Synthesis and structure of microporous layered tin(IV) sulfide materials

Abstract

Synthetic methods have been developed which yield large single crystals and highly crystalline phase-pure microporous layered SnS-n materials. This allows study of the structure–property–function relations of these materials. The tin sulfide layer of the SnS-1 structure type contains hexagonally shaped 24-atom rings which are constituted by six Sn₃S₄ broken-cube cluster building units, linked together by double bridge Sn(µ-S)₂Sn sulfur bonds. The SnS-3 structure type contains elliptically shaped 32-atom rings which are also constructed from six Sn₃S₄ broken-cube clusters. However, they are linked by double bridge Sn(µ-S)₂Sn sulfur bonds as well as tetrahedral edge-bridging Sn(µ-S₂SnS₂)Sn spacer units. The SnS-1 structure type [A₂Sn₃S₇ ] was obtained in the presence of A⁺=Et₄N⁺ , DABCOH⁺ (protonated 1,8-diazabicyclooctane), and a mixed template system of NH₄⁺ /Et₄N⁺ , while the SnS-3 structure type [A₂Sn₄S₉ ] emerged in the presence of A⁺=Prⁿ₄N⁺ and Buⁿ₄N⁺ . Various SnS-1 and SnS-3 structures are examined and compared in relation to the size/shape of constituent template cations. A particular kind of structure-directing function was observed, that is, larger template molecules create larger void spaces within and between the tin sulfide sheets. Unique framework flexibility was discovered for both structure types. In order to accommodate the size/shape changes of templates, the flexible porous tin(iv) sulfide layers are able to undergo a certain degree of elastic deformation to alter the architecture of void spaces within and between the layers, rather than forming a completely new porous structure type. This is believed to be responsible for the relatively small number of structure types so far discovered for tin(iv) sulfide-based microporous layered materials compared to the myriad of three-dimensional open-framework structure types found for the zeolites and aluminophosphates. The observed differences among the various SnS-1 or SnS-3 structures is significant and has resulted in distinct adsorption behavior towards guest molecules. The TPA-SnS-3 framework is also found to be pressure sensitive. This all bodes well for envisaged chemical sensor applications for this class of porous materials.