A. Fratiello et al., A DIRECT H-1, C-13, AND N-15 NMR-STUDY OF LUTETIUM(III)-ISOTHIOCYANATE COMPLEXATION IN AQUEOUS SOLVENT MIXTURES, Journal of solution chemistry, 25(11), 1996, pp. 1071-1082
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.