Re‐investigation of Barium‐Gold(I)‐Tetra‐Thiostannate(IV), Ba[Au 2 SnS 4 ], with Short Au I ···Au I Separation Showing Luminescence Properties

Directed Dehydration as Synthetic Tool for Generation of a New Na 4 SnS 4 Polymorph: Crystal Structure, Na + Conductivity, and Influence of Sb‐Substitution

We present the convenient synthesis and characterization of the new ternary thiostannate Na₄SnS₄ (space group I41/acd ) by directed removal of crystal water molecules from Na₄SnS₄⋅14 H₂O. The compound represents a new kinetically stable polymorph of Na₄SnS₄, which is transformed into the known, thermodynamically stable form (space group P4‾21c ) at elevated temperatures. Thermal co‐decomposition of mixtures with Na₃SbS₄⋅9 H₂O generates solid solution products Na_4−xSn_1−xSb_xS₄ (x=0.01, 0.10) isostructural to the new polymorph (x=0). Incorporation of Sb⁵⁺ affects the bonding and local structural situation noticeably evidenced by X‐ray diffraction, ¹¹⁹Sn and ²³Na NMR, and ¹¹⁹Sn Mössbauer spectroscopy. Electrochemical impedance spectroscopy demonstrates an enormous improvement of the ionic conductivity with increasing Sb content for the solid solution (σ_25°C=2×10⁻³, 2×10⁻², and 0.1 mS cm⁻¹ for x=0, 0.01, and 0.10), being several orders of magnitude higher than for the known Na₄SnS₄ polymorph.