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

The electronic spectra o f bromo complexes o f main group metal ions with an s2 electronic configuration (SnBr3~, PbBr3~, PbBr42_, SbBr4~, SbBr63~, BiBr4~, BiBr63~) in acetonitrile show long-wavelength absorption bands which are assigned to metal-centered sp transitions. Com­ pared to the corresponding chloro complexes the sp bands o f the bromo complexes appear at longer wavelength due to sp/LM CT mixing (LMCT = ligand-to-metal charge transfer). As a result o f this mixing the luminescence which originates from low-energy sp excited states is much weaker than that o f the chloro complexes. Moreover, some o f the bromo complexes (e.g. BiBr4~) undergo a photochemical redox decomposition induced by LMCT excitation.