Preparation, spectroscopic and structural studies on charge-transfer complexes of 2,9-dimethyl-1,10-phenanthroline with some electron acceptors

Charge-transfer (CT) complexes formed in the reactions of 2,9-dimethyl-1,10-phenanthroline (Me2phen) with some acceptors such as chloranil (Chl), picric acid (HPA) and chloranilic acid (H2CA) have been studied in the defined solvent at room temperature. Based on elemental analysis and infrared spectra of the solid CT-complexes along with the photometric titration curves for the reactions, obtained data indicate the formation of 1:1 charge-transfer complexes [(Me2phen)(Chl)] (1), [(Me2phenH)(PA)] (2) and [(Me2phenH)(HCA)] (3), respectively, was proposed. In the three complexes, infrared and 1H NMR spectroscopic data indicate a charge-transfer interaction and as far as complexes 2 and 3 are concerned this interaction is associated with a hydrogen bonding. The formation constants for the complexes (KC) were shown to be dependent upon the nature of the electron acceptors used. The X-ray structure of complex 3 indicate the formation of dimeric units [Me2phenH]2[(HCA)2] in which the two anions (HCA)− are connected by two O–H⋯O hydrogen bonds whereas the cations and anions are joined together by strong three-center (bifurcated) N–H⋯O hydrogen bonds. Furthermore, the cations are arranged in a π–π stacking.