Molecular Precursor Role in the Synthesis of ZrMVI2O8, MVI = Mo, W: Isolation and Properties of Zr3Mo8O24(OiPr)12(iPrOH)4

Abstract

The studies of zirconium isopropoxide solvate, Zr(OiPr)4·iPrOH(I), interaction with molybdenum oxoisopropoxide in different solvents (HOiPr, hexane) revealed I to be the only isolable crystalline product in alcohol. In hexane I crystallized from Zr-rich solutions (up to Zr : Mo = 1 : 2 ratio). From the solutions with Zr : Mo = 1 : 2 ratio repeatedly dried in vacuo and subsequently redissolved in hexane, the crystallization of Zr3Mo8O24(OiPr)12(iPrOH)4(II) occurred slowly with 12% yield. II can be recrystallized from hexane, but is destroyed by iPrOH which causes the formation of I. Thermal decomposition of II in air at 800°C (2 h) gives a single phase ZrMo2O8(III). Hydrolysis studies of hexane solutions, prepared in a manner analogous to those, from which II was obtained, showed that single-phase samples of III could be obtained when a thin layer of solution was left for hydrolysis and evaporation of solvent in a moist air and then annealed at 800°C (2 h). The same kind annealing of a xerogel, obtained by hydrolysis with water solutions in iPrOH and subsequent drying at 100°C gave a complex mixture of phases where III was not even the major component. No Zr-W complex was isolable under analogous conditions. From the xerogel, obtained by hydrolysis with H2O/iPrOH, ZrO2 and WO3 crystallized separately on heating. Only traces of ZrW2O8(IV) were obtained along with individual oxides when 1% water in ether was applied for hydrolysis. Molecular precursor is therefore crucial for obtaining III, IV.