Preparation and spectroscopic studies on charge-transfer complexes of 2,2′-bipyridine with picric and chloranilic acids

Charge-transfer (CT) complexes formed on the reaction of 2,2′-bipyridine with some acceptors such as picric acid (HPA) and chloranilic acid (H2CA) have been studied in CHCl3 and MeOH at room temperature. Based on elemental analysis and IR spectra of the solid CT complexes along with the photometric titration curves for the reactions, the data obtained indicate the formation of 1:1 charge-transfer complexes [(bpyH)(PA)] and [(bpyH2)(CA)], respectively. The infrared and 1H NMR spectroscopic data indicate a charge-transfer interaction associated with a proton migration from the acceptor to the donor followed by intramolecular hydrogen bonding. The formation constants (KC) for the complexes were shown to be dependent on the structure of the electron acceptors used.