New Layered Compounds through Polysulfide Flux Synthesis;A2Sn4S9(A=K, Rb, Cs) Present a New Form of the [Sn4S9]2−Network

Abstract

Crystals of Cs2Sn4S9, Rb2Sn4S9, and K2Sn4S9were synthesized by reacting Sn with Cs2Sx, Rb2Sx, or K2Sxfluxes at 500°°C. They can also be prepared as microcrystalline products through direct combination reactions at temperatures ranging from 720 to 750°C. The new ternary sulfide Cs2Sn4S9crystallizes in the orthorhombicPnmaspace group, the new ternary sulfide Rb2Sn4S9crystallizes in the orthorhombic P212121space group, and the new ternary sulfide K2Sn4S9appears to be isostructural with Rb2Sn4S9, as determined through X-ray powder diffraction. The structures of Cs2Sn4S9, Rb2Sn4S9, and K2Sn4S9consist of nearly identical [Sn4S9]2−layers which are stacked in two different arrangements. Alkali metal Cs+, Rb+, and K+cations are located between the layers. Raman and far-IR spectroscopic data confirm the presence of the [Sn4S9]2−layer in all three compounds. Single crystal optical spectra indicate that Cs2Sn4S9, Rb2Sn4S9, and K2Sn4S9are wide band-gap semiconductors with bandgaps of 2.66 eV, 2.65 eV, and 2.66 eV, respectively.