Charge-transfer complexes formed in the reaction of 1,4,7,10-tetraazacyclododecane with p-electron acceptors Siham Y. AlQaradawi a,⇑ , Adel Mostafa b , Hassan S. Bazzi b a Department of Chemistry and Earth Sciences, College of Arts and Sciences, Qatar University, P.O. Box 2713, Doha, Qatar b Department of Chemistry, Texas A&M University at Qatar, P.O. Box 23874, Doha, Qatar highlights " Five CT-complexes of the donor TACDD with several p-acceptors are obtained. " These CT-complexes are characterized through IR, UV-vis spectra, elemental and thermal analysis. " K CT , e CT , DG 0 , E CT and Ip are calculated. graphical abstract article info Article history: Received 1 October 2012 Received in revised form 31 December 2012 Accepted 3 January 2013 Available online 11 January 2013 Keywords: Charge-transfer TACDD TCNQ TBCHD Spectra abstract The reactions of the electron donor 1,4,7,10-tetraazacyclododecane (TACDD) with the p-electron acceptors 7,7,8,8-tetracyanoquinodimethane (TCNQ), tetracyanoethylene (TCNE), 2,3-dichloro-5,6-dicy- ano-p-benzoquinone (DDQ), 2,3,5,6-tetrachloro-1,4-benzoquinone (CHL) and 2,4,4,6-tetrabromo-2, 5-cyclohexadienone (TBCHD) were studied spectrophotometrically in chloroform at room temperature. The electronic and infrared spectra of the formed molecular charge-transfer (CT) complexes were recorded. The obtained results showed that the stoichiometries of the reactions are fixed and depend on the nature of both the donor and the acceptor. Based on the obtained data, the formed charge-transfer complexes were formulated as [(Donor)(Accep- tor) 2 ] for the donor (TACDD) and the acceptors TCNQ, TCNE, DDQ, CHL and TBCHD. These CT-complexes were isolated as solids and have been characterized through electronic and infrared spectra as well as elemental and thermal analysis measurements. The formation constants (K CT ), charge transfer energy (E CT ), molar extinction coefficients (e CT ), free energy change DG 0 , ionization potential Ip and oscillator strength f of the formed CT-complexes were obtained. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction The study of charge-transfer interactions between various elec- tron donors contains donor atoms, such as nitrogen, oxygen or sul- fur and p-acceptor has attracted increased interest over the last years. This is due to the important role of charge-transfer com- plexes play in biological systems and for quantitative estimations of drugs beside that they act as intermediates in a wide variety of reactions involving nucleophiles and electron deficient molecules [1]. Some of the CT-complexes show interesting physical properties such as electrical conductivities [2–7]. It has been cleared that both polyazacyclic and aza-aromatics compounds react with p-acceptors to form stable CT-complexes. The several applications that CT-complexes can make are including electronics, solar cells, optical devices and others [8–11]. Cyclen or 0022-2860/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.molstruc.2013.01.005 ⇑ Corresponding author. Tel.: +974 55507904; fax: +974 44835750. E-mail address: siham@qu.edu.qa (S.Y. AlQaradawi). Journal of Molecular Structure 1037 (2013) 209–217 Contents lists available at SciVerse ScienceDirect Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc