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

Abstract

The sandwich-type uranium(IV)-polyoxometalate Na₆ [U₃ (SbW₉ O₃₃ )₂ ]·22H₂ O was prepared and investigated by FT-IR and UV-VIS methods. The uranium(IV) coordination at the trilacunary Keggin units shifts the ν_as (W-O_b,c -W), ν_as (W=O_d ), ν_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 ³ H₄ 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).