A DIRECT H-1, C-13, AND N-15 NMR-STUDY OF LUTETIUM(III)-ISOTHIOCYANATE COMPLEXATION IN AQUEOUS SOLVENT MIXTURES

A direct, low-temperature hydrogen-1, carbon-13, and nitrogen-15 nucle ar magnetic resonance study of lutetium(III)-isothiocyanate complex fo rmation in aqueous solvent mixtures has been completed. At -110 degree s C to -120 degrees C in water-acetone-Freon mixtures, ligand exchange is slowed sufficiently to permit the observation of separate H-1, C-1 3, and N-15 NMR signals for coordinated and free water and isothiocyan ate ions. In the C-13 and N-15 spectra of NCS-, resonance signals for five complexes are observed over the range of concentrations studied. The C-13 chemical shifts of complexed NCS- varied from -0.5 ppm to -3 ppm from that of free anion. For the same complexes, the N-15 chemical shifts from free anion were about -11 ppm to -15 ppm. The magnitude a nd sign of the N-15 chemical shifts identified the nitrogen atom as th e binding site in NCS-. The concentration dependence of the C-13 and N -15 signal areas, and estimates of the fraction of anion bound at each NCS-:Lu3+ mole ratio, were consistent with the formation of [(H2O)(5) Lu(NCs)](2+) through [(H2O)Lu(NCS)(5)](2-). Although proton and/or lig and exchange and the resulting bulk-coordinated signal overlap prevent ed accurate hydration number measurements, a good qualitative correlat ion of the water H-1 NMR spectral results with those of C-13 and N-15 was possible.