Hg5AsS2I3 - A Narrow-Band-Gap 2D Layered Compound with Different Trapped I- Anions.

A new layered compound, Hg5AsS2I3, has been synthesized in the quaternary system mercury/arsenic/chalcogen/halogen by a moderate-temperature solid-state reaction. The compound crystallizes in the space group C2/ c of the monoclinic system, and its structure consists of ∞1[Hg(1)2Hg(2)2As2/2S2] eight-membered-ring chains bridged by Hg atoms to form [Hg(1)2Hg(2)2Hg(3)As2/2S2] layers with inner- and interlayer electrostatic interactions between I and Hg. The optical properties were investigated by means of diffuse reflectance and FTIR spectra. The electronic band structures, along with density of states (DOS) calculations by DFT, indicate that the title compound is a semiconductor, and its optical absorption mainly leads to charge transitions from I-5p, As-4p and S-3p states to Hg-6s states, and both I(1) and I(2) atoms contribute to the top of the valence bands. [ABSTRACT FROM AUTHOR]