Spectroscopic studies of the charge-transfer interactions of halide ions

Solvent effects on the CTTS transitions of halide ions have been examined with particular reference to the role of hydrogen bonding. Hydrogen bonding of halide ions with methanol and water has been studied quantitatively. Thermodynamics for the interaction of halide ions with CCl4 have been reported in CH2Cl2 and CH3CN solvents; CCl4 undoubtedly acts as an acceptor in these systems. Charge-transfer interactions of halide ions with mono-,di- and tri-nitrobenzenes have been investigated in some detail. The donor ability of halide ions varies in the order, I− > Br− > Cl−, as expected on the basis of the ionization potentials. The acceptor ability of nitrobenzenes varies in the expected order, trinitrobenzene > dinitrobenzene > nitrobenzene. Charge-transfer energies for the interaction of halide ions with CCl4 as well as trinitrobenzene do not fall in line with energies found with these acceptors and aromatic donors. Photolysis of a solution of iodide ion in t-butanol in the presence of trinitrobenzene increases the concentration of the radical anion of trinitrobenzene.