Abstract
Owing to their combined open-framework structures and semiconducting properties, two-dimensional thio-stannates show great potential for catalytic and sensing applications. One such class of crystalline materials consists of porous polymeric [Sn3S7 2-] n sheets with molecular cations embedded in-between. The compounds are denoted R-SnS-1, where R is the cation. Dependent on the cation, some R-SnS-1 thio-stannates transition into amorphous phases upon dispersion in water. Knowledge about the fundamental chemical properties of the thio-stannates, including their water stability and the nature of the amorphous products, has not yet been established. This paper presents a time-resolved study of the transition from the crystalline to the amorphous phase of two violet-light absorbing thio-stannates, i.e. AEPz-SnS-1 [AEPz = 1-(2-amino-ethyl)-piperazine] and trenH-SnS-1 [tren = tris-(2-amino-ethyl)-amine]. X-ray total scattering data and pair distribution function analysis reveal no change in the local intralayer coordination during the amorphization. However, a rapid decrease in the crystalline domain sizes upon suspension in water is demonstrated. Although scanning electron microscopy shows no significant decrease of the micrometre-sized particles, transmission electron microscopy reveals the formation of small particles (∼200-400 nm) in addition to the larger particles. The amorphization is associated with disorder of the thio-stannate nanosheet stacking. For example, an average decrease in the interlayer distance (from 19.0 to 15.6 Å) is connected to the substantial loss of the organic components as shown by elemental analysis and X-ray photoelectron spectroscopy. Despite the structural changes, the light absorption properties of the amorphisized R-SnS-1 compounds remain intact, which is encouraging for future water-based applications of such materials.
Highlights
Porous thiometallates are an interesting group of compounds due to their combined open frameworks and semiconducting properties (Seidlhofer et al, 2010; Wu et al, 2015a; Tang et al, 2018)
In order to track the water-mediated amorphization of the compounds, powder X-ray diffraction (PXRD) and X-ray total scattering data were collected for series of samples, which had been dispersed in water for different durations
Based on PXRD, total scattering, electron microscopy and X-ray photoelectron spectroscopy (XPS) data, we propose the following mechanism for the amorphization: water diffuses into crystalline R-SnS-1 and acts as a base
Summary
Porous thiometallates are an interesting group of compounds due to their combined open frameworks and semiconducting properties (Seidlhofer et al, 2010; Wu et al, 2015a; Tang et al, 2018). The powder X-ray diffraction (PXRD) patterns change substantially over time, whereas the real-space timeresolved PDFs show no change in the local tin sulfide coordination, pointing to preservation of the fundamental structural motifs (i.e. the Sn3S4 broken cube clusters) in the thiostannate sheets. Structural details such as the average domain size and interlayer distance have been extracted from analysis of PXRD and PDF data. Minute amounts of these fine particles could be isolated, confirming their presence in low concentration
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