Thermodynamic Study on the Effect of O2N2-azacrown Macrocyclic Ring-size in Complexation with [60]Fullerene

Abstract

The interaction of [60]fullerene with a series of 15–19-membered macrocycles containing an O2N2-donor set has been investigated by UV-visible spectroscopy. The formation constants arising from the complexation of [60]fullerene with these azacrown macrocycles, having various ring size, were determined in CHCl3 media applying Benesi-Hildebrand equation. The stoichiometry has been found by the Job method in each case. The thermodynamic parameters, for example, formation enthalpies (ΔHo) and entropies (ΔSo), for these complexation were also determined. Experimentally, it was found that macroring size of the azacrown has a prominent effect on azacrown complexation with [60]fullerene in terms of their association constants (K). The best K value was measured for 18-membered ring size in which a 1:1 complexation with [60]fullerene was dominant. Monitoring this complexation by 1H NMR spectroscopy, the chemical shift changes recorded for CH2 groups on the macroring introduced its nitrogen groups as the main interaction sites.