CONFORMATIONAL-ANALYSIS OF CROWN-ETHERS - PART 3 - ALKALI AND ALKALINE-EARTH CATION COMPLEXES OF 15-CROWN-5

An extensive conformational search of 15-crown-5 complexes with the al kali and alkaline earth cations was performed with an extended MM3 for ce field. A detailed comparison of the search results with crystallogr aphic data establishes that the model accurately predicts the structur al features of these compounds. An improved method is reported for sca nning a macrocycle conformer cavity to determine the preferred metal i on size. We demonstrate that the variations in ligand strain for diffe rent conformers as a function of metal size rationalize the crystallog raphically observed variations in 15-crown-5 conformation as a functio n of metal ion size and charge. (C) 1998 Elsevier Science B.V.