Synthesis, Structure And Characterization Of New Large Polyoxometalate Cluster Based On Lacunary Dawson-Type Building Blocks

The aim of this thesis is the synthesis of new polyoxotungstates compounds on the basis of Dawson-type polyoxoanion clusters, which are bridged by transition metal. Some new polyoxotungstates compounds have been synthesized under conventional conditions and characterized by elemental analyses, IR, TG and single crystal X-ray diffractions.1. Four new polyoxometalate compounds on the basis of trivacant Dawson-type polyoxoanions cluster, which coordinated by the Feâ…¢ions, have been synthesized and structurally characterized: Na₈(HTMA)₄[(Fe^IIIOH₂)₂(Fe^III)₂(P₂W₁₅O₅₆)₂]·20H₂O (1) Na₂₆[Fe₁₂(OH)₁₈(Na-hmta)₄ (H₂O)(P₂W₁₅O₅₆)₄]·72H₂O (2) K₂Na₁₂(HTMA)₂[Fe₈(OH)₁₂(P₂W₁₄O₅₄)₂]·32H₂O (3) Na₉(CH₃-hmta)₄(hmta)₂[{Fe_10-xW_xH_15-3xO₁₅(hmta)₂}(P₂W₁₃O₅₁)₂]·70H₂O (x = 0.18) (4)Compound 1 is constructed from sandwich-type polyoxoanions, which are charge-balanced by HTMA(TMA=trimethylamine)cations. Compound 2 exhibits an interesting 3D architecture which four Fe^III tri-substituted Wells–Dawson units linked together through Fe–O–Fe bonds giving a perfect Td symmetry. Compound 3 was obtained from the aqueous reaction system containing [Fe₃O(CH₃COO)₆(H₂O)₃]NO₃·7H₂O, the polyoxoanion [α-P₂W₁₅O₅₆]^12- ({P₂W₁₅}). Compound 4 is the first polynuclear FeIII cluster based on both inorganic O-donor polyoxometalate ligand and organic N-donor ligand hexamethylenetetramine (hmta).2. One new polyoxometalate compounds on the basis of vacant Dawson-type polyoxoanions cluster, which coordinated by the Cu²⁺ ions, have been synthesized and structurally characterized: (NH₄)₂[(CH₃)₃NH]₆[P₂W₁₆Cu₂(OH)₆]·16H₂O(5). Compound 5 consists of a dicopper^II-substituted Dawson polyoxoanion.