Electronic spectra of pure uranyl(V) complexes:: Characteristic absorption bands due to a UVO2+ core in visible and near-infrared regions

To clarify the electronic spectral properties of uranyl(V) complexes systematically, we measured absorption spectra of three types of pure uranyl(V) complexes: [(UO2)-O-V(dbM)(2)DMSO](-), [(UO2)-O-V(saloph)DMSO](-), and [(UO2)-O-V(CO3)(3)](5-)(dbm = dibenzoylmethanate, saloph = N,N'-disalicylidene-o-phenylenediaminate, DMSO = dimethyl sulfoxide). As a result, it was found that these uranyl(V) complexes have characteristic absorption bands in the visible-near-infrared (NIR) region, i.e., at around 640, 740, 860, 1470, and 1890 nm (molar absorptivity, epsilon = 150-900 m(-1.)cm(-1)) for [(UO2)-O-V(dbM)(2)DMSO](-), 650, 750, 900, 1400, and 1875 nm (epsilon = 100-300 m(-1.)cm(-1)) for [(UO2)-O-V(saloph)DMSO](-), and 760, 990, 1140, 1600, and 1800 nm (epsilon = 0.2-3.6 M(-1.)cm(-1)) for [(UO2)-O-V(CO3)3]5(-).. These characteristic absorption bands of the uranyl(V) complexes are attributable to the electronic transitions in the (UO2+)-O-V core because the spectral features are similar to each other despite the differences in the ligands coordinated to the equatorial plane of the (UO2+)-O-V moiety. On the other hand, the c values Of [(UO2)-O-V(CO3)(3)](5-) are quite smaller than those of [(UO2)-O-V(dbM)2DMSO]- and [UVO2(saloph)DMSO]-. Such differences can be explained by the different coordination geometries around the center uranium in these uranyl(V) complexes. Consequently, the absorption bands of the uranyl(V) complexes in visible-NIR region were assigned to f-f transitions in the 5f(1) configuration.