A NEW MIXED-VALENCE VANADIUM PHOSPHATE WITH AN INTERSECTING TUNNEL STRUCTURE - KV3P4O17

A new mixed-valence vanadium phosphate KV3P4O17 was isolated and its structure was determined from single-crystal X-ray diffraction data. This mixed valence phase crystallizes in the orthorhombic space group P212121, with a = 7.8654(5) Å, b = 10.0104(7) Å, c = 16.2715(8) Å, V = 1281.2(2) Å3, Z = 4, R = 0.053, and Rw = 0.062 for 701 unique reflections with I > 3σ(I). The structure can be described as built from ReO3-type infinite chains running along a. Laterally, in the (001) plane, chains are linked by P2O7 diphosphate groups, to form a three-dimensional framework. This host lattice delimits six-sided tunnels running along a, intersecting with brownmillerite zig-zag tunnels running along b. The potassium cations are located at the intersection of the two types of tunnels. Structural relationships with other mixed framework, and especially with diphosphate tungsten bronzes with hexagonal tunnels, are discussed. © 1992.