Thermal properties of heterometallic oxymethoxy derivatives of rhenium, niobium, and tantalum

Using vapor pressure measurements (membrane manometer), we have studied the thermal decomposition of bi-and trimetallic rhenium-containing oxymethoxy derivatives with the general formula (Nb1−x Tax)4O2(OMe)14(ReO4)2 (x = 0, 0.3, 0.5, 0.7, 1). The thermal stability of the complexes has been shown to significantly depend on their composition and to correlate with the structural changes induced by partially ordered isomorphous substitution of tantalum for niobium. The phase composition of the products of (Nb1−x Tax)4O2(OMe)14(ReO4)2 decomposition has been determined by x-ray diffraction. The results demonstrate that the thermal decomposition of the oxymethoxy complexes in a closed system leads to the formation of crystalline phases at relatively low temperatures (≃ 160°C). The decomposition products consist of Re-Nb-O and Re-Ta-O oxides similar in structure to L-Ta2O5.