First examples of sulfides in the quaternary A/Cd/Sn/S (A = Li, Na) systems: molten flux synthesis and single crystal X-ray structures of Li2CdSnS4, Na2CdSnS4 and Na6CdSn4S12

Abstract

Three new sulfides Li₂CdSnS₄ (1), Na₂CdSnS₄ (2) and Na₆CdSn₄S₁₂ (3), have been synthesized using a molten flux of alkali-metal polysulfides and structurally characterized by single crystal X-ray diffraction studies. Both the layered compound 1 and the three-dimensional compound 2 have tetrahedral anionic frameworks of (CdSnS₄)²⁻ and, for charge compensation, alkali-metal cations. The two-dimensional compound 3 has Na⁺ ions interleaved between anionic (CdSn₄S₁₂)⁶⁻ layers with an octahedral framework. Compounds 1, 2 and 3 are structurally related to Cu₂CdGeS₄, LiAlSe₂ and Na₂SnS₃ respectively. Compound 2, as determined from its diffuse reflectance spectrum, is a semiconductor with a band gap of 1.52 eV.