Combining NMR spectroscopy and quantum chemistry as tools to quantify spin density distributions in molecular magnetic compounds

NMR signal shifts of paramagnetic molecules are a measure of the spin density at the respective nuclei. The success of the method depends heavily on the analysis of the various shift contributions which are reviewed. While traditional treatments were based on ligand-field theory, recent progress is due to quantum chemical approaches. The restrictions of the analyses are compared. Solution- and solid-state results are considered and emphasis is laid on the distinction of spin density in s- and p-type orbitals. Specific examples are nitronyl nitroxide radicals and paramagnetic metallocenes. The latter demonstrate how the analysis may depend on the spin state of the molecule.