Solvothermal Syntheses of Two New Thiostannates and an In‐Situ Energy Dispersive X‐ray Scattering Study of Their Formation

Abstract

AbstractTwo new thiostannates, (DBNH)2Sn3S6 (1) and (DBNH)2Cu6Sn2S8 (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 Sn3S4 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 coexist, 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, 69451 Weinheim, Germany, 2009)