EVIDENCE FOR CATION-PI INTERACTIONS IN CALIXCROWN-CENTER-DOT-KPIC COMPLEXES FROM X-RAY CRYSTAL-STRUCTURE ANALYSIS AND ENERGY CALCULATIONS

The crystal and molecular structures of the 1,3-diisopropoxy-p-tertbut yl calix[4]arene crown-5 fixed in the partial cone conformation and th at of its potassium picrate salt have been determined by single crysta l X-ray diffraction studies, Energy calculations have been performed t o gain more insight on the stabilizing cation...ligand interactions, T he calculation of the total potential energy indicates that the contri bution which comes from the electrostatic polarization induced by the electric field of the cation on the rotated nucleus gives a net stabil izing contribution of almost 6 kcal/mol. A comparison between the mole cular geometry of some partial cone 1,3-disubstituted-p-tertbutylcalix [4]arene derivatives is reported and discussed in view of the preorgan ization principle.