Nuclear magnetic resonance relaxation study of I– and Na+ solvation structure in N-methylformamide (NMF) and preferential solvation of these ions in the mixture NMF—H2O

Abstract

Proton magnetic relaxation rates of HCONDCD₃, DCONHCD₃ and DCONDCD₂H caused by magnetic dipole–dipole interaction with ¹²⁷I and ²³Na in the ions I^– and Na⁺, respectively, have been measured. These results were obtained by the isotopic H/D substitution technique with extrapolation to the limit proton content → 0. From these data closest distances of approach between the interacting nuclei were derived which, with the geometry of the NMF molecule, yielded the ion–solvent configuration in the solvation sphere. The corresponding measurements for the formyl and methyl protons were performed in NMF–water mixtures over the whole composition range. The approximate degree of preferential solvation or preferential hydration could be derived from these measurements.