1H and 7Li NMR studies on the dynamics of water and cations in quasi-two-dimensional electrolyte layers of hydrated chalcogenides

Abstract

A complete set of NMR wide line data for the monolayered chalcogenide hydrates of the type A+0.33(H2O)y(TaS2)0.33− with A = Li, Na, K, NH4, Rb, and Cs shows a linear correlation between the enthalpy of hydration of A+ and the temperature which governs the transition from the rigid lattice to the range of ordered mobility. Measurement of the angular dependence of the two-spin splitting has provided further support for the model of structure and motion recently proposed for these materials. There is no indication of proton exchange processes other than a strong influence of the pH value. For fully hydrated sulfides Ax(H2O)zMS2 with A = Li and Na and M = Ta and Nb with bilayers of water, 1H and 7Li NMR wide line studies as well as measurements of the proton relaxation rates have given information on the dynamic structure. In the case of Li+, the reversible removal of water from the interlayer space is connected with a marked change of the coordination. The relaxation behavior of the intercalated water is accounted for by an asymmetric distribution of correlation times.