Solvent H-1 NMRD study of hexaaquochromium(III): Inferences on hydration and electron relaxation

The water proton nuclear magnetic relaxation dispersions (NMRD) of hexaaquo chromium(III) in water and in water-glycerol solutions were obtained at sev eral temperatures and viscosities. The data were analyzed in terms of the a vailable theories by taking into account the contributions from First spher e, second sphere, and outer sphere water molecules. A meaningful analysis w as possible by taking advantage of the structural model obtained from 170 r elaxation data, which was recently made available in the literature (Bleuze n, A.; Foglia, F.; Furet, E.; Helm, L.; Merbach, A.; Weber, J. J. Ain. Chem . Soc. 1996, 118, 12 777). Dynamic parameters, like the molecular rotationa l time, the exchange time of the water protons of the first coordination sp here, the correlation time for electron relaxation, and the magnetic field dependence of electron relaxation were obtained. The possible contribution to water proton relaxivity of second sphere water molecules for some other hexaaqua complexes is also discussed.