NMR shifts in paramagnetic systems: A nonmultipole expansion method

NMR shifts arising from the electron orbital angular momentum and the electron spin dipolar-nuclear spin angular momentum interactions using a nonmultipole expansion method are examined for a d electron in a crystal field of octahedral symmetry and with a tetragonal component. Bonding with the paramagnetic center is included. The NMR shifts are illustrated as isoshielding contour maps, and the results are compared with the multipole expansion method. It is shown that even when experimental data are successfully fitted by considering the NMR shifts as arising from the Fermi contact and the dipolar interactions, such an interpretation may lead to incorrect conclusions about the interactions within the paramagnetic system.