A direct carbon-13 and nitrogen-15 NMR study of samarium(III) complexation with nitrate and isothiocyanate in aqueous solvent mixtures

Abstract

The extent of inner-shell, contact ion-pairing between samarium(III)-nitrate and in a preliminary manner, samarium(III)-isothiocyanate, 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°C, permitting the observation of15N 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.1H NMR signals for bound water molecules in these mixtures were observed, but accurate hydration numbers can not yed be determined. In anhydrous or aqueous methanol mixtures,15N NMR signals for only three complexes are observed, with the dinitrato clearly dominating. Using15N and35Cl NMR chemical shift and linewidth measurements, the superior complexing ability of nitrate compared to perchlorate and chloride, was demonstrated. Successful preliminary13C and15N NMR measurements of Sm3+-NCS− interactions in water-acetone-Freon-22 mixtures also have been made. The13C NMR spectra reveal signals for five complexes, presumably Sm(NCS)2+ through Sm(NCS) 5 2− . In the15N NMR spectra, signals for only three complexes are observed (the result of insufficient spectral resolution.) displaced about +240 ppm from bulk anion.