An analysis of the electronic spectra of bis-amine cobalt halides: a novel effect of steric hindrance

Abstract

The electronic absorption spectra (5000–30,000 cm.^–1)(in chloroform) of thirty-three complexes of general formula (Amine)₂CoX₂ where the amine is quinoline, isoquinoline, 2,6-dimethylpyrazine, pyridine, or a 2-, 3-, or 4-substituted pyridine, and X is Cl, Br, I, NCS, NCO, or NCSe, are reported. The near-infrared absorption band is split into three well defined components, whose overall width is some 1500–2000 cm.^–1 greater than is observed in regular tetrahedral cobalt derivatives (such as CoX₄^2–). These three components are assigned to the ⁴B₂â†�⁴A₂, ⁴A₂â†�⁴A₂, and ⁴B₁â†�⁴A₂ transitions in C_2v symmetry. With the exception of one band the absorption spectra are virtually independent of the amine throughout the entire region studied. The supposed ⁴B₂â†�⁴A₂ component of the near-infrared absorption decreases in energy by as much as 1000 cm.^–1 when the complex contains an α-substituted pyridine. A simple group-theoretical argument consistent with the occurrence of inter-ligand repulsions is suggested to explain this phenomenon. Mean values of 10Dq and B are computed and discussed.