The Cyclic 48-Tungsto-8-Phosphate [H7P8W48O184]33- Contant-Tézé Polyanion and Its Derivatives [H6P4W24O94]18- and [H2P2W12O48]12-: Structural Aspects And Reactivity

Abstract

Polyoxometalates (POMs) are discrete, anionic metal-oxo clusters of early transition metals in high oxidation states (e.g., WVI, MoVI, VV) usually comprised of edge- and corner-shared MO6 octahedra. Lacunary POMs are defect heteropolyanions mainly of the Keggin or Dawson type, and they can be formed by the loss of one or more MO6 octahedra by controlled base hydrolysis. The largest subclass of POMs are tungstophosphates, and several lacunary derivatives are known, such as the Keggin-based [PW11O39]7- and [PW9O34]9-, and the Dawson-based [P2W17O61]10- and [P2W15O56]12-. This review is based on the cyclic 48-tungsto-8-phosphate [H7P8W48O184]33- (P8W48) as well as its smaller derivatives [H6P4W24O94]18- (P4W24), and [H2P2W12O48]12- (P2W12), with a focus on structural aspects, solution stability and reactivity. All three polyanions can be considered as inorganic multidentate O-donor ligands that coordinate with d, f or p-block metal ions. Here we provide a comprehensive overview of guest metal-containing derivatives of the P8W48 wheel, the P4W24 half-wheel and the P2W12 quarter wheel. The structures containing P2W12 as a building unit are presented in a sequence of increasing number of POM units in the resulting assembly. Transition metal-containing POMs have been of interest for decades due to their remarkable capability of forming novel and unexpected structures associated with interesting and relevant physicochemical properties (e.g., catalysis, magnetism, biomedicine, electrochemistry), and this also applies for derivatives containing P8W48, P4W24 and P2W12.