Peroxo-Thorium(IV)-Containing Heteropolytungstates and Their Oxo-Analogues: Synthesis, Structure and Solution Studies

We report the synthesis of peroxo-thorium(IV)-containing silico- and germanotungstates, [Th₃(μ₃-O₂)(OH)₂(H₂O)₃(A-α-XW₉O₃₄)₂]^12- (X = Si, Th₃O₂Si; Ge, Th₃O₂Ge), prepared in aqueous solution via a straightforward two-step procedure: (1) reaction of thorium(IV) cations with trilacunary polytungstate precursors, followed by (2) the addition of hydrogen peroxide. In the absence of hydrogen peroxide, we were able to obtain the oxo-analogues, [Th₃(μ₃-O)(OH)₃(H₂O)(A-α-SiW₉O₃₄)₂]^13- (Th₃Si) and [Th₃(μ₃-O)(OH)₃(A-α-GeW₉O₃₄)₂]^13- (Th₃Ge), respectively. All four polyanions crystallized as hydrated mixed rubidium-sodium salts. Single-crystal X-ray diffraction revealed that the four polyanions Th₃O₂Si, Th₃O₂Ge, Th₃Si, and Th₃Ge consist of two {A-α-XW₉O₃₄} fragments sandwiching a central, triangular thorium core. The structures of Th₃O₂X (X = Si, Ge) comprise a central peroxo-group with a rare side-on μ₃-coordination mode between the three thorium centers, representing the first example of peroxo-thorium(IV)-containing polyoxotungstates. Furthermore, ¹⁸³W NMR and electrochemical studies in solution were performed.