Synthesis, structural characterization, and physical properties of Cs2Ga2S5, and redetermination of the crystal structure of Cs2S6

Abstract

The reaction of CsN3 with GaS and S at elevated temperatures results in Cs2Ga2S5. Its crystal structure was determined from single-crystal X-ray diffraction data. The colorless solid crystallizes in space group C2/c (no. 15) with V = 1073.3(4) Å(3) and Z = 4. Cs2Ga2S5 is the first compound that features one-dimensional chains ∞(1)([Ga2S3(S2)(2-)] of edge- and corner-sharing GaS4 tetrahedra. The vibrational band of the S2(2-) units at 493 cm(-1) was revealed by Raman spectroscopy. Cs2Ga2S5 has a wide bandgap of about 3.26 eV. The thermal decomposition of CsN3 yields elemental Cs, which reacts with sulfur to provide Cs2S6 as an intermediate product. The crystal structure of Cs2S6 was redetermined from selected single crystals. The red compound crystallizes in space group P1 with V = 488.99(8) Å(3) and Z = 2. Cs2S6 consists of S6(2-) polysulfide chains and two Cs positions with coordination numbers of 10 and 11, respectively. Results of DFT calculations on Cs2Ga2S5 are in good agreement with the experimental crystal structure and Raman data. The analysis of the chemical bonding behavior revealed completely ionic bonds for Cs, whereas Ga-S and S-S form polarized and fully covalent bonds, respectively. HOMO and LUMO are centered at the S2 units.

Keywords: cesium; density functional calculations; gallium; solid-state structures; sulfur.