Polyoxometalates in Artificial Photosynthesis: Development of Chromophores and Water Oxidation Catalysts Open Access
Zhao, Chongchao (2013)
Published
Abstract
Polyoxometalates (POMs) have been gaining increasing interest in several research fields, especially in catalysis. The development of POM-based water-oxidation catalysts (WOCs) recently has brought unprecedented attention to POMs. The general focus of this thesis is to explore the structural features of POMs and their applications in artificial photosynthesis (AP); the specific focus is to develop POM-based chromophores and WOCs for AP.
The first part of thesis reports the synthesis, structures and
reactivity of POM-supported metal carbonyl complexes. Dimeric
structures based on [M(CO)3]+ (M = Re, Mn)
and lacunary POM ligands,
[X2W22O74(OH)2]12-
(X = Sb, Bi), [α-PW11O39]7-
and
[α2-P2W17O61]10-,
have been prepared and fully characterized. They show
"slipped-sandwich" and "twisted-sandwich" structures. Their
electrochemical and photochemical properties have been
investigated. This work has significantly expanded the area of
hybrid POMs.
The second part focuses on the use of these hybrid POMs as
chromophores for solar light conversion. A novel transition,
metal-to-polyoxometalate charge-transfer (MPCT), is characterized
for the first time. In complex
[P4W35O124{Re(CO)3}2]16-,
the donor is an embedded Re(I) center and the acceptor is the
all-inorganic d0 POM ligand,
[α2-P2W17O61]10-.
The high visible-region absorptivity
(ε470nm = 4000
M-1cm-1) results from a ReI-to-POM
CT transition. In complex
[P2W17O61{Re(CO)3}3{ORb(H2O)}(μ3-OH)]9-,
the donor is a trinuclear Re(I) cluster, so MPCT transition in this
system can be regarded as cluster-to-cluster CT. Ultrafast
spectroscopy and DFT theoretical calculations confirm instantaneous
(<50 fs) MPCT processes involving electron transfer from Re(I)
center(s) to POM ligand(s).
The third part addresses the preparation and characterization of
new cobalt(II) and tin(II) POMs. The structures and catalytic water
oxidation activity of several Co(II) POMs based on
[B-SbW9O33]9- were
investigated. Multiple Sn(II) POMs based on
[B-SbW9O33]9- and
[α-XW9O34]10- (X = Si, Ge)
are the highest nuclearity Sn(II) POMs known to date. They
crystallize as infinite three-dimensional all-inorganic frameworks
with porous channels. These Sn(II) POMs have high absorptivity in
the visible region, a feature characterized by spectroscopic
techniques.
Table of Contents
Chapter 1 Introduction: The Frontiers of Polyoxometalate
Chemistry ....................................................
................................................................................
1
1.1 General Properties of Polyoxometalates
......................................................................................................................................................................
2
1.2 Overview of POM Photochemistry
..............................................................................................................................................................................
5
1.3 Merging Organometallics with POM Chemistry
..............................................................................................................................................................
10
1.4 Transition-Metal-Substituted POMs with Applications in
Catalytic Water Oxidation
.............................................................................................................
16
1.5 Metal-to-Metal Charge-Transfer Chromophores
...........................................................................................................................................................
21
1.6 Goal of This Work and Outline
..................................................................................................................................................................................
25
References
................................................................................................................................................................................................................
27
Chapter 2 Metal Carbonyl Complexes Supported on Subvalent
SbIII/BiIII-centered Polyoxoanions
...............................................................................................
35
2.1 Introduction
.........................................................................................................................................................................................................
36
2.2 Experimental
.........................................................................................................................................................................................................
37
2.2.1. Materials and Instrumentation
..............................................................................................................................................................................
37
2.2.2. Synthesis
.........................................................................................................................................................................................................
38
2.2.3. Crystallography
..................................................................................................................................................................................................
39
2.3 Results and
Discussion.............................................................................................................................................................................................
42
2.3.1 Synthesis
...........................................................................................................................................................................................................
42
2.3.2
Structures...........................................................................................................................................................................................................
44
2.3.3 Spectroscopic and Computational Studies
.................................................................................................................................................................
46
2.4 Conclusions
...........................................................................................................................................................................................................
56
References
.................................................................................................................................................................................................................
