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.