The [Ti₁₂Nb₆O₄₄]¹⁰⁻ Ion—A New Type of Polyoxometalate Structure

Abstract

Titanates and niobates are among the most promising materials to catalyze the photolysis of water to yield molecular hydrogen and oxygen. Solid-phase titanoniobate species, such as MTiNbO₅ (M=H, Li, K), have been attracting significant interest, but to our knowledge only one discrete homoleptic polyoxotitanoniobate cluster has so far been described, the cluster Na₈[Ti₂Nb₈O₂₈]. Herein we describe a second discrete homoleptic polyoxotitanoniobate cluster and a whole new class of polyoxometalates (POMs). This titanoniobate anion, [Ti₁₂Nb₆O₄₄]^10–, is about 1.5 nm in size, is stable in water at near-neutral pH, and, most interestingly, has a central cavity. As a result, it is most similar to, but much larger than, the Lindqvist ions and the central cavity is unique.