Structures of Dithiophosphinate Complexes of the Lanthanides in the Solid and Solution by X-Ray Diffraction and Paramagnetic NMR

Abstract

The determination of the structures of lanthanide complexes in solution poses certain problems. Even the determination of the point symmetry of the lanthanide ion from spectroscopic data is not always unambiguous as the crystal field splittings are small and may not always be resolved at normal temperatures. Paramagnetic NMR is a powerful tool for obtaining geometric information in solution. However, the total observed isotropic shifts are the sum of a dipolar term and a scalar term, and only the dipolar contribution is structure dependent (1). In the past this has limited the experiment to the measurement of proton shifts which are predominantly dipolar in origin. We have since developed a method for separating the dipolar and scalar contributions to the total observed shifts (2) and thus may study any nucleus in a complex that has a non-zero spin. A bonus in this procedure is that we also obtain the value of the hyperfine coupling of the observed nucleus with the unpaired electron spin at the same time, thus obtaining a measure of the covalency of the metal-ligand bond.