Anomaly of the basicity of water in mixed solvents

Abstract

Intermolecular interactions between water and N, N-dimethylformamide (DMF) in their mixtures were investigated by Raman spectroscopic and X-ray diffraction methods and by molecular orbital calculations. The Raman spectroscopic and X-ray diffraction measurements indicated the formation of water-DMF associates or clusters in the mixtures. Theoretical calculations for the electron density of H 2O-HOH-OH 2, ▪ of electron density on the oxygen atom of the water molecule in the DMF-HOH-DMF associate due to the accumulation of electrons transferred from DMF to the oxygen atom of the terminal water molecule. The increase resulted in a larger donicity of the terminal H 2O compared to normal water. Although the donor number D N of the water molecule in the DMF-H 2O-DMF associate was not determinable, it was estimated to be D N ∼ 30 from the behavior of the preferential solvation of the cobalt(II) ion in water-DMF mixtures.