Solvothermal syntheses of two new thiostannates and an in-situ energy dispersive X-ray scattering study of their formation

Abstract

Two new thiostannates, (DBNH)2Sn3S6 (1) and (DBNH)2Cu6- Sn2S8 (2), were synthesized under solvothermal conditions using Cu, Sn, S and DBN (DBN=1,5-diazabicyclo[4.3.0]non-7-ene). Compound 1 is a rare example of a mixed-valent thiostannate. The SnII center exists in the rare trigonal pyramidal coordination environment, whereas SnIV is tetrahedrally coordinated. The chain-anion is composed of alternating Sn 3S4 semi-cubes and Sn2S2 rings. The structure of 2 consists of undulated anionic layers with amine molecules between the layers. The layers may be viewed as a heteroatom 63 graphene layer constructed of condensed CuS3 triangles and SnS4 tetrahedra. The two thiostannates coexistI, and this was investigated with in-situ energy dispersive X-ray scattering under solvothermal conditions. Prior to the formation of 1 and 2, a crystalline intermediate appears, which disappears after 60 min. Then reflections of 2 start to grow, and reflections of 1 appear some time later. The appearance of a thiostannate(IV) species followed by the crystallization of a mixed-valent thiostannate(II,IV) species suggests that complex redox reactions are occurring under the solvothermal conditions. Syntheses without Cu in the reaction slurry lead to the formation of 1 within a very short time period. The results of the in-situ studies clearly indicate that the presence of Cu species in solution retards the nucleation and crystallization of 1. The crystalline intermediate was quenched with ex-situ experiments. All syntheses performed with this intermediate do not lead to the crystallization of 1 or 2, i.e., there is no direct relation between these three crystalline compounds. The spectroscopic and thermal properties of 1 and 2 are also discussed. © Wiley-VCH Verlag GmbH & Co. KGaA.