Synthesis, Characterization, and Catalytic Water Oxidation Study of the Mixed Transition-Metal Polyoxometalate [Mn2Ni2(H2O)2(PW9O34)2]10- and Associated Cation Effects. Restricted; Files Only

Abstract

The novel mixed transition-metal polyoxometalate (POM), [Mn2Ni2(PW9O34)2]10- (Mn2Ni2) was synthesized and characterized via single-crystal x-ray diffraction. The x-ray diffraction data of the tetramethylammonium salt of Mn2Ni2 was solved and refined with an R1 value of 3.16%. The POM did not exhibit any water oxidation activity, its cyclic voltammetric behavior suggests a rapid oxidative event followed by a slower, staggered two-electron reductive event. The POM was synthesized after attempts to crystallize [Fe2Ni2(PW9O34)2]10- (Fe2Ni2) resulted in the precipitation of the previously reported [Fe4(PW9O34)2]6- (Fe4). The synthesis of Mn2Ni2 highlights the role of cation addition in the development of mixed-metal POMs and provides insight into possible synthetic routes for Fe2Ni2. This thesis builds on the work of Meilin Tao, who synthesized [Co2Ni2(PW9O34)2]10-, and Natalie Uhlikova, who worked on the synthesis of Fe2Ni2, in the Hill lab.

Table of Contents

(1) Introduction.....1

(2) Experimental Section.....5

2.1 Methods and Materials.....5

2.2 Syntheses and Characterization.....6

2.2.1 TBAFe4.....6

2.2.2 CsFe4.....8

2.2.3 The ammonium salt of [Fe6(PW9O34)2(PW7On)2]x-.....8

2.2.4 TBAZn2Ni2/Zn4.....9

2.2.5 TBAMn2Ni2.....10

2.2.6 CsMn4.....13

2.2.7 TMAMn2Ni2.....15

2.2.8 CsMn2Ni2.....18

2.3 Redox Properties and Catalytic Water Oxidation Activity.....18

2.3.1 Cyclic Voltammetry.....18

2.3.2 Water Oxidation.....19

(3) Results and Discussion.....19

3.1 Fe(II) Oxidation.....19

3.2 Parameters Dictating Crystallization.....22

3.2.1 Transition Metal Addition.....23

3.2.2 Concentrations of Reactants.....24

3.2.3 Hydrolytic Stability of Transition Metals in the Central Belt.....24

3.2.4 Counter-Cation Addition.....25

3.3 Limitations in Characterization Techniques.....29

3.4 Water Oxidation Mechanism and Mn2Ni2.....31

(4) Remaining Experiments.....34

4.1 Synthesis of Fe2Ni2.....34

4.1.1 Protocol A.....34

4.1.2 Protocol B.....34

4.1.3 UV-Vis Spectroscopy to Distinguish Fe2Ni2 from Fe4.....35

4.2 Remaining Mn2Ni2 Characterizing Data.....35

(5) Conclusion.....35

(6) References.....37

Figures, Tables and Equations

Figure 1.....2

Figure 2.....5

Figure 3.....7

Figure 4.....9

Figure 5.....11

Figure 6.....13

Figure 7.....15

Figure 8.....16

Figure 9.....19

Figure 10....21

Figure 11....22

Figure 12....23

Figure 13....26

Figure 14....28

Figure 15....31

Figure 16....32

Figure 17....33

Table 1.....12

Table 2.....14

Table 3.....17

Table 4.....27

Table 5.....29

Equation 1.....1

Equation 2.....1

Equation 3.....1

Equation 4.....20

Equation 5.....20

Equation 6.....20

Equation 7.....20

Equation 8.....25

Equation 9.....25

About this Honors Thesis

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School	Emory College
Department	Chemistry
Degree	B.S.
Submission	Honors Thesis
Language	English
Research Field	Chemistry, Inorganic
Palavra-chave	Inorganic Synthesis Polyoxometalate
Committee Chair / Thesis Advisor	Craig L. Hill, Emory University
Committee Members	Eri Saikawa, Emory University Cora MacBeth, Emory University

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