[en] 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 v_as(W-O_b,c-W), v_as(W=O_d), v_as(W-O_a) 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 p_π-d_π electronic transitions in the W=O bonds (at 46640 cm^-1 for the ligand and 47280 cm^-1 for the complex) and d_π-p_π-d_π transitions in tricentric W-O-W bonds (at 40880 cm^-1 for the ligand and 39920 cm^-1 for the complex). (author)