SnGa 2 GeS 6 : synthesis, structure, linear and nonlinear optical properties

A new sulfide, SnGa 2 GeS 6 , has been synthesized, which represents the first member in the quaternary Sn/M/M′/Q (M = Ga, In; M′ = Si, Ge; Q = S, Se, Te) system. It adopts a new structure type in the non-centrosymmetric space group Fdd 2. In the structure, Sn 2+ is coordinated to a distorted square-pyramid of five S atoms, demonstrating the stereochemical activity of the lone electron pair, while the Ge atom and Ga atom are both tetrahedrally coordinated to four S atoms. The SnS 5 square-pyramids and the MS 4 (M = Ga, Ge) tetrahedra are connected to each other via corner and edge-sharing to generate a three-dimensional framework. The compound exhibits a powder second harmonic generation signal at 2 μm whose strength is about one-fourth that of the benchmark material AgGaS 2 , which may be explained in view of the macroscopic arrangement of the SnS 5 square-pyramids and the MS 4 tetrahedra. Moreover, based on UV-vis-NIR spectroscopy measurements and the electronic structure calculations, SnGa 2 GeS 6 has two optical transitions at about 1.12 eV and 2.04 eV respectively.