Synthesis, Crystal Structure, and Thermal Properties of Na₅[SnS₄]Cl·13H₂O

Reaction of Na₂S with SnCl₄·5H₂O in aqueous alkaline sodium hydroxide solution leads to the formation of Na₅[SnS₄]Cl·13H₂O (1). The compound crystallizes monoclinic in space group P2₁/m with two formula units in the unit cell. In the crystal structure the Na⁺ cations are octahedrally coordinated and are linked into layers by bridging water molecules, μ₃ bridging Cl^– anions and μ_1,1 bridging S atoms of [SnS₄]^4– anions. Extended hydrogen bonding interactions generate a three-dimensional network. Investigations using differential thermoanalysis, thermogravimetry, and differential scanning calorimetry shows that upon heating in open crucibles the water can be removed leading to the formation of the anhydrate that is stable at room temperature and does not transform back into compound 1. Storage of the anhydrate in a desiccator over a water atmosphere leads first to formation of Na₄SnS₄·14H₂O followed by crystallization of the title compound. After longer storage times NaCl appears as a second crystalline phase. If the thermal measurements are performed in a self-produced atmosphere, compound 1 transforms partly into Na₄SnS₄·14H₂O with an increasing amount of this phase with increasing temperature. Synthetic investigations reveal that crystallization of compound 1 sensitively depends on the water content of acetone, which is used for precipitation of 1. Reacting Na₄SnS₄·14H₂O directly with NaCl afforded formation of complex mixtures.