The effect of spin delocalization on the proton magnetic relaxation in transition metal hexaaquo ions

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Abstract
The calculation of the effect of covalency on the electron–nuclear dipolar relaxation in low spin d5 complexes was extended to include all octahedral transition metal complexes. In particular, an expression was given for hexaaquo complexes and numerical calculations were performed for the hexaaquomanganese (II) ion. Taking into account spin delocalization, the calculated dipolar relaxation is larger than the value obtained using the point dipole appproximation. This effect was found to be relatively small for hexaaquo complexes owing to cancellations in the contributions from spin densities in the various water molecular orbitals. The result of the proton–manganese distance obtained from NMR relaxation times is compared with the available crystallographic data.