Complexation of three uranium(IV) ions at two α-B-[SbW9O33]9- trilacunary Keggin units. A spectroscopic investigation

The sandwich-type uranium(IV)-polyoxometalate Na6[U3(SbW9O33)2] x 22H2O was prepared and investigated by FT-IR and UV-VIS methods. The uranium(IV) coordination at the trilacunary Keggin units shifts the vas(W-Ob,c-W), vas(W=Od), vas(W-Oa) antisymmetric stretching vibration bands in the 700/950 cm-1 region of the FT-IR spectrum of U(IV)-complex. The visible electronic absorption spectrum of the complex indicates a 3H4 electronic ground state of uranium ions and a quasicubic local symmetry around them. The UV electronic spectra of the U(IV)-POM complex and of the ligand present the broad bands assigned to pπ-dπ electronic transitions in the W=O bonds (at 46640 cm-1 for the ligand and 47280 cm-1 for the complex) and dπ-pπ-dπ transitions in tricentric W-O-W bonds (at 40880 cm-1 for the ligand and 39920 cm-1 for the complex). (author)