, the reaction has been found to be highly reproducible.

This is reminiscent of the intercalation of pyridine into M003

reported by Johnson et al. [3a,b], where the synthesis performed with the
total exclusion of moisture was found to be very tedious. Prolonged heating

for ca. 1 month at 160-180 0C in sealed tubes with intermediate regrinding
was found necessary to ensure complete reaction of M003. However, we

found out that complete intercalation of pyridine into M003 can occur in

less than a week in the presence of water [27].

It is also very feasible that hydroxide ions could be acting as a
mineralizer, helping the microcrystals of the product to grow bigger
through a dissolution/reprecipitation equilibrium [28]. The highly
crystalline nature of the material as observed from its X-ray powder
diffraction pattern (Figure 2.1a) and scanning electron micrographs
(Figure 2.4) is very likely to be an attribute of the mineralizer effect of the

hydroxide ion.

Compound II, (the precursor of (PANI)XM003), was prepared by

the reaction of M003, aniline and H20 in 49: 196 : 1 molar ratio in a

vacuum-sealed Pyrex ampoule at 185 0C for 20 days. It should be noted
that the amount of water used for the formation of II is ca. 40 times less
than that used for synthesizing 1. Consequently, a longer reaction time is
needed for complete intercalation to take place. The dark-blue color of 11
implies that the layers in this compound are reduced to a considerable
extent. It should be noted that the loading OH and II are identical.

However, the ratio of anilinium to aniline must be higher in II because of

66

15KU X4BGQ 9908-“

 

. . I .\

. . .
A! :1

f

 

1.60 c5094

80 9965

Figure 2.4. SEM micrographs of I.

67

its higher degree of reduction. An accurate ratio of anilinium to aniline in
II could not be determined from TGA under oxygen flow since the amount
of aniline present is very small. The therrnogram of II (Figure 2.5)
distinguishes itself from that of I in that it reveals no discernable step
corresponding to the evolution of aniline. Thus compound II consists

mostly of anilinium and can essentially be formulated as
(C6H5NH3+)0.4M°O3-

XRD of 11 (Figure 2.1b) shows that the anilinium molecules are
arranged primarily in a bilayer fashion (d-spacing = 20.1 A). A minor
phase is observed where the intercalants are oriented as monolayers (d-
spacing = 13.5 A). The bilayer configuration is consistent with the higher
degree of reduction of the layers in 11 (Scheme 2.3). The d-spacing of
compound II is comparable to Schollhom's intercalation compound of

aniline into M003, which was reported to have a d-spacing of 19.6 A.

 

 

M003
W“: + NH3

 

 

20.1 A

+ MNH; +NH3

 

 

 

Scheme 2.3. Proposed arrangement of anilinium in II.

68

 

 

 

 

 

103 r 1 r 1 r r r l r r r 1 r 1 1

97.25“ h

:0 91.5“ '"

85.75“ "
Mifl
80 r r I 1 r r T 1 r I T l I r I

0 131.2 262.5 393.8 525

Temperature(°C)

Figure 2.5. TGA of II under oxygen flow.

69

FTIR spectroscopy (Figure 2.6a) confirms the presence of aniline
and anilinium vibrations. Similar to the 1, compound II also shows
evidence of a small amount of hydrogen bonding between the aniline and
anilinium molecules as observed by the occurence of two low intensity
peaks at 2606 cm'1 and 2566 cm-1.

The Electron paramagnetic resonance (EPR) spectrum of II
(recorded at 273 K) shows two signals (Figure 2.7a). The broad low
intensity peak at g = 1.9449 is assigned to M05+ centers consistent with
those reported in the literature [29]. This signal is expected since the M003
slabs are reduced to a certain extent. The high intensity peak observed at g
= 2.0141 is typical of an organic radical type of compound, perhaps
protonated emeraldine. At first glance, the presence of this peak is baffling
since FTIR spectroscopy does not show the formation of polyaniline.
However, in order to account for this signal, an extraction experiment was
performed on II by treatment with a fairly strong basic solution. This

results in digestion of the M003 framework as well as dissolution of the

aniline and anilinium present. EPR of the recovered black material, at 273
K, shows only one very strong signal with a gvalue of 2.0466 (Figure 2.7b)
and this explains the origin of the intense peak in the EPR spectrum of II.
The X-ray diffraction pattern of the extracted product reveals its
amorphous nature and FTIR spectroscopy (Figure 2.8b) confirms its

organic character.

GPC measurements on the extracted product from II (Figure 2.10a)
showed 3 molecular weight bands. A major band (80 %) with Mn = 1712
and M.,, = 2518 followed by an ill-defined band (ca. 15 %) with calculated

E)

 

(a)

 

 

 

°/. Transmittance

(b)

(C)

(d)

 

 

4000 3590 3100 2770 2360 1950 1530 1130 750 $0
wavenumber (cm‘)

Figure 2.6. FI‘IR of (a) II, (b) (PANI)XM003, (c) Extracted PANI from
(PANI)XM003 and (d) Chemically synthesized bulk PANI.

71

Figure 2.7. EPR of (a) II, (b) Extracted product from 11, (c)
(PANI)XM003, (d) Extracted PANI from (PANI)XM003 and (e)

Chemically synthesized bulk PANI.

72

L

f‘

 

L

(b)

 

 

1"

(C)

 

(d)

 

 

17'

(9)

F—

 

 

' 3500 GAUSS

7Z3

“.2 73.

X TWITIRNCE
57.2 82.7

51.7

 

 

 

 

18.2

 

3500 3100 zizo 2500 1§50 1550 1130 120 TF310
unvenunaen

.' .2

(b)

2 IMNSHITIMCE
85.7 70.2 75.7

59.2

 

 

 

§3.7

3500 3100 2170 2500
an 1600 1550 1130 fzo "Této

Figure 2.8. FTIR of (a) Extracted product from I and (b) Extracted
product from II.

74

 

 

 

 

 

 

   

     

 

 

 

L
j

j

j
............................. W.

. . _ 3

*

= = 1 ‘1 1 ° 1

3.5 1 1 l 1 1 IV

30 32 34 36 38 4O 42 44
Retention Time (min)

Figure 2.9. Calibration curve for determining MW of extracted products

from 11 and I.

75

 

 

 

 

(a)
(b)
e 1 4
30 60
Retention Time (min)
——>

Figure 2.10. GPC of (a) Extracted product from II and (b) Extracted

product from I.

76

Mn = 425 and Mw = 460. No reasonable information can be extracted fom
the minor band (ca. 5%) since it is beyond the limit of the calibration
curve. The extracted product must therefore be an oligomer of polyaniline,
a by-product of the intercalation reaction. The extracted product was found
to be an insulator (O'RT < 10’6 S/cm) and does not have a protonated form
since upon treatment with 1M H2804 no visible change in its FTIR
spectrum was observed. EPR spin quantitation experiments were
performed on the extracted product along with the acid-treated product and
the calculated spins/mol values of the two samples were compared. The two
values were practically identical, the order of magnitude being 2.7 x 1021
(Table 2.1). In comparison, PANI-HCI was found to have 4 x 1022
spins/mol whereas neutral PANI a lesser value of 1.7 x 1021 spins/mo]. The
EPR signal of the extracted product from II must therefore be due to
defects in the oligomeric chains similar to that reported for polyaniline
[30].

Oligomeric by-products have also been observed in the intercalation
of pyridine into TaSz [23, 31]. It seems that small amount of coupling co-
products are inevitable with the intercalation of certain Lewis bases into
transition metal oxides and dichalcogenides. The stoichiometry of II
written as (C6H5NH3+)0.4M003 is thus an insufficient description of the
intercalation compound. Increasing the amount of water in the intercalation
reaction drastically decreases the amount of coupling products. An
extraction experiment performed on I, gave a very small amount of a
black product (ca. 0.03% by mass) whose FTIR spectrum (Figure 2.8a)
shows organic vibrations that are quite similar to those of the extracted

product from 11. This extracted product also gave an EPR signal at room

77

.38 Em co 385% .3 use...

 

 

 

 

 

 

 

 

 

 

 

3 08% M: 5a Hz: 3. EN meozxczsc

€23: use =

2: 32m 8:: fix: x 03 sec .385 3225

mm 89$

2: 22m 822 6.2 2 RN 8:85 .58ng

«.23 3:;

n: 4.3% .33 3+2 x 26 =

3.2 3. n2.

20: 85082
$953 0:

353%

 

 

78

temperature ( gvalue = 2.0071). GPC data of the extracted product from I
(figure 2.10b) gave a major band (98 %) with M., = 1520 and Mw = 5353.

Indeed our observations can be correlated to those of Lomax [31]

who reported that the amounts of oxidative coupling products for the
intercalation of pyridine into TaSz fall with increasing amounts of water.

2.3.2. Intralayer Polymerization of Anilinium in M003

Oxidation of I with external oxidizing agents such as (NH4)28203,

FeCl3, ozone and atmospheric oxygen (at ambient and elevated

temperatures) proved to be very difficult and did not yield the intercalated
polymer. This is ascribed to the fact that the material is an insulator, a
consequence of the low degree of reduction of the M003 sheets. The
inability of the material to conduct makes the transfer of electrons from the
encapsulated aniline and anilinium to the oxidant molecules located at the

periphery of the layers, impossible.

On the other hand, oxidation of II was found to be facile with
(NH4)28203. This is due to the fact the layers in compound II are more
reduced and therefore more conductive. Hence, transfer of electrons from
the encapsulated anilinium to the oxidant molecules is tremendously
facilitated. Experimentally, it was found that two equivalents of the oxidant
optimizes the formation of intercalated polyaniline. It is worth noting here
that different authors have used different stochiometries for the
polymerization of bulk polyaniline itself. For instance, Hand and Nelson

use a quantity of the chemical oxidant which is in excess of the

79

corresponding stoichiometric quantity [32]. However, in the synthesis of
bulk polyaniline, MacDiarmid et al. have used a stoichiometric equivalent
of the oxidant [33] but also a substoichiometric ratio of monomer to
oxidant of 1: 0.25 [34]. It has been reported by Genies that a large excess
of oxidizing agents lead to polymer degradation and they suggest a quantity
of oxidant inferior to the stoichiometric equivalent [35]. Our experimental
results with the oxidation of II support the report by Genies. We found
that a large excess of peroxydisulfate (10 equivalents or even 4
equivalents) yielded low molecular weight intercalated polyaniline as
evidenced by FTIR spectroscopy (Figure 2.11a,b) and GPC measurements
(Figure 2.12 a,b) of the extracted polymers. The sharp and narrow features
of the FTIR peaks are characteristic of oligomeric polyanilines [36]. Table
2.2 summarizes the GPC data for the extracted polymers for the various
amounts of oxidant used. Clearly, the molecular weight MW of the polymer
increases with decreasing amount of oxidant from 10 equivalents to 4.
However, 2 equivalents of peroxydisulfate gave optimum results and the
resulting product, (PANI)xMoO3 was fully characterized. It was found that
the polymerization reaction is mostly independent of the concentration of
the oxidant solution and reaction time. Nevertheless, the polymerization
reaction was allowed to proceed for a short time (usually 75 minutes) in
order to avoid the possible exchange of intercalated anilinium for NH4+
from the peroxydisulfate. The water used in the oxidation reaction of II
was cooled in ice prior to use. The initial cold temperature of the reaction
favors the oxidation of aniline since the polymerization process is

considerably exothermic [37].

80

5011 s;
5

.302

 

 

(a)

2 TBflNfiHITTflNCE
38.0

20..
A

 

21.

 

 

 

15.5

3500 3T00 2770 2500 1650 13715" 1130 720 310
HAVMH

89.1
J

62.2

55.3
L

(b)

X TflflNSHITTflNCE
‘00.

”’05

35.6

7

 

 

37.

350 3&0 2770 2500 1500 15110 1130 750 '310
MM

Figure 2.11. FTIR spectrum of (a) (PANI)xMoO3 synthesized by using 10
equiv. of (NH4)23208 and (b) (PANI)xMoO3 synthesized by using 4 equiv.
Of (NH4)28208.

81

(a)

 

 

 

(b) k

L l l
l l ‘1

0 30 60

Retention Time (min)
——>

 

Figure 2.12. GPC of (a) PANI extracted from (PANI)xMoO3, synthesized
by using 10 equiv. of (NH4)23203 and (b) PANI extracted from
(PANI)xMoO3, synthesized by using 4 equiv. of (NH4)28208. (calibration

curve of Figure 2.9 was used for MW determination).

 

82

3.3.2 80 .3 55% N.N can...

 

 

3 428 z:
05.528 as 8.855. 38520

. 1|. 838$ H 6038 H coagh
8. N . m 3N N . m 8N N . 2 ~ongi
n u _ 8:8... 8N8 u _ 8:3... on: u _ 882.. .o .333 N 5.3 = _o .385 3:25

 

~._ .1. N 558$

4N .1. _ 8:8...

Ev u N 858$
mg: n _ 558$

03. u N 8:8...
NE... u_ 8:8...

MWonNeizv
.o .233 v 53 = .o .38... 8225

 

m._ u N 558$

Em n N 558$

84 u N 85....

 

 

 

85325

_.N u _ 558$ 2.3." _ 558$ cm_N n _ 558$ .3 .550 2 .23 :3 8:55— 58:55
no.— u N 558$ cow u N 558$ an u N 558$

m._ u _ 558$ wEN .1. _ 558$ N2.— " _ 558$ = .55 .885 53855
3.. u N 558$ 3 u N 558$ on u N 558$

Wm H _ 558$ mnmm u _ 558$ CNS u _ 558$ :55 .855. ngm

 

 

 

 

 

 

 

10.3.18.

 

 

83

Recently, Fu and Elsenbaumer performed a quantitative calorimetric
experiment on the polymerization of aniline and found that the enthalpy
change leading to the formation of the emeraldine form of polyaniline is
-105 kcal/mol of aniline when aniline is in excess [38]. Polymerization in
acidic medium should be avoided since it leads to dissolution of the
inorganic framework. Direct spectroscopic evidence for the formation of
polyaniline was obtained from FTIR spectroscopy which reveals the
signature of the protonated form of PANI (emeraldine salt) (Figure 2.6b).
The spectrum also shows that the M003 layers are still reduced because the
spectral pattern in the fingerprint region (925 - 310 cm-1) remains
unchanged. This suggests that the polyaniline (positively charged) is
trapped inside the gallery region of the negatively charged host; the
reduced layers are behaving as 'dopant' ions. It is worthwhile to note that
no acidic medium is necessary to yield the protonated form of the polymer.
The source of protons for the polymer is the anilinium. This is analogous
to the diffusion of aniline in the protonated form of zeolite Y which upon
oxidation with aqueous (NH4)28208 yields emeraldine salt in the zeolite
pores [13]. The fact that we obtained the protonated form of polyaniline
supports the reaction pathway proposed in Scheme 2.2. The encapsulated
polyaniline can be isolated from its matrix by treating (PANI)xMoO3 with
a 2% aqueous solution of sodium hydroxide followed by 1M HCl. The
FTIR spectrum of the extracted product is virtually identical to that of bulk
emeraldine salt (see Figure 2.6 c,d).

The stoichoimetry (PANI)0.7MoO3 is unusually high and is not the

expected value. Assuming complete polymerization of intercalated
molecules, we would expect the stoichoimetry to be (PANI)0.4M003.

84

Therefore, we must accept that a portion of the polymer either extends
outside of the M003 particles or exists as a separate phase. The
composition (PANI)0.7MoO3 was determined by elemental analyses of

carbon, hydrogen and nitrogen (the % of M003 was determined by

difference). The composition obtained from elemental analysis was further
verified by TGA under oxygen flow. The high polymer content is

explained by the fact that 8042' formed during the oxidation process is
capable of digesting the reduced M003 framework. This hypothesis is

confirmed by performing control experiments where aqueous (NH4)ZSO4
was stirred with (PANI)O.7MoO3 for several hours at room temperature.
TGA of the resulting product shows that (PANI)0.7MoO3 becomes
(PANI)].0M003 due to partial dissolution of the reduced M003 sheets.

The X-ray powder pattern of (PANI)O.7MoO3 (Figure 2.1c) reveals

a basal spacing of 13.7 A which represents an interlayer expansion of 6.7

A. This is consistent with a monolayer of the polyaniline chains arranged
roughly perpendicular to the M003 planes and this is similar to that

reported for (PPV)xMoO3 [6], (PANDXFeOCl [10d] and (PANDXVZOS

[11a] (Scheme 2.4). It is interesting to note that the anilinium ions are
positioned predominantly as bilayers in II and at the outset or during the

polymerization process they must rearrange in a monolayer fashion with
their phenyl rings perpendicular to the M003 sheets.

85

I M003 T

 

 

 

 

Scheme 2.4. Orientation of polyaniline chains inside M003 layers.

Additional evidence of PANI between the M003 layers derives from

scanning electron microscopy (SEM) (Figure 2.15) which shows that the
surface of the microcrystals are smooth and clean as in its precursor phase
(Figure 2.14) and pristine M003 (Figure 2.13). No amorphous material is
observed that could be attributed to external polyaniline. Bulk polyaniline
itself, as observed under SEM is shown to have a very featureless and
amorphous character (Figure 2.16). This technique provides supporting
evidence that the polyaniline is inside the layered host in (PANI)xMoO3 but

cannot rule out the fact that some fraction of PANI may be outside.

86

 

 

Figure 2.13. SEM micrographs of pristine M003.

87

 

 

Figure 2.14. SEM micrographs of H.

88

‘c‘x- .\ '
.
-.~ ‘_
- v.5 .. . .z
\t
.

,15Ku X9488 2219

 

ISKU X8688 8892 1.8U CEUSB

 

Figure 2.15. SEM micrographs of (PANI)XM003.

89

 

 

Figure 2.16. SEM micrographs of PANI.HC1.

90

Gel permeation chromatography was performed on the PANI
extracted from (PANI)xMoO3 and the data are compared with those of
chemically synthesized bulk polyaniline. The base form of the isolated
polymer dissolves in N-methylpyrrolidinone (NMP). The GPC data of the
polymer solution (Figure 2.18) show two molecular weight fractions,
namely, a major (94 %) fraction with Mn = 4850 and Mw = 24200 and a
minor fraction with Mn = 280 and Mw = 290. The latter corresponds to
aniline trimer which did not undergo any further polymerization due to the
constrained environment in which the reaction had to take place. The
molecular weight of the major fraction is only 1/3 that of chemically
synthesized bulk polyaniline (Mn = 7714, Mw = 68854). This is also a
consequence of the restrictive nature of the polymerization process. The
relatively low molecular weight of the polyaniline from (PANI)xMoO3
provides further evidence that the polymer was formed inside the inorganic

framework.

It is quite conceivable that some PANI may be formed on the surface
of M003 as a result of deintercalation of the monomer from II during the
oxidation process. However this possibility was ruled out through a series
of experiments probed by Energy Dispersive Spectroscopy (EDS). If some
polymer were outside it is reasonable to assume that either 8042' or HSO4'
would be acting as dopant (counter) anions. Elemental analysis showed

sulfur only at the impurity level. However, treatment of an aqueous
suspension of (PANI)xMoO3 with a 2M aqueous solution of NaCl did not

show Cl' incorporation through SO42‘/Cl‘ exchange. The EDS spectrum of

the resulting product did not show the Ka peak for chlorine which proves

that Cl' is not present in the material.

91

 

 

 

7.0 a

6.0 -
3
2' 5.0 -
‘63 .
3

4.0 -

3.0 . . . , .

20 30 40 so

time (min)

Figure 2.17. Calibration curve used in determining MW of extracted PANI
from (PANI)xMoO3, synthesized by using 2 equiv. of (NH4)2S208.

92

 

l l
30 60

Retention Time (min)
——>

o-r-

Figure 2.18. GPC of extracted PANI from (PANI)xMoO3, synthesized by
using 2 equiv. of (NH4)28208.

93

In contrast, when bulk PANI-H804 samples are treated with aqueous
solutions of 2M NaCl or HCl, complete SO42'/Cl' exchange does occur. The
EDS spectrum showed complete disappearance of the Ka peak for sulfur

and the emergence of the new Ka peak for chlorine.

