A Polyoxo-Polyolato Complex of Tantalum(v) with a Double Adamantane-Like [Ta_7O_(12)]~(11+) Core

摘要

In their highest oxidation state, some of the early transition metals, such as V, Nb, Ta, Mo and W, have a pronounced tendency to form polynuclear, oxo-bridged aggregates in aqueous solution. Polyoxometallate anions like [V_(10)O_(28)]~(6-), [M_6O_(19)]~(8-) (M = Nb, Ta), [Mo_7O_(24)](6-), [Mo-8O_(26)]~(4-) and [H_2W_(12)O_(40)]~(6-) are well known representatives of this type. The formation of polynuclear complexes is currently being intensively investigated, since such species can be regarded as discrete intermediates in the process of hydrolytic polymerization, which starts from a mononuclear species and leads to the solid oxide. The question arises whether the structural principles of the resulting solid can already be recognized in such intermediate species. A novel molecular architecture of a polynuclear oxo complex would thus be of special interest, since it could open routes to new materials. We have recently demonstrated that polyalcohols with a tripodal arrangement of the hydroxy groups are particularly suitable for stabilizing such polynuclear oxo complexes in solution, since the coordinated polyalcohols shield the periphery of the complex and thus prevent further aggregation. Starting with [Ta(tdci)_2]~(5+) (1, tdci = 1,3,5-trideoxy-l,3,5-tris(dimethylamino)-cis-inositol) as the mono-nuclear precursor, this strategy has now been used to prepare a heptanuclear complex having a unique, purely "inorganic" Ta_7O_(12) core with a double adamantane-like structure.