Thermodynamics of Host Guest Interactions between Fullerenes and a Buckycatcher

(1)H NMR and isothermal titration calorimetry (ITC) experiments were employed to obtain reliable thermodynamic data for the formation of the 1:1 inclusion complexes of fullerenes C60 and C70 with the buckycatcher (C60H28). NMR measurements were done in toluene-d8 and chlorobenzene-d5 at 288, 298, and 308 K, while the ITC titrations were performed in toluene, chlorobenzene, o-dichlorobenzene, anisole, and 1,1,2,2-tetrachloroethane at temperatures from 278 to 323 K. The association constants, Ka, obtained with both techniques are in very good agreement. The thermodynamic data obtained by ITC indicate that generally the host-guest association is enthalpy-driven. Interestingly, the entropy contributions are, with rare exceptions, slightly stabilizing or close to zero. Neither ?H nor ?S is constant over the temperature range studied, and these thermodynamic functions exhibit classical enthalpy/entropy compensation. The ?Cp values calculated from the temperature dependence of the calorimetric ?H values are negative for the association of both fullerenes with the buckycatcher in toluene. The negative ?Cp values are consistent with some desolvation of the host-cavity and the guest in the inclusion complexes, C60@C60H28 and C70@C60H28.