Synthesis, properties, and crystal structure of Cu3Mo8O23X2 (X = Cl, Br, I)

Single crystals of the Cu3Mo8O23X2 compounds were grown by chemical transport reactions at the lower temperature of a gradient 873-823 K without extra transport agent (auto transport). As DTA/TG measurements indicate, the gaseous compounds, necessary for chemical transport reactions, are formed by partial decomposition of Cu3Mo8O23X2 at 873 K. Cu3Mo8O23Br2 crystallizes with the orthorombic space group Pbcm (a = 4.021(1), b = 22.978(2), c = 21.673(2) Angstrom, Z = 4). The crystal structure consists of pentagonal columns (1)(infinity)[Mo6O7O20/2] linked by additional MoO6/2 octahedra. All the polyhedra(pentagonal bipyramide, octahedra) are distorted. Infinite chains (1)(infinity)[Cu3Br2] along [100] are arranged in tunnels with s-like square shape, left open by the pentagonal columns. Cu3Mo8O23Cl2 (a=4.010(1), b= 22.942(2), c = 21.639(2) Angstrom) and Cu3Mo8O23I2 (a = 4.052(1), b = 23.075(2), c = 21.719(2) Angstrom) are isotypic.