Solid-State and Aqueous Ion-Exchange Reactions of Layered KInSnS ₄ and NaInSnS ₄ Compounds and Ionic Conductivities of AInSnS ₄ (A = Li, Na, K, Rb, Cs, Tl) Compounds at Room Temperature

Layered NaInSnS 4 and KInSnS 4 compounds undergo instantaneous solid-state ion-exchange reactions to the extent of 17–98% with solid AX and AX 2 (A = Li, Na, K, Rb, Cs, Tl, NH 4, Cu, Ag, Ca, Sr, Ba, Pb, Zn, Cd, Hg, guanidinium, anilinium; X = Cl, I, NO 3 ) compounds, when simply ground together in a pestle and mortar for about 5–10 min under ambient conditions. A comparative study of ion-exchange reactions in solid state and aqueous media, each with stoichiometric and excess AX/AX 2 reactants, reveals that the extent of ion exchange is greater in aqueous media and that the ion-exchange products are largely metastable and independent of reaction conditions. The solid-state ion-exchange reactions are mostly topotactic and significantly facile for the water-insoluble AX/AX 2 compounds, and some of them involve drastic color changes. As determined by single-crystal X-ray diffraction (XRD), KInSnS 4 ( C ) and its aqueous ion-exchanged RbInSnS 4 ( C ) are isostructural layered analogues of a new modification comprising honeycomb octahedral [InSnS 4 ] − anionic layers and K + and Rb + cations with trigonal prismatic coordination. The structure-dependent ionic conductivities of nine AInSnS 4 (A = alkali metals, thallium) compounds range from 1.88 × 10 –5 to 3.95 × 10 –11 S/cm at room temperature, and layered KInSnS 4 has a relatively high ionic conductivity, in accordance with its high ion-exchange capability.