109Ag NMR-Studies of the Selective Solvation of the Ag+ -Ion in Water-Ethylamine-Mixtures and of the Coordination of Halide-Anions to the Silver-Ethylamine Solvate Complexes

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Abstract
109Ag chemical shift measurements of 0.02 up to 3 molar solutions of AgNO3, AgCl, and AgBr in solvent mixtures of H2O (W) and ethylamine (ea) were performed. The extremely long relaxation times T1 and T2 were determined with new techniques. The Ag+ -ion in solvent mixtures of W and ea shows a strongly selective solvation by ea. The 109Ag chemical shift of the solvate complex [Ag ea2]+ surrounded solely by W is δ2 = (335 ± 2) ppm (referred to the Ag+-ion in W). A further solvation in addition to the inner solvation sphere was determined; this solvation is not or only weakly selective. There is a rapid chemical exchange; the lifetime of the inner solvation sphere is long compared with the Larmor period, whereas the solvation outside this sphere is changed in times shorter than the Larmor period. In contrast to the NO3- -anion, the halide anions Cl- and Br- are partly coordinated to the [Ag ea2]+ complex. The equilibrium constants for this coordination were determined as well as the chemical shifts of the [Ag ea2 · Cl] and the [Ag ea2 · Br] complexes. The bromine ion is coordinated for shorter times than the Larmor period, whereas the time of the coordination of the chlorine ion may be comparable to the Larmor period or shorter.

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