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

Abstract

The electronic spectra of bromo complexes of main group metal ions with an s² electronic configuration (SnBr₃ ^-, PbBr₃ ^-, PbBr₄ ^2-, SbBr₄ ^-, SbBr₆ ^3-, BiBr₄ ^-, BiBr₆ ^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. BiBr₄-) undergo a photochemical redox decomposition induced by LMCT excitation.