K 3BiAs 6Se 12: A two-dimensional bismuth selenoarsenate containing crown-shaped anions [As 3Se 6] 3−

Abstract

Single crystals of K 3BiAs 6Se 12 were obtained from the reaction of Bi, with in situ formed fluxes of K 2Se 3, As 2Se 3, and Se at 500 °C. The compound crystallizes in the trigonal space group P 3 ¯ (No. 147) with a = 9.7478(7), c = 7.6525(6) Å, V = 629.72(8) Å 3, Z = 1. The [Bi(As 3Se 6) 2] 3− anion possesses a two-dimensional layered structure with trigonal symmetry consisting of [BiSe 6] octahedra and crown-like cyclic [As 3Se 6] 3− units formed by three corner-sharing trigonal pyramidal [AsSe 3] 3− anions. The [As 3Se 6] 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 Bi 3+ ion is in an almost perfect octahedral geometry. The overall arrangement of the Bi 3+ cations and the [As 3Se 6] 3− anions is related to the CdI 2-type structure with the cations situated on the Cd 2+ and the anions on the I − sites, respectively. The K + cations are located between the [Bi(As 3Se 6) 2] 3− layers. The K(1) + cation is coordinated by 9 Se 2− anions from four [As 3Se 6] 3− units, one above and three below, in an irregular geometry, whereas the K(2) + cation is surrounded by six Se 2− anions from four [As 3Se 6] 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.