Electronic energy levels in hexahalotellurate(IV) complexes

The electronic spectra of the octahedral Tecl_6^(2-) and TeBr+6^(2-) complexes are reported and assigned. s → p transition a_(lg)σ^* → t_(lu)σ^* gives rise to three spin-allowed bands in TeCl_6^(2-) (32,880; 34,480; 35,680 cm^(-1)) and TeBr_6^(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 TeCl_6^(2-); analogous transitions appear at 37,000 and 42,600 cm^(-1) in TeBr_6^(2-). The observed spectral data indicate that the "inert" 5s^2 Te(IV) electrons, which reside in the a_(lg)σ^* level, are partially delocalized to the halide ligands.