Synthesis, crystal and electronic structure, and optical properties of two new chalcogenide-iodides: Ba(3)Q(4)I(2) (Q = S, Se)

Two new ternary chalcogenide-iodides, Ba3S4I2 and Ba3Se4I2, were synthesized through high-temperature solid-state reactions, and their structures were determined via single-crystal X-ray diffraction. Both compounds are isostructural and crystallize in the monoclinic space group C2/c (no. 15) with unit cell parameters of a = 14.507(4)/15.080(7) angstrom, b = 10.104(3)/10.400(5) angstrom, c = 8.206(2)/8.383(4) angstrom, beta = 101.847(4)/103.206(8)degrees, and Z = 4 for Ba3S4I2/Ba3Se4I2, respectively. The crystal structure of Ba(3)Q(4)I(2) (Q = S, Se) is constructed from Q(2)(2-) dumbbells and isolated I1- anions, which are surrounded by Ba2+ cations. According to UV/Vis spectroscopy, Ba3S4I2 is a semiconductor with a bandgap of 2.45(5) eV. Quantum-chemical calculations predict that Ba3S4I2 and Ba3Se4I2 are wide bandgap semiconductors with bandgaps of 2.50 and 2.06 eV, respectively. Electron localization function analysis of chemical bonding indicates covalent interactions in the Q(2)(2-) dumbbells.