2.3.3. Charge Transport Properties

Compound I is an insulator. The room temperature conductivity of
II is 2 x 10-6 S/cm (Figure 2.1%). However, (PANI)xMoO3 shows a
dramatic increase in electrical conductivity by three orders of magnitude
with a room temperature value of ca. 0.003 S/cm (Figure 2.1%). This
value is lower than the average value reported for bulk PANI [39] and this
is in good agreement with the intercalated model for PANI inside a

semiconducting layered host. Similar trends have been observed for
(PPV)xMoO3 [6], (PANI)xFeOCl [10d] and (PANDXVZOS [11a]. Variable

temperature measurements for polycrystalline pellets of (PANI)xMoO3 are
shown in Figure 2193 and are characteristic of thermally activated
transport. Variable temperature thermoelectric power (TP) measurements
(figure 2.20) show a more interesting and informative behavior. At 345 K,
the Seebeck coefficient , S, is relatively small , about + 8.6 uV/K and
decreases linearly with falling temperature to ca. +4.6 uV/K at 235 K, the
lowest temperature measured. The positive values of the thermopower and
the positive slope of the curve implies that the composite material is
intrinsically a p-type metallic conductor, suggesting that the observed

thermally activated conductivity is due to the grain boundaries between
(PANI)xMoO3 crystallites.

94

 

 

 

 

-2
-4 — (a)
E p r
2 ‘6 ’_ (J00 O
9?. . o
O
b t o
a: A (b)
O ‘8 i— AA
_1 AA
>— AA
_ AA
AA
-10 p as,
_ Q a
A
- A
-12 1 l 1 1 1 l 1 1
2 4 6 8 1O 12

1000/T emperature (1/K)

Figure 2.19. Variable temperature conductivity data on pressed pellets of
(a) (PANI)xMoO3 (b) 11.

95

 

10
‘ O
’_ O

A __ O
x 8 ‘5
S , Ooooooo% o
1 * O 0W9
v 63mm
2 6.. .1353 o
m 0.;? o
3 F O (D
o t. 00 00
Q t 0000
O 4._
E b-
b
q) .
.C t
l— 2__

O l 1 141111 111 l l l l l l l l l l l l l l l 111

 

 

 

200 225 250 275 300 325 350
Temperature (K)

Figure 2.20. Variable temperature thermoelectric power data on pressed
pellet of (PANI)xMoO3.

96

The thermopower experiment suggests that the predominant charge
carriers are holes, implying that the intercalated polymer is playing a more
active role than the (M003)x' layers. The protonated form of PANI has

been shown to be a p-type metallic conductor from thermopower studies
[40]. If the charge transport were predominantly through the (M003)"'

layers an n-type conductivity would be expected.

2.3.4. Spin Quantitation using EPR

Room temperature EPR spin quantitation experiments were
performed on all the intercalation compounds synthesized and the spins/mol
values are tabulated in Table 2.1 along with other information gathered
from the EPR spectra. I was found to have 7.55 x 10+20 spins/mol,
whereas II 6.37 x 10+21 spins/mol. This confirms that II is about eight
times more reduced than I and explains the ease with which 11 can be
oxidized and the difficulty associated with the oxidation of I. The higher
number of spins calculated for (PANI)xMoO3 at room temperature (2.14 x

10*22 spins/mol) is due to the contribution of the protonated form of PAN I
inside the layers of M003. The EPR of (PANI)xMoO3 (Figure 2.7c) shows
that it has roughly the same peak width as that of chemically synthesized
bulk polyaniline (Figure 2.7c), indicating that there is no significant
interaction of the intercalated polymer with Mo5+ centers. However, the
low intensity broad peak observed in II is no longer visible. This is due to
the fact that this peak is completely masked by the large spin concentration

arising from the protonated form of PANI.

97

2.3.5. Solid State UV/Vis/Near-IR Spectroscopy

Heeger et al. reported that polyaniline doped with camphor sulfonic
acid (PANI-CMSA) is soluble in common solvents such as chloroform, m-
cresol, pyrrolidine and tripropylamine [41]. The as-made PANI-CMSA has
a room temperature conductivity similar to PANI-HCI of ca. 2-5 S/cm [42].
However, recently MacDiarmid et al. showed that PANI-CMSA processed
into free-standing film from its solution in m-cresol exhibits a very high
conductivity of ca. 200 S/cm [42]. This increase in conductivity is
attributed solely to the conformational change of the polymer chains from
‘coil-like’ in the bulk form to ‘rod-like’ when processed from m-cresol.

The ‘rod—like’ conformation favors conductivity in the intramolecular
chains Wintramolecular) as well as conductivity in between the chains

(“intermolecular)- The increase in conductivity in the two directions

clearly arises from the more favorable overlap of the p-orbitals along the
chains and in between the chains. The properties of this processed polymer
are completely different from its original form. First, it is quite crystalline
as shown from its X-ray diffraction pattern (the bulk polymer itself is
amorphous). Second, because of the metallic character of the m-cresol-
processed-polymer, its solid-state UV-Vis/Near-IR spectrum exhibits a
dramatic change from the bulk polymer which shows the usual localized
polaron absorptions at 439 nm and 780 nm. Therefore, films cast from m-
cresol solution show an absorption at 439 nm and a very intense free-
carrier tail commencing at 1000 nm and increasing steadily in intensity to
2600 nm. The free-carrier tail is consistent with delocalized electrons in
the polaron band. The conductivity of the cast film dropped to the value of

ca. 80 S/cm, (still a very high value) upon removal of all the m-cresol and

98

the free-carrier tail is still observable from solid-state UV-visible/Near-IR
spectroscopy. Thus, we decided to use this type of spectroscopy as a
diagnostic tool to probe the conformation of the PANI chains inside M003.

The PANI chains in (PANI)xMoO3 should be well-oriented (the

primary aim of this work) and its solid state UV-visible/Near-IR spectrum
should be comparable to PANI~CMSA processed from m-cresol. We
performed a series of solid state UV-visible/Near-IR experiments. First,
the precursor phase of (PANI)xMoO3, II, shows two absorption bands at
232 nm and at 573 nm (Figure 2.21) and these are attributed to the small
amount of oligomeric polyaniline. In contrast, I shows only one band at
298 nm (Figure 2.22). (PANI)xMoO3 (Figure 2.23) does not show any of
the localized absorption bands observed in bulk PANI-HCl (Figure 2.24).
Rather, a high intensity tailing band is observed, beginning at 350 nm and
increasing in intensity up to 2500 nm, the maximum wavelength observed
by our instrument. This free-career tail is similar to that observed by
MacDiarmid et al. for the PANI-CMSA/m-cresol system and is also due to
delocalized electrons in the polaron band. Therefore, these data further

support our conclusions that the polymer chains are intercalated in M003.
That (PANl)xMoO3 does not exhibit an absorption band at 440 nm,

contrary to the PANI-CMSA/m-cresol system is due to the fact the M003

itself absorbs in that region (Figure 2.25). The extracted polymer from
(PANI)xMoO3 (Figure 2.26) still shows a tail-like feature in its solid-state

UV-visible/Near-IR spectrum, suggesting that the polymer chains retain
their ‘rod-like’ configuration outside M003. Solid-state UV-visible/Near-
IR technique provides a very important diagnostic tool in probing the

structure of conductive polymers in constrained environments. It shows

99

that we have indeed formed polyaniline inside the M003 layers and

complements the other techniques that we have employed.

100

 

 

 

 

5 L l 1 l

4.. ..
t:
.g 3 1 -
E-
8
.o 2- -
<2

1 - _

0 r r r r

190 652 1 1 14 1576 2038 2500
nm

Figure 2.21. Solid state UV-Visible/Near-IR spectrum of II. BaSO4 was

used as reference.

101

 

 

 

 

 

7 1 l l l
6- ..
5 ..
8
.5 4_ .—
E'
<
2- _
1 - -
O I I I I
190 652 1 1 14 1576 2038 2500

nm

Figure 2.22. Solid state UV-Visible/Near-IR spectrum of I. BaSO4 was

used as reference.

102

 

0.35
0.3 1 (a)
0.25 -
0.24

0.15‘

Absorption

0.1-

 

0.05

 

 

O I T T r T f U T r I U V r V I

190.0 767.5 1345.0 1922.5 2500.0

 

nut
35 l L L l
3‘ (b) ‘

G
.12., 2,5. -
e-
a
D N .-
< 2

1.5- -

 

 

 

1 r I I r
190 652 1 1 14 1576 2038 2500

nm

Figure 2.23. Solid state UV-Visible/Near-IR spectrum of (PANI)xMoO3,
(a) using CdS as reference and (b) using BaSO4 as reference. The

absorption dips above 1900 nm in both spectra are due to H20.

103

 

 

 

 

60 l l l l

50- -
.5 40‘ ‘
8' 30- -
m
8

20- -

10- -

0 r . 1 1

190 652 1114 1576 2038 2500
nm

Figure 2.24. Solid State UV-Visible/Near-IR spectrum of bulk PANI.HCl.

BaSO4 was used as reference.

104

 

 

5 J 1 l l
4- _
:1 3‘ '-
.9.
E- 2- _
5
U)
.o
< 1- _
0- ..
-1

 

 

 

I I
190 652 1114 1536 2088 2500
nm

Figure 2.25. Solid state UV-Visible/Near-IR spectrum of M003. BaSO4

was used as reference.

105

 

 

 

 

 

 

 

 

 

0.2
(a)
= 0.15-
02
E'-
c 0.1-
U)
.5
<
0.05-
OI r t I I I I I I r I I I r
190.0 767.5 1345.0 1922.5 2500.0
nm
5.5 I 1 l l
b
5‘ () _
_ 4.5~ »
E’. 4. _
i 3.54 _
3~ _
2.5 I r I f
190 652 1114 1576 2038 2500
nm

Figure 2.26. Solid state UV-Visible/Near-IR spectrum of extracted
PANI from (PANI)xMoO3, (a) using CdS as reference and (b) using

BaSO4 as reference. The absorption dips above 1900 nm in both spectra

are due to H20.

106

2.4. Concluding Remarks

This work describes the synthesis and characterization of two intercalation
compounds of aniline in M003, namely, I and II. Spectroscopically, it was
shown that compounds I and II are different. The salient feature of
compound II that makes it a successful precursor to (PANDXMoOg is its
high degree of reduction. Compound I being an insulator could not afford
(PANI)xMoO3. This work demonstrates that the intercalation of conductive
polyaniline is possible inside M003 inspite of its poor oxidizing power.
This was achieved by first inserting aniline into M003 in the presence of a
trace amount water, followed by treatment of the resulting template with
(NH4)28203. The presence of water was shown to be a key feature for the
insertion of aniline into M003; a minute amount of which produces the
precursor phase of (PANI)xMoO3. The molecular weight of the polymer
formed inside M003 is dependent upon the quantity of oxidant used. Large
amounts of the oxidant gave low molecular weight PANI whereas small
quantities favor higher molecular weight of the polymer. An arsenal of
experimental techniques has been used to prove that the polymer is formed
inside the layered host and not outside. Solid-state UV-visible-Near-IR
spectroscopy confirmed that we have indeed achieved our goal of orienting

the chains of polyaniline inside the M003 layers. (PANI)xMoO3 may find

applications as cathodes in high-energy density lithium batteries.

This is the second example of a conjugated polymer inserted into
M003. The first being the intercalation of PPV into M003 [6]. Due to the
poor oxidizing ability of M003, judicious synthetic strategies had to be
employed in both cases. The introduction of conductive polymers into

M003 is a breakthrough since it now opens up the realm of the

107

intercalation chemistry of this layered host which was formerly limited to
small molecules and ions [3]. It would be very exciting to explore the
possibility of intercalating other conductive polymers such as
polythiophene, polypyrrole and many others into M003 . Here, also, new
creative synthetic methodolologies have to be developed. New synthetic
methodologies for the insertion of polymers in non-oxidizing layered hosts

are currently being developed in our laboratory [43].

108

REFERENCES

[1] (a) Kihlborg, L. Arkiv Kemi. 1963, 21, 357-364. (b) McCarron, E. M.
IH; Calabrese J. Solid State Chem. 1991, 21, 121-125.

[2] Wachs, I. E.; Segawa, K. In Characterization of Catalytic Materials,
Wach, I. E. (Ed.), Butterworth-Heinemann, 1992.

[3] (a) Johnson, J. W.; Jacobson, A. J.; Rich, S. M.; Brody, J. F. J. Am.
Chem. Soc. 1981, 103, 5246-5247. (b) Johnson, J. W.; Jacobson, A. J.;
Rich, S. M.; Brody, J. F. Revue de Chimie Minerale 1982, 12, 420-431.
(c) Lerf, A., Lalik, E.; Kolodziejski, W.; Klinowski, J. J. Phys. Chem.
1992, 2_6_, 7389-7393. ((1) Thomas, D. M.; McCarron III, E. M.; Mat. Res.
Bull. 1986, _2_1_, 945-960. (e) Schollhom, R.; Kuhlmann, R.; Besenhard, J.
0. Mat. Res. Bull. 1976, u, 83-90. (1') Sch’ollhom, R.; Schulte-Nolle, T.;
Steinhoff, G. J. Less Common Met. 1980, _7_1, 71-78. (g) Dickens P. G.,
Hibble S. J. Solid State Ionics 1986, _2_2, 69-73. (h) Chatakondu, K.; Green,
M. L. H.; Qin, J.; Thompson, M. E.; Wiseman, P. J. J. Chem. Soc. Chem.
Commun. 1988, 223-225. (i) Green, M. L. H.; Qin, J.; O'Hare, D.;
Bunting, H. E.; Thompson, M. E.; Marder, S. R.; Chatakondu, K. Pure &
Appl. Chem. 1989, 6_1(5), 817-822. (j) Kanatzidis, M. G.; Marks, T. J.
Inorg. Chem. 1987, 2_6_, 783-784. (k) Ganguli, A. K.; Ganapathi, L.;
Gopalakrishnan, Rao, C. N. R. J. Solid State Chem. 1988, 14, 228-231.

109

[4] (a) Desilvestro; J. Haas, O. J. Electrochem. Soc. 1990, 131, 5c. (b)
Murphy; D. W., Christtian, P. A. Science 1979,2315, 651-656. (c)
Whittingham, M. S. J. Electrochem. 5001975123, 315-320. ((1)
Besenhard, J. 0.; Heydecke, J.; Wudy, E.; Fritz, H. P.; Foag, W. Solid
State Ionics 1983, 8, 61-71.

[5] (a) Machida, K—I.; Enyo, M. J. Electrochem. Soc. 1990, 131, 1169-
1175. (b) Lampert, C. M. Solar Energy Mat. 1984, u, 1. (c) Guerfi, A.;
Dao, Lé H. J. Electrochem. Soc. 1989, 136, 2435-2436.

[6] (a) Nazar, L. F.; Zhang, 2.; Zinkweg, D. J. Am. Chem. Soc. 1992,
LE, 6239-6240. (b) Nazar, L. F.; Yin, X. T.; Zinkweg, D.; Zhang, Z.;
Liblong, S. Mat. Res. Soc. Symp. Proc. 1991, 210, 417-422.

[7] Bissessur, R.; DeGroot, D. C.; Schindler, J. L.; Kannewurf, C. R.;
Kanatzidis, M. G. J. Chem. Soc. Chem. Commun. 1993, 687-689.

[8] (a) "Proceeding of the lntemational Conference on Science and
Technology of Synthetic Metals (ICSM'88)" Aldissi, M. (Ed.) Synth. Met.
1989, 27-29, and references therein. (b) Skotheim, T. A. (Ed.) In
Handbook of Conductive Polymers, Marcel Dekker: New York, Vol. 1, 2,
1986. (c) Marks, T. J. Science 1985, 2_21, 881-889.

 

[9] Miller, J. S. Adv. Mater. 1993, 5, No. 7/8 587-589 and references

therein.

110

[10] (a) Kanatzidis, M. G.; Tonge, L. M.; Marks, T. J.; Marcy, H. 0.;
Kannewurf, C. R. J. Am. Chem. Soc. 1987,1_Q2, 3797-3799. (b)
Kanatzidis, M. G.; Marcy, H. 0.; McCarthy, W. J.; Kannewurf, C. R.;
Marks, T. J. Solid State Ionics 1989, 3213.3, 594-608. (c) Kanatzidis, M.
G.; Hubbard, M.; Tonge, L. M.; Marks, T. J.; Marcy, H. 0.; Kannewurf,
C. R. Synth. Met. 1989, 28, C89-C95. ((1) Wu, C.-G.; Kanatzidis, M. G.;
Marcy, H. 0.; DeGroot, D. C.; Kannewurf, C. R., Kostikas, A.;
Papaefthymiou, V. Adv. Mater. 1990, 2, 364-366.

[11] (a) Kanatzidis, M. G.; Wu, C.-G.; Marcy, H. 0.; Kannewurf, C. R. J.
Am. Chem. Soc. 1989, 111, 4139-4141. (b) Wu, C.-G.; Kanatzidis, M. G.;
Marcy, H. 0.; DeGroot, D. C.; Kannewurf, C. R. Polym. Mater. Sci. Eng.
1989,61, 969-973. (c) Wu, C.-G.; Kanatzidis, M. G.; Marcy, H. 0.;
DeGroot, D. C.; Kannewurf, C. R. NATO Advanced Study Institute;
Lower Dimensional Systems and Molecular Devices; Metzger, R. M., Ed.
Plenum Press: New York, 1991; pp 427-434. (e) Kanatzidis, M. G.; Wu,
C.-G.; Marcy, H. 0.; DeGroot, D. C.; Kannewurf, C. R. Chem. Mater.
1990, 2, 222-224.

[12] Matsubayashi, Gen-etsu; Nakajima, H. Chem. Lett. 1993, 31-34.

[13] Bein, T.; Enzel, P. Synth. Met. 1989, 22, E163-El68. (b) Enzel, P.;
Bein, T. J. Phys. Chem. 1989, 23, 6270-6272.

[14] Inoue, H.; Yoneyama, H. J. Electroanal. Chem. 1987, 231, 291-294.

111

[15] (3) Liu, Y.-J.; Kanatzidis, M. G. Inorg. Chem. 1993, 32, 2989-2991.

[16] Liu, Y.-J. DeGroot, D. C.; Schindler, J. L.; Kannewurf, C. R.;
Kanatzidis, M. G. J. Chem. Soc. Chem. Commun. 1993, 593-596.

[17] (a) Glemser, 0.; Lutz, G. Z. Anorg. Allg. Chem. 1951, 11, 264. (b)
Glemser, 0.; Lutz, G. Z. Anorg. Allg. Chem. 1952, 262, 93. (c) Glemser,
0.; Lutz, G. Z. Anorg. Allg. Chem. 1956, 285, 173.

[18] Lyding, J. W.; Marcy, H. 0.; Marks, T. J.; Kannewurf, C. R. IEEE
Trans. Instrum. Meas. 1988, 31, 76-80.

[19] Marcy, H. 0.; Marks, T. J.; Kannewurf, C. R. IEEE Trans. Instrum.
Meas. 1990, 32, 756-760.

[20] Hsu, C.-H., Peacock, P. M.; Flippen, R. B.; Manohar, S. K.;
MacDiarmid, A. G. Synth. Met. 1993, 6, 233-237.

[21] (a) Wendlandt, W. W.; Hecht, H. G. Reflectance Spectroscopy;
Interscience Publishers: New York, 1966. (b) Kotiim, G. Reflectance

Spectroscopy; Springer Verlag: New York, 1969.
[22] (a)Yu, L. T.; Borredon, M. S.; Jozefowicz, M.; Belorgrey, G.; Buvet,

R. J. Polym. Sci. 1989,11), 2931. (b) Genies, E. M.; Boyle, A.;
Lapkowski, M.; Tsintavis, C. Synth. Met. 1990, 16, 139-182.

[23] Schollhom, R.; Zagefka. Mat. Res. Bull. 1979, _1_4, 369-376.

112

[24] (a) Clements R.; Wood, J. L. J. Mol. Structure 1973, 11, 265-285.
(b) Masri, F. N.; Wood, J. L. J. Mol. Structure 1972, 14;, 201-216. (c)
Masri, F. N.; Wood, J. L. J. Mol. Structure 1972 14 217-227. (d)

9—’

Zeegers-Huyskens, T. Spectrochim. Acta 1967, 23A, 855-866.

[25] (a) Bernard, L.; McKelvy, M.; Glaunsinger, W. Solid State Ionics
1985, 15, 301-310. (b) Ong, E.W.; Eckert, J.; Dotson, L. A.; Glaunsinger,
W. S. Chem. Mater. 1994, in press.

[26] Joy, P. A.; Vasudevan, S. J. Am. Chem. Soc. 1992, 113, 7792-7801.
[27] Bissessur, R.; Kanatzidis, M. G. Unpublished results.

[28] Laudise, R. A. Chem and Eng News 1987, 65 (39) 30-43.

[29] Petrakis, L.; Meyer, P. L.; Debies, T. P. J. Phys. Chem. l980,_8_4,
1020-1029.