56
Chapter 3 Mono-lacunary Polytungstate-supported Metal Carbonyl
Complexes
..........................................................................................................................
59
3.1 Introduction
............................................................................................................................................................................................................
60
3.2 Experimental
............................................................................................................................................................................................................
61
3.2.1. Materials and Instrumentation
.................................................................................................................................................................................
61
3.2.2. Synthesis
............................................................................................................................................................................................................
62
3.2.3. Crystallography
....................................................................................................................................................................................................
64
3.2.4. Electrochemistry
...................................................................................................................................................................................................
65
3.3 Experimental
............................................................................................................................................................................................................
65
3.3.1 Synthesis and Crystal Structures
..............................................................................................................................................................................
65
3.3.2 Electrochemistry
....................................................................................................................................................................................................
77
3.4 Conclusions
.............................................................................................................................................................................................................
78
References
...................................................................................................................................................................................................................
79
Chapter 4 Spectroscopic and Computational Studies of a
Metal-to-Polyoxometalate Charge Transfer Molecular Chromophore
.............................................................
87
4.1 Introduction
............................................................................................................................................................................................................
88
4.2 Experimental
...........................................................................................................................................................................................................
90
4.2.1. Synthesis
............................................................................................................................................................................................................
90
4.2.2. Transient Spectroscopic Studies
..............................................................................................................................................................................
91
4.3 Results and
Discussion................................................................................................................................................................................................
93
4.3.1. Steady-state Specstrocopy
....................................................................................................................................................................................
93
4.3.2. Computational Studies
............................................................................................................................................................................................
95
4.3.3. Transient Spectral and Kinetic Analysis
......................................................................................................................................................................
97
4.4 Conclusions
..............................................................................................................................................................................................................
102
References
....................................................................................................................................................................................................................
102
Chapter 5 An Inorganic Chromophore Based on a Molecular Oxide
Supported Metal Carbonyl Cluster:
[P2W17O61{Re(CO)3}3{ORb(H2O)}(μ3-OH)]9-
................................. 106
5.1 Introduction
.............................................................................................................................................................................................................
107
5.2 Experimental
.............................................................................................................................................................................................................
108
5.2.1. Synthesis
.............................................................................................................................................................................................................
108
5.2.2 Crystallography
.......................................................................................................................................................................................................
111
5.2.3 Spectroelectrochemistry
...........................................................................................................................................................................................
113
5.2.4. Transient Spectral and Kinetic Analysis
.......................................................................................................................................................................
114
5.2.5. Computational Procedures and Modeling
......................................................................................................................................................................
115
5.3 Results and
Discussion..................................................................................................................................................................................................
116
5.3.1. Structral studies
.....................................................................................................................................................................................................
116
5.3.2. Steady-state spectroscopy
......................................................................................................................................................................................
120
5.3.3. Transient spectroscopy
............................................................................................................................................................................................
123
5.3.4. Computational modeling of CO
streching........................................................................................................................................................................
131
5.4 Conclusion
.................................................................................................................................................................................................................
133
References
......................................................................................................................................................................................................................
134
Chapter 6 Cobalt(II) and Tin(II) Complexes Based-on Trivacant
Polyoxoanion Ligands: Synthesis, Structures, Physicochemistry and
Catalytic Water Oxidation Activity ........ 139
6.1 Introduction
...............................................................................................................................................................................................................
140
6.2 Experimental
...............................................................................................................................................................................................................
142
6.2.1. Materials and Instrumentation
....................................................................................................................................................................................
142
6.2.1. Syntheses
..............................................................................................................................................................................................................
143
6.2.2. X-Ray crystallography
...............................................................................................................................................................................................
147
6.3 Results and
Discussion...................................................................................................................................................................................................
148
6.3.1 Characterization of Cobalt(II) POMs
..............................................................................................................................................................................
148
6.3.2 Water-oxidation Activity of
Na10[{Co(H2O)3}2{WO2}2(SbW9O33)2]
....................................................................................................................................
151
6.3.3 Characterization of Tin(II) POMs
..................................................................................................................................................................................
152
6.3.4 Spectroscopic Study of Tin(II) POMs
............................................................................................................................................................................
157
6.4 Conclusions
................................................................................................................................................................................................................
160
References
......................................................................................................................................................................................................................
161
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