MIXED-VALENT MOLYBDENOTUNGSTEN MONOPHOSPHATE RB2MO2WO5(PO4)(3) - AN INTERCONNECTED TUNNEL STRUCTURE

A new mixed valent molybdenotungsten monophosphate Rb2Mo2WO5(PO4)(3) h as been synthesized, It crystallizes in the P2(1)/n space group with a = 10.756(2) Angstrom, b = 9.493(1) Angstrom, c = 15.478(3) Angstrom, beta = 108.99(2)degrees, The structure of this phase consists of corne r-sharing single MO6 octahedra, M2O11 bioctahedral units, and monophos phate PO4 groups forming large interconnected tunnels running along b and a where the rubidium cations are located. The complex host lattice [Mo2WP3O17](infinity) can be described by the assemblage of enantiomo rphic [M3P3O20](infinity) chains running along a. A preferential occup ation of two out of three octahedral sites by molybdenum is observed a nd a distribution of the hexavalent and pentavalent species in these d ifferent sites is proposed, The rather large Rb-O distances observed f or the three kinds of rubidium sites suggest possible mobility of the Rb+ cations in agreement with their high thermal factors. (C) 1997 Aca demic Press.