A DIRECT C-13 AND N-15 NMR-STUDY OF EUROPIUM(III) COMPLEXATION-NITRATE AND EUROPIUM(III)-ISOTHIOCYANATE COMPLEXATION IN AQUEOUS SOLVENT MIXTURES

A direct, low-temperature nuclear magnetic resonance spectroscopic stu dy of europium(III)-nitrate contact ion-pairing has been completed, an d preliminary results for europium(III)-isothiocyanate have been obtai ned. In water-ocetone-Freon mixtures, at - 110 degrees C to - 120 degr ees C, four N-15 NMR signals are observed for coordinated nitrate ion. Area evaluations of the signals and their concentration dependence in dicate the formation of Eu(NC3)(2+), Eu(NO3)(2+), and two higher compl exes, possibly the tetra-, with either the penta- or hexanitrato. This correlates well with similar N-15 NMR results obrained for Ce(III), P r(III), Nd(III), and Sm(III). As a result of a higher dielectric const ant, complex formation is significantly less in water-methanol mixture s, wherein only three complexes form with Eu(NO3)(2)('+) dominating at the highest anion concentrations. Competitive complexing experiments in water-methanol also were made by Cl-35 NMR chemical shift and linew idth measurements, as well as N-15 NMR. Initial experiments with the E u3+-NCS- system show four coordinated anion signals, displaced from th e bulk anion peak by about -250 ppm and -2,500 ppm in the C-13 and N-1 5 NMR spectra, respectively. Area evaluations are consistent with the presence of Eu(NCS)(2+) through Eu(NCS)(4)(1-) in these solutions. A c onsideration of the chemical shifts identified the nitrogen atom as th e site of binding in the NCS-. A discussion of these preliminary resul ts, as well as those for several other metal-ions, will be presented.