Optical rotatory power of co-ordination compounds. Part XVII. The circular dichroism of trisbipyridyl and trisphenanthroline complexes

Abstract

The circular dichroism spectra of (+)-[Cr(bipy)₃]³⁺, (+)-[Rh(phen)₃]³⁺. (+)-[Rh(bipy)₃]³⁺, (+)-[Co(phen)₂-(NO₂)₂]⁺, and (–)-[Co(bipy)₂(NO₂)₂]⁺, are reported, and the corresponding spectra of trisbipyridyl and tris-phenanthroline complexes previously studied have been remeasured over a more extended frequency range under higher resolution. The criteria proposed for determining the frequency-order of the principal exciton, c.d. bands derived from the coupling of long-axis polarised ligand π-excitations are reappraised, and it is concluded that the methods based primarily on isotropic absorption data are contraindicated. A method based largely on the c.d. data is used to obtain the frequency-order, and thence the stereochemical configuration of a range of isomers in the bis- and tris-bipyridyl and -phenanthroline series.