The Influence of Structural Effects on the Complexing Ability of Crown Ethers III. Rubidium Complexes Formed by the Ligands of the 18C6 Typ

A combined AM 1 and molecular mechanics study of the complexation of the rubidium cation by nine substituted crown ethers, L, containing 18 atoms of macroring 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, Eint, which was computed for the clusters LRb+(CH3OH)6 in their lowest energy conformations. This is demonstrated by the linear correlation found by plotting logKs vs. Eint, where Ks stands for stability constant of a complex. The appropriate Ks values were calculated on the basis of cyclic voltammetric measurements.