[30] Javadi, H. H. S.; Laversanne, Epstein, A. J.; Kohli, R. K.; Scherr, E.
M.; MacDiarmid, A. G. Synth. Met. 1989, 22, E439-E444.

[31] Lomax J. P. Ph.D. thesis, Northwestern University, Evanston, Illinois,
June 1986.

113

[32] (a) Hand, R. L.; Nelson, R. F. J. Electrochem. Soc. 1978, 125, 1059-
1069. (b) Hand, R. L.; Nelson, R. F. J. Am. Chem. Soc. 1974, 26, 850-
860.

[33] (a) MacDiarmid, A. G.; Chiang, J. C.; Halpem, M; Huang, W. S.; Mu,
S. L.; Somasiri, N. L. D.; Wu, W.; Yaniger, S. 1. Mol. Cryst., Liq. Cryst.
1985, 121, 173-180. (b) MacDiarmid, A. G.; Somasiri, N. L. D.;
Salaneck, W. R.; Lundstrom, I.; Liedberg, B.; Hasan, M. A.; Erlandsson,
R.; Konrasson, P. in "Springer series in Solid State Sciences”, Vol. 63,

Springer, Berlin, 1985, page 218.

[34] MacDiarmid, A. G.; Chiang, Richter, A. F.; Somasiri, N. L. D.in
"Conducting Polymers Special Edition". Alcaer, L. (Ed). 1987, 105-120.

[35] (a) Genies, E. M.; Tsintavis, C. J. Electroanal. Chem., 1987, 125,
109- 128. (b) Genies, E. M.; Syed, A. A.; Tsintavis, C.; Mol. Cryst., Liq.
Cryst. 1985, 1_2_1_, 181-186.

[36] (a) Lu, F.-L.; Wudl, F.; Nowak, M.; Heeger, A. J. J. Am. Chem. Soc.
1986, 1_0_8_, 8311-8313. (b) Shacklette, L. W.; Wolf, S.; Gould, S.;
Baughman, R. H. J. Chem. Phys. 1988, 16, 3955-3961. (c) Cao, Y.; Li, 8.;
Xue, Z.; Guo, D. Synth. Met. 1986, _1_6, 305-315.

[37] Geniés, E. M.; Boyle, A.; Lapkowski, M.; Tsintavis, C. Synth. Met.
1990, 36, 139-182.

114

[38] En, Y.; Elsenbaumer, R. Chem. Mater. 1994, 6, 671-677.

[39] Manohar, S. K.; MacDiarmid, A. G.; Cromack, K. R.; Ginder, J. M.;
Epstein, A. J. Synth. Met. 1989, 22, E349-E356.

[40] (a) Zuo, F.; Angelopoulos, MacDiarmid, A. G.; Epstein, A. J. Phys.
Rev. B 1987, 36, 3475-3478. (b) Travers, J. P.; Chroboczek, J.; Devreux,
F.; Genoud, F.; Nechtchein, M.; Syed, A.; Genies, E. M.; Tsintavis, C.
Mol. Cryst. Liq. Cryst. 1985, _1_2_1, 195-199.

[41] Cao, Y.; Smith, P.; Heeger, A. J. Synth. Met. 1992, {L8, 91-97.

[42] Min, Y.; MacDiarmid, A. G.; Epstein, A. Polymer Prepr. Am. Chem.
Soc., Div. Polym., 1994, 36, No. 1, 231-232.

[43] Wang, L.; Kanatzidis, M. G. Work in progress.

115

Chapter 3

Encapsulation of Polymers into M052 and Metal to Insulator

Transition in Metasable MoSz.

116

Abstract

The following polymers, poly(ethylene-oxide), poly(propylene
glycol), poly(vinylpyrrolidinone), methyl cellulose, poly(ethylenimine),
poly(ethylene) and Nylon-6 were inserted into M082. This was achieved by
addition of the polymer solutions to aqueous suspensions of single layers of
M052. This causes flocculation during which the M082 layers sandwich the
polymer chains to give well-ordered single phase products. The d-spacings
of these polymer-intercalated phases range from 10.3 A in
(polyethylene)3,0MoS2 to 21.1 A in (PVP)0.76M082. The encapsulation of
conjugated polyaniline was also achieved by addition of the polymer
dissolved in N-methylpyrrolidinone to an aqueous suspension of
delaminated MoSz layers. This also resulted in a well-ordered single-phase
product with an interlayer spacing of 10.4 A, which is consistent with a
monolayer of the polymer chain lying parallel to the M082 sheets. All the
intercalation compounds were found to be conductive with the exception of
(Nylon-6)3.6M082 and (polyethylene)3.oMoS2. The conductivity of the
other intercalation compounds were in the range of 0.1- 0.0004 S/cm.
Four-probe electrical conductivity and thermopower measurements of
pressed pellets of (PANI)0.35MoSz, (PEI)0,33M082 and (PEO)1,oMoS2
show that the charge transport in these materials is p-metallic. Below 9 K,
the conductivity and thermopower of (PANI)0,35M082 indicate a sudden
transition to the insulating state. The conductivity of (PANI)0.35MoSz
decreases by five orders of magnitude below 9 K. A similar behavior is
observed for (PEI)0,33M082 and (PEO)1,0M082 in the low temperature

regime. For example, the conductivity of (PEO)1.0M082 decreases

117

abruptly by six orders in magnitude below 14 K, while its thermopower
becomes difficult to measure due to the high resistance. The metal to
insulator transition in these polymer/M082 nanocomposites is new, since it
is not known for either the polymers or M082.

All the intercalation compounds were characterized by X-ray
diffraction powder patterns, electrical conductivity measurements,
thermogravimetric analysis, differential scanning calorimetry, and

scanning electron microscopy.

118

3. 1 . Introduction

The insertion of polymers (conjugated and saturated) in layered host
materials and other structurally well-organized environments is a t0pic of
considerable interest because the resulting organic/inorganic nanostructures
can possess novel electrical, structural, and mechanical properties [1,2].
Such systems can potentially exhibit hybrid properties synergistically
derived from both the host and the guest [3]. For example, recently
researchers from Toyota prepared new molecular-scale nanocomposites
made from saturated polymers (Nylon-6 and other plastics) intercalated in
clay layers [4]. These products show extraordinary mechanical strength far
greater than that attainable or expected by simply mixing the components.

Encapsulation of polymers in constrained environments is still rare
as opposed to the insertion of small molecules. The redox intercalative
polymerization (RIP) of conjugated polymers in VzOs-nHzO and FeOCl as
mentioned in chapters 1 and 2 produces well-ordered compounds with
enhanced electrical properties [5]. This process works only with suitably
oxidizing hosts and can potentially be applied to other hosts to the extent
that they can accept electrons at a low enough potential. Therefore, non-
oxidizing hosts are not suitable for RIP.

Due to the lack of highly oxidizing hosts, we are currently
developing new synthetic methodologies for introducing polymers in non-
oxidizing hosts. Our goal is to broaden the scope of the field of hybrid
materials. The insertion of polyaniline into M003, a relatively poor
oxidant, was achieved by first inserting aniline into M003 followed by
oxidation of the resulting template with (NH4)28203 (see chapter 2). As an

extension of this work, we turned our attention to M082. We have also

119

expanded the scope of guest species to saturated polymers with solid-
electrolyte properties such as poly(ethylene-oxide), poly(propylene glycol),
poly(vinylpyrrolidinone), poly(ethylenimine) and methyl cellulose. Our
interest in these polymeric materials lies in the future development of all-
solid-state batteries. In addition we have also included Nylon-6 and
poly(ethylene), two robust engineering polymers as intercalants and our
reasons for doing so is to proceed along the same line as the Toyota
researchers.

M082 is a very attractive layered material for investigation because it
is readily available. It occurs naturally as its mineral, molybdenite [6].
MoSz is already an important material with several practical applications.
For instance, it is extensively being used as a catalyst for the
hydrodesulfurization (HDS) process [7], which involves the removal of
sulfur from organosulfur compounds in oil.

Similar to graphite, MoS2 is also being used as a solid lubricant [8]
because of its layered character. The layers are held together by weak van
der Waals forces and as such slippage of the layers in the direction parallel
to the layers occursvery easily, giving rise to its lubricating properties.
Experimental measurements of the lattice vibration frequencies by Wietting
et al. in 1971 actually proved that the forces between the layers are not
very strong [9].

In addition, M082 can be used as a cathode material in lithium high
energy density rechargeable batteries [10]. In general, layered materials are
potential canditates as cathode materials when coupled with lithium metal as
the anode [11].

The intercalation reaction of lithium into M082 is very exothermic.

Since, the process also occurs electrochemically, the energy released can be

120

harnessed to obtain a reversible battery system. The electrochemical
reaction (Eq. 1)

discharging
L1 '1' M082 ‘ ‘ LixMOSZ ------- Eq.l
charging

 

fufills all the requirements of an anode/cathode couple for a secondary
battery, namely:

(a) high reversibility

(b) little change in free energy over the composition range, i.e, x

(0) high free energy of reaction

((1) wide range of x

(e) little structural change of M082 upon intercalation

(f) high diffusivity of Li into M082

(g) Inertness of M082 towards electrolytes

However, M082 is a semicondutor (CRT = 10'5 S/cm). Therefore to
make MoSz a viable cathode in rechargeable batteries, it has to be made
conductive enough in order to be accessible for the electron liberated from
the lithium anode. This is usually achieved by coating it with conductive
graphite or carbon black [12].

Inspite of the tremendous importance of MoSz in practical
applications, its intercalation chemistry using conventional redox
techniques has been limited to those of alkali and alkaline earth metals [13].

The M0 being in the +4 state is very hard to reduce. However, recently

121

MoSz was shown to disperse into an aqueous suspension of single layers by
reacting LixMoS2 with water [14]. Flocculation of the layers in the
presence of small molecules resulted in intercalation compounds [15]. We
have exploited this property and used single layer MoSz in water and
polymer solutions to produce novel polymer/M082 nanocomposites [16].

3.2. Experimental

3.2.1. Reagents: M082 was purchased from Cerac (1 micron particle
size) and was used without any further purification. n-BuLi was purchased
from Aldrich as a 2.5 M solution in hexanes. The concentration of n-BuLi
was adjusted to 1 M by adding freshly distilled hexanes during lithiation
reactions. Poly(ethylene-oxide) (MW: 100,000 and 5,000,000),
poly(propylene glycol) (MW: 1,000), poly(vinylpyrrolidinone) (MW:
10,000), poly(ethylenimine) (MW: 55,000), methyl cellulose (MW:
63,000), Nylon-6 (MW: 10,000) and poly(ethylene) (ultra-high MW) were

purchased from Aldrich Chemical Company and were used as received.

3.2.2. Synthesis of Neutral PANI

PANI-HCl (emeraldine salt) was first prepared as described in
chapter 2. The PANI-HCI was then allowed to equilibrate in 0.05 M NaOH

solution for several days. The product was then filtered off and was washed

122

abundantly with distilled water. It was then allowed to dry under suction
followed by drying under dynamic vacuum. The product was found to be
insulating by four probe conductivity measurement at room temperature
and dissolves in N-methylpyrrolidinone, both of which are characteristic of
the neutral form of PANI (emeraldine base) [17].

3.2.3. Synthesis of LiMoSz

Hexane used in this experiment was dried by refluxing over CaHz
for 2 days under a nitrogen blanket. It was freshly distilled prior to use.
M082 (6.2 g, 38.8 mmol) was transferred to a Schlenk-flask which was
evacuated overnight in a Schlenk-line. It was then backfilled with nitrogen
and evacuated for about 15 minutes. This process was repeated two more
times and the flask was kept purged with nitrogen gas. Freshly distilled
hexane (72 ml) was added to the flask, followed by careful addition of 3
equivalents of n-BuLi (48 ml, 117 mmol) by means of a gas-tight syringe.
It should be borne in mind that 'n-BuLi' is actually an hexamer of
butyllithium which dissociates to a very minor extent [18]. For simplicity,
the reagent n-butyllithium is simply referred to as 'n-BuLi'. The reaction
mixture was allowed to stir under nitrogen for 2 days. The product of the
reaction was then filtered off by using the Schlenk technique [19]. The
product was washed repeatedly with portions of freshly distilled hexane
transferred to the Schlenk-frit by means of a gas-tight syringe. The washed
product was dried overnight in the Schlenk-frit, which was connected to

the vacuum-line. The X-ray diffraction pattern of the product is consistent

123

with the formation of LixM082 and elemental analysis suggests the

composition LiM082.

3.2.4. Preparation of MoSz Single Layers

To LiMoSz (0.2 g, 1.2 mmol) in a 125 ml Erlenmeyer flask was
added 20 ml of distilled water and the suspension was sonicated for 1.5

hours, with occasional vigorous agitation of the flask. This procedure leads

to complete exfoliation of the M082 layers.

3.2.5. Intercalation of Neutral Polyaniline (PANI) into MoSz

Neutral PANI (0.06 g, 0.66 mmol) was dissolved in 40 ml of NMP
with the help of sonication. The solution was added to an aqueous
suspension of MoSz single layers and the reaction mixture was allowed to
stir at room temperature for 2 days. It was then centrifuged and washed
with NMP several times. The reaction mixture was then filtered off by
using suction and was further washed with NMP until the filtrate was
colorless. The black product isolated was further washed with ethanol and
then ether. It was allowed to dry under suction followed by drying under
dynamic vacuum. The material analyzes for (PANI)0,35M082 from
elemental analysis and TGA under oxygen flow. Observed, % C: 12.21; %
H: 1.05; % N: 2.45; % M082 by difference: 84.29. Calculated, based on
(PANI)0.35M0$2, % C: 13.13; % H: 0.91; % N: 2.55; and % MoSz by
difference: 83.41.

124

3.2.6. Intercalation of Poly(ethylene-oxide) (PEO) into MoSz

PEO of MW 100,000 or 5,000,000 (0.053 g, 1.2 mmol) was
dissolved in 20 ml of distilled water. The polymer solution was added to an
aqueous suspension of single M082 layers. The reaction mixture was
allowed to stir at room temperature for 2 days. It was then centrifuged
several times and washed with distilled water. It was filtered off by using
suction from a water aspirator, washed with distilled water, followed by
washing with ethanol and ether. The product was allowed to dry under
suction followed by drying in a vacuum oven at room temperature. For
either MW of PEO used, the material analyzes for (PEO)1,oMoSz from
elemental analysis and TGA under oxygen flow. Observed % C: 12.11; %
H: 1.98; % O: 9.12; % M082 by difference 76.79. Calculated based on
(PEO)1_oMoSz, % C: 11.76; % H: 1.96; % O: 7.84: % MoSz by difference:
78.44.

3.2.7. Intercalation of Poly(propylene glycol) (PPG) into MoSz

PPG (1.2 g, 1.2 mmol)) was dissolved in 25 ml of distilled water
and the solution added to an aqueous suspension of single MoSz layers. The
reaction was performed as described in section 3.2.6. The work-up of the
reaction mixture was also performed as described in 3.2.6. The isolated
material analyzes for (PPG)0,5MoSz from TGA under oxygen flow.
Calculated, based on (PPG)0,5M0S2, % C: 9.52; % H: 1.59; % O: 4.23; %
M032 : 84.66

125

3.2.8. Intercalation of Poly(vinylpyrrolidinone) (PVP) into
MoSz

PVP (0.13 g, 1.2 mmol) was dissolved in 20 ml of distilled water
and the polymer solution added to an aqueous suspension of single M082
layers. The synthesis and isolation of the intercalated phase was performed
as described in 3.2.6. The composition of the isolated material was found to
be (PVP)o,76MoS 2 from TGA under oxygen flow. Based on
(PVP)o,76M082, calculated % C: 22.39; % H: 2.80; % O: 4.98; % M082:

69.83.

3.2.9. Intercalation of Methyl Cellulose (MCel) into M082

Methyl cellulose (0.5 g, 1.2 mmol) was dissolved in 100 ml of
distilled water. The viscous polymer solution was mixed with a freshly
prepared suspension of M082 single layers. The reaction was performed as
described in 3.2.6 and the product of the reaction isolated as described in
3.2.6. The material analyzes for (MCel)o,26M082 as determined from TGA
under oxygen flow. Based on (MCel)o,26M082, calculated % C: 21.11; %
H: 3.13: % O: 15.63; % MoSz: 60.13.

3.2.10. Intercalation of Poly(ethylenimine) (PEI) into MoSz

An amount of PEI (0.4 g, 9.3 mmol) was dissolved in 3 ml of

distilled water. (The polymer was available from Aldrich as an aqueous

126

50% by weight solution). The polymer solution was added to an aqueous
suspension of M082 single layers. The reaction was performed and the
product isolated as described in 3.2.6. The composition of the product is
(PEI)o,33MoSz as determined from TGA under oxygen flow. Calculated
based on (PEI)o,33MoSz, % C: 10.18; % H: 2.12; % N: 5.94; % M082:
82.76.

3.2.11.1ntercalation of Nylon-6 into MoSz

LiMoSz (0.1 g, 0.60 mmol) was transferred to a 100 ml round-
bottom flask. Distilled water (5 ml) was added to the flask and the
suspension was sonicated for 1.5 hours in order to generate single layers of
M082. It was then refluxed for a few minutes. An amount of Nylon-6,
(0.54 g mmol, 4.78 mmol) was dissolved in 15 ml of CF3CHzOH and the
solution was heated just below the boling point of the solvent. The hot
Nylon-6 solution was transferred to the hot suspension of M082 single
layers. The reaction mixture was refluxed for 2 days. It was then filtered
hot by using suction from a water-aspirator and washed with hot
CF3CH20H. The product was allowed to dry under suction before drying
under dynamic vacuum. The material analyzes for (Nylon-6)3,6M082 from
TGA under oxygen flow. Calculated based on (Nylon-6)3,6M082, % C:
45.73; % H: 6.99; % N: 8.89; % O: 10.16; % M0S2 : 28.23.

127

3.2.12. Intercalation of Poly(ethylene) into MoSz

An amount of poly(ethylene) (0.08 g, 5.7 mmol) was dissolved in 20
m1 of decalin by refluxing overnight. The hot decalin solution of the
polymer was added to an aqueous suspension of single layers of M082
which was prepared as described in 3.2.4. The reaction mixture was
refluxed for 3 days. The product was hot-filtered and washed with ethanol
and ether, and dried in vacuum. The material analyzes for
[-(-CH2-)n]3,oMoSz from TGA under oxygen flow. Based on
[-(-CH2-)n]3,oM082, calculated % C: 17.82; % H: 2.97; % M082: 79.21.

3.2.13. Preparation of Restacked MoSz

An aqueous suspension of single layers was prepared as described in
3.2.4. 20 m1 of distilled water was added to the suspension and the reaction
mixture was allowed to stir at room temperature for 2 days. The reaction
mixture was then centrifuged and the product obtained was washed with
distilled water several times. It was then washed with distilled water
followed by ethanol and ether and dried under vacuum at room

temperature. The X-ray diffraction pattern shows an interlayer spacing of
6.2 A.

128

3.3. Physicochemical Methods

X-ray diffraction powder pattern, infra-red spectroscopy,
thermogravimetric analysis, scanning electron microscopy and charge

transport measurements were performed as described in chapter 2.

Differential Scanning Calorimetry (DSC).

DSC was performed with a computer-controlled Shimazdu DSC-50 thermal
analyzer under a nitrogen atmosphere at a flow rate of 35 ml/min. The
samples were crimped in aluminum pans inside a nitrogen-filled glovebox.
The pan was placed on the DSC-50 detector and an empty aluminum pan of
equal mass was crimped and placed on the reference side. The samples
were heated to the desired temperature at 5 oC/min and cooled to 50 0C at
5 OC/min, unless specified otherwise. The reported DSC temperatures are
peak temperatures with a standard deviation of 0.5 0C. The adopted
convention in displaying the data is exothermic peaks occur at positive heat

flow while endothermic peaks occur at negative heat flow.

Magnetic Susceptibility Measurements. Variable temperature
magnetic susceptibility data were collected on a Quantum Design
instrument at a fixed magnetic field between 5000 and 20000 gauss,
depending on the saturation of the sample as a function of magnetic field. A
known quantity of the material was placed in a plastic bag and purged with
helium gas before closing. Measurements were made with an ascending

temperature ramp from 2K to 300K.

129

3.4. Results and Discussion

The intercalation of lithium into M082 is a redox reaction where,
Bu' transfers electrons to the M082 sheets. To balance the negative charge
on the layers, Li+ ions insert into the gallery space of the host (Eq. 2).

