New layered compounds through polysulfide flux synthesis; A(2)Sn(4)S(9) (A= K, Rb, Cs) present a new form of the [Sn4S9](2-) network

Crystals of Cs2Sn4S9, Rb2Sn4S9, and K2Sn4S9 were synthesized by reacting Sn with Cs2Sx, Rb2Sx, or K2Sx fluxes at 500 degrees C. They can also be prepa red as microcrystalline products through direct combination reactions at te mperatures ranging from 720 to 750 degrees C. The new ternary sulfide Cs2Sn 4S9 crystallizes in the orthorhombic Pnma space group, the new ternary sulf ide Rb2Sn4S9 crystallizes in the orthorhombic P2(1)2(1)2(1) space group, an d the new ternary sulfide K2Sn4S9 appears to be isostructural with Rb2Sn4S9 , as determined through X-ray powder diffraction. The structures of Cs2Sn4S 9, Rb2Sn4S9, and K2Sn4S9 consist of nearly identical [Sn4S9](2-) layers whi ch are stacked in two different arrangements. Alkali metal Cs+, Rb+, and K cations are located between the layers. Raman and far-IR spectroscopic dat a confirm the presence of the [Sn4S9]2(-) layer in all three compounds, Sin gle crystal optical spectra indicate that Cs2Sn4S9, Rb2Sn4S9, and K2Sn4S9 a re wide band-gap semiconductors with bandgaps of 2.66 eV, 2.65 eV, and 2.66 eV, respectively. (C): 1998 Academic Press.