Partial molar volume study of the complexes of calix[4]naphthalenes with [60]fullerene in different solvents

Calix[4]naphthalenes are a class of cavitands or container molecules that p ossess deeper cavities than those of analogous calix[4]arenes. Earlier stud ies of the complexation of [60]fullerene (C-60) with the C-4-symmetrical en do-calix[4]naphthalene (1) and its tert-butyl-substituted derivative (2) sh ow that they form supramolecular 1 : 1 complexes with C-60 in benzene, tolu ene or CS2 solution with relatively high association equilibrium constants (K-assoc). Reported herein are densitometer-derived standard partial molar volume changes for the complexation, in these respective solvents, of C-60 and the calix[4]naphthalenes 1 and 2. In the case of the C(60)subset of2 co mplexes, the results are consistent with a solvophobic effect postulated pr eviously. The results obtained for the C(60)subset of1 complexes however su ggest that in addition to a solvophobic effect, other factors may be operat ing.