A H-1, N-15, AND Y-89 NMR-STUDY OF YTTRIUM(III)-ISOTHIOCYANATE COMPLEXES IN AQUEOUS SOLVENT MIXTURES

A direct, low-temperature hydrogen-1, nitrogen-15, and yttrium-89 NMR study of inner-shell complex formation between yttrium(III) and isothi ocyanate ion in aqueous solvent mixtures has been completed. At -105 t o -115 degrees C in water-acetone-Freon 12 mixtures, ligand exchange i s slow enough to permit the observation of separate N-15 NMR signals f or the mono-, di-, and triisothiocyanato complexes of Y(III), displace d upheld by 14 to 17 ppm from the free anion signal. Coordination to Y -89 is strong enough to produce observable J coupling of about 14 Hz i n the N-15 signals. This coupling and an analysis of the magnitude and sign of the N-15 chemical shifts indicate binding occurs at the anion nitrogen atom. Area integrations of these signals indicated an overal l total of 2 mol of SCN- complexed per mole of Y(III), with the diisot hiocyanate complex dominating even at the highest anion concentrations studied. The H-1 spectra of these solutions revealed multiple coordin ated water signals, the areas of which led to Y(III) hydration numbers of six in the absence of SCN- to about four at the highest concentrat ions of this anion. The Y-89 NMR spectra of these systems also reveale d a maximum of three complexes, with signals appearing upheld from tha t of the free metal ion by 3 to 15 ppm. Preliminary N-15 NMR results a re presented for the isothiocyanate complexes of lanthanum(III), lutet ium(III), aluminum(III), magnesium(II), and paramagnetic samarium(III) . (C) 1994 Academic Press, Inc.