Optical rotatory power of co-ordination compounds. Part IX. The effect of ring conformation on the circular dichroism of cobalt(III) diamine complexes

Abstract

Circular dichroism spectra are reported for a series of tris-diaminecobalt(III) complex ions with different combinations of the two main conformations of the two main conformations of the three chelate rings, for trans-bis-diamine complexes, and for a series of tris-chelate oxalato-diamine complexes. It is found that the circular dichroism of the visible wavelength region reflects primarily the stereochemical configuration of a chelate rings around the metal ion, whereas the sign and the magnitude of the circular dichroism associated with the charge-transfer absorption in the ultraviolet region is governed additionally by the particular conformation of each of the chelate rings. In molar extinction coefficient units, the charge-transfer circular dichroism maximum of the tris-diamine complexes is made up additively from the combributions –20 for the M and +20 for the P configuration and +8 for the m-synclinal and -8 for the p-synclinal conformation of each chelate ring. These conformational contributions account for the charge-transfer circular dichroism of the trans-bis-diamine complexes and, with modified configurational contributions, for that of the oxalato-diamine complexes.