The Structure of Ion-pairs of Λ- and Δ-[Co(en)3]3+ Ions with l-Tartrate and Related Anions as Deduced from Circular Dichroism Spectra

Abstract

Abstract The circular dichroism (CD) spectra of optical antipodes of [Co(en)3]3+ and [Co(pn)3]3+ were measured in the presence of l-tartrate, l-tartranilate or related dicarboxylate ions. l-Tartrate(2−) ions gave a large and stereoselective effect on the CD spectra; the CD change was greater for the Λ-complex than for the Δ-complex. Hydrogen-l-tartrate(1−) and l-tartranilate(1−) ions also caused stereoselective CD changes. On the other hand, succinates-(2−) and l-malate(2−) ions gave small and non-stereoselective CD changes, and undissociated tartaric acid gave no CD change. From a comparison of the results, it was concluded that two hydroxyl and one carboxylate groups of the L-tartrate ion form hydrogen bonds with three N–H groups of the tris(diamine)cobalt(III) ion of the lel form.