Abstract
The crystalline two-dimensional thiostannate Sn3S7(trenH)2 [tren = tris(2-aminoethyl)amine] consists of negatively charged (Sn3S72−)n polymeric sheets with trenH+ molecular species embedded in-between. The semiconducting compound is a violet light absorber with a band gap of 3.0 eV. In this study the compound was synthesized and functionalized by introducing the cationic dyes Methylene Blue (MB) or Safranin T (ST) into the crystal structure by ion exchange. Dye capacities up to approximately 45 mg/g were obtained, leading to major changes of the light absorption properties of the dye stained material. Light absorption was observed in the entire visible light region from red to violet, the red light absorption becoming more substantial with increasing dye content. The ion exchange reaction was followed in detail by variation of solvent, temperature and dye concentration. Time-resolved studies show that the ion exchange follows pseudo-second order kinetics and a Langmuir adsorption mechanism. The pristine and dye stained compounds were characterized by powder X-ray diffraction and scanning electron microscopy revealing that the honeycomb hexagonal pore structure of the host material was maintained by performing the ion exchange in the polar organic solvent acetonitrile, while reactions in water caused a break-down of the long-range ordered structure.
Highlights
The (Sn3S72−)n thiostannate layers are composed of Sn3S4 broken-cube clusters held together by double bridge Sn-(μ-S)2-Sn covalent bonds
The molecular cations are statically disordered in the crystal structure of Sn3S7(trenH)[233], and the nature of the embedded cationic species has not been verified in previous studies
In order to investigate the nature of the templating cation, a solid-state 13C{1H} CP/MAS nuclear magnetic resonance spectroscopy (NMR) spectrum was acquired for a sample of as-synthesized Sn3S7(trenH)[2] (Fig. 2)
Summary
The (Sn3S72−)n thiostannate layers are composed of Sn3S4 broken-cube clusters held together by double bridge Sn-(μ-S)2-Sn covalent bonds. This creates a honeycomb-like structure with 24-atom hexagonal pores with a size www.nature.com/scientificreports/. As the (Sn3S72−)n layers and the cationic species are only held together by electrostatic interactions, the interlayer distance is flexible and depends on the cation size. This enables post-synthetic exchange of the intercalated cations. Solid state NMR spectroscopy was used to investigate the nature of the cationic species of the parent compound Sn3S7(trenH)[2]
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