  We derive a general formula for the paramagnetic NMR nuclear shielding tensor
of an open-shell molecule in a pure spin state, subject to a zero-field
splitting (ZFS). Our findings are in contradiction with a previous proposal. We
present a simple application of the newly derived formula to the case of a
triplet ground state split by an easy-plane ZFS spin Hamiltonian. When $kT$ is
much smaller than the ZFS gap, thus a single non-degenerate level is thermally
populated, our approach correctly predicts a temperature-independent
paramagnetic shift, while the previous theory leads to a Curie temperature
dependence.
