Polarized crystal absorption spectra and electronic states of tetraethylammonium hexabromodiplatinate(II)

Polarized crystal electronic absorption spectra are reported at 300/sup 0/ and 15/sup 0/K for normally cleaved crystals of (N(C/sub 2/H/sub 5/)/sub 4/)/sub 2/Pt/sub 2/Br/sub 6/. The spectra provide the polarization of the transitions with respect to the three molecular axes of the Pt/sub 2/Br/sub 6//sup 2 -/ ion. The excited states have been assigned under the D/sub 2h/ point group symmetry of the ion. There is sufficient delocalization of the d electrons that both spin-forbidden and spin-allowed d reverse arrow d transitions have strongly enhanced intensities and have dipole-allowed character in contrast to the PtBr/sub 4//sup 2 -/ ion. Although the energies of d reverse arrow d transitions are similar for PtBr/sub 4//sup 2 -/ and Pt/sub 2/Br/sub 6//sup 2 -/, M reverse arrow L charge-transfer transitions occur at lower energies for the dimeric ion. The polarization of these intense transitions indicates that they correspond to electron transfers from terminal bromides. (auth)