Yasuharu OHMORI,* Masaaki KOJIMA,* Setsuo KASHINO* and Yuzo YOSHIKAWA (*Okayama Univ.)
[J. Coord. Chem. 39, 219 (1996)]
The ion-association constants between the optically active complex cations ((LAMBDA)-or (DELTA)-[Si(phen)3]4+) and the resolving agent anions ([Sb2{(+)-tart}2]2-, tart = tartrate(4-) ion) were determined spectrophotometrically. Ion-association between the complex cation and the eluent anion occurred in two steps and the stereoselective interaction was observed in the second step. The second-step association constant for the (LAMBDA)-enantiomer (K2 = 1.41 x 103) is larger than that for the (DELTA)-enantiomer (K2=1.07 x 103). The second-step association plays a dominant role in determining the elution order in column chromatographic resolution. The molecular mechanics calculations for the ion-associated species were performed to obtain information about the microscopic interaction between the ions. The total strain energy for the species containing the (LAMBDA)-enantiomer is smaller than that for the (DELTA) -enantiomer and this can explain the experimental finding that the (LAMBDA)-enantiomer is eluted faster than the (DELTA)-enantiomer.