Spectral intensity and charge distributions in the tetrahedral chromophores, bis(3-amino-2-methylpropane-24thiolato)- and diacetatobis(ethylenethiourea)-cobalt(II)

Abstract

Ligand-field analyses of both transition energies and relative intensities are reported for the spin-allowed ‘d–d’ bands of bis(3-amino-2-methylpropane-2-thiolato) cobalt(II). Energy {e_λ} and transition moment {^Lt_λ} parameter values that reproduce experiment are critically compared with each other and with similar quantities from an earlier analysis of diacetatobis(ethylenethiourea) cobalt(II). The nature of the parameterization scheme in the intensity model is described and the chemical significance of its variables is reviewed and developed. The thiolate ligands in the first chromophore are revealed as strong σ donors but essentially π innocent. The thiourea ligators in the second chromophore are only weak bases but the acetates are shown to be both good σ and π donors. It is argued that the electron distribution in these cobalt–oxygen bonds is relatively well polarized towards the metal and contracted about the internuclear axis. These latter conclusions arise from an analysis of the spectral intensities.