M082 4» nBuLi

 

LiMoSz + 1/2Bu-Bu --------- Eq. 2

The reaction between n-BuLi and MoS2 occurs readily at room
temperature. It was carried out under strictly anhydrous conditions since
both the n-BuLi and LiMoSz are sensitive to moisture. Figure 3.1
compares the X-ray diffraction pattern of LiMoSz with that of pristine 2H-
MoSz. In LiMoS2 (Figure 3.1b) the M082 layers have expanded by 0.14 A.
As a result of the intercalation reaction, significant loss in crystallinity
occured, as observed from the broad feature of the peaks. Formation of

single layers of M082 was easily achieved by adding water to the LiMoSz
(Eq. 3).

 

LiMoSz + tzO (MoSz)single layers + xLiOH + (x/2) H2 ----Eq. 3

130

(a)

 

 

t. 1110

Intensity (Arbitrary Unit)

(D)

W

0.0 10.0 26.0 ' 36,0 ' 40'0 ' 50,0 ' son
26 (degrees)

 

 

 

Figure 3.1. XRD of (a) pristine M082 and (b) LiMoSz.

131

Contrary to the report by Frindt et al. [20], this reaction was not
found to be violent. Equation 3 is analogous to the reaction of lithium
metal with water. Here, the reducing agent is the negatively charged M082
layers (MoS2') which get oxidized by water, forming neutral M082 single
layers, LiOH and H2. This reaction has been misinterpreted in the literature
by several authors [21] who have described the formation of single layers
by the reaction of the intercalated lithium with H20. This is chemically
impossible since lithium is thought to exist as Li+.

Equation 3 written as such, does not provide any clue to the
mechanistic pathway involved. Scheme 3.1 conceptually illustrates a
possible mechanistic pathway leading to the formation of single layers.
Treatment of LiMoSz with water first produces a hydrated phase,
Lix(H20)yM082 [15a, 22]. The driving force for the formation of this
hydrated phase is coordination of H20 molecules to the lithium ions.
Reaction of the negatively charged layers with the interlamellar water
molecules forms hydrogen gas and lithium hydroxide trapped inside the
layers. The hydrogen gas inside the M082 layers diffuses out, forcing the
layers apart. Our research confirmed that sonication tremendously helps in
the formation of single layers. Frindt et al. characterized the identity of the
single layers formed in Equation 3 through a combination of X-ray
diffraction studies, computer simulation and seaming tunneling microscopy
[23].

The single neutral layers have a tendency to restack, but in the
presence of foreign species in the vicinity, they restack with the foreign
species trapped in between. Frindt et al. capitalized on the exfoliation and

restacking property of M082. They were able to sandwich a plethora of

132

 

.NmoE dB 393. Ema; ho gang—8 wagofi @353 655285 38qu ._.m 25.3w

€99: 33:0me
I]: -EO+5

//\
ml: -20.:

a

 

 

 

mmezmommva:

 

awe:

 

£9: £95 .5 +5 +5

T

of l s -
NEO+~1H NIO+1H +~1H +_1H +_l— HWH m C

 

 

 

 

 

 

 

 

133

Host Interlayer Host

 

 

 

Expansion (A) Interlayer Expansion
f A
MoS2-Ferrocene 11.8 5.6
M082-Styrene l 1.5 5.3
MoSz-Stearamide 56.8 50.6

 

M082-Benzene 6,2 -_-

 

 

 

 

 

Table 3.1. Intercalation compounds prepared by Frindt et al.

134

small molecules in between M082 sheets [24]. Table 3.1 gives a select
number of intercalation compounds prepared by Frindt el al. No interlayer
expansion is reported for the Benzene-M082 system, since the benzene.) gets
very easily desorped from the M082 layers. This is explained by the fact
that the force of attraction between any intercalated species and M082
layers is merely the weak van der Waals interaction.

Recently, Guay et al. [25] did X-ray absorption studies on a series of
intercalation compounds of organic molecules in M082, prepared by the
exfoliation and flocculation method. They were looking for evidence for
the existence of an interaction between the S atom and the organic molecule
located in between the layers. No such evidence was found, regardless of
the interlayer spacing of the intercalation compound. This suggests that the
guest and host assemblies are held together by van der Waals bonds. In a
way, this is reassuring for us, since we are interested in encapsulating
soluble polymers inside the M082 layers. The low molecular weight solvent
molecules could therefore be easily desorbed by pumping under vacuum so
that only stable, single-phase products could be obtained.

All the intercalation compounds of M082 prepared by Frindt et al.
were prepared in a two phase-system as shown in Scheme 3.2 which
illustrates the insertion of ferrocene into M082. When ferrocene dissolved
in CCl4 is added to an aqueous suspension of single layers, a two-phase
system is observed. Upon vigorous agitation, a phase separation occurs
where the single layers leave the aqueous suspension and collect at the
interface of the water and organic solvent. Since the layers have a tendency
to restack, they do so with the ferrocene molecules sandwiched in between

as shown in Scheme 3.2.

135

.53.“? 82903. a $5: .8 £22 oz: 058:“: .8 .5832: .~.m oEocom

Nmoieficouotob

 

 

 

A

 

 

 

8.329: 3828.. 05 E93. :00
03:7. Nmos. «553:8 A
seated. 0:38

 

of

Al

52?? ommsméah

 

€93. “ism «mo—2‘1.
0:. AI

 

0:823
3.2m .. Al

:00 Al

 

 

136

However, from our investigation we found that for intercalation to
take place a two-phase system is not necessary. For instance, we were able

to encapsulate PANI into M082 by adding a solution of neutral PANI in

NMP (a water-miscible solvent) to an aqueous suspension of single layers

(Eq. 4).

 

(MoSz)sing1¢ layers + xPANI (PANDXMoSz ------ Eq. 4

Evidence that (PANI)xM082 is an intercalation compound was
obtained from X-ray powder data (Figure 3.2) which clearly shows the
first two (001) basal reflections. The interlayer spacing of (PANI)xM082 is
10.37 A. This represents an expansion of the M082 layers by 4.2 A, in
good agreement with what is expected for a monolayer of PANI lying flat
in the van der Waals gap (Scheme 3.3). The stoichiometry
(PANI)o,35M082 was determined by elemental analysis and thermal
gravimetric analysis measurements under oxygen flow. The material is
stable up to 230 0C under oxygen flow at which point there is a rapid
weight loss to give the stable M003 phase as verified from XRD and FTIR
spectroscopy.

Thermal gravimetric analysis does not show evidence for the
cointercalation of NMP and water in (PANI)xM082. However, in order to
exclude the possibility that NMP and/or water is inside the layers and PANI
is outside, we performed two control experiments. First, treatment of an
aqueous suspension of M082 single layers with water does not give a
hydrated phase, but merely M082 layers which restack with nothing
trapped in between after rigorous washing and drying under vacuum (Eq.

5). A hydrated phase does form, but the trapped water molecules desorb

137

 

 

(Arbitrary Unit)

 

 

Intensity

 

2 16.5 31 45.5 60
2 Theta (degrees)

Figure 3.2. XRD of (PANI)o,35M082.

 

138

o
10.37A

d=

 

Scheme 3.3. Representation of the lamellar arrangement of (PANI)0,35M082.

139

upon washing and drying. Second, treatment of an aqueous suspension of
single layers with neat NMP does not form the intercalated product,
(NMP)xM082. Such a phase did form in the beginning, but the NMP
desorbed from the layers after rigorous washing and drying, forming only
restacked M082 (Eq. 6). (PANDXMoSz shows excellent thermal stability up
to 260 0C, under nitrogen and this is consistent with having PANI inside
the M082 layers.
washing

MOS ( 'n 16 la rs) + H O . b restacked MoS ----- . 5
2 51 g ye 2 drying 2 Eq

 

washing

 

MOS; (single layers) + HzO/N MP > restacked M082 ----- Eq. 6

diving

Figure 3.3 shows an X-ray diffraction pattern of restacked M082. As
observed, the d-spacings are similar to those of pristine 2H-MoSz.
However, the peaks are considerably broader, which indicates a poorer
stacking order.

Fourier transform infra-red spectroscopy (FTIR) of (PANI)xM082
shows weak peaks that can be attributed to PANI. Although a considerable
amount of the polymer exists in the material, the weak intensities of the
PANI vibration peaks are due to the highly conductive nature of the
material (vide infra ) which reflects infra-red radiation. However, PANI
can be extracted from (PANI)xM032 by treatment with hot concentrated
sulfuric acid for a brief period of time. This leads to dissolution of the
metal-dichalcogenide framework. FTIR spectroscopy of the extracted

product reveals the vibrations of PANI.

.140

 

(Arbitrary Unlt)

 

 

 

 

Intensity

I

W

16.5 31 45.5 60
2 Theta (degrees)

N

Figure 3.3. XRD of restacked M082.

141

dag—£8. 3?.-o.w:_m 2: $5: .3 £22 35 .5522. he :ezflzmnagm in maze—Em

mmCEXCoEboE
€934 awe—2 33:0me

l //\\
i cons—em $833

 

 

 

 

 

 

 

142

We have also been able to intercalate a wide range of other polymers
such as poly(vinylpyrrolidinone) (PVP), poly(ethylene-oxide) (PEO),
poly(propylene glycol) (PPG), methyl cellulose (MCel) and
poly(ethylenimine) (PEI) which are water-soluble polymers. These were
conveniently inserted into M082 by adding aqueous solutions of the
polymers to an aqueous suspension of single molecular layers of M082 (see
Scheme 3.4). Intercalation of Nylon-6 was performed at high temperature
to avoid precipitation of the polymer. It was observed that addition of a
solution of Nylon-6 in CF3CH20H to cold water resulted in precipitation or
the polymer in the form of fibers. To circumvent this problem, the amount
of water used in exfoliating LiMoSz was decreased by half and both the
exfoliated layers and polymer solution were heated for a few minutes
before mixing. The reaction mixture was refluxed during the entire
reaction time. In the case of poly(ethylene), the reaction was carried out at
100 0C to keep the polymer in solution.

X-ray diffraction patterns show that all polymer intercalates has .3
layered structures as suggested by the intense (001) basal reflections and
indicate well-defined mono-or bilayers of polymers in the gallery space
(Figures 3.4, 3.5, 3.6). The d-spacings, interlayer expansions and other
properties for all intercalates are tabulated in Table 3.2. The largest M082
layer separations were obtained from PVP and MCel. It is interesting to
note that intercalation of poly(ethylene) in a layered material has not been
reported in the past and for the case of M082 it can only be achieved by the
single layer technique. Clearly, this demonstrates the versatility and wide

range of applicability of the technique.

143

 

Unlt)

(a)

 

 

lntenelty(Arbltrery
\_

1 ¥ A

 

 

 

 

16.5 31 45.5 6 o
2 Theta (degrees)

N

 

(b)

 

(Arbltrery Unlt)

 

lntenetty

 

 

1 l

2 16.5 31 45.5 60
2 Thete (degrees)

 

 

(C)

 

(Arbitrery Unlt)

 

tntenelty

l 1

2 16.5 31 45.5 60
2 Thete (degreee)

Figure 3.4. XRD of (a) (PEO)1.0M082 (MW 100,000). (b) (PEO)1.0M082
(MW 5,000,000) and (c) (PPG)0.5MoSZ.

 

 

 

144

 

(a)

(Arbitrery Unlt)

 

 

 

 

lntenelty
['1

l l

 

 

 

 

 

 

 

 

 

 

 

 

2 16.5 31 45.5 60
2 Thete (degreee)
’a'
a
g i (b)
3
E
5.
ad
'5
e
3
s 1 '1 ‘j-NI
2 16.5 31 45.5 60
2 Thete (degreee)
"é
a
(C)
t;
8
‘2';
b
s. [l
P:
'3
e
2

2 16.5 31 45. 5 60
2 Thete (degreee)

Figure 3.5. XRD of (a) (PVP)0.76MOSZ, (b) (MCel)0.26MOSZ and (C)
(PEI)0.33M032.

145

 

]

(Arbitrary Unlt)

:

 

 

 

 

lntenalty

1 1 1

16.5 31 45.5 60
2 Theta (degrees)

 

N

 

(b)

(Arbitrary Unlt)

 

 

 

lntenelty

 

 

 

l 11“ if =‘

2 16.5 31 45.5 so
2 Theta (degreee)

Figure 3.6. XRD of (a) (Nylon-6)3.6M082 and (b) (polyethylene)3_oMoSZ.

146

Ame—2 SE EoEbom we cog—swaaoco 2: Ed... 3:850 2:52 we bmfifizm .N.m 22a...

 

 

 

 

 

 

 

 

 

 

 

Com 3mm v.3 QEZ N6 v.3. Geode Nmosnmdcz<5
24 EN 92v 525% 5; 3. 3: is 2:: «22:536-:
cNm RN o.c_v :cuzemdozo; m.: m: coed. Nmezefieeeazv
mmm mam _.c 533 oé 2: ooodm 3.523235%
mNN EN voccd .653 NJ; «tom ooofia 32.23.2325
EN :3” Sad Ba; 0.3 :m 08.9 «mesonsge
0mm cam N .c 5:; No 1m _ coo; Nmozmgga:
oom CNN Ned .253 m w 03 ooodoofi «me—29:8:
emm mmm _d 5:..3 _ 2 ma: sodo— «mosaiofiv
AUOVNZ aovwd

_SE was .E E L Harlow a a; 333.3 Hail—

 

 

 

 

 

 

 

 

 

147

3.4.1. Thermal Stabilities of Nanocomposites

All the (polymer)xM082 nanocomposites synthesized showed good
thermal Stabilities both under nitrogen and under oxygen flow. The
Stabilities are higher than 200 0C in all cases (Table 3.2). However, we
found that most of the nanocomposites are more stable than their respective
bulk polymers under oxygen flow. Under nitrogen flow the reverse
behavior is observed. For instance, (PEO)1,0M082 is more stable under
oxygen flow than the bulk polymer itself. The latter decomposes at 164 0C
whereas the former is stable up to 250 0C after which rapid loss in weight
and oxidation is observed, forming stable M003 (Figure 3.7). Under
nitrogen, bulk PEO has a greater stability (onset of decomposition at 366
0C) than the nanocomposite material which starts to decompose at 300 0C
(see Figure 3.8). Similar trends were observed for methyl cellulose, PVP,
poly(ethylene) and their respective nanocomposites. The thermal Stabilities
are listed in Table 3.3.

148

 

 

 

 

 

 

 

120
80"
E L
60-
o\°
20-
o IUIIIIUIIIIIIITIIIIIIIIIIIIIIIIIII
O 100 200 300 400 500 600 700
Temperature(°C)

Figure 3.7 TGA of (a) bulk PEO and (b) (PEO)MoSz under oxygen flow.

149

 

 

 

 

 

120
100 w
3
o\0 60
4° (a)
20 L
0 l l l l l l

 

 

 

0 100 200 300 400 500 600 700
Temperature(°C)

Figure 3.8. TGA of (a) bulk PEO and (b) (PEO)MoSz under nitrogen

flow.

150

 

 

 

 

 

 

 

 

 

 

 

 

 

under 02 Flow (0C) under N2 Flow (0C)
bulk PEO 164 366 '
(PEO)1.()M082 250 300
bulk PVP 146 390
(PVP)0.76M082 240 270
bulk methyl cellulose 203 310
(Mcel)0,26MoSz 210 225
bulk Nylon-6 287 381
(Nylon-6)3,6M032 277 320
bulk Polyethylene 239 452
{(-CH2-) } 3.0MoSz 274 425

 

Table 3.3. Comparison of thermal stability of polymer/M082

nanocomposites with their respective bulk polymers.

 

151

3.4.2. Scanning Electron Microscopy (SEM)

SEM micrographs on restacked MoS2 and all (polymer)xM082
samples were taken and compared with those of pristine M082. SEM of a
(polyethylene)3,oMoSz sample shows an amorphous phase due to the
externally lying polymer. The remaining (polymer)xM082 samples and
restacked MoS2 show considerable loss in crystallinity with respect to
pristine M082. This is consistent with the rather broad peaks observed in
the X-ray diffraction patttems. The average particle size of restacked M082
and all (polymer)xM082 samples were determined from the Scherrer

formula

D = ML Eq. 7
51/2 :1: C089

where D is the average particle size in A, A is the wavelength of the Cu-
Ka X-ray radiation (1.5418 A), 131/2 is the peak width at half-height in
degrees and 0 is the position of peak in degrees. K is a constant depending
on the shape of the crystallites. Assuming that the crystallites are perfect
spheres, K is assigned a value of 0.9. 57.3 is the conversion factor for

radians to degrees. The Scherrer formula can be simplified to Eq. 8.

D = M Eq. 8
[3]/2 :1: C089

152

The average particle size of restacked M082 and all (polymer)xM082
samples was calculated to be in the range 60-70 A. SEM shows that
exfoliation and restacking of the M082 layers results in relatively ordered
materials as opposed to amorphous phases. The driving force for the

formation of polymer-intercalated phases is the maximization of the

interface interactions between the polymer molecules and M082 particles.

15KU 81880 @001 10.0U CE094

 

Figure 3.9. SEM micrographs of pristine MoS2.

_,'|,

15KU X1800 0005 10.0U CE094

 

‘..'
;"l
I ..

0003

 

Figure 3.10. SEM micrographs of restacked MoSz.

155

 

 

Figure 3.11. SEM micrographs of (PANI)0,35M0S2.

156

 

7»- :53" .
ISKU x320 0002 103.00 05094

i u,
. . 3, L
is »"- It

 

Figure 3.12. SEM micrographs of (PEO)1,0M082.

157

”a "V 'wri.‘

0012 100.0U CE094

 

 

Figure 3.13. SEM micrographs of (PPG)0_5MoSz.

15KU X1000 000? 10—. 0U BEDS-4

 

: g .
15KU X360 0010 100. 0U CE094

 

Figure 3.14. SEM micrographs of (PVP)()_76M082.

 

 

Figure 3.15. SEM micrographs of (MCel)0,26M082.

15KU X1800 0005 10.0U 08094

J. - .

15KU X2000 0003

 

Figure 3.16. SEM micrographs of (PEI)0,33M082.

161

 

A

 

15KU X1800 0006 10.0U CE0944

Figure 3.17. SEM micrographs of (Nylon-6)3_6M082.

162

I”

a

15KU X 0009 100.0U CE094

 

 

Figure 3.18. SEM micrographs of (polyethylene)3,0MoS2.

163

3.4.3. Charge Transport Measurements

The charge-transport properties of (PANI)0,35M082 were explored
by four-probe electrical conductivity and thermoelectric power
measurements of pressed pellet samples in the temperature range 5-300 K.
The material was found to be highly conductive, reaching values of 0.4
S/cm, which ranks among the highest reported for polymer/host
nanocomposites [5, 26]. However, the measurements show weak, thermally
activated behavior for temperatures above 50 K (Figure 3.19a). The
corresponding thermoelectric power data show a p-type metallic behavior,
as indicated by the small and positive Seebeck coefficient (Figure 3.1%). A
remarkable feature of both the thermopower and especially the
conductivity data is an abrupt transition in the transport behavior at low
temperature. Between 8 and 9 K the conductivity of the sample drops by
three orders of magnitude. Below this reversible transition the sample
displays a very strong temperature dependent behavior, with the
conductivity changing by an additional factor of 100 between 5 and 8 K.
The inset of Figure 3.1% shows an expanded view of the region 4-16 K
where the reversible transition occurs. The transition region was measured
with both increasing and decreasing temperature, and the data show
excellent agreement. As seen in Figure 3.1%, the thermoelectric power
changes drastically near 30 K, with weak variation in thermopower at
higher temperatures but with rapidly varying response below this point.
These data have not been corrected for the contribution of the Au sample
leads because that process has reduced accuracy below 50 K, and therefore
corrected data would preclude showing the transition region. For

temperatures less than ca. 13 K, the sample resistance increased to values

164

 

 

 

 

 

E
2
(D A
v E .5
o
3 i0. (3) g, -7 O
8 l
-8 1
a 8 i
‘_j‘ '95“‘$"‘§"“‘?6‘“13"“1‘T“Ts
Temperature (K)
-10L—1____L__. -L_.__a.___.L 1 P l L l_-_.
0 50 100 150 200 250 300
Temperature (K)
12 1-....- -- _,_ H m--- -_ _.._._.._,
10

 

 

 

Thermopower (uV/K)
m

 

 

 

l :s l
4 l- i
2 '
0 71 L l l 1 1 .___1_-,,l_1__L L LL‘LLJ l L LL 1 1 l 1 l r r ' i

0 50 100 1 50 200 250 300

Temperature (K)

Figure 3.19. (a) Variable temperature electrical conductivity data of
(PANI)0.35M0S2 (b) Variable temperature thermopower data of
(PANImsMosz '

165

such that accurate thermoelectric power measurements could not be taken
and this provides further evidence of a transition to an insulating state in
this material. It is important to note that different pressed pellets of this
material were used for the two transport measurements and this may
account for the variations in the apparent transition temperature.

