Reducing the NMR Line Widths of Quadrupole Nuclei by Employing Supercritical Solvents

An outline of the use of supercritical solvents in NMR spectroscopy is given, with emphasis on instrumentation and applications. Especially the advantages of the low viscosity of supercritical solvents, resulting in appreciable reductions of the line widths of NMR resonances of quadrupole nuclei (I > 1/2), are discussed. The main focus of the review is on the development of transition metal and 14N NMR spectroscopy, to aid the analysis of transition metal complexes. The choices of the supercritical solvent and ligand modifications are discussed in the context of solubility and reduction of the line width.