The NMR isoshielding diagram for an f-electron system in a crystal field environment of octahedral symmetry

Abstract

A general expression using a nonmultipolar expansion technique is derived for the NMR shift resulting from the f-electron orbital angular momentum and the f-electron spin dipolar-nuclear spin angular momentum interaction, where the f electron is in a crystal field environment of octahedral symmetry. From this expression all the multipolar terms are determined. For both the f 1 and f 13 ions in a crystal field of octahedral symmetry the exact solution for the NMR shift, ΔB, is compared with various approximations such as the effect of neglecting the crystal field and the magnetic field mixing of the two J levels and the multipolar terms. In addition an analysis of the temperature dependence of the exact solution further illustrates that considerable care must be taken in interpreting NMR results in paramagnetic systems. Finally, the variations in the isoshielding diagram is interpreted in terms of the predominant energy level of the ground state and this is governed primarily by the crystal field parameters.