Crystal structure of urusovite Cu[AlAsO5]: a new type of a tetrahedral aluminoarsenate polyanion

The crystal structure of the new mineral urusovite Cu[AlAsO5] has been dete rmined (monoclinic system, sp. gr. P2(1)/c, a = 7.335(1) Angstrom, b = 10.2 55(1) Angstrom, c = 5.599(1) Angstrom, beta = 99.79(1)degrees, V = 415.0(1) Angstrom(3), Z = 4). The structure is solved by direct methods and refined to R = 0.048 (wR = 0.103). The structure is built by open-branched {uB, (2 )(infinity)}[AlAsO5](2-) layers parallel to the (100) plane. The layers con sist of two-link chains of (t)(infinity)[Al2O6] tetrahedra, which are paral lel to the z-axis and are connected through the [AsO4]-groups. The sharing- edges [CuO5] tetragonal pyramids link the aluminoarsenate layers to form a three-dimensional framework. The established layer is the second example of an tetrahedral aluminoarsenate polyanion. (C) 2000 MAIK "Nauka/Interperiod ica".