The crystal structure of α-copper vanadate

The crystal structure of α-copper vanadate has been determined and refined by full-matrix least-squares procedures using automatic diffractometer data to a residual R = 0.050 (R_w = 0.059). The space group is rhombohedral, $\text{R}\text{3}$, with hexagonal unit cell a = 12.857(3) and c = 7.161(2) Å (a_R = 7.797(2) Å and α = 111.06(1)°). On the basis of the detailed structural analysis the contents Cu_7?xV₆O_19?x with x = 0.22 are proposed for the rhombohedral cell. Copper is in the divalent and vanadium in the quadrivalent state. The structure is based on a cubic close-packed array of oxygen ions with the vanadium ion occupying an octahedral site, one copper in a partially occupied octahedral site and the other copper in a tetrahedral site. The latter is one of the few examples of tetrahedrally coordinated copper.