Wideline XH NMR Study on Hydrated Layered Sulfides K0.5(H 2O)2/[NbS2] and Na0 5(H 2O)2/[NbS2]

Layered ternary chalcogenides AxMX2 (A = al­ kali metal, M = transition metal, X = S, Se) of group IV b to VI b elements may be prepared either by reactions a t high temperatures (600-1000 °C) from the elements1 and via alkali halide m elts2 or at low temperatures from the corresponding binary phases MX2 by intercalation of alkali metals from liquid ammonia3. Both series of compounds were found to be able to undergo topotactic solvation re­ actions with polar solvents4. Structurally the resul­ ting phases (A+)x(solv)y[MX2]x_ have to be described in terms of negatively charged [MX2]x_ layer units with solvated cations A+ between the chalcogenide sheets. The chemical behaviour of these compounds is characterized by their polyelectrolyte nature, i.e. easy exchange of solvent molecules and cations in contact with electrolyte solutions. The solvated niobium and tantalum phases are of particular interest with respect to their physical properties, as they are the first known group of superconducting polyelectrolytes5. Variation of cations and solvent molecules allows a systematic