Mechanism of Chiral Recognition of Octahedral Metal Complexes Effected by Bis(μ-d-tartrato)-diantimonate(III) Anion in Solution. I. Association Models and Their Application to Some [Co(N)6]3+-Type Complexes

An association model has been proposed which accounts for how bis(μ-d-tartrato)-diantimonate(III) anion, [Sb2(d-tart)2]2− ion recognizes the chirality of [Co(en)3]3+ (en=ethylenediamine) and some related cation complexes in solution. In this model, two oxygen atoms of the chiral anion, i.e., the carboxylic oxygen atom (coordinated to the Sb atom) of one d-tartrate moiety and the alcoholic oxygen atom (coordinated to the same Sb atom) of the other d-tartrate moiety, are hydrogen-bonded to the two amine protons in [Co(en)3]3+ which are directed along either the C3 or C2 axis. When these hydrogen bonds are formed along the C3 axis (C3 association), [Sb2(d-tart)2]2− ion forms a more favorable ion pair with Λ-[Co(en)3]3+, whereas it does with Δ-[Co(en)3]3+ if the two amine protons directed along the C2 axis are utilized for hydrogen bonding to it (C2 association). This model is successfully applied to the interpretation of chromatographic behavior of some [Co(N)6]3+-type complexes as well as of their related complexes with amine or phosphine ligands.