The compounds Ba2An(S2)2S2 (An = U, Th) have been synthesized by reactions of the elements with BaS and S at 1273 and 1173 K, respectively. These isostructural compounds crystallize in a new structure type in the tetragonal space group D4h15-P4 2/nmc. The structure comprises Ba2+ cations and ∞2[An(S2)2(S)24-] layers. The An4+ cations in these layers are arranged linearly and are bridged by S2- anions. Coordination about the An center, which has symmetry 4Ì...m2, consists of two S22- ions and four S2- ions. Thus, the compounds are charge-balanced with An 4+. No other alkali-metal actinide chalcogenides are known that contain chalcogen-chalcogen bonds. Optical measurements on Ba 2Th(S2)2S2 indicate a direct band gap of 2.46(5) eV. Density functional theory calculations, performed with the HSE exchange-correlation potential, lead to band gaps of 2.2 and 1.8 eV for Ba2Th(S2)2S2 and Ba 2U(S2)2S2, respectively, thus demonstrating the utility of applying this functional to 5f-electron systems.
ASJC Scopus subject areas
- Inorganic Chemistry
- Physical and Theoretical Chemistry