The influence of structural effects on the complexing ability of crown ethers. III. Rubidium complexes formed by the ligands of the 18C6 type

A combined AM1 and molecular mechanics study of the complexation of the rub idium cation by nine substituted crown ethers, L, containing 18 atoms of ma croring is presented. The role of microsolvation was incorporated into the models by studying the complexes surrounded by six methanol molecules. The substituent effect is related to the interaction energy, E-int, which was c omputed for the clusters LRb+(CH3OH)(6) in their lowest energy conformation s. This is demonstrated by the linear correlation found by plotting logK(s) vs. E-int, where K-s stands for stability constant of a complex. The appro priate K-s values were calculated on the basis of cyclic voltammetric measu rements.