A MIXED-VALENT MOLYBDENOTUNGSTEN PHOSPHATE NA-1-RELATED TO THE PHOSPHATE TUNGSTEN BRONZES(X(MO,W)(2)O5PO4 CLOSELY)

A new mixed valent molybdenotungsten phosphate Na-1+x(Mo, W)(2)O5PO4 h as been synthesized. It crystallizes in the space group P 2(1)2(1)2(1) with a = 4.853(1) Angstrom, b = 8.516(1) Angstrom, c = 16.646(1) Angs trom The host lattice [Mo0.15W1.85PO9](p)roportional to consists of co rner-sharing MO(6) octahedra (nl = Mo, W) and PO4 tetrahedra forming e lliptic tunnels running along a where the sodium ions are located; the latter are distributed over two kinds of sites that are partly occupi ed. In fact, the [Mo0.15W1.85PO9](infinity) framework can be described as built up from ReO3-type ribbons parallel to (0 1 2) and (0 1 <0 1 (2)over bar>) alternately, connected through PO4 tetrahedra forming a fish bone array. Taking into consideration the presence of abnormally short Mo-O and W-O bonds corresponding to the existence of one free co rner per octahedron, the distribution of the different species-Mo(V), W(V), and W(VI)-is discussed on the basis of the formula Na-1.3((Mo0.1 5W0.15W1.70VI)-W-V-W-V)O5PO4. (C) 1996 Academic Press, Inc.