Synthesis, crystal and band structures, and optical properties of a new framework mercury pnictides: [Hg4As2](InBr3.5As0.5) with tridymite topology

A new framework compound, [Hg4As2](InBr3.5As0.5) (1), has been prepared by the solid-state reaction of Hg2Br2 with elemental In and As at 450 degrees C. Compound 1 crystallizes in the space group P-63/mmc of the Hexagonal system with two formula units in a cell: a = b = 7.7408(6) angstrom, c = 12.5350(19) angstrom, V = 650.47(12) angstrom(3). The crystal structure of 1 features a novel 3D framework, [Hg4As2](2+) with tridymite topology. The optical properties were investigated in terms of the diffuse reflectance and infrared spectra. The electronic band structure along with density of states (DOS) calculated by OFT method indicates that the present compound is semiconductor, and the optical absorption is mainly originated from the charge transitions from Br-4p and As-4p states to Hg-6s and In-5p states. (C) 2010 Elsevier B.V. All rights reserved.