Role of Entropy and Autosolvation in Dimerization and Complexation of C₆₀ by Zn₇ Metallocavitands

The supramolecular chemistry of bowl-shaped heptazinc metallocavitands templated by Schiff base macrocycles has been investigated. Dimerization thermodynamics were probed by ¹H NMR spectroscopy in benzene-d₆, toluene-d₈, and p-xylene-d₁₀ and revealed the process to be entropy-driven and enthalpy-opposed in each solvent. Trends in the experimentally determined enthalpy and entropy values are related to the thermodynamics of solvent autosolvation, solvent molecules being released from the monomeric metallocavitand cavity into the bulk solvent upon dimerization. The relationship established between experimentally measured dimerization thermodynamics and autosolvation data successfully predicts the absence of dimerization in CH₂Cl₂ and CHCl₃ and was used to estimate the number of solvent molecules interacting with the monomeric metallocavitand in solution. Host–guest interactions between heptazinc metallocavitands and fullerene C₆₀ have also been investigated. Interestingly, metallocavitand-C₆₀ interactions are only observed in solvents that facilitate entropy-driven dimerization suggesting entropy and solvent autosolvation may be important in explaining concave-convex interactions.