Synthesis and Structural Characterization of Quaternary Thorium Selenophosphates: A₂ThP₃Se₉ (A = K, Rb) and Cs₄Th₂P₅Se₁₇

Single crystals of A2ThP3Se9 (A = K (I), Rb (II)) and Cs4Th2PsSe17 (III) form from the reaction of Th and P in a molten A2Se3/Se (A = K, Rb, Cs) flux at 750 °C for 100 h. Compound I crystallizes in the triclinic space group P1̄ (No. 2) with unit cell parameters a = 10.4582(5) Å, b = 16.5384(8) Å, c = 10.2245(5) Å, α = 107.637(1); β = 91.652(1); γ = 90.343(1)°, and Z = 2. Compound II crystallizes in the triclinic space group P1̄ (No. 2) with the unit cell parameters a = 10.5369(5) Å, b = 16.6914(8) Å, c = 10.2864(5) Å, α = 107.614(1)°, β = 92.059(1)°, γ = 90.409(1)°, and Z = 2. These structures consist of infinite chains of corner-sharing [Th2Se14] units linked by (P2Se6)4- anions in two directions to form a ribbonlike structure along the [100] direction. Compounds I and II are isostructural with the previously reported K2UP3Se9. Compound III crystallizes in the monoclinic space group P2l/c (No. 14) with unit cell parameters a = 10.238(1) Å, b = 32.182(2) Å, c = 10.749(1) Å; β = 95.832(1)°, and Z = 4. Cs4Th2P5Se17 consists of infinite chains of corner-sharing, polyhedral [Th2Se13] units that are also linked by (P2Se6)4- anions in the [100] and [010] directions to form a layered structure. The structure of III features an (Se2)2- anion that is bound η2 to Th(2) and η1 to Th(1). This anion influences the coordination sphere of the 9-coordinate Th(2) atom such that it is best described as bicapped trigonal prismatic where the η2-bound anion occupies one coordination site. The composition of III may be formulated as Cs4Th2(P2Se6)5/2(Se2) due to the presence of the (Se2)2- unit. Raman spectra for these compounds and their interpretation are reported.