Further correlations of the CTTS solvent scale for halides with νmax for the solvated electron

Abstract

A linear correlation is presented between the absorption maxima of the first absorption bands of bromide and chloride, in a wide range of solvents at 298 K and ν_max for solvated iodide in the same solvents. The solvents include acetone, nitriles, phosphates, H₂O, D₂O and fluorinated aliphatic alcohols. The correlation between the CTTS solvent scale for iodide and the absorption maxima of the solvated electron at 298 K in 38 solvents and solvent mixtures has been extended and brought up to date. The linear correlation for iodide is of the form ν_max(e^–_solv)=[ν_max(I^–_solv)× 1.59–56.30]× 10³ cm^–1. At ν_max(e^–_solv)= 0, ν_max values of 35.41, 39.78 and 43.68 × 10³ cm^–1 were derived for iodide, bromide and chloride, respectively. These values are consistently higher than the ionisation potentials of the corresponding free ions. On subtraction of the ionisation potentials, an “excess energy” value of 10.57, 12.52 and 13.91 × 10³ cm^–1 is obtained for iodide, bromide and chloride, respectively. A plot of the “excess energy” values against the crystallographic radii of the halide ions was found to give a linear relationship. These and other results are discussed. In particular, the ability to predict ν_max for the solvated electron for a solvent in which ν_max for iodide is known is stressed.