Synthesis, Crystal, and Electronic Structure of Ba3Sb2Q7 (Q = S, Se)

Two new barium antimony chalcogenides, Ba3Sb2S7 and Ba3Sb2Se7, were synthesized from elements by high‐temperature solid‐state reactions. The crystal structures were determined by means of single‐crystal X‐ray diffraction. Both compounds are isostructural and crystallize in a new structure type in the monoclinic space group C2/c (No. = 15) with unit cell parameters of a = 18.305(2)/18.904(5) Å, b = 12.202(1)/12.651(3) Å, c = 13.117(1)/13.554(3) Å, and β = 110.134(1)/109.839(4)° for Ba3Sb2S7/Ba3Sb2Se7, respectively. The crystal structures are comprised of Ba cations, trigonal‐pyramidal [SbQ3]3–, and [SbQ4]3– units (Q = S, Se). In the SbQ4 unit, one vertex is a Q2 dumbbell instead of a single Q atom. Quantum‐chemical calculations show that the sulfur‐containing compound is an indirect semiconductor with a high density of states below the Fermi level. ELF analysis shows highly polarized Sb–S bonds and unusual torus‐shaped ELF distributions around the terminal sulfur atom of the S2 dumbbell. According to UV/Vis measurements Ba3Sb2S7 is an indirect semiconductor with a bandgap of 2.1 eV.