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Controlling the Synthesis of New Polyoxometalates and Removing Their Crystallographic Disorder

O'Halloran, Kevin Patrick (2011)
Dissertation (142 pages)
Committee Chair / Thesis Adviser: Hill, Craig L
Committee Members: Hagen, Karl S ; MacBeth, Cora
Research Fields: Chemistry, General
Keywords: Polyoxometalate; Crystallography; Organometallic; Polyanion; Controlled synthesis; Keggin
Program: Laney Graduate School, Chemistry
Permanent url: http://pid.emory.edu/ark:/25593/91xz1

Abstract


Abstract


Crystallographic disorder encompasses a wide range of frequently-encountered
problems in many areas of chemistry. These problems include, but are not limited to,
positional disorder, occupational disorder, solvent disorder, libration and twinning.
Often, crystallographic disorder is discovered in the early stages of investigation and
further efforts with that system are abandoned because the pertinent questions cannot
be answered at the resolution provided by a disordered crystal structure. Therefore,
this problem deserves quite a bit of attention. In the field of polyoxometalates
(POMs), several of these disorder problems are routinely encountered. Many times
they are satisfactorily addressed, but other times the data is abandoned because of
poor resolution. Therefore, we sought to address this problem for a particular class of
POMs where discrete positional disorder is currently limiting research progress. We
chose mono-substituted derivatives of three archetypal POMs: Keggin-, Wells-
Dawson- and Knoth-type structures. To achieve this, we introduced a covalently-
bound phenyltin unit into the polyanion structure and crystallized the resulting
complexes (Chapter 1). The results show that the phenyl group effectively removes
crystallographically-imposed symmetry elements that cause positional disorder in the
unit cells.


The controlled synthesis of molecules is a fundamental principle of many areas of
chemistry. In this process, chemical reactions are planned and carried out in a
stepwise, logical manner; a process to which many achievements in chemistry owe
their discovery. However, many POM complexes are still formed serendipitously
from a mixture of various starting reagents. Therefore, the field of POMs would
benefit from a controlled synthesis method. This prompted us to develop such a
method by the stepwise removal of a tungsten unit from a POM and subsequent
replacement with a new metal ion. We achieved this by the hydrolytic decomposition
of a polytungstate with the judicious adjustment of pH value and crystallization
conditions (Chapter 2). The results show that this method successfully generated
three new complexes and may create opportunities for new complexes in POM
research.


New polyoxometalates are continually being discovered with applications in
various emerging fields of research. Often these POMs contain multiple d-electron-
transition metals. We have prepared and characterized six such POMs (Chapter 3).

Table of Contents

Table of Contents

CHAPTER ONE: REMOVING COMMON CRYSTALLOGRAPHIC DISORDER IN THREE DIFFERENT MONOSUBSTITUTED POLYOXOMETALATE SYSTEMS .....1

1.1 ABSTRACT .....1
1.2 INTRODUCTION .....2
1.3 RESULTS AND DISCUSSION .....7
1.4 EXPERIMENTAL .....19
General methods and materials .....19
Synthesis of ((CH3)2NH2)4[Sn(C6H5)PW11O39]•5H2O (1) .....22
Synthesis of K7[Sn(C6H5)P2W17O61] (2) .....23
Synthesis of ((CH3)2NH2)7[Sn(C6H5)P2W17O61]•20H2O (2') .....23
Synthesis of ((CH3)2NH2)6K[Sn(C6H5)(H2O)P2W20O70(H2O)2]•11H2O (3).....24
X-ray crystallography .....25
1.5 CHARACTERIZATION DATA FOR COMPLEXES 1-3 .....28
1.6 CONCLUSIONS .....39
REFERENCES .....40

CHAPTER TWO: CONTROLLED SYNTHESIS OF A UNIQUE MaMbMc(PW9)2 SANDWICH-TYPE COMPLEX VIA AN UNPRECEDENTED SYNTHETIC ROUTE .....48
2.1 ABSTRACT .....48
2.2 INTRODUCTION .....49
2.3 RESULTS AND DISCUSSION .....51

2.4 EXPERIMENTAL .....60

General methods and materials .....60

Synthesis of Rb6K5[Sn(C6H5)(H2O)P2W19O69(H2O)] (4) .....61

Synthesis of Rb2K6[(Sn(C6H5)(H2O))2P2W19O69(H2O)] (5) .....62

Synthesis of ((CH3)2NH2)Rb4K4[Cu(H2O)Sn(C6H5)(H2O)-P2W19O69(H2O)] (6) .....63

X-ray crystallography .....64

2.5 CHARACTERIZATION DATA FOR COMPLEXES 4-6 .....69
2.6 CONCLUSIONS .....78
REFERENCES .....79

CHAPTER THREE: MULTI-D-ELECTRON-CONTAINING POLYOXOMETALATES AS USEFUL COMPLEXES IN EMERGING RESEARCH AREAS .....82
3.1 ABSTRACT .....82
3.2 INTRODUCTION .....82
3.3 RESULTS AND DISCUSSION .....85
3.4 EXPERIMENTAL .....101
General methods and materials .....101
Synthesis of [(a-P2W15O56)MnIII3MnIVO3(CH3COO)3] (8a) by the generation of the Mn4O3 cluster in situ .....103
Synthesis of [(a-P2W15O56)MnIII3MnIVO3(CH3COO)3] (8a) by fragmentation of Mn12O12 .....103
Synthesis of K2Na14[Mn4(H2O)2(P2W15O56)2 ] (9) .....104
Synthesis of ((CH3)2N)4Na6[O(FePW11O39)2] (10) .....105
Synthesis of ((CH3)2N)7Na3[O(FePW11O39)2] (11) .....105
Synthesis of Cs8Na6[PdII3(SiW9O34)2] (12) .....106
Synthesis of K11Na3[PdII3(SiW9O34)2] (13) .....107
X-ray crystallography .....107
3.5 CHARACTERIZATION DATA FOR COMPLEXES 8-13 .....113
3.6 CONCLUSIONS .....120
REFERENCES .....122

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