Syntheses, structures, and properties of sulfides constructed by SbS4 teeter-totter polyhedra: Ba3La4Ga2Sb2S15 and BaLa3GaSb2S10

Abstract

Two new pentanary sulfides Ba₃La₄Ga₂Sb₂S₁₅ (1) and BaLa₃GaSb₂S₁₀ (2) have been discovered by high temperature solid state reactions. Ba₃La₄Ga₂Sb₂S₁₅ features a new zero-dimensional structure type, which consists of unique isolated Sb₂S₇ dimers and GaS₄ tetrahedra. In contrast, with less GaS₄ tetrahedra in the formula, BaLa₃GaSb₂S₁₀ forms a one-dimensional structure which is constructed by teeter-totter (SbS₄)_n chains and isolated GaS₄ tetrahedra. On the basis of UV/Vis spectroscopy, their band gaps are determined to be 2.42 and 2.15 eV, respectively, which are much wider than that of analogue La₄FeSb₂S₁₀ (1.0 eV). In addition, theoretical studies illustrate the important role of Ga in expanding the band gaps with respect to Fe atoms. The calculated crystal orbital Hamilton population and electron localization function confirm that the long Sb–S bonds in Ba₃La₄Ga₂Sb₂S₁₅ (2.932(2) Å) and BaLa₃GaSb₂S₁₀ (3.216(5) and 3.219(5) Å) have weak but nonnegligible bonding interactions.