The charge transport properties of other polymer/M082
nanocomposites were determined by four-probe electrical conductivity
measurements of pressed pellets. The room temperature conductivity
values are listed in Table 3.2. Except for the case of (polyetlrylene)3,oMoSz
and (Nylon-6)3,6M082 which are insulators, the conductivity of the other
polymer/M082 nanocomposites are in the range 0.1-0.0004 S/cm. These are
high values and this is intriguing because the polymers themselves are
insulators (CRT < 10‘6 S/cm) and MoS2 is a semicondutor (CRT = 10'5
S/cm). On the other hand, it is not so surprising that the room temperature
conductivity of (PANI)0,35M052 is high (0.4 S/cm). Even though we
started with neutral PANI, it is possible that protonation of the polymer
occured during the reaction to yield the conductive emeraldine salt.
Variable temperature electrical conductivity measurements for
(PEO)1_oMoS2 (MW = 100,000), however, indicate a suprisingly high
conductivity value as shown in Figure 3.20a. In the temperature range 50-
300 K, the material exhibits thermally activated behavior. Variable
temperature electrical conductivity measurements cannot conclusively tell
whether the material is a semiconductor or a metal since the measurements
were done on a pressed pellet and, as such, interparticle resistance cannot
be eliminated. However, variable temperature thermopower measurements
give more insight into the nature of the conductivity. Since it is a non-zero

current technique, interparticle resistance is less important. The

166

thermopower data of (PEO)1,0M082 indicate that the material is a p-type
metallic conductor, as observed from the very small and positive Seebeck
coefficient (Figure 3.20b). A marked feature in both the conductivity and
the thermopower is an abrupt, well-defined transition at ca. 14-15 K.
Below 14 K, the conductivity decreases by six orders of magnitude while
the thermopower suddenly discontinues its upward slope and drops to

negative values.

167

 

 

 

A l
g Q atlnnmiwt .i 1
$73. 3; 5 '
b 6 ((1% ((5 I r
g : 7 i ({5} i i
3 AH l
J '8 g, {1“ l
e 4 9 l 1
1H 1
101i?) (1‘1 .1....1-..a..t_ r .l. .
l o s 10 15 20 25
L T (K)
-12 _l_.-._L__--..-L. -1..- 1-----1.__-1___1___l-_._L- l l
0 50 100 150 200 250 300

Temperature (K)

 

 

 

 

 

g
>
3-
3
3
E
O
.C
F. -31”
-4.511)l1.1111111.LLillttiLtLl_i_llr
0 50 100 150 200 250 300

Temperature (K)

Figure 3.20 (a) Variable temperature conductivity data of (PEO)1.0M0S2
and (b) variable temperature thermopower data of (PEO)1.OM082.

168

Log 0 (S/cm)

 

 

 

l 1 l 1 l l L 1
50 100 150 200 250

Temperature (K)

Figure 3.21. Variable temperature conductivity data of (PEI)0_33M082.

169

 

 

 

 

 

{3_
E? _
b l—
a -7_
_J ..

-9...

.11_ 1 l 1 l 1 l 1 l 1 l 1

0 50 100 150 200 250 300

Temperature (K)

Figure 3.22. Variable temperature conductivity data of restacked M082.

170

 

 

 

 

-1.5
:2 1 ($0
\ <9)
i -2 0 )— CI% 0
O
O 0
£31 ~ wo$®m 525493
0 " (9
g ~ dbmo Cb
g .2 5 _ @353
" r 5 Q90
0
~ 0cm?
-3.0 L i L l J l L 1 1 PL 1 l l l l l L 1 L l 1 1
so 100 150 200 250 300

Temperature (K)

Figure 3.23. Variable temperature thermopower data of restacked MoSz.

171

This type of behavior is not typical for a normal metal. However, a
similar anomalous decrease in conductivity at low temperatures has been
reported for certain layered metallic dichalcogenide phases when doped
with metal ions, e.g lT-Tio,035Tao.91582, 1T-Nbo,15Tao,3582, 1T-
Hfo,035Tao,91582 [27]. The metal to insulator transition in these systems has
been attributed to a charge density wave (CDW); a coupled periodic
distortion of the conduction electron density with respect to the crystal
lattice [28]. Even though the nature of the transition is not well-understood
at the moment, we believe that a similar CDW effect might be operative at
low temperature (<14 K), creating an electronic instability. The charge
transport properties of (PEI)0,33M082 was found to be similar to that of
(PEO)1,0M082. The room temperature conductivity of (PEI)0_33M082 is
high (0.1 S/cm) and it also shows a metal to insulator transition at ca. 14 K
as can be seen from its variable temperature conductivity data (Figure
3.21).

Variable temperature electrical conductivity measurements were
performed on plain restacked M082 (Figure 3.22). The measurements were
done on pressed pellets. The conductivity was high reaching a value of 0.01
S/cm at room temperature. Interestingly enough, in restacked M082, no
abrupt transition corresponding to a metal to insulator transition is
observed in the variable temperature electrical conductivity data (Figure
3.22). This is attributed to the fact that the sample was somewhat aged.
This was also observed in an aged (PEO)1,0M082 sample, where the metal
to insulator transition was no longer observed.

Variable temperature thermopower data were also measured on
restacked MoSz (see Figure 3.23). The data show that the values are very
small and negative (2.7-1.8 uV/K) in the temperature range 80 - 300 K.

172

Therefore, contrary to (PEO)1,0M082 and (PANI)0,35M082, restacked

M082 is an n-metal.

3.4.4. Structural Transformation of M082 layers upon

Intercalation

The metallic character of (PEO)1,0M082, (PANI)o,35M082,
(PEI)0,33M082 and restacked M082 is explained by considering the
structure of MoSz in these materials. Pristine 2H-MoSz undergoes a
structural transformation upon intercalation with lithium in which the
coordination of Mo3+ atom becomes octahedral from trigonal prismatic
[23a, 29]. The band diagram of 2H-MoSz indicates that it is a
semiconductor [30] (Figure 3.24a). In 2H-MoSz each layer will be referred
to as D3h-M082. Upon reaction of LiMoSz with water, single M082 layers
form by rapid oxidation which leaves the Mo4+ atom trapped in an
octahedral coordination, thereby stabilizing a metastable structure for an
MoSz layer. Thus the latter is a kinetic product. Scheme 3.5 compares the
stability of the various M082 phases. In the metastable structure of MoSz,
each MoSz layer will be referred to as Oh-M082. Figure 3.24 shows the
qualitative band diagram associated with the D3h-M082 and Oh-M082
layers. The trigonal prismatic modification develops a band gap between
the filled dz2 and empty dx2-y2, xy band. In the octahedral modification the
dxy, dz2 and dx2-y7- orbitals overlap to form a single band which is
populated by two electrons, producing a metallic system [31]. Figures 3.25
and 3.26 show the proposed structure of MoSz in the Oh form. This

structural modification of M082 is analogous to the structure of CdIz or

173

Ti82. This structure is referred to as lT-MoSz, where the 1 implies that
there is one layer per unit cell and the T stands for the fact that the layers

form a two-dimensional lattice of trigonal symmetry.

174

 

 

 

835...— 2.25—
223588
5.31%: 29.5

.8339 «mo—z Set? .«o @523. 3:23— .m.m 0.5—Em

 

 

 

 

 

 

 

 

 

 

. _
N... :
mm“ . W.
o< o? .mxdxvu
me
Q» £ch
:O SM:

283.398 Aosaemta _acowEv

£22: «mezim

175

\
I

(A) (B)

j Mo-S antrbonding ’12

j dyz. xz band

 

d xz,yz band

> dxz-y2.xy band

band-gap E g

>
U)
L.
Q)
C
LU

Energy

 

‘

7 7
dx'-y“. xy. 2' band

 

 

d 22 band

 

 

Mo-S
bondmg

 

Density of States Density of States

Figure 3.24. Comparison of qualitative band diagram of (A) ZH-MoSZ with
that of metastable lT-MoSz (B),(shaded bands are filled).

176

 

 

 

Figure 3.25. Structure of 1T-MoSz, looking parallel to the layers.

177

 

 

Figure 3.26. Structure of 1T-MoSz, looking perpendicular to the layers.

178

Differential Scanning Calorimertry (DSC) studies on our restacked
Oh-M082 layers show that the layers transform to the thermodynamically
more stable form (D3h-form) at ca. 100 0C, by observation of an
exothermic peak at that temperature (Figure 3.27). The transition is
irreversible with constant mass. It is interesting to note that the transition is
very broad, the peak width at half height being ca. 55 0C. The
transformation from Oh-M032 to D3}. could also be probed by conductivity

measurements of heated samples. For example restacked M082 (CRT = 0.1-
0.4 S/cm) goes insulating upon heating under vacuum. Variable
temperature magnetic susceptibility measurements show a dramatic drop in
susceptibility values for the heated sample (Figure 3.28b). The unheated
sample shows a temperature independent Pauli-like paramagnetism in the

temperature range (50-100K) (Figure 3.28a). All these experimental
observations are consistent with the transformation from Oh-M082 to D3}.
-MoSz.

179

 

101°C

o>

mW "exothermis
C.) O
A
N 01
1 l

I
0
oo
01

l

l J

 

 

 

.. endothemg

—L
o
01
l
d
.1

I I I I I I I I I l I I I

50 81.25 112.5 143.75 175
Temperature(°C)

Figure 3.27. DSC of restacked M032.

180

 

 

 

 

 

 

 

 

0.0on! (a)
1-
E
N I
,-
I
I
U
Mal-M..-
o.ooeo - . . , . A
o 100 200 300
Temperature (K)
1.00e-3
8006-4
0))
6.00e-4
:a
I
4.008-4‘3
E d-
.. ‘1.
2.00e-4‘ |
.
. ”GM-u... .
5296-23" "llaflnaur
-2.00e-4 ' I ' I f
0 100 200 300

Temperature (K)

Figure 3.28. (a) Plot Xm versus temperature for (a) restacked M082 and (b)
heated restacked MoSz under vacuum at 185 0C.

181

Recently, Wypych and Schollhorn reported the preparation of IT-
MoSz from a different method [32]. The steps in the preparation are
outlined in Scheme 3.6. First the synthesis of KM082 was achieved in a
series of steps. KzMoO4 was reacted with dry hydrogen sulfide for 12
hours and subsequently at 470 0C for 12 hours. The resulting product was
reduced at 850 0C with a mixture of hydrogen and nitrogen for 72 hours to
form the black KMoSz. The latter was repeatedly washed with water until
the washings were almost neutral. The washing process causes a partial
oxidation of KMoSz, forming the hydrated phase K1-x(H20)yM082. The
hydrated layered chalcogenide was thereafter oxidized to M082.
Preliminary single crystal X-ray data of the product indicates that the
compound has a distorted layered structure where the molybdenum is
coordinated to the sulfur atoms in an octahedral fashion. This new IT-
MoSz was found to be metallic from its thermopower data and Pauli-like
paramagnetism. The lT-phase is metastable and reverts to the 2H form on

heating. The structural change was probed by DTA. An exothermic peak

was observed at ca. 95 0C. Our conclusions is that our restacked M082 and
Schollhom's 1T-MoSz are one and the same product.

Interestingly, the conversion temperature varies depending on the
polymer involved and the associated d-spacing. (PVP)0,76MoSz shows the
highest conversion temperature and plain restacked MoSz the lowest. Table
3.4 tabulates (polymer)xM082 phases along with their corresponding d-

spacings and the maximum temperature at which the structural conversion

(Tc,Max) took place as determined from DSC experiments. Figure 3.29
shows a plot of d-spacing as a function of Tc(Max). The heating rates in the
DSC experiments were kept fixed at 5 0C. These data suggest that

communication between the layers is somehow important in

182

.NmoE-t m.Eo£E:om go cocmccfl 2t 9 mafia“: 33m .c.m oEocom

game-.093.- -5mmd + Nm2). A .......... «mafiagomzvmnf .o

mIm\x + IOXx + mwo§>AOmva-Fx A ....... ONT. 3 +x V + mmofix .m

0 0mm 2: E .u at.
mmosi A115. ........ 6: 0605-115 ----- m + v o m .
$9 312%: u Emiuoomm m I O _2 x <

183

 
  
 
   

   

 

 
 

 

 

 

 

 

I D-Spacing (A) 1 To (Max., 0C) *
Restacked MoSz 6.2 101
(PEI)0,33M082 10.2 127
(PPG)0,5M082 14.6 144
(PEO)1,oMoSz 14.7 138
(Mcel)0.26M032 20.4 141
(PVP)0,76M032 21.0 165

 

 

 

 

 

Table 3.4, Showing TC(Max, 0C) for various MoSz systems. Heating rate

was kept fixed at 5 OC/min.

184

 

Dspacing(A)

 

 

 

1 I I I l I I I I I I I I I I I l I—I

100 120 140 160 180
Tc(max), °C

Figure 3.29. Plot of d-spacing as a function of Tc(Max).

 

200

185

facilitating the Oh ---> D31. transition. How this happens, however, is not

well-understood.
Upon aging, lT-MoSZ reverts to the more stable semiconductive

form. This is consistent with our observations that an aged (PEO)MoSz
sample shows three orders of magnitude lower conductivity compared to a
freshly prepared sample. However, the transformation from O1, to D3}, is
slow and seems to take months to complete. The increase in resistance of
the sample with time is correlated with the kinetically slow transformation
of Oh-M082 to D3h-MoSZ. On the other hand, an increase in temperature
greatly accelerated this transformation. This is reflected in the observed
low conductivities of (Nylon-6)3.5M082 and (polyethylene)3.oMoSZ which
were synthesized by refluxing the respective reaction mixtures. In these
samples the M082 layers are mostly in the D31. form.

Since the structural transformation occurs even at room temperature

we decided to probe the activation energy (Ea), of the transformation. A
convenenient way of measuring Ea is from DSC experiments. This is a
standard method approved by the American Society for Testing of
Materials (ASTM) [33]. The position of exothermic or endothermic peaks
as observed from DSC experiments, shift to higher temperatures with
increasing heating rates. The data can usually be fitted in an Arrhenius type

equation (Eq. 9).
ln([3) = -Ea/RT + A ---------- Eq. 9

where, [3 is the heating rate in K/min., E, is the activation in J/mol, R is the
molar gas constant (8.131 J mol-1 K'l), T is the maximum temperature at

which the exothermic or endothermic peak occurs and A is a constant.

186

If a straight line graph is obtained then, Ea can be extracted from the

slope of the curve. Successful applications of this method have been made
by Rai et al. [34]. From the dependence of the glass transition and
crystallization temperatures on the heating rate, the activation energy for
structural relaxation and the activation energy of crystallization were
determined for a number of Se-Te glassy systems. In separate work,
Pinnavaia et al. were able to determine the activation energy for the self-
polymerization of an epoxy resin [35].

For restacked MoS2 with increasing heating rates, the conversion
temperature shifts to higher values (Figure 3.30). The results from these
experiments are tabulated in Table 3.5. The data were fitted in the
Arrhenius equation (Eq. 9) and a straight line graph was obtained as shown
in Figure 3.31. From the slope of the graph the activation energy was
calculated to be 0.68 Kcal/mol (2.85 KJ/mol). The low value of the
activation energy is not surprising since the structural transformation
occurs at room temperature as probed by conductivity measurements.

A similar set of experiments were performed on (PEO)MoSz. Figure
3.32 shows DSC curves of (PEO)MoSz at various heating rates. The results
from this set of experiments are tabulated in Table 3.6. The data fit very
well in the Arrhenius equation and the resulting curve is shown in Figure
3.33. For (PEO)MoSz the activation energy was calculated to be 0.77
Kcal/mol, a slightly higher value. It seems that Ea increases with d-spacing.
This hypothesis was verified by doing a similar set of DSC experiments on
(PVP)0,76M082, the polymer/M082 nanocomposite with the largest d-
spacing. The Ea calculated for this material was found to be 1.06 Kcal/mol.
Table 3.7 summarizes the activation parameters calculated for the different

nanocomposites. These DSC studies suggest than a higher d-spacing

187

1 1

11111111111111_

3'

1 111111111111111111111
>5
0.
A A
0 v (D

 

1111111111L1144111111141111 111111111111L1

(a)

rlrrrrrrrrrlrrrrrrrlIrrrrrrm

100 150 2:10
Temperature (00)

UI
0

Figure 3.30. DSC of restacked MoS2 at heating rates of (a) 5 (b) 10 (c) 15
(d) 20 and (e) 25 OC/min.

188

.Nmo—z 33083. :o 863m 38:: 88.. 353% 2:52 .3 baa—Ezm .m.m 033—.

 

 

 

 

 

 

 

 

 

 

 

 

Sat >4 mm SN 5 2; mm
Ade ONT hm com S. m: cm
And: Wm mm 9: we vfi 3
8.2V mm mm #2 an 5: 2
8%: in mm we we z: m

22:5: .8582 Ewe; :2 a

3.5.6 3.23m 523 see.

 

68286... 68:88.

 

 

Gov
2am wage:

 

189

 

 

a = 0.68 Kcal/mol (2.85kJ/mol)
5. 68 -:

ln(heating rate)

 

 

 

d
d
1
5,62 IITIWIIIIIIIIIIIII

0.0024 0.00245 0.0025 0.00255 0. 0026
T.1(K )

Figure 3.31. Arrhenius plot for restacked M082.

190

(

3-

Egg

3

mW
1111111111111114111111111111111111441
>5
0" o

 

 

rrrrrrrrrlrrrrrj

so 92.5 135 177.5 220
Temperature (00)

Figure 3.32. DSC of (PEO)MoS2 at heating rates of (a) 5 (b) 10 (c) 15 (d)
20 and (e) 25 OC/min

191

.NmoS—QXOmn—v :0 3:5: 0:25— .55 cosine 2.32 we bus—83m .cd 035.

 

 

 

 

 

 

 

 

 

 

 

 

 

on 2.2V 9m NNN an :L WN

cm 363 Ram CNN mm m3 om

5m Cum: m.m com me o2 2

mm 3%: 5m mom 3. .9 o—

Nm . 3%: Wm X: E. wmfi m

Se 8.3V Ym >2 we we: _
935.33 324.353 uq we. as 3.595
game 55% gees-a. 4551:3521. 5.1553 51.5.1552

 

 

192

 

5.8

.
5.759

S”
V
1..

11L1

.1

111111

ln(heating Rate)
01
or m
a ‘1‘

555-}

4

Ba: 0.77Kcal/mol (3.24 KJ/mol)

 

 

5.5% .-

I I I I

0.00225 0.0023 0.00235 0.0024 0.00245

I I

 

[ I I I I I fij I I

Tc"(K'l)

Figure 3.33. Arrhenius plot for (PEO)1.oMoSZ.

 

193

   

 

 

Restacked MoSz 6.2 0.68 (2.85)
(PEO)1.oM082 16.3 0.77 (3.24)
(PVP)o.76M0$2 21.1 1.06 (4.42)

 

 

 

 

 

Table 3.7. Summary of activation parameters measured for various M082

systems.

194

stabilizes the Oh-M082 structure, by rendering communication between the
layers increasingly more difficult. The relatively low activation energy of
the Oh ---> D31, transition can be explained by the relatively facile nature
of this process. This is because the transition involves a change in the
atomic layer stacking sequence which in Oh is ABC type (for every atomic
S, Mo, S layer) while for D3), is ABA type which can be achieved by a
simple slippage of a single 8 atom layer by a unit cell along the a-axis.

We do not observe melting and recystallization of the polymers in
our DSC experiments for most of the nanocomposites prepared, except for
(Nylon-6)3,6M0S2 and for (polyethylene)3,oMoSz (vide infra ). For
instance, the DSC of (PEO)1,0M082 shows no melting and recrystallization
of the intercalated PEO. This suggests that the structure of the intercalated
polymer has altered. Bulk PEO itself melts at 73 0C and recrystallizes at 48
0C (Figure 3.34).The discrepancy between these two temperatures is due to
thermal lagging. For (Nylon-6)3,6M082 and (polyethylene)3,oMoS2 the
observed melting and recrystallization are from the polymer molecules
outside the MoS2 particles. It is very difficult to wash the excess Nylon-6
and polyethylene used. As mentioned above, no broad exothermic peaks
corresponding to the structural transformation from Oh-MoSZ to D3},-
M082 are observed in the DSC of these materials since they were prepared
at high temperatures. Both (Nylon-6)3,6M082 and (polyethylene)3,oMoSz
show endothermic peaks at 220 0C and 150 0C respectively, which are due
to melting of the externally lying polymers. Upon cooling, exothermic
peaks are observed at 201 0C and at 122 0C, which correspond to

recrystallization of the respective polymers (see Figures 3.35 and 3.36).

