A MOLYBDENUM(V) DIPHOSPHATE WITH A TUNNEL STRUCTURE - BETA-K2MO2O4P2O7

A new Mo(V) diphosphate with a tunnel structure, beta-K2Mo2O4P2O7, has been synthesized. This phase can be considered as a low temperature f orm of the monophosphate alpha-K2Mo2O3(PO4)(2). It crystallizes in the space group Pbcn with a = 9.314(1) Angstrom, b = 8.868(1) Angstrom, c = 10.954(2) Angstrom. The [Mo2P2O11]infinity framework consists of co rner-sharing bioctahedral Mo2O10 units and eclipsed P2O7 groups. It ca n be described as the assemblage of two enantiomorphic [Mo2P2O12]infin ity layers parallel to (010), themselves built up of [Mo2P2O12]infinit y chains, running along c. In these chains one Mo2O10 unit alternates with one P2O7 group along c. Each Mo2O10 unit of two edge-sharing octa hedra has two free apices, leading to the classical geometry of the Mo (V) octahedra characterized by an abnormally short Mo-O bond. The fram ework delimits tunnels running along b, where the potassium ions are l ocated with a tricapped trigonal prismatic coordination. (C) 1995 Acad emic Press, Inc.