Spectroscopic and Thermodynamic Studies on Charge Transfer Complex Formation between 2-Aminopyridine and 2,5-Dihydroxy-p-benzoquinone

Author： Al-Ahmary Khairia Habeeb Moustafa Al-Solmy Eman

Publisher： Springer Publishing Company

ISSN： 0095-9782

Source： Journal of Solution Chemistry, Vol.39, Iss.9, 2010-10, pp. : 1264-1277

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Abstract

Charge transfer complex formation between 2-aminopyridine (2AP) as the electron donor with 2,5-dihydroxy-p-benzoquinone (AHBQ) as the π-electron acceptor has been investigated spectrophotometrically in acetonitrile (AN) and 50% acetonitrile + 50% 1,2-dichloroethane (V/V), (ANDC). The stoichiometry of the complex has been identified by Job’s method to be 1:1. The Benesi-Hildebrand equation has been applied to estimate the formation constant (K _CT) and molecular extinction coefficient (ε). It was found that the value of K _CT is larger in ANDC than in AN. The thermodynamic parameters are in agreement with the K _CT values in that the enthalpy of formation (−∆H) has a larger value in ANDC than in AN, suggesting higher stability of the complex in ANDC. The complex formed between 2AP and DHBQ has been isolated as a solid and characterized using elemental analysis, FTIR, and ¹H NMR measurements. Moreover, it has been found that the formed complex involves proton transfer in addition to charge transfer.