Evidence for cation-π interactions in calixcrown·KPic complexes from X-ray crystal structure analysis and energy calculations

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