Design of bifunctional hybrid ultramicroporous materials Bhawna Kumari, Yassin H Andaloussi (England), Michael J. Zaworotko (Wales), Soumya Mukherjee (India) Bernal Institute, Department of Chemical Sciences, University of Limerick, Limerick V94 T9PX, Ireland. Crystal engineering is the branch of chemistry that explores the design, properties, and applications of crystals and is illustrated by the prominence of porous coordination networks (PCNs), including metal–organic frameworks (MOFs) and hybrid coordination networks (HCNs). 1 HCNs consist of both inorganic and organic ligands, and their ultramicroporous (<7 Å) variants are known as Hybrid Ultramicroporous Materials (HUMs). 2 HUMs provide three levels of compositional modularity that enable tailored pore environments driven benchmark gas separation performances, often facilitated by energy-efficient recyclability and easy scalability. Among sorbents relevant to the separation of commodity chemicals, combining strong electrostatics (from anionic/inorganic pillars with exposed electronegative atoms) and right pore size (from organic ligands) gives an edge to HUMs. For example, in 2013, Nugent et al . synthesized SIFSIX-3-Zn (SIFSIX = SiF 6 2-, 3 = pyrazine) with a pore size of 3.84 Å, which was the first foray into HUMs setting a trace carbon capture benchmark. 3 Thanks to the crystal engineering of this generation-1 HUM prototype, generation-2 variants, SIFSIX-3-Ni and SIFSIX-18-Ni- b (18= 3,3′,5,5′-tetramethyl- 1 H ,1′ H -4,4′-bipyrazole) soon found relevance in direct CO 2 capture from air, under dry and humid conditions, respectively. 4 With the use of bespoke azolate and pyridyl ligands, crystal engineering of HUMs is paving the way for us to fine-tune the narrow pores’ functions. It is particularly important to control pore and surface hydrophobicity signatures by harnessing the right azolate/pyridyl/mixed ligands, which offer just the right pore size and pore chemistry to the HUMs they afford. In light of the literature, we set out to investigate the adsorptive separation of mixed pyridyl-pyrazole-based HUMs, which remain understudied. Our strategy is to advance the adsorptive gas/vapor separations in modular families of bifunctional HUMs, by synergizing “ the best of both Worlds ” from both types of linker modalities: pyridyl and pyrazole. The prototypal example of a mixed pyridyl- pyrazole-based HUM is shown below.
Fig. 1. Schematic illustration of the synthesis of a mixed pyridyl-pyrazole functionalized HUM. 5 References 1. Mukherjee, D. Sensharma, K-J. Chen, M. J. Zaworotko, Chem. Commun ., 2020 , 56 , 10419-10441. 2. Mukherjee, M.J. Zaworotko, Trends Chem ., 2020 , 2 , 506-518. 3. Nugent, Y. Belmabkhout, S. D. Burd, A. J. Cairns, R. Luebke, K. Forrest, T. Pham, S. Ma, B. Space, L. Wojtas, M. Eddaoudi, M. J. Zaworotko, Nature , 2013 , 495 , 80-84. 4. Mukherjee, N. Sikdar, D. O’Nolan, D. M. Franz, V. Gascon, A. Kumar, N. Kumar, H. S. Scott, D. G. Madden, P. E. Kruger, B. Space, M. J. Zaworotko, Sci. Adv ., 2019 , 5 , 1-7. 5. Kumar, S. Mukherjee, N. C. Harvey-Reid, A. A. Bezrukov, K. Tan, V. Martins, M. Vandichel, T. Pham, L. M. van Wyk, K. Oyekan, A. Kumar, K. A. Forrest, K. M. Patil, L. J. Barbour, B. Space, Y. Huang, P. E. Kruger, M. J. Zaworotko, Chem , 2021 , 7 , 3085-3098.
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