Quaternary rare-earth sulfide LaSnGa3S7: Synthesis, structure, thermal and optical properties

The quaternary rare-earth sulfide LaSnGa3S7 was prepared by reaction of La, SnS, Ga2S3, and S at 1173 K. Single-crystal X-ray diffraction analysis revealed that it adopts a new monoclinic structure type (space group P21/n, a = 11.3555(9) Å, b = 9.6177(5) Å, c = 11.5137(8), β = 115.693(9)°, Z = 4) featuring a three-dimensional (3D) anionic framework built up of two-dimensional (2D) Ga–S layers formed by corner-sharing [GaS4] tetrahedra and unique [Sn2S8] dimers formed by edge-sharing [SnS5] units, with the intervening voids filled by La cations. An optical band gap of 2.39 (2) eV, as deduced from the UV–vis–NIR diffuse reflectance spectrum, is consistent with the yellow colour of the crystals. Thermal analysis suggests that LaSnGa3S7 melts incongruently. The electronic structure of LaSnGa3S7 is obtained through the first-principle calculations.