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

Abstract

Calix[4]naphthalenes are a class of cavitands or container molecules that possess deeper cavities than those of analogous calix[4]arenes. Earlier studies of the complexation of [60]fullerene (C₆₀) with the C₄-symmetrical endo-calix[4]naphthalene (1) and its tert-butyl-substituted derivative (2) show that they form supramolecular 1∶1 complexes with C₆₀ in benzene, toluene 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 C₆₀ and the calix[4]naphthalenes 1 and 2. In the case of the C₆₀⊂2 complexes, the results are consistent with a solvophobic effect postulated previously. The results obtained for the C₆₀⊂1 complexes however suggest that in addition to a solvophobic effect, other factors may be operating.