Controlling the Synthesis of New Polyoxometalates and RemovingTheir Crystallographic Disorder Open Access

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

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 COMPLEXES4-6 .....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)Mn^III3Mn^IVO3(CH3COO)3] (8a) by the generation of the Mn4O3 cluster in situ .....103

Synthesis of [(a-P2W15O56)Mn^III3Mn^IVO3(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 ofCs8Na6[Pd^II3(SiW9O34)2] (12) .....106

Synthesis ofK11Na3[Pd^II3(SiW9O34)2] (13) .....107

X-ray crystallography .....107

3.5 CHARACTERIZATION DATA FOR COMPLEXES 8-13 .....113

3.6 CONCLUSIONS .....120

REFERENCES .....122

About this Dissertation

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School	Laney Graduate School
Department	Chemistry
Degree	PhD
Submission	Dissertation
Language	English
Research Field	Chemistry, General
Keyword	Crystallography Controlled synthesis Polyoxometalate Keggin Polyanion Organometallic
Committee Chair / Thesis Advisor	Hill, Craig L, Emory University
Committee Members	Hagen, Karl S, Emory University MacBeth, Cora, Emory University

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