Alkoxide Route to Mixed Oxides of Rhenium, Niobium, and Tantalum. Preparation and X-ray Single-Crystal Study of a Novel Rhenium−Niobium Methoxo Complex, Nb2(OMe)8(ReO4)2

Thermal decomposition of complex oxomethoxo compounds Nb 4 O 2 (OMe) 14 (ReO 4 ) 2 ( I ) and Ta 4 O 2 (OMe) 14 (ReO 4 ) 2 ( II ) has been investigated. The decomposition of ( II ) at temperatures exceeding 100 °C results in the formation of MeOMe, MeOCH 2 OMe, MeOH, and H 2 O vapor and is accompanied by sublimation at temperatures over 135 °C. Plausible mechanisms of the processes studied are discussed. A new bimetallic methoxo compound, Nb 2 (OMe) 8 (ReO 4 ) 2 ( III ), was synthesized by interaction between Re 2 O 7 and Nb 2 (OMe) 10 in toluene solution and its structure was determined by means of an X-ray single-crystal study. The structure can be considered as a product of substitution for terminal methoxo groups with two perrhenate groups in dimeric Nb 2 (OMe) 10 molecules. Decomposition of II in an inert atmosphere at 900 °C gave a Re−Ta mixed oxide phase, supposedly based on the L-Ta 2 O 5 structure. Decomposition of I and III under similar conditions leads to the formation of rhenium−niobium oxide phases. The results obtained provide a basis for the alkoxide approach to the synthesis of oxide and metallic rhenium-based materials.