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

Solvent effects on the electronic spectra of dicyanobis(1,10-phenanthroline )iron(II) have been investigated in thirteen pure solvents and twenty binar y solvent mixtures. In pure solvents, the shifts of the nu (max) values are found to depend on more than one of the known solvent parameters (AN, alph a, beta, DN and pi*). AN, alpha and pi* are found to be the most important solvent parameters, exerting a considerable effect on the solvatochromic sh ifts of the title complex. The preferential solvation of dicyanobis(1,10-ph enanthroline)iron(II) in binary solvent mixtures has been investigated by m onitoring the metal-ligand charge transfer band of the indicator complex. O rganic solvents are preferred near the indicator complex in aqueous binary solvent mixtures (negative deviation), except in regions rich in MeCN, Me2C O and 1,4-dioxane, where water molecules are preferred over the organic com ponent (dual behavior). However, the indicator complex is preferentially so lvated by the component which has the higher acceptor number in non-aqueous binary solvent mixtures. Negative deviation was observed in binary mixture s of CHCl3 and Me2CO with alcohols and positive deviation in mixtures of CH Cl3 with THF, DMSO and Me2CO. Different criteria were considered to evaluat e the extent of preferential solvation in different solvent mixtures, viz., the local molar fraction (X-A(L),), the excess function (DeltaX), 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 dif ferent solvent parameters.