195

 

 

 

 

 

 

09 2.5‘ 48°C
E2: : J
E 0.125‘ W
- [s

E -2.25-
'53 «
gé-4.625‘ “
5: ‘
5; ‘
V ‘ 73°C

-7 IIIIIIIIIIIIIIIIIIITIIIIlIIIIlIIIr

 

 

0 50 100 150 200 250 300 350
Temperature (°C)

Figure 3.34. DSC of bulk PEO.

196

9
u.

 

O
l

”.2229113551119,

.9
LII
l

 

220°C

 

‘sadethsms mW
T

I
u—e
u.

 

IIIITIIIIITIIIIIIIIIIIII[IrjIlIII

50 100 150 200 250 300
Temperature (°C)

0

Figure 3.35. DSC of (Nylon-6)3,6MoS2.

 

350

197

 

 

 

 

 

3

1 122°C

.25 2-

5: 17

O.

:31 0

3 -

E 1

.25 ‘2'

E3

51-3"

as

81 '4‘

V 150°C
‘5 IIII1ITIIrTIIIIIIrIlIIIIIIIIIIIIIF

 

0 50 100 150 200 250 300 350
Temperature (°C)

Figure 3.36. DSC of (polyethylene)3,oMoS2.

198

3.4.5. Structural Distortion in Oh-M0S2

The band diagram proposed for Oh-M082 (Figure 3.24b) is for an
idealized situation where it is assumed that the Mo atoms are bonded to the
S atoms in a perfectly octahedral configuration. The band diagram shown
in Figure 3.24 indicates that restacked M082 and polymer-intercalated
samples such as (PEO)1,oMoS2 and (PANI)0,35M082 should be n-type
metals. However, experimentally from therrnpower studies it was shown
that polymer-intercalated phases such as (PEO)1,oMoS2 and
(PANI)0,35MoS2 exhibit p-type metallic character. To account for the
observed p-metallic character, a strong structural distortion of the
octahedral environment in Oh-MoS2 is proposed. An elongation of all the
Mo-S bonds (trigonal distortion), would result in splitting of the dx2-y2,
xy,22 band into two bands, one with lower energy namely, the dx2-y2,xy
band and the dz2 band with higher energy (Scheme 3.7). The dx2-y2,xy
band is half-filled and as such the charge carriers can be either electrons or
holes. The type of carrier responsible for charge transport in such a
situation would be dictated by the mobility of the electrons versus holes.
Thermopower studies show that restacked M082 is an n-metal suggesting
that the electrons are more mobile than the holes in this material. On the
other hand, in polymer-intercalated phases such as (PEO)1_0M082 and
(PANI)0,35M0$2, the holes are moving faster than electrons which give
rise to their p-metallic character. The structural distortion proposed in Oh-
MoSz can further be used to explain the metal to insulator transition
observed in (PANI)(),35MoS2, (PEO)1,0M082 and (PEI)0,33M082. The
half-filled dx2-y2,xy band as shown in Scheme 3.7, is unstable and can

therefore be further split up into two bands, the d,y band of lower energy

 

 

 

(Peierls
populate
Clearly-
propose:
our syst

not full)

199

(Peierls type distortion or charge density wave) which is completed
populated by electrons and the empty dx2-y2 band of higher energy.
Clearly, this type of situation gives rise to an insulating state. Hence, this
proposed model can explain the metal to insulator transition observed in
our systems. Why this reversible transition occurs at low temperatures is

not fully understood.

200

 

 

 

 

 

 

 

 

 

 

'11
de-yz- xy- 22 band /cl-(2 3,3 band)
)5
9..“
3 \
m “I 7 band gap
de-yz. xy band
(halt-tilled)
117 i D
dxy band

 

 

Density of states

Scheme 3.7. Splitting of the dx3-y2,xy,z7- band. due to structural distortion

and the dx2-y3, xy band due to the Peierls type distortion in Oh-MoS2.

201

3.4.6. Effect of Pressure on Conductivity of (Polymer)xMoS2

samples

During the course of the our DSC experiments, we found out that if
too much pressure is applied while crimping the DSC cell, no exothermic
peak corresponding to the transformation from Oh-M082 to D3h-M082 is
observed. Therefore, in addition to temperature, pressure is also
responsible for inducing the structural transformation. To confirm our
observations from DSC experiments, the conductivity of a (PEO)MoSz
pressed pellet (diameter: 1.2 cm) was probed as a function of increasing
pressure. From 8.8 x 106 lbs/m2 to 8.8 x 107 lbs/m2 of applied pressure,
the resistance of the sample stays virtually constant at a value of ca. 40
ohms. From 8.8 x 1071bs/m2 to 1.9 x 108 lbs/m2 of applied pressure the
resistance of the sample increases slowly. But an abrupt increase in
sample's resistance to 6048 ohms is observed at 2.0 x 108 lbs/m2. Figure
3.37 shows the plot of sample resistance as a function of applied pressure in
lbs/m2

202

 

 

 

 

7000

a 6000- O

E 5000-

9

a) 4000-

8

3 3000-7

m

'53 2000-

o

9‘ 1000- .

0..

054mm, - - -
0 11108 2‘108

Pressure (Pounds/m2)

Figure 3.37. Plot of resistance of a (PEO)1,0M082 sample as a function of

applied pressure. The resistance was measured by the four-probe method.

203

3.4.7. Magnetic Susceptibility Measurements

The magnetization of the samples as a function of field, B (gauss)
were measured and they all saturate with increasing field strength as shown
in Figures 3.38, 3.39 and 3.40. Variable temperature magnetic
susceptibility measurements on the (polymer)xM082 samples were
performed at high field in the saturation portion as determined from the
magnetization curves. Figures 3.41- 3.46 show the Xm and Xm’l plots, both
as a function of temperature, for the (polymer)xM032 samples. All samples
exhibit complex, non Curie-Weiss behavior. The spins/mol of all samples at

room temperature were calculated by using Equation 10 shown below

N = M.MW/g13Sm ------- Eq. 10

where M is the magnetization of the sample at various temperatures in
electromagnetic unit (emu), MW is the molecular weight of the sample, g is
the g-tensor for the free electron (2.00), B is the Bohr magneton constant
(9.1 x 10 '21), S is the spin of a free electron (1/2) and m is the mass of the
sample in grams.

The calculated spins/mol values are roughly of the same order of
magnitude for all samples as shown in Table 3.8. The rather low spins/mol
values of these materials are consistent with their metallic character. Since,
all the polymers are insulators, the calculated number of spins are from the
metallic MoSz layers which are in the Oh structural form. Of course the
presence of a small amount of paramagnetic impurities cannot be ruled out.
Magnetic susceptibilty measurements on restacked MoS2 and on

(polymer)xM082 samples provide supporting evidence that the M082 layers

1116381111 -

 

 

204

in these materials are in the 0}, form. In contrast, magnetic susceptibility

measurements on 2H-MoSz show that it is a diarnagnetic material.

205

 

 

 

0.0045 1 1 1 -

g o.o0337-
: . 0 Temperature: 300K 1
.2 1 1
3 o.o0225~ r
.22. 18 (a) 1
~ ‘ 1
0) -
ED 1
5 0.00112
2

61>

O 1 r F T m r"
o 4000 sooo 12000 15000 zoooo

Field (gauss)

0.” 1111111LL1111111L11l
(b)

0000000
00 0000000

0.0015: ° _-

 

IIIVT

IIIT
O

4 o Temp.= 300 K
0.001 c

1 1

11L1

Magnetization (emu)

0.0005 -

r.
'0
'0
O

T

 

J 1 1 1

 

 

O I I I I I I— I I r I I I I I I I l I I I

o 4000 8000 12000 16000 20000
Field (gauss)

Figure 3.38. Magnetization of (a) (PANI)035M082 (b) (PEO)1,0M082 as a
function of field in gauss.

 

 

 

 

 

 

 

 

')m11111L41114L14LL1111L
' - a a a a a a
A " E) a a a a
D - El 3 E!
E 0.0008- El 13 a a
3 - a
.5 ~ (3) 1'
13 00006-1 a 1
fl 4
ac: T - 300 K ‘
a, 0.0004 emp- — ‘-
re
2 I
0.0002 —
01 I I I I I I I I I I I l I I I r I I I
0 4000 8000 12000 16000 20000
Field (gauss)
0.05
Gain-.3..--...'.-
0.04- l
’5
5 (b)
: °~°3‘ Temp. = 300 K
.9- 1
3 u
N
g: o.o2
o
=
on
a
2 0.01
0.00 . r , . , f
10000 20000 30000
Field (gauss)

Figure 3.39. Magnetization of (a) (PPG)o,5MoSZ and (b) (PVP)o,76MoS2

as a function of field in gauss.

207

 

 

 

 

 

 

 

 

one
(a)
I a I I a a
; a I a I I I
E 0.02 4 a
3 I
2 Temp. = 300 K
I:
a
N
'5
2 0.01 - a
on
a
2
0m #— V r T r f
0 10000 20000 30000
Field (gauss) '
0.003
1 I I I I I (b)
A . I . - . . . .
3 .'l..
E I
3 0.002 1
= I
.2
_3 1. Temp. = 300 K
3
E
5‘ 0.001
2
0.000 f - - - r -
0 10000 20000 30000
Field (gauss)

Figure 3.40. Magnetization of (a) (MCel)o,26M'082 and (b) (PEDo,33MoSz

as a function of field in gauss.

208

 

0.002:

Xm

 

 

0.0015 1

0.001 “

 

 

 

 

0.0005? T I I l I fil—
0 50 100 150 200 250 300

Temperature (K)

 

  

600

 

.5
O
O

1AJ111J111

TIIIIUIIIIIIITTTIIITTIF

 

 

 

200 T I I l l
0 50 100 150 200 250 300

Temperature (K)

Figure 3.41. (a) Plot of 1m versus temperature for (PANI)o,35M032

(b) Plot of Xm '1 versus temperature.

209

 

0.007
0.006 :
0.005 -

I

0.004

Xm

0.003

 

0.002

 

 

 

O 001 1 1 l l 1
0 50 100 150 200 250 300

Temperature(K)

550
500
450

 

350
300 ..
250 g
200 T

150 l l l I l l
0 50 100 150 200 250 300 350
Temperature(K)

Xm' 1

 

 

 

 

Figure 3.42. (3) Plot of Xm versus temperature for (a) (PEO)1,oM082 and

(b) the corresponding xm'l versus temperature plot.

210

 

 

 

 

 

 

 

 

I (a)
I
0.002 " I
I
I
I
. I
5 u
I
0.001 - ‘5.-
I
..-. . I . I I . ' I .
0.000 I - v - fl
0 100 200 300
Temperature (K)
2000
(b) . I '
«I I I u
I ' I
I.-
f"
3 1000‘ .-
I
I
I
0 . r - . -
0 100 200

Temperature (K)

Figure 3.43. Xm versus temperature plot for (PPG)o,5M082 and (b) the
corresponding xm'l versus temperature plot.

211

 

 

 

 

 

 

 

 

0.0025 f r l l r w TL
0 50 100 150 200 250 300
Temperature
4 L L l l l L
001 E
« L-
350: f
1 C
300% r
250% E
x i _
200i 3
j b-
‘ I
150 I l I I I
o 50 100 150 200 250 300
Temperature

Figure 3.44. (a) Plot of Xm versus temperature plot for (PVP)0,75M082

and (b) the corresponding Xm'l versus temperature plot.

212

 

 

 

 

 

 

 

 

 

o.oor
0.005 (a)
+I
I
I'-
0.004-1
a
R
.I
0.0034 'I-.
I a . . a
I I
0.002 , - , f j
0 100~ 200 300
Temperature (K)
400
I, u 1
(b) I a I I
I
4 -' i
I.-
300" ll
.7
5
-
zoo-E
100 I . I
0 100 200 300
Temperature (K)

Figure 3.45. (a) Xm versus temperature plot for (MCel)o,25M082 and (b)
the corresponding Xm'l versus temperature plot.

213

 

0.0012 "
0.0010

0.0008

Xm

 

 

 

 

0.0000 . r . , . _1
0 100 200 3m

Temperature (K)

 

 

 

 

 

 

r Y

0 100 200 300

Temperature (K)
Figure 3.46. (a) Xm versus temperature plot for (PEI)0,33M082 and (b) the

corresponding xm'l versus temperature plot.

214

  

Spins/formula unit

    

 

 

 

 

 

(PANI)0,35M052 1.5 x 1021 0.0025
(PEO)1,0M032 1.7 x 1021 0.0028
(PPG)05MOSZ 1.3 x 1021 0.0022
(PVP)0.76M032 2.3 x 1021 0.0038
(Mcel)o,23MoSz 6.0 x 1021 0.01

(PEI)0,83MOSZ 6.9 X 1019 0.0001

 

 

 

 

 

Table 3.8. Spins/mol values of various (polymer)xMosz samples calculated

from field dependent magnetization curves.

215

3.5. Conclusions

This work shows that the direct intercalation of polymers into MoSz
is possible by using the exfoliation and restacking property of M082. This
method of direct insertion is superior to the technique where the monomers
are first inserted and then polymerized by external sources. The latter
technique results in low molecular weight polymers and in other side
products that have to be dealt with as was clearly illustrated in Chapter 2.
With the former technique, potentially very large molecular weight
polymers can be encapsulated in the lamellar host as was demonstrated by
the insertion of ultra-high molecular weight polyethylene into M082. Even,
highly oxidizing hosts such as FeOCl and V205~nH20 which are capable of
undergoing in-situ intercalation/polymen'zation reactions do not lead to
high molecular weight polymers.

The high electrical conductivities of the (PEO)1,oM082,
(PEI)0.33MoSz and (PPG)0,5M082 with respective values of 0.1, 0.1 and
0.2 S/cm are among the highest reported among polymer/host
nanocomposites. These materials can offer two advantages as cathodes in
solid state high energy density batteries. First, the encapsulated polymers
when coupled with Li would provide the desired high conductivity for Li+
motion in the cathode material and second, the high electronic conductivity
of the layers would obviate the addition of conductive additives such as
graphite and carbon black.

Since, the conductivity of the polymer/host nanocomposites
disappears upon applied pressure, they may have potential as pressure
sensors. In addition, these nanocomposites could be used in the fabrication

of novel temperature switches for a number of applications such as quality

216

control and remote environmental monitoring, since they lose their
conductivity irreversibly with increasing temperature. The prospects for
such applications would be significantly brightened if a way was found to
stabilize the Oh-M082 over time. The conductivity of the nanocomposites
could also be exploited for potential applications including, electromagnetic
shielding, antistatic mats and coatings.

The exfoliation/restacking property of M082 has been exploited to
produce novel lamellar nanocomposite materials. The method appears to be
general and should apply to a large variety of other soluble polymers
including conductive polymers via soluble precursor routes such as poly(p-
phenylene vinylene) and poly(p-phenylene) [36]. The methodology
described here works very well for polymers and small molecules [21a]
and it should work equally well for other species such as organometallic

compounds, liquid crystals, organic dyes and molecular clusters.

217

REFERENCES

[1] (a) Day, P.; Ledsham, R. D. Mol. Cryst. Liq. Cryst. 1982, 8Q, 163-
174. (b) Tieke, B. Mol. Cryst. Liq. Cryst. 1983, 21, 119-145. (c) Cox, S.
D.; Stucky, G. D. J. Phys. Chem. 1991, 21, 710-720. ((1) Pereira, C.;
Kokotailo, G. T.; Gorte, R. J. J. Phys. Chem. 1991, 25, 705-709.

[2] (a) Enzel, P.; Bein, T. J. Phys. Chem. 1989, 23, 6270-6272. (b) Enzel,
P.; Bein, T. Chem. Mater. 1992, 5, 819-824. (c) Enzel, P.; Bein, T. J.
Chem. Soc., Chem. Commun. 1989, 1326-1327. (C!) Bein, T.; Enzel, P.
Angew. Chem., Int. Ed. Engl. 1989, 23, 1692-1694. (e) Pillion, J. E.;
Thompson, M. E. Chem. Mater. 1991, 3, 777-779.

[3] (a) Nazar, L. F.; Zhang, Z.; Zinkweg, D. .I. Am. Chem. Soc. 1992,
LIA, 6239-6240. (b) Mehrotra, V.; Giannelis, E. P. Solid State Ionics
l992,5_1, 115-122. (c) Mehrotra, V.; Giannelis, E. P. Solid State
Commun. 1991, 11, 155-158. ((1) Soma, Y.; Soma, M.; Harada, 1. Chem.
Phys. Lett. 1983, _92, 153-156.

[4] (a) Okada, A.; Kawasumi, M.; Kurauchi, T.; Kamigaito, O. Polymer
Prepr. Am. Chem. Soc., Div. Polym., 1987, E, No. 2, 447. (b) Okada, A.;
Kawasumi, M.; Usuki, A.; Kojima, Y.; Kuraughi, T.; Kamigaito, 0. Mat.
Res. Soc. Symp. Proc. l990,_1_7_1, 45-50. Okada, A.; Kawakado, M.
Japanese Patent Application No. Sho 60 [1985]-217396.

218

[5] (a) Kanatzidis, M. G.; Wu, C.-G.; Marcy, H. 0.; Kannewurf, C. R. J.
Am. Chem. Soc. 1989, l_1_1_, 4139-4141. (b) Wu, C.-G.; Kanatzidis, M. G.;
Marcy, H. 0.; Degroot, D. C.; Kannewurf, C. R. Polym. Mater. Sci. Eng.
1989, Q, 969-973. (c) Kanatzidis, M. G.; Wu, C.-G.; Marcy, H. 0.;
Degroot, D. C.; Kannewurf, C. R. Chem. Mater. 1990, 2, 222-224. ((1)
Kanatzidis, M. G.; Tonge, L. M.; Marks, T. J. J. Am. Chem. Soc. 1987,
L02, 3797-3799. (e) Kanatzidis, M. G.; Wu, C.-G.; Marcy, H. 0.;
Kannewurf, C. R. Adv. Mater. 1990, 2, 364-366.

[6] Greenwood, N. N., Eamshaw, A. Chemistry of the Elements,
Pergamon Press, 1984, p 1168.

[7] Weisser, O. and Landa, S. Sulfided Catalysts, Their properties and
Applications, Pergamon, New York, 1973.

[8] Fleischauer, P. D. Thin Solids Films 1987, 1%, 309-322.

[9] Wieting, T.; Werble, J. Phys. Rev. 1971, g}, 4286.

[10] (a) Tributsch, H. Faraday Discuss. Chem. Soc. 1980, 10, 190-205. (b)
Julien, C.; Saikh, S. I.; Nazri, G. A. Mater. Sci. Eng. 1992, B15, 73-77.

[11] (a) Whittingham, M. S. Prog. Solid State Chem. 1978, _1_2, 41-99. (b)
Murphy, D. W., Christian, P. A. Science 1979, 205, 651-656. (c)

Whittingham, M. S. J. Electrochem. Soc. 1976, 1_2_§, 315-320.

[12] Whittingham, M. S. J. Electrochem. Soc. 1979, 22, 303-310.

219

[13] (a) Schollhom, R.; Weiss, A. J. Common Met. 1974, 36,, 229-236. (b)
Somoano, R. B.; Hadek, V.; Rembaum, A. J. Chem. Phys. 1973, 58, 697-
701. (c) Somoano, R. B.; Hadek, V.; Rembaum, A.; Samson, S.; Woollam,
J. A. J. Chem. Phys. 1975, 62, 1068-1073. ((1) Somoano, R. B.; Rembaum,
A. Phys. Rev. Lett. 1971, 21, 402-404. (e) Rudorf, V. W. Chimia 12, 489-
499.

[14] (a) Gee, M. A.; Frindt, R. F.; Joensen, P.; Morrison, 8. R. Mater.
Res. Bull. 1986, 21_, 543-549. (b) Divigalpitiya, W. M. R.; Morrison, S.
R.; Frindt, R. F. Thin Film Solids 1990, 186, 177-192.

[15] (a) Divigalpitiya, W. M. R.; Frindt, R. F.; Morrison, S. R. Science
1989, 216, 369-371. (b) Tagaya, H.; Hashimoto, T.; Karasu, M.; Izumi,
T.; Chiba, K. Chem. Lett. 1991, 12, 2113-2116.

