Proton Magnetic Resonance Solvation Study of Sc(NO3)3, Y(NO3)3, and Th(NO3)4 in Water–Acetone Mixtures

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Abstract
Cation coordination measurements of Sc(NO3)3, Y(NO3)3, and Th(NO3)4 in water–acetone mixtures have been made by a proton magnetic resonance method. At low temperatures, solutions of these salts exhibit separate proton resonance signals for bulk water and water molecules in the primary solvation shell of the cation. Integration of these signals provides a direct measure of the number of water molecules coordinated to the cation. Values of 3.9, 2.4, and 2.9 were obtained for Sc(III), Y(III), and Th(IV), respectively, over a range of salt and solvent concentrations. These values may reflect extensive ion pairing in these solutions, particularly in the Y(III) and Th(IV) cases. The PMR spectra of Th(IV) solutions revealed multiple signals for the protons of coordinated water molecules, lending evidence to the postulate of ion pairing in these systems.