INDUCED CIRCULAR-DICHROISM SPECTRA OF SOME ACHIRAL AND RACEMIC COBALT(III)-AMINE COMPLEXES IN AQUEOUS (R,R)-TARTRATE AND (R,R)-TARTRATOANTIMONATE(III) SOLUTIONS

The induced circular dichroism (ICD) spectra were measured in the first d-d transition region for the following cobalt(III)-amine complexes in aqueous solutions of (R,R)-tartrate and (R,R)-tartratoantimonate(III) anions; [Co-(en)n(NH3)6-2n]3+ (n=0-3) and cis-[Co(en)2(RNH2)2]3+ (R=methyl and ethyl). It was found that a single negative CD band was induced for all the complexes in (R,R) -tartrate solution, while a single positive one was induced for most of them in (R,R)-tartratoantimonate(III) solution; the ICD developed in it was composed of a single negative band for [Co(en)3]3+ and of two bands with opposite sign for trans-[Co(en)2(NH3)2]3+ and cis-[Co(en)2(EtNH2)2]3+. The ICD spectra obtained for racemic complexes were interpreted in terms of differential interactions of Λ- and Δ-enantiomers with (R,R)-tartrate or (R,R)-tartratoantimonate(III), and an attempt was made to correlate the sign of their ICD spectra with their chromatographic behavior on an SP-Sephadex ion-exchanger with these chiral anions as an eluent.