[16] (a) Bissessur, R.; Kanatzidis, M. G.; Schindler, J. L; Kannewurf, C. R.
J. Chem. Soc. Chem. Commun. 1993, 1582-1585. (b) Bissessur, R.;
Kanatzidis, M. G.; Schindler, J. L; Kannewurf, C. R. Chem. Mater. 1993,
5_, 595-596.

[17] (a) Epstein, A. J.; Ginder, J. M.; Zuo, F.; Bigelow, R. W.; Woo, H.-S.;
Tanner, D. B.; Richter, A. F.; Huang, W.-S.; MacDiarmid, A. G. Synth.
Met. 1987,18, 303-309. (b) Monkman, A. P.; Adams, P. Synth. Met.
1991, 40, 87-96.

220

[18] Wakefield, B. J. The Chemistry of Organolithium Compounds,
Pergarnon Press, New York 1974.

[19] Shriver, D. F. The Manipulation of air-sensitive compounds, second
edition, Wiley, New York, 1986.

[20] Joensen, P.; Frindt, R. F.; Morrison, S. R. Mater. Res. Bull. 1986, 21,
457-461.

[21] (a) Divigalpitiya, W. M. R.; Frindt, R. F.; Morrison, S. R. Thin Film
Solids 1990, 188, 173-179. (b) Santiago, Y.; Cabrera, C. R. J.
Electrochem. Soc. 1994, 142, 629-635. (c) Ruiz-Hitzky, E.; Jimenez, R.;
Casal, B.; Manriquez, V.; Santa Ana, A.; Gonzalez, G. Adv. Mater. 1993,
5_, 738-741.

[22] Bissessur, R.; Kanatzidis, M. G. Unpublished results.

[23] (a) Yang, D.; Sandoval, S. J.; Divigalpitiya, W. M. R.; Irwin, J. C.;
Frindt, R. F. Phys. Rev. B. 1991, 48, 12053-12056. (b) Qin, X. R.; Yang,
D.; Frindt, R. F.; Irwin, J. C. Ultramicroscopy 1992, 42-44(part A), 630-
636.

[24] Divigalpitiya, W. M. R.; Frindt, R. F.; Morrison, S. R. Appl. Surf
Sci. 1991, 48142, 572-575.

[25] Gauy, D.; Divigalpitiya, W. M. R.; Bélanger, D.; Feng, X. H. Chem.
Mater. 1994, 6, 614-619.

221

[26] (a) Wu, C.-G.; Kanatzidis, M. G.; Marcy, H. 0.; DeGroot, D. C.;
Kannewurf, C. R. NATO Advanced Study Institute; Lower Dimensional
Systems and Molecular Devices; Metzger, R. M.; Ed. Plenum Press: New
York, 1991, pp 427-434. (b) Nazar, L. F.; Yin, X. T.; Zinkweg, D.
Zhang, Z. Liblong, S. Mat. Res. Soc. Symp. Proc. 1991, 2_1_Q, 417-422. (c)
Bissessur, R.; DeGroot, D. C.; Schindler, J. L.; Kannewurf, C. R.
Kanatzidis, M. G. J. Chem. Soc. Chem. Commun. 1993, 687-689.

[27] DiSalvo, F. J.; Wilson, J. A.; Bagley, B. G.; Waszczak, J. V. Phys.
Rev. B 1975, _1_2, 2220-2235.

[28] DiSalvo, F. J. Surf. Sci. 1976, 58, 297-311.

[29] Py, M. A.; Haering, R. R.; Can. J. Phys. 1983, 6;, 76-84.

[30] Bromley, R. A.; Phys. Lett. 1970, 33A, 242-243.

[31] Mattheis, L. F.; Phys. Rev. B 1973, 8, 3719-3740.

[32] Wypych, F.; Schollhom, R.; J. Chem. Soc. Chem. Commun. 1992,
1386-1388.

[33] Annual Book of ASTM Standards 1979, 5:828, 601-608.

[34] Agarwal, P.; Rai, J. S. P., Kumar, A. Phys. & Chem. Solids 1990, 8_1_,
227-230.

222

[35] Kaviratna, P. D.; Lan, T.; Pinnavaia, T. J. P. Polymer Prepr. Am.
Chem. Soc., Div. Polym. 1994, 85, No. 1, 788-789.

[36] Wang, L., Kanatzidis, M. G. Work in progress.

223

Chapter 4

Intercalation 0f the Cobalt Chalcogenide Clusters, C06Q3(PR3)5,

[Q = S, Se and Te and R : Phenyl, n-Butyl and Ethyl] into
M082. Formation of Pillared Sulfided Layers.

224

Abstract

Molecular clusters of the general formula, C06Q3(PR3)5, where Q =
S, Se, Te and R = ethyl, n-butyl and phenyl have been intercalated into
M082. This was accomplished by mixing CH2C12 solutions of the cluster
compounds with aqueous suspensions of single layers of MoSz. The new
inclusion solids have well-defined interlayer spacings depending on the
encapsulated cluster. For the Co6S3(PPh3)5 cluster, the interlayer spacing
varies from 21.5 A in [C0683(PPh3)3]o,093M082 (I) to 10.9 A in
[Co6S3]o,o3MoS2. Thermal gravimetric analyses show that all the
intercalation compouds are stable up to ca. 200 0C, after which rapid
weight loss corresponding to the evolution of phosphine ligands is
observed. Variable temperature magnetic susceptibility measurements on
[C0688(PPh3)3]0.093M0$2 (I) and [C0688(PPh3)4]0.046M082 (II) reveal
Curie-Weiss behavior similar to the unintercalated guest species
C06S3(PPh3)6. The ueff of I is 3.1 BM per formula unit and that of II 1.9
BM. The molecule, Co6S3(PPh3)6, itself exhibits a ucff value of 6.1 BM.
The tteff values for the intercalated phases are consistent with the amount
cluster molecules loaded into the M082 sheets. Variable temperature
magnetic susceptibility measurements on C06S3(PBu3)6, C06Se3(PBu3)6,
C06Se3(PEt3)5, Co6Te3(PBu3)6, Co6Te3(PEt3)(, and on their intercalated
products into MoSz also reveal Curie-Weiss behavior. The ueff values of
the intercalated phases were found to be consistent with the loading of the
cluster molecules into the M082 layers. The porosity of some of the
intercalated phases was probed by BET surface area measurements.
[Co6Te3(PEt3)y]o,06M082 was found to have a surface area of 29.2 mZ/g,
which is five-fold higher than that of bulk MoS2 itself. The surface area of

225

[C06Se3(PEt3)y]o,06M082 was found to be 14.2 m2/g and upon removal of
the residual phosphine ligands the surface area value increased to 22.1

m2/g. These findings illustrate the first examples of pillared sulfided

layers.

226

4.1. Introduction

Materials with open frameworks, i.e void spaces, have long been
sought after because of their technological importance in the field of
separation science and catalysis. The pore diameter of these materials can
range from 5 A to 1000 A [1]. Depending upon the pore diameter, these
materials can be classified as either microporous (5-20 A), mesoporous
(20-500 A) or macroporous (500-1000 A). Examples of microporous
solids are the ubiquitous zeolites which are crystalline aluminosilicate
compounds with periodic three-dimensional framework structures. The
narrow pore size distribution of these materials make them ideal for size
specific applications in absorption, molecular sieving and shape-selective

catalysis [2]. Mesoporous materials consist of pillared layered solids, e.g,

clays pillared with polyoxocations such as [A11304(OH)24]7+ ,
[Zr4(OH)1¢3.x]x+ [3] and ultra large pore size zeolites recently synthesized
by Mobil Research group [4]. Macroporous solids consist of gels [S] and
porous glasses [6] which have very broad pore size distribution.

The first pillaring of a layered structure was reported in 1955 by
Barrer and MacCleod [7]. They were able to pillar montmorillonite clay
layers with tetraalkylammonium ions. These materials were shown to have
interlayer porosity and selective absorption properties. At that time,
pillared clays could not compete with zeolites which were already in
widespread use. However, in the early 1980's, a revival of interest in
pillared clays occured when it was realized that the pore size of these
materials could be made larger than that in Faujastite zeolites. This was a

breakthrough in the development of molecular sieves.

227

In addition to tetraalkylammonium ions, other cations have been used
as pillaring agents for clays and these include polynuclear hydroxyl metal
cations [3 b,c] , metal chelate complexes [8], bicyclic amine cations [9] and
polyoxocations as mentioned above. By varying the size and spacing of the
pillars or both, the pore size could be controlled to suit the need of a
particular application. The eventual goal is to have pillared materials which
could be used as catalysts for cracking large hydrocarbon molecules such as
those found in residual crude oils.

So far pillaring has been done almost exclusively on clays. But, there
have been reported cases where polyoxocations such as [A113O4(OH)24]7+
and [Bi5(OH)12]6+ have been incorporated into M003 and TaSz [10], by
cation exchange of the sodium bronzes of these layered materials with
solutions of the pillaring agents. The surface area and porosity of these
materials have not been probed. Therefore, the question still remains as to
whether these are truly porous materials.

Intercalation of the cluster molecule, [Fe683(PEt3)6]2+ has also been
accomplished into TaSz by cation exchange of the sodium ions in
Nao,33TaSz [11]. However, no surface area measurement or pore size
distribution on the intercalation compound has been reported.

With the aim of designing porous networks analogous to zeolites by
using the pillaring phenomenon, we pick MoS2 as the layered structure.
Our reason for doing so is that M082 is a material with several practical
applications such as in hydrodesulfurization (HDS) [12], solid lubrication
[13] and high energy density lithium batteries [14] , all of which have been
emphasized in Chapter 3. The cluster compounds we pick as the
intercalants are the well-characterized cobalt clusters of the general type
Co6Q3(PR3)6 prepared by Steigerwald et a1. [15] and Hong et al. [16]. The

228

motive behind using cobalt clusters as the pillars is that cobalt species are
being used as promoters for MoS2 as far as HDS is concerned [17].
Pillaring M082 with C06Q3(PR3)5 could provide materials with interesting
HDS properties.

In chapter 3, the encapsulation of polymers into MoS2 is fully

described. This was made possible only by using the exfoliation and
restacking property of MoSz. By using this versatile methodology,

intercalation of a large number of cobalt clusters into MoS2 has been

achieved.

229

4.2. Experimental

4.2.1. Reagents: MoSz was purchased was Cerac and was used without
any further purification. CHzClz was purchased from commercial sources
and was used as received. Hexanes used in the preparation of LiMoSz were

dried over CaHz and distilled under nitrogen prior to use.

4.2.2. Physicochemical Methods

X-ray diffraction, thermogravimetric analysis and energy dispersive
spectrosc0py were performed as described in Chapter 2. Elemental
Analyses were performed at Galbraith Laboratories, in Knoxville,
Tennessee and at Michigan State University, on a Therrno Jarrell Ash
Polyscan 61 E, emission spectrometer by using an inductively coupled
plasma (ICP) source. UV-visible spectroscopy was performed on a Hitachi,

U-2000 spectrophotometer.

Magnetic Susceptibility Measurements.

Variable temperature magnetic susceptibility measurements were

performed as described in Chapter 3. All the cluster compounds and their

intercalation compounds into MoS2 obey the Curie-Weiss law (Eq. 1).

Xm = C/(T-G) """" Eq.1

230

where Xm = is the molar magnetic susceptibility in emu/mol and T is the

temperature in Kelvin, 0 is the correction factor for the non-zero intercept,

when xm'l is plotted versus T. C is a constant and is given by Eq. 2.

C = (tummy/3k ------- Eq. 2

where llcff is the effective magnetic moment, N is the Avogadro's number

(6.02 x 1023), B is the Bohr Magneton constant ( 9.1 x 1021), k is the
Boltzmann constant (1.38 x 10'7-3 JK'1).

The constant C was determined from the slope of the graph of Xm'l
versus temperature. It was then substituted in Eq. 2, to obtain [Jeff values.

BET Surface Area measurements.

BET surface area measurements were performed on a Quantasorb Jr.
Sorption System by using ultra-pure nitrogen gas as the absorbate and ultra
-pure helium gas as the carrier. Samples were outgassed at ca. 100 0C
before performing measurements. Surface areas of samples were

determined by using the BET equation [18].

231

4.2.3. Synthesis of Cluster Compounds

Cluster compounds of the general type, C05Q3(PR3)5, were
synthesized and purified as described in references [15] and [16]. The
clusters were characterized by SEM/EDS analysis to verify their
compositions. They were also characterized by UV-visible spectroscopy

and thermogravimetric analysis.

4.2.4. Synthesis of Intercalation Compounds

LiMoSz was prepared as described in Chapter 3. Aqueous
suspensions of MoSz single layers were produced as described in Chapter
3. To the single layers were added CH2C12 solutions of the cluster
compounds. The reaction mixtures were allowed to stir at room
temperature for 2 days. The products were collected by filtration and
washed thoroughly with CH2C12- They were allowed to dry at room

temperature in a vacuum oven.

232

4.3. Results and Discussion

Synthesis of the cluster compounds were easily achieved by using
known literature procedures [15, 16]. The UV-visible spectra of the
clusters showed 3 absorption bands (figure 4.1), consistent with those
reported in the literature. The results are tabulated in Table 4.1. Semi-
quantitative EDS/SEM analysis was used to verify the elemental
composition of the clusters.

The thermal stabilities of the cluster compounds were determined by
thermogravimetric analysis under nitrogen flow (Figures 4.2 and 4.3). The
following order in thermal stabilities was oberved; Co6Te3(PEt3)5 <
C06Te3(PBu3)(, < Co6Se3(PEt3)6 < CoeSg(PBu3)5 < Co6Se3(PBu3)6 <
CoaSg(PPh3)6; Co6S3(PPh3)6 being the most stable and C06Te3(PEt3)6, the
least stable. The results are summarized in Table 4.2. As observed from the
therrnograms, most of the decompositions are clean, giving single-phase
products which are stable over a wide temperature range. To determine the
identity of these single-phased products, pyrolysis experiments were
carried out on the clusters at 450 0C for 2 hours in Pyrex tubes, sealed
under vacuum. The products were washed with acetone and dried under
vacuum. They were analyzed by X-ray diffraction (Figure 4.4) and their

compositions determined from elemental analysis.

233

 

 

 

 

féf’a- a?
V V

 

 

 

 

 

 

 

a)
o
c
at
'9
8
.0
<
(d)
1
(e)
(f)
200 400 600 500 1000

nm

Figure 4.1. UV-Visible spectrum of (a) C0683(PPh3)5, (b) C0683(PBu3)5
(C) C06568(PBU3)6. (d) CosTes(PEt3)6. (e) C06T€8(PBUB)6 and (f)

C06868(PEI3)6.

234

Cluster molecule Absorbance (max) in nm

   

 

 

 

 

 

C06$8(PPh3)6 500, 431, 345
C0683(PBu3)6 469, 412, 339
CosSe3(PBu3)6 497, 440, 369
Co6Teg(PEt3)6 537, 471, 395
C06T€8(PBUB)6 538, 473, 397
Co6Se8(PEt3)6 497, 439, 367

 

 

 

 

Table 4.1. Summary of UV-visible results on cluster compounds.

: Cluster compound I Thermal stability (N2)
, a__ 0C 5

235

 

 

Composition of
- rol sed uroduct

 

 

 

 

 

 

C0688(PPh3)6 251 CoS
C0683(PBU3)6 230 C08
C06368(PBU3)6 236 CoSez
C06Tes(PEt3)6 55 CoTez
C06T€8(PBU3)6 196 CoTez
C06S€8(PEt3)6 214 CoSez

 

 

 

 

Table 4.2. Thermal stability of cobalt clusters.

236

 

 

 

 

1m LILLILLI.11...111.IL1..1r.ixxiult
P 1
- 1
p 4
39.. (a) ..
- 1
c- ' ‘
3 » -
fi 72-1 l-
r 4
h ‘
- q
561 -
P ‘
D 1
_ L
40 ,

 

 

 

o 100 200 300 400 500 600 700
Temperature (°C )

 

 

105
.
.
1 (b)
91-
q
q
d '4
3 77‘
3Q .
.
.
54..
d
4
< x
50 .fi.,..4-,...-,....,....,....,...

 

 

 

0 100 200 300 400 500 6a) 700
Temperature ('C)

 

E

(C)

IW1
:1 3

2

AJAJLALAIAAAIAAA

 

L

YYVY"TVYYY'Yvr'rVVITV'r'TYVYITrV

0 100 200 300 400 500 Gm 700
TemperathC)

fl

 

 

 

8

Figure 4.2. TGA of (a) Co6Se3(PBu3)6, (b) Co6Seg(PEt3)6 and (c)
C06Te3(PBu3)6.

237

 

 

 

 

 

vavrrvvv'vvvvrvvvv'rTvv'vv

0 100 2d) 300 an son can 100
TemperatnrePC)

 

“1 (b)

 

 

 

 

0 lm 200 300 4m am an m
TemperatuePC)

 

95W!

 

 

p
INL
1 a 1 1 l A A a A l

0 m a 1
Term (°C)

Figure 4.3. TGA of (a) CosTe3(PEt3)6, (b) CoaSg(PBu3)5 and (c)
C0683(PPh3)6.

238

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1500
g (A)
D
g; 1000
.2
‘3
S
.7? 500
M111. ”111.1111
.5.
0 1
2 15.5 31 45.5 so
2-Theta(degrees)
14m
"' In) 3
g ( )
E 1011)
“5! am
.e ‘°°
a 400
a
'5 200
0
2 10.5 31 48.5 I.
2-Theta(<bpeea)
500
‘5‘ (C)
3 400
S‘
.33 30°
2
<
v 200
a
2
2 100
.s
0 1 I n
2 10.5 31 45.5 60
2-Theta(degrees)

Figure 4.4. XRD of pyrolysed products of (a) Co6Se3(PBu3)5, (b)
Co6Te3(PBu3)6 and (c) C06S3(PBu3)5.

239

Intercalation of the cluster molecules into MoSz was easily and
conveniently achieved by adding CH2C12 solutions of the cluster compounds
to aqueous suspensions of single layers of M082. Equations 3, 4, and 5
summarize the synthetic procedure leading to the general intercalated phase
[C05Q3(PR3)y]xM082. Scheme 4.1 illustrates the intercalation process,
using C0683(PPh3)6 as an example.

MoS2 + BuLi ...... > LiM082 + 1/2 BuBu Eq. 3

LJMOSZ + XHZO ----- > (M082)singlc layers '1' XLJOH '1' (X’Z)H2 Eq. 4

(M082)sing1c layers + xC06Q8(PR3)6 ------ > [C06Q8(PR3)y]xMoS2 Eq5

Table 4.3 summarizes all the intercalated phases synthesized, along
with their respective interlayer spacing, interlayer expansions relative to
MoS2 and elemental compositions. Elemental analysis shows complete or
partial loss of phosphine ligands in most of the intercalated products. The
loss of triphenylphosphine ligands in land II is explained by steric
crowding of the huge cluster compound in the gallery space of the layered
host. Partial ligand loss was also observed in the intercalation compound
[Fe5S3(PEt3)3]o,05Ta82 [11] and was attributed to steric crowding in the
gallery space of the host. Since PPh3 is bulkier than PEt3 , it is not
surprising that we do see partial ligand loss in I and 11. Less
triphenylphosphine is lost in 11 since the cluster concentration is lower than
in I, thus less steric crowding is experienced. Interestingly enough,
complete loss of phosphine ligands was observed when Co6Te3(PBu3)5,
Co6Te3(PEt3)6 and Co6S3(PPh3)6 are used as the

240

.302 SE oAmcmmvmmooU we coca—meoz: .3» 082%

293. 38:25“. mmozxcmflmaov

// \\ .quMSnmnmvwmocu . ..

 

 

of

£22:
+5 +3 +5
+5 +5 +5
+5 +5 +5

Nwe:

 

 

 

 

 

same

 

 

 

 

241

.83an 35.888 configurefi mo racism m6 29¢.

