Date of Award

12-2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Chemistry

Advisor

Hwu, Shiou-Jyh

Committee Member

Creager, Stephen

Committee Member

Tennyson, Andrew

Committee Member

He, Jian

Abstract

Herein, several new salt-inclusion solids (SISs) featuring electronically reduced Keggin polyoxometalate (POM) clusters were isolated for the first time using molten-salt high temperature (> 500 oC) synthetic method. These POM-based SISs are novel all-inorganic materials featuring an integrated lattice of ionic halide salt and covalent metal oxide clusters. Due to the weak interactions at the interface between these two chemically dissimilar lattices, these POM SISs are soluble in aqueous and polar solvents. While POM compounds are well-studied and are routinely synthesized in solution, the synthetic method presented in this dissertation yielded several POM solids with interesting structures and infrequently observed, reduced oxidation states of the transition metal cations. This dissertation focuses on describing the high temperature (> 500 oC), salt-inclusion synthesis of several all-inorganic, reduced polyoxometalate clusters. Four chapters with different chemical systems are presented. Chapters 3, 4, and 5 feature related Keggin-based POM compounds: namely the one electron reduced, Cs6I3Na(PMo12O40), POM compound in Chapter 3; the two electron reduced family of compounds, Cs6X2Na(PMo12O40) where X2 = Cl2, ICl, Br2, and I2 in Chapter 4; and the highly reduced family of compounds, Cs6X2M(PMo12O40) where M3+ = Ti, V, Mn, Fe and X2 = Cl2, Br2 and I2 in Chapter 5. In addition, a series of hybrid inorganic-organic compounds based on reduced polyoxovanadates (POVs) are presented in Chapter 6 where a novel method using pre-synthesized soluble POVs was used. These results demonstrate the utility of salt-inclusion chemistry in regards to water-soluble POM salts that can be used for various transformative studies of biomedical and catalytic relevance. Antibacterial tests in aqueous solution of the two electron reduced POMs (Chapter 4) show that the Staph. A. bacterial strains (SA1199, SA1199B, MRSA) are more susceptible to inhibition by the reduced POMs, presented herein, compared to their fully oxidized counterparts (e.g. Na3PMoVI12O40•2H2O). Replacing the Na+ cation in the two electron reduced POM with transition metals (Ti, V, Mn and Fe) resulted in the isostructural highly reduced family of compounds in Chapter 5. These novel POM SISs feature infinite one-dimensional (1D) transition metal-oxide chains with interlinked Keggin clusters, {-M-(PMo12O40)-}∞. These chains feature unusual square antiprismatic eight-coordinate environments of the transition metals chelated by the Keggin clusters and forming chains along the tetragonal (P4/ncc), c crystallographic direction. The unusual eight-coordination of the first-row transition metals is the first such example in an all-inorganic compound with oxo-based ligand environment. The compounds presented in this dissertation were characterized by several solid-state and solution-based characterization techniques including: single crystal and powder X-ray diffraction, biomedical properties of soluble POMs, magnetic susceptibility, spectroscopy (UV-vis and IR), electrochemical properties, and thermogravimetric analysis. The work presented in this dissertation is significant for several reasons: 1) this opens up a new method for synthesis of POM solids; 2) isolation of electronically reduced POMs is favored using the high-temperature, molten-salt method; 3) this method produced novel POM-based SISs that are otherwise unattainable using conventional methods; 4) unusual structures and local geometry (e.g. metal-oxide connectivity along c and eight-coordination of transition metals) could give rise to interesting properties, including water-soluble clusters, to be studied in the near future; 5) in regards to the solids synthesized in Chapter 6, a new understanding of the interaction between anionic POV clusters and organic ligands with respect to the nature of bonding is learned; 6) finally, the synthesis of POM SISs illustrated, once more, the versatility and utility of the salt-inclusion synthetic method.

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