A direct carbon-13 and nitrogen-15 NMR study of cerium(III)-isothiocyanatecomplexation in aqueous solvent mixtures

A study of lanthanide complexation with isothiocyanate is underway using a multinuclear magnetic resonance technique. For isothiocyanate solutions in water-acetone-Freon mixtures at low temperature, -85--125 degrees C, ligand exchange is slow enough to permit the observation of C-13 and N-15 NMR sig nals for coordinated and free anions. For the Ce3+-NCS- system, four coordi nated anion signals, displaced from the free anion signal by about +450 to +550 ppm for N-15 and +50 to +80 ppm for C-13, are observed. The C-13 and N -15 spectral data are complementary, showing a signal area concentration de pendence and measured coordination numbers consistent with the formation of Ce(NCS)(2+) through Ce(NCS)(4)(1-). In water-methanol, the extent of compl exing is decreased, presumably because of the higher dielectric constant of this medium. In addition, the results of a competitive study of NCS- and C l- ion binding, carried out using Cl-35 NMR, is presented.