Artificial synthesis of covalent triazine frameworks for local structure and property determination Catherine Mollart, Sarah Holcroft, Michael Peach, Adam Rowling and Abbie Trewin Department of Chemistry, Lancaster University, Lancaster, LA1 4YB, UK Microporous organic polymers, such as hyper-crosslinked polymers, conjugated microporous polymers and covalent triazine frameworks (CTFs) are a class of porous material that has been explored for applications including energy storage, gas adsorption, heterogeneous catalysis, and chemical separations. 1 However, despite showing promise for various applications, these frameworks are amorphous (as they are kinetic products) and often insoluble, meaning that traditional characterisation techniques such as single-crystal x-ray diffraction (XRD) and solution-state nuclear magnetic resonance do not provide much help in determining the structure. Simulations prove vitally important to understanding the atomic structure and properties of these materials, but to truly replicate the experimental system, we must consider several factors, including the full synthetic conditions and catalytic pathway. In this work, we have artificially synthesised CTF-1 (first synthesised by Cooper et al .) 2 using our in-house Ambuild code. 3 Our artificial synthesis pathway is designed to follow each step in the acid-catalysed triazine ring formation mechanism, which allows us to not only model the idealised end product of an extended triazine framework, but also to explore the intermediate structures formed during the synthesis that are visible in the experimental infrared (IR) spectrum. Our simulated structure is able to replicate the porosity of the experimental structure, and we obtain a simulated powder XRD pattern with no evidence of crystallinity, as expected. We are also able, by generating simulated IR spectra of small fragments of our Ambuild structure, to conclude that the experimental CTF-1 structure contains the chemical features included within our simulated model, including neutral intermediates, rings, ring precursors, and triazine rings, along with absorbed carbon dioxide, water, and hydronium ions within the pore structure. 3
References 1. S. Das, P. Heasman, T. Ben and S. Qiu, Chem. Rev., 2017, 117, 1515–1563. 2. S. Ren, M. J. Bojdys, R. Dawson, A. Laybourn, Y. Z. Khimyak, D. J. Adams and A. I. Cooper, Adv. Mater., 2012, 24, 2357–2361. 3. C. Mollart, S. Holcroft, M. J. G. Peach, A. Rowling and A. Trewin, Phys. Chem. Chem. Phys., 2022, 24, 20025–20029.
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