Synthesis, structure, and spectroscopy of two ternary uranium(IV) thiophosphates: UP₂S₉ and UP₂S₇ containing P₂S₉^2- and P₂S ₇^2- ligands

The two ternary uranium thiophosphate compounds were isolated from polychalcogenide flux reactions. UP₂S₉ crystallizes in the tetragonal space group P4₂/mcm with two formula units per unit cell, where a = 7.762(1) and c = 9.691(3) Å. UP₂S₇ crystallizes in the orthorhombic space group Fddd with 16 formula units per unit cell, here a = 8.919(3), b = 15.198(4), and c = 30.104(9) Å. Both compounds were characterized through single crystal X-ray, UV-vis-NIR, and Raman spectroscopy. The structures of the two compounds are formed from [US ₆]^8- chains connected to each other by either the tridentate-chelating P₂S₉ ^4- in UP ₂S₉ or the P₂S₇ ^4- in UP₂S₇ resulting in 3D frameworks. These two ligands have different geometries, but they exhibit similar coordination modes, comparable to the ethane-like P₂S₆ ^4-. The uranium cations in both compounds can be assigned an unambiguous oxidation state of +4. The two compounds are semiconductors with nearly identical band-gaps of 1.41 eV.