On the hydration of the lutetium(III) Ion in water acetone mixtures. A 1h and 35Cl NMR study

Abstract

The hydration of the Lu 3+. ion was studied by 1H- and 35ClNMR spectroscopic methods in water- acetone mixtures at low temperatures. The observed hydration number obtained by the 'NMR peak-area' method is not constant, but decreases with increasing Lu(C10 4) 3 and C10 4 − ion concentrations, as well as with rising acetone-to-water ratio. The hydration number obtained for 2.92 M, 2.00 M, 1.17 M, 0.82 M and 0.49 M Lu(C10 4) 3 solutions are 6.3 ± 0.12, 6.5 ± 0.12, 7.2 ± 0.2, 7.9 ± 0.17 and 8.7 ± 0.45, respectively. From these data, a primary hydration number n h ≥ 9 can be deduced for dilute solutions. The decrease of the hydration number with increasing Lu(C10 4) 3 and acetone concentration can be explained assuming the coordination of the CIO 4 − ions in the inner shell of Lu 3+ and/or the decrease of the coordination number of Lu 3+ in more concentrated solutions, mainly due to water activity changes. The relaxation rate of the 35C1 nucleus of the perchlorate ion increases with the increase of the Lu 3+ concentration, consistent with the assumption of the perchlorate ion coordination.