Electronic Energy Levels in Hexahalotellurate(IV) Complexes

The electronic spectra of the octahedral TeCl₆^2- and TeBr₆^2- complexes are reported and assigned. The s → p transition a_1gσ* → T_1uσ* gives rise to three spin-allowed bands in TeCl₆^2- (32,880; 34,480; 35,680 cm^-1) and TeBr₆^2- (28,470; 29,730; 30,850 cm^-1). These data are taken as evidence that the excited singlet states are distorted to lower symmetry, probably C_2v. The lowest allowed halide → Te(IV) charge transfer transitions are at 44,170 cm^-1 and somewhat higher than 52,000 cm^-1 in TeCl₆^2- ; analogous transitions appear at 37,000 and 42,600 cm^-1 in TeBr₆^2-. The observed spectral data indicate that the “inert” 5s² Te(IV) electrons, which reside in the a_1gσ* level, are partially delocalized to the halide ligands.