Directed Dehydration of Na4Sn2S6 ⋅ 5H2O Generates the New Compound Na4Sn2S6: Crystal Structure and Selected Properties

Abstract

AbstractThe new thiostannate Na4Sn2S6 was prepared by directed crystal water removal from the hydrate Na4Sn2S6 ⋅ 5H2O at moderate temperatures. While the structure of the hydrate comprises isolated [Sn2S6]4− anions, that of the anhydrate contains linear chains composed of corner‐sharing SnS4 tetrahedra, a structural motif not known in thiostannate chemistry. This structural rearrangement requires bond‐breakage in the [Sn2S6]4− anion, movements of the fragments of the opened [Sn2S6]4− anion and Sn−S−Sn bond formation. Simultaneously, the coordination environment of the Na+ cations is significantly altered and the in situ formed NaS5 polyhedra are joined by corner‐ and edge‐sharing to form a six‐membered ring. Time‐dependent in situ X‐ray powder diffraction evidences very fast rehydration into Na4Sn2S6 ⋅ 5H2O during storage in air atmosphere, but recovery of the initial crystallinity requires several days. Impedance spectroscopy demonstrates a mediocre room‐temperature Na+ ion conductivity of 0.31 μS cm−1 and an activation energy for ionic transport of Ea=0.75 eV.