Synthesis, crystal and band structures, and optical properties of a new quaternary metal pnictidehalide: (Hg2Cd2As2Br)Br.

A new quaternary cadmium and mercury pnictidehalide semiconductor (Hg2Cd2As2Br)Br (1) has been prepared by the solid-state reaction of HgBr2 with elemental Cd and As at 420 degrees C. Compound 1 crystallizes in the space group Pmma of the orthorhombic system with two formula units in a cell: a = 8.791(4) A, b = 4.701(2) A, c = 9.779(6) A, V = 404.2(3) A(3). The structure of 1 is composed of parallel slabs bridged by linearly coordinated Hg atoms to form a 3D cationic network with the channels occupied by discrete Br anions, in which the layer consists of interlinks of linear (HgAs2Br2) tetrahedral chains and (CdAs2Br) trigonal chains. The optical properties were investigated in terms of the diffuse reflectance and Fourier transform infrared spectra. The electronic band structure along with the density of states (DOS) calculated by the DFT method indicate that compound 1 is a semiconductor with an indirect band gap and that the optical absorption mainly originates from the charge transitions from the Br2-4p and As-4p to Cd-5s and Hg-6s states.