Optical rotatory power of co-ordination compounds. Part XIII. Circular dichroism of hetero-trischelated metal complexes of bipyridyl and phenanthroline

Abstract

Absorption and circular dichroism spectra are reported for the hetero-trischelated complexes [M phen₂bipy]ⁿ⁺ and [M bipy₂phen]ⁿ⁺ of nickel(II) and osmium-(II) and -(III)(bipy = 2,2′-bipyridyl and phen = 1,10-phenanthroline). The exciton theory of optical activity is developed for the hetero-trischelated complexes with two-fold rotational symmetry, and it is found that the relative rotational strengths and frequencies of the circular dichroism bands of the complexes studied in the 30,000–40,000 cm.^–1 region are in satisfactory agreement with the model. The dipole strengths of the isotropic absorption of the complexes show less satisfactory agreement with the theory, and the discrepancies are attributed to a minor contribution to the absorption from excitations of a charge-transfer and internal ligand origin which are polarised along the short in-plane axis of the ligand. These excitations do not contribute to the optical activity which derives principally from long-axis polarised ligand transitions. The (+)-isomers of the complexes studied are found to have the same configuration P(C₂), as that of (–)-[Fe phen₃]²⁺ established by X-ray crystallography.