Preferential solvation studies using the solvatochromic dicyanobis(1,10-phenanthroline)iron(II) complex

Abstract

Solvent effects on the electronic spectra of dicyanobis(1,10-phenanthroline)iron(II) have been investigated in thirteen pure solvents and twenty binary solvent mixtures. In pure solvents, the shifts of the ν_max values are found to depend on more than one of the known solvent parameters (AN, α, β, DN and π*). AN, α and π* are found to be the most important solvent parameters, exerting a considerable effect on the solvatochromic shifts of the title complex. The preferential solvation of dicyanobis(1,10-phenanthroline)iron(II) in binary solvent mixtures has been investigated by monitoring the metal–ligand charge transfer band of the indicator complex. Organic solvents are preferred near the indicator complex in aqueous binary solvent mixtures (negative deviation), except in regions rich in MeCN, Me₂CO and 1,4-dioxane, where water molecules are preferred over the organic component (dual behavior). However, the indicator complex is preferentially solvated by the component which has the higher acceptor number in non-aqueous binary solvent mixtures. Negative deviation was observed in binary mixtures of CHCl₃ and Me₂CO with alcohols and positive deviation in mixtures of CHCl₃ with THF, DMSO and Me₂CO. Different criteria were considered to evaluate the extent of preferential solvation in different solvent mixtures, iz., the local molar fraction (X_A^L), the excess function (ΔX), the iso-solvation point (X_B^iso) and the preferential solvation constant (K_A/B). The preferential solvation data have been linearly correlated with the different solvent parameters.