Absorption spectra and CT transitions of compounds containing ReI(CO)3Cl, S2+ and Se2+ as donors and o-benzoquinone diimine as acceptor

The electronic spectra of the cations [(BQDI)SeII]2+ and [(BQDI)SII]2+ are compared to that of [(BQDI)ReI(CO)3Cl] with BQDI = o-benzoquinone diimine. While these species show a BQDI-localized ππ∗ absorption between 300 and 360 nm, a longer-wavelength band extends to the visible region. This absorption is attributed to a CT transition from ReI (λmax = 538), SeII (λmax = 432) and SII (λmax = 360 nm) to the π∗ orbitals of BQDI. The analogy of MLCT and related CT transitions involving non-metals as CT donors is emphasized.