MIXED-VALENT MOLYBDENUM MONOPHOSPHATES WITH AN INTERSECTING TUNNEL STRUCTURE - A(3)O(2)(MOO)(4)(PO4)(4) (A=RB, TL)

New mixed valent monophosphates A(3)O(2)(MoO)(4)(PO4)(4) with an inter secting tunnel structure have been isolated for A = Rb, Tl. The struct ure of the Rb-phase has been solved from a single crystal X-ray diffra ction study. It crystallizes in the space group C222(1) with a = 14.22 2(1) Angstrom, b = 14.223(1) Angstrom, and c = 19.227(4) Angstrom. The structure is in fact closely related to that of the Mo(V) monophospha te K2O(MoO)(2)(PO4)(2). It consists of similar double layers [Mo2P2O11 ]infinity parallel to (001) and it is deduced from this Mo(V) monophos phate by a rotation of one double layer out of two of 180 degrees, so that it can be described as a chemical twin of the phosphate K2O(MoO)( 2)(PO4)(2). The geometry of the MoO6 octahedra is characteristic of Mo (V) in spite of the mixed valent Mo(V)-Mo(VI). The bond valence calcul ations suggest a delocalization of the electron between the two octahe dra of the bioctahedral units Mo2O11. (C) 1994 Academic Press, Inc.