Solvothermal Syntheses and Characterizations of Four Quaternary Copper Sulfides BaCu3MS4 (M = In, Ga) and BaCu2MS4 (M = Sn, Ge).

Hydro(solvo)thermal syntheses of quaternary copper sulfides containing alkaline earth metal ions remain a great challenge because of the low solubility of Cu-S compounds. Herein, a new facile solvothermal method was developed, and four quaternary copper sulfides, i.e., BaCu3InS4 (1), BaCu3GaS4 (2), BaCu2SnS4 (3), and BaCu2GeS4 (4), were prepared using excess sulfur as a mineralizer. Compound 1 possesses a novel three-dimensional (3D) anionic [Cu3InS4]2- framework constructed by an 8-membered ring of [Cu4S4] and [Cu2In2S4] alternatively. Compound 2 features a unique 3D anionic [Cu3GaS4]2- framework composed of [Cu3GaS10]n14n- anionic chains and 8-membered rings, in which [Cu4S4] and [Cu2Ga2S4] reside alternatively. Compounds 3 and 4 feature 3D anionic [Cu2MS4]2- (M = Sn, Ge) frameworks composed of CuS4 and MS4 tetrahedra with Ba2+ located in the channels. It is worth noting that different 3D Cu-S frameworks exist in the title crystal structures, in which main group ions are incorporated. This paper provides a new synthetic strategy for new quaternary sulfides.