Abstract
We present the synthesis, crystal structures and optical properties of three thiostannates prepared by using 1-(2-aminoethyl)piperazine (AEPz) as structure directing agent. Two of the thiostannates are layered materials (AEPz-SnS-1 and AEPz:EtOH-SnS-1) consisting of [Sn3S72−]n sheets with organic cations located in-between. The third compound is a molecular thiostannate (Sn2S6(AEPzH2)2) composed of dimeric Sn2S64− and AEPzH22+. In preparation of the layered compounds, the use of AEPz as the only solvent results in AEPz-SnS-1 with regular hexagonal pores and crystallographically disordered organic cations. In contrast, a mixture of AEPz and absolute ethanol gives AEPz:EtOH-SnS-1 with distorted hexagonal pores and ordered cations between the layers. The influence of cation order on the light absorption properties and the material thermal stability was investigated through thermal treatment of the layered compounds up to 200 °C. Both compounds show colour changes when heated, but cation order results in larger thermal stability. For AEPz-SnS-1, a decreased inter-layer distance and substantial loss of organic matter was observed when heated. However, pair distribution function analysis reveals that the local in-layer thiostannate structure of AEPz-SnS-1 remains unchanged. In contrast, AEPz:EtOH-SnS-1 does not undergo noticeable structural changes by the thermal treatment. All materials are optical semiconductors with band gaps of 3.0–3.1 eV.
Highlights
The formation mechanism of R-SnS-1 type compounds has been reported to occur via a polymerization process in which a cationic species R is used as structure directing agent under solvothermal conditions
We have presented the synthesis of thiostannates using 1-(2-aminoethyl)piperazine (AEPz, Fig. 1c) as solvent and structure directing a gent[33,36], but without focusing on the crystal structures in detail
In the study by Walther et al.[36] enzyme-like activity was demonstrated for the compounds, and only the fundamental structure was reported for layered AEPz:EtOH-SnS-1 and molecular S n2S6(AEPzH2) without in-depth studies of e.g. cation–anion interactions and crystal packing
Summary
The formation mechanism of R-SnS-1 type compounds has been reported to occur via a polymerization process in which a cationic species R is used as structure directing agent under solvothermal conditions. Even though several R-SnS-1 type compounds have been reported, many unanswered questions remain with respect to the role of the structure directing agent on the resulting structure in terms of e.g. cation order/disorder and regular versus distorted hexagonal pores These structural properties might influence the material band gap and the compound stability. As the same structure directly amine (AEPz) uniquely gives two different layered R-SnS-1 compounds with ordered and disordered cations, respectively, the influence of cation order on some material properties were studied. This was done by investigating the light absorption properties and thermal stability of the compounds by diffuse reflectance spectroscopy (DRS), PXRD and X-ray total scattering and pair distribution function (PDF) analysis
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