A direct, low-temperature hydrogen-1, nitrogen-15, and yttrium-89 NMR study of inner-shell complex formation between yttrium(III) and isothiocyanate ion in aqueous solvent mixtures has been completed. At -105 to (-115^{\circ} \mathrm{C}) in water-acetoneFreon 12 mixtures, ligand exchange is slow enough to permit the observation of separate ({ }^{15} \mathrm{~N}) NMR signals for the mono-, di-, and triisothiocyanato complexes of (\mathrm{Y}(\mathrm{III})), displaced upfield by 14 to (17 \mathrm{ppm}) from the free anion signal. Coordination to ({ }^{89} \mathrm{Y}) is strong enough to produce observable (J) coupling of about (14 \mathrm{~Hz}) in the ({ }^{15} \mathrm{~N}) signals. This coupling and an analysis of the magnitude and sign of the ({ }^{15} \mathrm{~N}) chemical shifts indicate binding occurs at the anion nitrogen atom. Area integrations of these signals indicated an overall total of (2 \mathrm{~mol}) of (\mathrm{SCN}^{-})complexed per mole of (\mathrm{Y}(\mathrm{III})), with the disothiocyanate complex dominating even at the highest anion concentrations studied. The ({ }^{\prime} \mathrm{H}) spectra of these solutions revealed multiple coordinated water signals, the areas of which led to (Y) (III) hydration numbers of six in the absence of (\mathrm{SCN}^{-})to about four at the highest concentrations of this anion. The ({ }^{89} \mathrm{Y}) NMR spectra of these systems also revealed a maximum of three complexes, with signals appearing upfield from that of the free metal ion by 3 to (15 \mathrm{ppm}). Preliminary ({ }^{15} \mathrm{~N}) NMR results are presented for the isothiocyanate complexes of lanthanum(III), lutetium(III), aluminum(III), magnesium(II), and paramagnetic samarium(III). c. 1994 Academic Press, Inc.