Stable supramolecular complex of porphyrin macroring with pyridyl and fullerenyl ligands

Binding constants and thermodynamic parameters for 1:1 complexation of a porphyrin macroring, self-assembled from three trisporphyrinatozinc through imidazole-Zn coordination on the terminal porphyrins, with several multidentate pyridyl and fullerenyl ligands were examined. In benzonitrile, the ligand having one fullerenyl and two coordinative pyridyl moieties surprisingly afforded the highest affinity. The thermodynamic data of the complexation indicated that an unusual and fairly large positive entropic change, which may be attributed to extensive desolvation of the solutes especially from the large cavity of porphyrin macroring and fullerene surface, significantly contributed to the enhancement of the binding constant.