The Proton NMR Shifts and the Local Electric Field in Solid MgCl₂·6H₂O and in AlCl₃ Solution

Abstract

The proton NMR shifts Δσ of the water molecule co-ordinated to the cation in the crystal hexahydrate of magnesium chloride as well as in the aqueous solution of aluminium chloride relative to the pure liquid water at 0°C, have been observed. These shifts would largely depend on the component of the electric field F_⁄⁄ (e.s.u.) parallel to the direction of the OH bond of a water molecule, produced by the surrounding ions or neighbouring water molecules. The observed shifts Δσ are found to depend practically linearly on the calculated values of F_⁄⁄, and can be represented approximately by an empirical formula Δσ=5.0×10⁻⁶ F_⁄⁄+4.2 (ppm), where H→O direction being taken to be positive.