Ethylidene Pyridine Bisphosphonate based Polyoxometalates Synthesis Structure and Properties

Abstract

Polyoxometalates (POMs) as molecular metal oxygen anionic cluster possessing high oxidation state of early transition metals such as WV/VI, MoV/VI, VIV/V etc, have attracted tremendous interest owing to their large structural diversity with incredible applications in the field of energy, catalysis, magnetism and biology. Such compounds are formed by the condensation of metal salts in weakly acidic condition via the process of olation by the connection of M-O-M bonds with close-cage type structure, and even encapsulating hetero elements such as P, Sb, As, Si, etc. Various transition metal (3d, 4d) and rare earth metal (4f) substituted heterometallic polyoxometalate structures have been reported, advancing their chemical and physical properties. newlineRecently, a new class of heteropolyoxometalate structures based upon the bisphosphonate moiety have been reported in the literature. In sharp contrast to the conventional polyoxometalate structures, such compounds usually exhibit an open structure type, with the ditetrahedral hetero group(s) situated on the outside of the polyanion structure. These structural features allow for the tuning of the properties of the polyanions such as stability, solubility and polarity by modifying the nature or substituent of the hetero groups within the bisphosphonate ligands. In this thesis we report the synthesis, characterization and applications of pyridine-based bisphosphonate-polyoxometalate derivatives. The presence of the heteroaromatic functional group upon the bisphosphonate moiety provides us with an additional functionality to explore from, namely, the location of the heteroatom upon the aromatic ring. newline