Spectrophotometric and thermodynamic study of supramolecular complexes of [60]- and [70]fullerenes with a number of calix[n]arenes

Abstract

[60]- and [70]fullerene have been shown to form 1 ∶ 1 supramolecular complexes with (i) 49,50,51,52,53,54,55,56-octamethoxy-5,11,17,23,29,35,41,47-octa(4-tert-butyl)calix[8]arene (1), (ii) 37,38,39,40,41,42-hexamethoxy-5,11,17,23,29,35-hexa(4-tert-butyl)calix[6]arene (2) and (iii) 37,39,41-trimethoxy-38,40,42-trihydroxy-5,11,17,23,29,35-hexa(4-tert-butyl)calix[6]arene (3) in three different solvents, namely CCl₄, toluene and o-xylene, by electronic absorption spectroscopy. Charge transfer absorption bands of the complexes have been identified in CCl₄ from which ionisation potentials of the calixarenes have been obtained. Isosbestic points have been found in the cases of C₆₀·1 and C₆₀·2 complexes in toluene and o-xylene. Formation constants of the complexes have been determined at four different temperatures from which the enthalpies and entropies of formation of the complexes have been obtained. Moreover, the formation constant of C₆₀·3 is higher than that of C₆₀·2 at all of the four temperatures studied. This has been rationalised in terms of a high degree of preorganisation of the host 3 through intramolecular H-bonding at its lower rim.