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 (ΔH^o) and entropies (ΔS^o), 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.

Keywords:

• Fullerene
• macrocycle
• azacrown
• complexation

Acknowledgments

Financial support from Research Office of Sharif University of Technology and Iran National Science Foundation is greatly acknowledged.