The Quest for Mixed-Metal Alkoxides Based on Zinc: Synthesis and Characterization of Zinc-Tantalum Oxoisopropoxides

The Zn-Ta, Zn-Nb, Zn-Ti and Zn-Pb systems have been investigated with regard to the formation of mixed-metal alkoxides using infra-red as well as NMR (H-1, (207)pb). Lewis acid-base reactions between alkoxides, and between alkoxides and zinc acetate, as well as metathesis reactions, have been considered. Zinc alkoxides are polymeric and quite inert with respect to the formation of heterometallic alkoxides. Their inertness can be overcome in the case of tantalum isopropoxide by using a in situ, freshly prepared colloidal suspension of Zn(OiPr)(2). Metathesis reactions are another means of ensuring the formation of mixed-metal zinc-transition metal (M = Ta, Nb, Ti) alkoxides. The solid-state structure determination of [Ta2Zn(mu-O)(mu(3)-O)(mu-OiPr)(3)(OiPr)(4)I](2) 2 makes it possible to establish that of the non-halide derivative [ZnTa2O2(OiPr)(8)](2)1. H-1 NMR data indicate that the structures of both aggregates are retained in solution. Hydrolysis-polycondensation reactions of 2 and 1 give after thermal treatment Ta2ZnO6 with traces of Ta2O5 and of Ta2Zn3O8 and pure Ta2ZnO6 respectively.