Synthesis,Structural Characterization,and Physical Properties of Cs2Ga2S5, and Redetermination of the Crystal Structure of Cs2S6

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) ų and Z=4. Cs₂Ga₂S₅ is the first compound that features one‐dimensional chains ${{{\hfill 1\atop \hfill \infty }}}$ 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 ${P\bar 1}$ with V=488.99(8) ų 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.