Abstract

Recently, attention has been paid to Cr(V) complexes of polyols or sugars, which are also stable in biological systems. We have tested the usefulness of complementary ENDOR studies, which, as is well-known, can resolve hyperfine splittings not observable by EPR and thus provide information about the interaction between a paramagnetic center and the neighboring magnetic nuclei. The 'H ENDOR spectra recorded at the same temperature (Figure 2) are more revealing because for all complexes they clearly resolve distinct couplings for the different protons. Two coupling constants (AH)i = 0.40 and 1.16 MHz are observed for The finding is consistent with the presence of two classes of nonequivalent protons. The smaller coupling is attributed to the hydrogens of the methyl groups, as expected for a mechanism arising predominantly through atom-to-atom spin polarization. On the other hand, the larger coupling constant derives from the methine protons.

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