A6U3Sb2P8S32 (A = Rb, Cs): quinary uranium(IV) thiophosphates containing the [Sb(PS4)3](6-) anion.

The reaction of A2S3/U/P2S5/S at 500 °C affords the quinary U(IV) thiophosphates A6U3Sb2P8S32 (A = Rb, Cs). These compounds contain {U3(PS4)2[Sb(PS4)3]2}(6-) layers separated by alkali metal cations. The layers are composed of trimeric uranium units connected to each other by the thiophosphato-antimonite anion, [Sb(PS4)3](6-). This unit contains a central Sb(III) cation bound by three [PS4](3-) anions, creating a trigonal pyramidal environment around Sb(III). Each uranium cation is surrounded by eight sulfides in a distorted square antiprism that shares two edges with two other US8 units to form a trimeric [U3S18](24-) cluster. Magnetic susceptibility measurements indicate that the close proximity of the U(IV) within these clusters leads to antiferromagnetic ordering at 53 K. Reflectance spectroscopy indicates that these compounds are semiconductors with a band gap of 1.48 eV.