METASTABLE HEXAGONAL MOLYBDATES - HYDROTHERMAL PREPARATION, STRUCTURE, AND REACTIVITY

Hydrothermal treatment of acidified M(2)MoO(4) solutions at 150 degrees C for 3 days leads to a range of structures depending on the metal M. Hexagonal molybdates with the general formula (My . zH(2)O) Mo6-xO18-xH4x-y are formed when M is a small cation, such as Na+, NH4+ and Ag+. These molybdates crystallize as hexagonal rods and have the space group P6(3)/m. The open structure of these hexagonal molybdates both allows the M ions in the tunnels to be readily mobile and permits the ready intercalation of additional cations such as hydrogen and lithium. Upon continuous ion exchange of sodium molybdate with 6 N HNO3, a new hydrate, MoO3 . 0.6H(2)O, was formed; subsequent dehydration of this hydrate results in the formation of a new hexagonal modification of ''MoO3.'' The structural features, thermal properties, diffusion, and reactivity of these phases have been determined and compared with phases synthesized by other methods. (C) 1995 Academic Press, Inc.