K3BiAs6Se12: A two-dimensional bismuth selenoarsenate containing crown-shaped anions [As3Se6]3-

Single crystals of K3BiAs6Se12 were obtained from the reaction of Si, with in situ formed fluxes of K2Se3, As2Se3, and Se at 500 degrees C. The compound crystallizes in the trigonal space group P (3) over bar (No. 147) with a = 9.7478(7), c = 7.6525(6)angstrom, V = 629.72(8)angstrom(3), Z=1. The [Bi(As3Se6)(2)](3-) anion possesses a two-dimensional layered structure with trigonal symmetry consisting of [BiSe6] octahedra and crown-like cyclic [As3Se6](3-) units formed by three corner-sharing trigonal pyramidal [AsSe3](3-) anions. The [As3Se6](3-) fragment is located on a 3-fold axis with three As atoms and three Se atoms forming a six-membered ring in chair conformation. The Bi3+ ion is in an almost perfect octahedral geometry. The overall arrangement of the Bi3+ cations and the [As3Se6](3-) anions is related to the CdI2-type structure with the cations situated on the Cd2+ and the anions on the I- sites, respectively. The K+ cations are located between the [Bi(As3Se6)(2)](3-) layers. The K(1)(+) cation is coordinated by 9 Se2- anions from four [As3Se6](3-) units, one above and three below, in an irregular geometry, whereas the K(2)(+) cation is surrounded by six Se2- anions from four [As3Se6](3-) units, two above and two below, in a perfect octahedral fashion. The title compound is characterized with UV/vis diffuse reflectance spectroscopy, IR and Raman spectra. (c) 2011 Elsevier B.V. All rights reserved.