1H shielding anisotropy in Mg(OH)2: The isolated OH− group

Abstract

The proton NMR shielding tensor was measured at room temperature in the hexagonal layered compound magnesium hydroxide. The isotropic shielding is 29.9±2 and the anisotropy is 12.7±2 ppm, on the 1H absolute scale. From a Gierke and Flygare (GF) analysis of the data the OH− spin–rotation constant was found to be 51±14 kHz. The GF contributions from the neighbors of a given OH− group were subtracted from the experimental shielding and corrections were made for the effects of vibrational motion to give an isotropic shielding of 29.9±2, with an anisotropy of 13.7±2 ppm, for an isolated OH−. The OH− shielding anisotropy is in good agreement with the ab initio calculations of Ratcliffe et al., but the isotropic shielding is not. Proton spin–lattice relaxation measurements at 300 and 77 K gave evidence of proton conductivity in Mg(OH)2.