Molecular complex of iodine with 2,3′-bipyridyl

Abstract

Thermodynamic data for the formation of a 1:1 charge-transfer (CT) complex of iodine with 2,3′-bipyridyl (2,3′-Bpy) in carbon tetrachloride solution have been obtained from measurements of the blue-shifted iodine band; Δ H 0 = −28.62±4.78kJ mol −1 and Δ S 0 = −54.7±1.6 Jmol −1K −1. Infrared spectra of the iodine complex of 2,3′-Bpy in solids, together with those of iodine—bromide and iodine—chloride complexes, have been measured. Comparing the spectra of three halogen complexes with that of 2,3′-Bpy, it is suggested that the nitrogen atom at the 3-position is involved in 1:1 complex formation. Far i.r. spectra of the iodine complex in cyclohexane solution and those of the three halogen complexes in solids have also been obtained. Assignments for the modified IX (X = I, Br and Cl) stretching and the intermolecular NI stretching vibrations have been proposed. The force constants were calculated under the assumption of a linear triatomic model, DIX, where D denotes the donor molecule. The results were compared with those for the pyridine (Py).IX complexes.