Adventures in topology: Exploring the energy landscapes of tetrahedral materials

Robert Bell (University College, London)

Over the last decade there has been a systematic effort to enumerate all topologically possible zeotype (i.e. tetrahedral TX2) frameworks. This has resulted in a number of databases of hypothetical frameworks, which, among other things, show that the structural variety of tetrahedral frameworks is much richer than we might expect based simply on those materials which are currently known. To evaluate the likelihood of synthesizing such hypothetical frameworks, the frameworks were geometry optimised in the form of SiO2 materials using interatomic potential methods, and the resulting predicted heats of formations and geometries compared to those of their synthesized counterparts1-3. This analysis showed that, while a sizeable fraction of the hypothetical frameworks studied would (as SiO2) have heats of formation in the same range as the overwhelming bulk of synthesized frameworks, the majority (amongst which the bulk of the frameworks with the novel structural motifs) lies tens of kJ/mol (SiO2) higher in energy because they can only be realized with severely distorted SiO4 tetrahedra. Recently, however, the previously hypothetical RWY framework (in which the T atoms of the sodalite framework are replaced with supertetrahedral T4X6 units), which we would deem unfeasible in a siliceous form, was synthesized as the Gallium Germanium Sulphide material UCR-20. This inspired us to study in detail the energy landscape of tetrahedral TX2 materials beyond silica. In this presentation we will report on our exploration of the energy landscapes of tetrahedral sulphide4 (SiS2, GeS2) and halide (BeF2, BeCl2) materials, which are dramatically different to that of silica, and potentially offer completely new and unexplored domains of polymorphism. References 1. M.D. Foster, O. Delgado-Friedrichs, R.G. Bell, F.A.A. Paz & J Klinowski, Angew. Chem. Intl. Ed., 42, 3896 (2003). 2.M.D. Foster, A. Simperler, R.G. Bell, O. Delgado-Friedrichs, F.A.A. Paz & J Klinowski, Nature Materials, 3, 234 (2004). 3 D. Majda, F.A. Almeida Paz, O. Delgado Friedrichs, A. Simperler, R.G. Bell, & J. Klinowski, J. Phys. Chem. C, 112, 1040 (2008). 4. M.A. Zwijnenburg, F. Cora & R.G. Bell, J. Am. Chem. Soc., 129, 12588 (2007).

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