Electronic Spectra and Photochemistry of Tin(II), Lead(II), Antimony(III), and Bismuth(III) Bromide Complexes in Solution

The electronic spectra of bromo complexes of main group metal ions with an s 2 electronic configuration (SnBr 3 - , PbBr 3 - , PbBr 4 2- , SbBr 4 - , SbBr 6 3- , BiBr 4 - , BiBr 6 3- ) in acetonitrile show long-wavelength absorption bands which are assigned to metal-centered sp transitions. Compared to the corresponding chloro complexes the sp bands of the bromo complexes appear at longer wavelength due to sp/LMCT mixing (LMCT = ligand-to-metal charge transfer). As a result of this mixing the luminescence which originates from low-energy sp excited states is much weaker than that of the chloro complexes. Moreover, some of the bromo complexes (e.g. BiBr 4 -) undergo a photochemical redox decomposition induced by LMCT excitation.