The temperature dependencies of lanthanide-induced NMR shifts: Evaluation of theoretical approaches and experimental evidence

Abstract

Bleaney's theory represents an excellent approximation in the calculation of the variation of magnetic susceptibility anisotropy as a function of f-electron configuration in complexes of trivalent lanthanide ions. Owing to certain approximations employed in his approach, Bleaney's prediction of a linear dependence of the anisotropy upon T −2 is not strictly correct. The more complete calculational procedure of Horrocks et al. predicts significant deviations from the simple T −2 temperature dependence in some cases. Experimental single-crystal magnetic anisotropy data on two axially symmetric Yb(III) complexes and a nonaxial Yb(III) shift reagent adduct reveal significant deviations from a linear dependence on T −2. Bleaney's assumption of an isotropic Landé splitting factor, g j is shown to be consistent with large g-tensor anisotropies of individual lanthanide ion levels and with large first-order Zeeman contributions to the observed shifts.