 

 

  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

N o 32.23 :88 as of 3. E
5.5 mmozaodgamavmmooo. a: 4.2 2: enamaemp
sec amozsdefiooa 3 2: NS fismemfiap
:5 awe—zaodaafiemfiooo. an 3 _ cs gazmavmoeoow
cc «mozaoéwfiga on 3 NS ogfivwfioom
as Saigogsmewfieoo. 3 3; E: 293306
2:3 NmozmsdeEgooa 4.: 9: NS flower 8
EB ~m02_8.o_§mesm§2 3 _ 0.: es 03$».sz
F: 3023863283328. 92 ”.2 NS oAamewomow
E Nmozgdegfiwomeoo. 4.: 92 2: 2325036
9: «mozzcdzmoou. 3. 2: NS 22%: 8
E: «mozgdzigmoou. «.2 4.2 _S cinemfio
:: «mozcaecéfikwmooo. cf N: as 23%:me
E «measozillewmeoo. 0.: 2m MS oflmgaemmoow

303mg 3%

 

 

242

intercalants in very low amounts (1/32 equivalent relative to M082),
resulting in [CoaTe3]o,02MoS2, [C05Te3]o,o3MoS2 and [C0683]o,o3M082,
respectively. The interlayer spacings of these resulting compounds suggest
that only the Cer3 core is inserted in between the MoS2 layers. Elemental
analyses showed the presence of carbon, hydrogen and phosphorous only at
the impurity level. This implies that the Co-P bonds in these clusters are
labile.

X-ray powder diffraction patterns of the intercalated compounds
reveal their layered character as depicted by well-defined (001) reflections
(Figure 4.5). The d-spacing of I is 21.5 A with an interlayer expansion of
15.3 A while that of II is 21.2 A with an interlayer expansion of 15 A;
both relative to pristine M082. The rather large interlayer expansions of I
and II are consistent with the inclusion of the cluster molecule in between
the M082 slabs. This is in good agreement with the dimension of the cluster
molecule as calculated by using molecular software.

Pyrolysis mass spectroscopy showed no evidence for the co-
intercalation of CHzClz on the rigorously vacuum-dried products. To
further confirm the absence of CHzClz, a blank experiment was performed
where an aqueous suspension of single MoSz layers was treated with
CH2C12 and the collected product washed thoroughly with water and
CHzClz. Analysis of the resulting product by X-ray powder diffraction did
not show evidence for the intercalation of either CHzClz and /or H20 .

All the intercalation compounds show fairly good thermal stabilities
under nitrogen. There seems to be no direct correlation between the

stabilities of the intercalation compounds and the nature of the chalcogen

Figure 4.5. XRD of

243

(a) [C06S8(PPh3)310.093M082
(b) [C0688(PPh3)4]0.046M082
(C) [C06Tes]0.03M032

(d) [C06T681002M082

(e) [C06T€8(PBUB)610.047M032

 

 

 

30.0

 

 

244

 

 

 

 

 

23.1

 

16.2
29(deg.)

9.4

 

2.5

 

 

 

 

0.
0
3
L _
m1
3 E
2 c o. A.
)
0
2.
A 8 T6“
19
2
[40
J 9
J 5
. . . . . 12. 4 _ d a _

2:5 33:23 2.23:: 2...: £3.32. 5.22...

245

atom Q and/or the nature of the phosphine ligands. Figure 4.6 depicts the
therrnograms of a select number of intercalation compounds prepared and
Table 4.5 lists the thermal stabilities of all the intercalation compounds.

4.3.1. Magnetic Susceptibility Measurements

Variable temperature magnetic susceptibility data were performed
on the cluster compounds as well as on their intercalation compounds into
MoS2. I and 11 show Curie-Weiss behavior with slight deviation in the low
temperature regime (< 5K) (figures 4.7 and 4.8). The unintercalated
cluster Co6S3(PPh3)6 also exhibits a similar behavior in the low
temperature region (Figure 4.9). The nature of this deviation is not well-
understood at the moment and may be due to weak antiferromagnetic
coupling at very low temperature. The ucff values calculated for I, II and
C0683(PPh3)6 are 3.1, 1.9 and 6.1 BM per formula unit, respectively. The
values calculated for I and II are consistent with the amount of clusters
trapped in between the M082 layers. Variable temperature magnetic
susceptibility measurements were performed on the other cluster molecules
and on their respective intercalation compounds in MoS2 and they also
show Curie-Weiss behavior. Figure 4.10 shows the variable temperature
magnetic susceptibility data of Co6Te3(PEt3)5 and Figures 4.11 - 4.13
shows the magnetic susceptibility data of a select number of the intercalated
phases synthesized. The ucff values of all the cluster compounds and
intercalated products are tabulated in Table 4.4. CoeSg(PPh3)6 and
C0683(PBu3)6 cluster compounds were found to be strongly paramagnetic
whereas C06Se3(PBu3)5 is a weak paramagnet.

246

 

105

98

saw:
8

83

 

 

 

75 l l l 1 1‘1

 

o 100 200 300 400 500 600 700
Temperature(°C)

Figure 4.6. TGA of (a) [C0683(PPh3)3]0.093M082,(b)
[C0638(PPh3)410.046M082.(C) [C06T681003M082 and (d)
[C06368(PEt3)610.023M032.

247

 

 

 

 

 

 

 

 

0.12 V V V V TV V V V v Vrmm er V V TV Vi V VVVVV
m ""32"--- - - - g
0.1 "° .°.’ l
:00 00° 1
0.08 i 7 "° 0° 3
E0 ’5 100 O00 :
b O 4
a 0.06 ; ‘° AAAAAAAAAAA ‘ - +1 1
x " O o 1.. 1|. 800 250‘; 300 '1
0.04 . o T""""""""’ -
I 0 i
0 02 i (88 1
- -1
° 1. 00 4
,, 000 4
O
0 ~1-....-......?.9.9.9.9.9.Q.9.0
0 50 100 150 200 250 300
Temperature(K)

Figure 4.7. Xm versus temperature plot for I. Inset graph shows xm'l

versus temperature.

0.06
0.05
0.04
0.03

E
X 0.02

Figure 4.8. Xm versus temperature plot for 11. Inset graph shows Xm'l

248

 

700 v - - - fi

. o
.00 : O
swig 0°
400 E o
300 L o

 

Xm'l
O

 

 

O
O
O
O
O

is».

00
..??.9.9.919.Q.Q.0.

so 100 150 200 250
Temperature(K)

A A a a l A

versus temperature.

 

249

 

 

 

 

 

 

 

 

0.35‘vv-rvv-vnnnn W-,...1
70 - - -- ......... -m’ .
0.3 to:- 00°: :
00;» oo 1
0.25 '7 “E o° :
L P5 30;L 00° :
0.2 10 “E’ J
:0 10%0 ‘ I
g 0.15 E 0 0° 00 m 100 200 200 m '3
I 0 7W1!) :
.1 : 3
0 I O 1
0.05:» 0 O :
0: Al ‘1““1““919-9aqhq4

0 50 100 150 200 250 300

Temperature(K)

Figure 4.9. 16111 versus temperature plot for Co6S3(PPh3)6. Inset graph

shows xm'l versus temperature.

250

 

 

 

 

 

 

 

 

0.1
1- an
15 o o
b C °
0.08 - 150 ~ 0 °
9 * o
O . o
D o
0 ... 1m - o
0.06 '0 ' ; 0 °
_0 5 * 0°
.8 mi.- 0°
E '0 I
0.04 ”o
N .
O 0 11..UL.1..1....1.U.1.1.111.”
” O
0.02 ._ 00 Temperature (K)
- O
00 O 0 o o
. ° 0 O o o
O llllllllllllLlllllllljlllllll
0 50 11!) 150 M 250 300

Temperature (K)

Figure 4.10. Xm versus temperature plot for Co6Teg(PEt3)5. Inset graph

shows Xm'l versus temperature.

251

 

 

 

 

0.08
3”
0.07 w o o o
0.06 250- o 0 °
0

0.05- '7 m“ 0° °
E o S 1504 0°C
X 0.04" 0 KIM 0°

0.03- 0 5°“ f

O 0 ‘

0.02 - 0.0 50.0 100.0 150.0 200.0 250.0 300.0 350.0
Temperature (K)
0.01 -

0000000000

0 IU'rrUUTTlrIIFIIrUI[ITIUIIIIUIUUT

O 50 100 150 200 250 300 350
Temperature (K)

 

 

 

Figure 4.11. Xm versus temperature plot for [C06Te3(PBu3)6]o,o47M082.

Inset graph shows xm'l versus temperature.

252

0.015

 

 

12(1)

10004 am
o°°

0.01 o o

.5 “-0 0°
N

O
O
% ‘°°‘
O
O
O

Xm

2(D‘

 

0.005 ..

 

0 I
0.0 50.0 100.0 150.0 200.0 250.0 3N0
szlbo Temperature (K)
00

O Ili'lliirlriilIIIUU'IIVIIUUr'

0 50 100 150 200 250 300
Temperature (K)

 

 

 

Figure 4.12. Xm versus temperature plot for [C068e3(PEt3)6]o,o31M082.

Inset graph shows Xm‘l versus temperature.

253

 

 

 

 

 

 

0.06 p 7
I an fl. 1
0.05 4% 500 at
1 o
" o
I O 400 0 ° I
0.04: O __ o o .
q ' 300 o I
1 5 o ,
003 r 0 2‘” 0° !
1 0° ‘
.4 O
E : O 100 1
X 002 — O 1
.1
4 o o,s...,....,....“WWW”,.... ,
< O 0.0 50.0 100.0 150.0 200.0 250.0 300.0 |
0.011 00 meflflm I
'1 000
o
3 ° ° ° 0 o o o o o
O T—T T rTTT Y T I r1 T T—I r I I T I Y TI I I I IfI]
0 50 100 150 200 250 300

Temperature (K)

Figure 4.13. Xm versus temperature plot for [C0683(PBu3)6]o,059M082.

Inset graph shows xm'l versus temperature.

254

Compound xm (emu/mol)
room tem . . value

    

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

CoeSg(PPh3)6 6.1 1.74 x 10-2
[C0683(PPh3)3]o,093M032 3.1 1.79 x 10'3
[C0683(PPh3)4]o,046M082 1.9 1.52 x 10'3
C0683(PBu3)6 7.1 4.4 x 10'3

[C0683(PBu3)6]o.059M032 2.29 1.91 x 10'3
CosSeg(PBU3)6 1.49 6.5 x 10'4

[C06868(PBU3)6]0.04M082 0.55 1.17 x 10-4
Co6Se3(PEt3)6 2.47 1.60 x 10‘3
[C06368(PEt3)6]0.031M032 1.98 1.01 x 103
CosTe3(PBu3)6 2.23 1.44 x 10'3
[C06Tes(PBU3)6]0.047M082 2.62 2.47 x 103
CoaTes(PEt3)6 3.85 5.52 x 103
[C06T68(PEI3)3]0.052M082 1.93 1.31 x 10-3

 

 

Table 4.4. Summary of magnetic susceptibility data.

255

4.3.2. Electrical Conductivity Data

The intercalation compounds were found to be conducting. The
room temperature conductivity values were in the range 3 x 10-3 - 9 x 10'4
S/cm. The values are listed in Table 4.5. The high conductivity is explained
by considering the structure of MoSz in these intercalation compounds.
Upon intercalation with lithium, 2H-MoSz undergoes a structural
transformation in which the coordination of the resulting Mo3+ atom
becomes octahedral from trigonal prismatic [19]. Upon reaction of LiMoSz
with water, single MoSz layers form by rapid oxidation which leaves the
Mo4+ atom trapped in an octahedral coordination, thereby stabilizing a
metastable structure for an M082 layer. Qualitative band structure
diagrams show that 2H-MoSz develops a band gap between the filled dzz
band and empty dxz-y2,xy band, while the octahedral modification results in
a partially populated band yielding a metallic state (Figure 4.14). The
octahedral form is metastable and converts slowly to the 2H form at room
temperature. The relatively low conductivity values of some of the
intercalated phases is explained by the fact that the transformation has

already occured to a slight extent in these materials.

256

 

 

 

 

 

 

 

 

Mo-S antlbondlng
/
3 — dam band — dyz, xz band
5 _d X2 -2y xy band -dz
Band Gap dzx -2y . xy. z Zband
dzz band
Mo-S bonding

Figure 4.14. Qualitative band diagrams of (a) 2H-MoSz and (b) MoSz in
the octahedral modification. Shaded bands are filled.

Intercalation compound

    

257

Thermal stability Room temperature

in nitroen 0C *

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[Cogsgwphpm 923M082 223 8.7 x 104
[Co§S§(PPh2)4]Q mfloSZ 234 5.6 x 10-3
, [Co§§§(PPh;)2]Q WMosz 216 2.1x 103
, 1 s 1 M08 218 3.7 x10‘3
[%S§(P8u2)§]g,9§9M082 207 9.9 x 104
[ s (PBu ) 1 MoS 203 5.8 x 103
mwauyélomm 187 4.3 x 104
[Co6Se8(PBug)610,0261\/1_<_5_s_2 196 2.5 x 10-3
[CogSeg(PEt3)6]o,o31MoSz 206 3.2 x 10-3
[Co§8e§(PEt2)§]Q 923M082 204 6.9 x 10'4
[C06Te3(PBu3)6]o.o47MoS; 158 4.3 x 10‘4
[C06T63]0.021\_/l_o_3_2 168 2.0 x 10’4
[CoQTe§(PEt})2]Q.Q§zMoSz 188 8.4 x 10‘3
[C06TC81003M032 200 5.6 x 10'4

 

 

 

 

* onset of weight loss

Table 4.5. Summary of thermal stability and conductivity data.

25 8
4.3.3. BET Surface Area Measurements

BET surface area measurements were performed on some of the
intercalated phases obtained in order to probe their porosity. Bulk M082
was found to have a surface area of 5.8 m2/g whereas restacked M082 has
been reported to have a slightly higher value of 8.4 m2/g [20]. However,
the following intercalation compounds, [CooTe3(PEt3),]o,o¢5Mosz,
[C05363(PEt3)y]0,05M032 and [C06363(PEI3)y]o,o3M032 were found to have
surface area values of 29.2 mZ/g, and 14.2 m2/g and 19.9 m2/g,
respectively. Compared to both bulk and restacked M082 these are
relatively high values and must be due to pores created by the pillaring
effect of the cluster molecules in the gallery space of the host. It is
interesting to note that [C068e3(PEt3)y]o,o3Mosz has a larger surface area
than [C068e3(PEt3)y]o,05Mosz which is due to the low concentration of the
cluster molecules in this phase, giving rise to less steric crowding and
therefore more void space. However, the surface area of
[Co68e3(PEt3)y]o,06M082 increases to a value of 22.1 mZ/g upon removal of

the residual phosphine ligands by heating under vacuum.

The values reported for the BET surface area are not as low as they
seem. The apparently low values are due to the fact that the our materials
contain heavy atoms. Had these materials been aluminosilicates, higher

surface area values would have been obtained.

259

4.4. Conclusions

This work demonstrates that the intercalation of large molecular
cobalt clusters into M082 is possible by using the exfoliation and restacking
property of MoSz. Once again, the immense potential of the single-layer
technique is demonstrated. BET surface area measurements show evidence
for the formation of pillared materials and this is the first reported case
for pillared sulfided layers. These intercalation compounds are attractive
since they possess a combination of magnetic and electrical properties.
They could potentially be used as catalysts for the HDS process, molecular

sieves and solid lubricants.

Further probing of the porosity such as pore size distribution of the
intercalation compounds are currently in progress. In addition,
intercalation of the cobalt clusters is being carried out on other transition
metal dichalcogenides such as TaSz, Ti82, Nsz and MoSe2 [21]. We are
currently expanding the range of cluster molecules to other structurally
well-characterized clusters such as F6638(PEI3)62+ [22], M0683(PR3)5 [23],
M0484(NH3)124+ [241.Pd8868(PPh3)6 [25] and Ni15815(PPh3)6 [26].

260

REFERENCES

[l] Behrens, P. Adv. Mater. 1993, 5, 127-132.

[2] Htilderich, W. F.; Hesse, M.; Naumann, F. Angew. Chem. 1988, M,
232.

[3] (a)Vaughan, D. E. W; Lussier, R. J.; Magee, J. S. US Patent 4176090,
Nov. 27, 1979. (b) Brindley, G. W.; Sempels, R. E. Clay Miner. 1977,
12,, 229. (c) Yamanaka, S.; Brindley, G. W. Clays Clay Miner. 1979, 21,
201.

[4] Kresge, C. T.; Leonowicz, M. E.; Roth, W. J.; Vartuli, J. C.; Beck, J. 8.
Nature 1992, 352, 710-712.

[5] Janowski, F.; Heyer, W.; Porb‘se Glaser, VEB Deutscher Verlag fur
Grund—stoflindustrie, Leipzig 1982.

[6] Iler, R. K, The Chemistry of Silica, Wiley, New York, 1979.

[7] Barrer, R. M.; MacLeod, D. M. Trans. Faraday Soc. 1955, 51, 1290-
1300.

[8] (a) Knudson. M. 1.; McAtee, J. L. Clays Clay Miner. 1973, 2.1,, 19. (b)
Traynor, M. F.; Mortland, M. M.; Pinnavaia, T. J. Clays Clay Miner.
1978. 25.. 319.

261

[9] (a) Mortland, M. M.; Berkheiser, V. E. Clays Clay Miner. 1976, 2A,
60. (b) Shabtai, J.; Frydman, N.; Lazar, R. Proc. 6th Int. Congr. Catal.
1976, hi, 1.

[10] (a) Nazar, L. F.; Yin, X. T.; Zinkweg, D.; Zhang, 2.; Liblong, S. Mat.
Res. Soc. Symp. Proc. 1991, 210, 417-422. (b) Lerf, A., Lalik, E.;
Kolodziejski, W.; Klinowski, J. J. Phys. Chem. 1992, 26, 7389-7393.

[11] (a) Nazar, L. F.; Jacobson, A. J. J. Chem. Soc., Chem. Commun.
1986, 570-571. (b) Nazar, L. F.; Jacobson, A. J. J. Mater. Chem. 1994, in

press.

[12] (a) Weisser, 0.; Landa, S. Sulfided Catalysts, Their Properties and
Applications, Pergamon, New York, 1973. (b) Chianelli, R. R. Cata. Rev.-
Sci. Eng. 1984, 26(3824), 361-393. (c) Prins, R.; De Beer, H. J.; Somorjai,
G. A. Cata. Rev.-Sci. Eng. 1989, 12(1&2), 1-41.

[13] Fleischauer, P. D. Thin Solid Films 1987, DA. 309—322.

[14] (a) Julien, C.; Saikh, S. 1.; Nazri, G. A. Mater. Sci. Eng. 1992, 311,
73-77. (b) Tributsch, H. Faraday Discuss. Chem. Soc. 1980, 20, 190-205.

[15] (a) Stuczynski, S. M.; Kwon, Y.-U.; Steigerwald, M. L. J. Organomet.
Chem. 1993, 442, 167-172. (b) Steigerwald, M. L.; Siegrist, T.;
Stuczynski, S. M. Inorg. Chem. 1991, 30, 4940-4945.

262

[16] (a) Hong, M.; Huang, 2.; Lei, X.; Wei, G.; Kang, B.; Liu, H.
Polyhedron, 1991, LQ, 927-934. (b) Hong, M.; Huang, 2.; Lei, X.; Wei,
G.; Kang, B.; Liu, H. Inorg. Chim. Acta. 1989, 152, 1-2.

[17] Prins, R. Supported Metal Sulfides, p. 109-127, In Characterization of
Catalytic Materials, Wachs, I. E. (Ed.), Greenwich, CT, 1992.

[18] Brunauer, S.; Emmett, P. H.; Teller, E. J. Am. Chem. Soc. 1938, 69,
309-319.

[19] (a) Yang, D.; Sandoval, S. J.; Divigalpitiya, W. M. R.; Irwin, J. C.;
Frindt, R. F. Phys. Rev. B. 1991,41, 12053-12056. (b) Py, M. A.;

Haering, R. R.; Can. J. Phys. 1983, 61, 76-84.

[20] Gee, M. A.; Frindt, R. F.; Joensen, P.; Morrison, S. R. Mat. Res. Bull.
1986, 11., 543-549.

[21] Heising, J. ; Kanatzidis, M. G. Work in progress.

[22] Agresti, A.; Bacci, M.; Cecconi, F.; Ghilardi, C. A.; Mildollini, S.
Inorg. Chem. 1985, 24, 689-695.

[23] Saito, T.; Yarnarnoto, N.; Yamagata, T.; Imoto, H. J. Am. Chem. Soc.
1988, 1.1.0. 1646-1647.

[24] Shibahara, T.; Kawano, E.; Okano, M.; Nishi, M.; Kuroya, H. Chem.
Lett. 1986, 827-828.

263

[25] Fenske, D. Fleischer, H.; Krautscheid, H.; Magull, J. Oliver, C.;
Weisgerber, 8. Z. Naturforsch 1991, 4612, 1384-1394.

[26] Hong, M.; Huang, 2.; Liu, H. J. Chem. Soc. Chem. Commun. 1990,
1210-1211.

111011an smrE UNIV. LIBRARIES
111111111111111111111111111111111111
31293010465346