The Layered Semiconductor Cu(Sb2S3)[AlCl4]

Abstract

Sb2S3 and CuCl were reacted in the ionic liquid [BMIm]Cl ⋅ 4.4AlCl3 (BMIm=1-n-butyl-3-methylimidazolium) at 200 °C. Upon cooling to room temperature, orange-red colored, air-sensitive crystals of Cu(Sb2S3)[AlCl4] precipitated. X-ray diffraction on a single-crystal revealed an orthorhombic crystal structure, in which cationic [Cu(Sb2S3)]+ layers are separated by tetrahedral [AlCl4]− anions. The uncharged Sb2S3 partial structure consists of one-dimensional strands with covalent Sb−S single bonds. The copper(I) cation is coordinated by three sulfur atoms and by one of chlorine atoms of the [AlCl4]– anion. An optical band gap of 2.14 eV was deduced from UV/Vis spectra. In very good agreement, a band gap of 2.07 eV results from DFT-based calculations involving a new implementation of the bifunctional formalism for the exchange energy. By treatment with 0.1 molar hydrochloric acid, AlCl3 was leached from Cu(Sb2S3)[AlCl4] yielding a compound with the presumed composition Cu(Sb2S3)Cl. Hydrolysis at higher pH resulted in Cu2–xS and Sb4O5Cl2.