S2: Synthesis of switchable MOFs and in situ X-ray diffraction studies of gas and liquid phase induced reversible structural transformations
Stefan Kaskel
In S2 we synthesize idealized model materials for the validation of predictive simulation methods (T1, T2) and in situ switching investigations in P1 and P2 with a focus on pillared layer MOFs. In order to understand the role of metals and corresponding bonding situation (hinge energetics, T1, T2), we synthesize model systems containing the di-nuclear paddle-wheel complexes (M2(O2C-R)4, M = Mn, Co, Ni, Cu, Zn) acting as nodes and 2,6-naphthalene dicarboxylate as linker (DUT-8). In this series, DUT-8(Ni) stands out in terms of volume change, while the other systems show a less pronounced gating effect. EPR spectroscopy is used in P2 to analyze the effect of metal deficiencies in the open and closed phase. Mixed metal systems (M1M2(O2C-R)4; M1≠ M2; M1, M2 = Mn, Co, Ni, Cu, Zn etc.) are synthesized to generate spectroscopically idealized model systems for studying in situ the switching phenomena using EPR spectroscopy (P2). The model systems are analyzed by the Brunner group (P1) with respect to switching kinetics and in mixture adsorption systems to identify selective host-guest interactions during mixture gas adsorption in situ. The Kaskel group elucidates the selectivity of host-switchability (QP4) in contact with liquid guests using well defined model materials (DUT-8(Ni) and fu-MOFs, S1). DUT-8(Ni) is used as a model system to study cooperative effects in the solid state transformation, i.e. particle size effects, and compositional variations. Thus, a key task will be to elaborate synthesis conditions for adjusting particle size distributions of DUT-8(Ni). Parallelized adsorption-diffraction and adsorption-EXAFS experimentation is used to clearly identify the key factors inducing step-wise transitions between closed and open phases.
Fig.1: The switchability of DUT-8(Ni) depends on crystal size. Below a critical crystal size, the material retains the open pore (op) phase and does not transform into the closed pore phase (cp).
P. S. Petkov, V. Bon, C. L. Hobday, A. B. Kuc, P. Melix, S. Kaskel, T. Düren, Th. Heine, “Conformational isomerism controls collective flexibility in metal–organic framework DUT-8(Ni)”, Phys. Chem. Chem. Phys. 2019, 21, 674-680 (doi: 10.1039/C8CP06600K).
N. Kavoosi, T. Savchenko, I. Senkovska, M. Maliuta, V. Bon, A. Eychmüller, S. Kaskel, "Selective pore opening and gating of the pillared layer metal-organic framework DUT-8(Ni) upon liquid phase multi-component adsorption", Microporous Mesoporous Mater. 2018, 271, 169-174 (doi: 10.1016/j.micromeso.2018.05.024).
A. Kultaeva, V. Bon, M. S. Weiss, A. Pöppl, S. Kaskel, “Elucidating the Formation and Transformation Mechanisms of the Switchable Metal–Organic Framework ELM-11 by Powder and Single-Crystal EPR Study”, Inorg. Chem. 2018, 57 (19), 11920-11929 (doi: 10.1021/acs.inorgchem.8b01241)
N. Kavoosi, V. Bon, I. Senkovska, S. Krause, C. Atzori, F. Bonino, J. Pallmann, S. Paasch, E. Brunner, S. Kaskel, “Tailoring adsorption induced phase transitions in the pillared-layer type metal–organic framework DUT-8(Ni)”, Dalton Trans. 2017,46, 4685-4695 (doi: 10.1039/C7DT00015D).
H. Miura, V. Bon, I. Senkovska, S. Ehrling, S. Watanabe, M. Ohba, S. Kaskel, "Tuning the gate-opening pressure and particle size distribution of the switchable metal-organic framework DUT-8(Ni) by controlled nucleation in a micromixer", Dalton Trans. 2017, 46, 14002-14011 (doi: 10.1039/C7DT02809A).
A. Krylov, A. Vtyurin, P. Petkov, I. Senkovska, M. Maliuta, V. Bon, T. Heine, S. Kaskel, E. Slyusareva, "Raman spectroscopy studies of the terahertz vibrational modes of a DUT-8 (Ni) metal-organic framework", Phys. Chem. Chem. Phys. 2017, 19, 32099-32104 (doi: 10.1039/C7CP06225G).
M. Mendt, F. Gutt, N. Kavoosi, V. Bon, I. Senkovska, S. Kaskel, A. Poeppel, ”EPR Insights into Switchable and Rigid Derivates of the Metal-Organic Framework DUT-8(Ni) by NO Adsorption“, J. Phys. Chem. C 2016, 120(26), 14246-14259 (doi: 10.1021/acs.jpcc.6b04984).
V. Bon, N. Klein, I. Senkovska, A. Heerwig, J. Getzschmann, D. Wallacher, I. Zizak, M. Brzhezinskaya, U. Mueller, S. Kaskel, “Exceptional adsorption-induced cluster and network deformation in the flexible metal-organic framework DUT-8(Ni) observed by in situ X-ray diffraction and EXAFS”, Phys. Chem. Chem. Phys. 2015, 17(26), 17471-17479 (doi: 10.1039/c5cp02180d).
H. C. Hoffmann, B. Assfour, F. Epperlein, N. Klein, S. Paasch, I. Senkovska, S. Kaskel, G. Seifert, E. Brunner, “High-pressure in situ 129Xe NMR spectroscopy and computer simulations of breathing transitions in the metal-organic framework Ni2(2,6-ndc)2(dabco) (DUT-8(Ni))”, J. Am. Chem. Soc. 2011, 133(22), 8681-90 (doi: 10.1021/ja201951t).
N. Klein, H. C. Hoffmann, A. Cadiau, J. Getzschmann, M. R. Lohe, S. Paasch, T. Heydenreich, K. Adil, I. Senkovska, E. Brunner, “Structural flexibility and intrinsic dynamics in the M2(2,6-ndc)2(dabco) (M = Ni, Cu, Co, Zn) metal-organic frameworks”, J. Mater. Chem. 2012, 22(20), 10303-10312 (doi: 10.1039/C2JM15601F).