The reaction of A(2)S(3)/U/P2S5/S at 500 C affords the quinary U(IV) thiophosphates A(6)U(3)Sb(2)P(8)S(32) (A = Rb, Cs). These compounds contain {U-3(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.