Stereoselective ion association of [Co(en)2(phen)]3+ with metal complex anions

Ion association constants of Λ- and Δ-[Co(en)2(phen)]3+ (en=ethylenediamine and phen=1,10-phenanthroline) with Δ-[Co(mal)2(gly)]2− (mal=malonate and gly=glycinate), Δ-[Co(ox)2(gly)]2− (ox=oxalate), and Δ-C1-cis(N)-[Co(ox)(gly)2]− in aqueous solution were determined at 25°C and an ionic strength of 0.01 M by the conductivity method. The preferred ion pair between [Co(en)2(phen)]3+ and the above three complex anions was ΔΔ (homochiral combination), contrasting with a heterochiral (ΛΔ) preference for the ion pair between [Co(en)3]3+ and the same complex anions. In addition, the discrimination factors, K(ΔΔ)/K(ΛΔ), in the [Co(en)2(phen)]3+ systems were appreciably larger than those in the corresponding [Co(en)3]3+ systems. The results are interpreted in terms of the interaction mode different from that of [Co(en)3]3+, and the ion association model responsible for the chiral recognition by [Co(en)2(phen)]3+ is proposed.