A DIRECT C-13 AND N-15 NMR-STUDY OF SAMARIUM(III) COMPLEXATION WITH NITRATE AND ISOTHIOCYANATE IN AQUEOUS

The extent of inner-shell, contact ion-pairing between samarium(III)-nitrate and in a preliminary manner, samarium(III)-isothiocyonate, has been determined by a direct, low-temperature, multinuclear magnetic resonance technique. In water-acetone mixtures containing Freon-12 or Freon-22, the slow exchange condition is achieved at -110 to -120 degrees C, permitting the observation of N-15 NMR resonance signals for bulk and coordinated nitrate. In these mixtures, signals are observed for Sm(NO3)(2+), Sm(NO3)(2)(+), and two higher complexes, possibly the tetranitrato with either the penta- or hexanitrato. H-1 NMR signals for bound water molecules in these mixtures were observed, but accurate hydration numbers cart not yed be determined. In anhydrous or aqueous methanol mixtures, N-15 NMR signals for only three complexes are observed, with the dinitrato clearly dominating. Using N-15 and Cl-35 NMR chemical shift and linewidth measurements, the superior complexing ability of nitrate compared to perchlorate and chloride, was demonstrated. Successful preliminary C-13 and N-15 NMR measurements of Sm3+-NCS- interactions in water-acetone-Freon-22 mixtures also have been made. The C-13 NMR spectra reveal signals for five complexes, presumably Sm(NCS)(2+) through Sm(NCS)(5)(2-). In the N-15 NMR spectra, signals for only three complexes are observed (the result of insufficient spectral resolution,) displaced about +240 ppm from bulk anion.