Crystal size versus paddle wheel deformability: selective gated adsorption transitions of the switchable metal–organic frameworks DUT-8(Co) and DUT-8(Ni)

Abstract

Crystal size versus paddle wheel deformability: selective gated adsorption transitions of the switchable metal-organic frameworks and † Switchable pillared layer metal-organic frameworks M 2 (2,6-ndc) 2 (dabco) (DUT-8(M), M ¼ Ni, Co, 2,6-ndc ¼ 2,6naphthalenedicarboxylate, dabco ¼ 1,4-diazabicyclo-[2.2.2]octane, DUT -Dresden University of Technology) were synthesised in two different crystallite size regimes to produce particles up to 300 mm and smaller particles around 0.1 mm, respectively. The textural properties and adsorption-induced switchability of the materials, obtained from both syntheses, were studied by physisorption of N 2 at 77 K, CO 2 at 195 K and nbutane at 273 K, revealing pronounced differences in adsorption behavior for Ni and Co analogues. While the smaller nano-sized particles (50-200 nm) are rigid and show no gating transitions confirming the importance of crystallite size, the large particles show pronounced switchability with characteristic differences for the two metals resulting in distinct recognition effects for various gases and vapours. Adsorption of various vapours demonstrates consistently a higher energetic barrier for the "gate opening" of DUT-8(Co) in contrast to , as the "gate opening" pressure for Co based material is shifted to a higher value for adsorption of dichloromethane at 298 K. Evaluation of crystallographic data, obtained from single crystal and powder X-ray diffraction analysis, showed distinct geometric differences in the paddle wheel units of the respective MOFs.These differences are further disclosed by solid-state UV-vis, FT-IR and Raman spectroscopy. Magnetic properties of DUT-8(Co) and DUT-8(Ni) were investigated, indicating a high-spin state for both materials at room temperature. Density functional theory (DFT) simulations confirmed distinct energetic differences for Ni and Co analogues with a higher energetic penalty for the structural "gate opening" transformation for DUT-8(Co) compared to DUT-8(Ni) explaining the different flexibility behaviour of these isomorphous MOFs.underlying structural phase transitions are triggered by adsorption or desorption of guest molecules and generally characterised by an activation energy barrier, which causes hysteresis in physisorption experiments. Due to their switchable nature, so porous crystals are oen discussed as materials with huge application potential in gas storage, 11 separation processes, 12,13 sensor technology 14,15 and catalysis. 16 Despite rapidly growing research in the eld of exible MOFs, 1,17-21 the role of critical factors inuencing and controlling framework switchability are barely understood. 22 As MOFs are modular networks, the exibility of the linker but also the hinges of the metal node are key features that affect switchability. The importance of metal-node hinges and their energetics for framework switchability has been widely investigated for compounds such as M(bdp) (M ¼ Co, Fe, bdp ¼ 1,4-benzenedipyrazolate), 11,23,24 M(m-OH)(bdc) (MIL-53, M ¼ Cr, Al, Fe, bdc ¼ 1,4-benzenedicarboxylate)...

Tailoring adsorption induced switchability of a pillared layer MOF by crystal size engineering

“…According to the crystallographic data, Zn…Zn distance in 1_op is 2.966 Å, which is significantly longer than in DUT-8(Ni) and DUT-8(Co) (2.653 and 2.691 Å). 33 (Table S1, ESI). 56 Particle size As we have reported for DUT-8(Ni) and DUT-8(Co), the switching characteristics are sensitive to crystal size distribution and it was also expected for DUT-8(Zn).…”

“…24 The same behaviour is also characteristic for submicron-sized crystals of DUT-8(Co). 33 The macro-sized crystals of DUT-8(Co), however, do not show any responsivity to nitrogen at 77 K or carbon dioxide at 195 K molecules during adsorption, in contrast to , that shows pronounced switchability under the same conditions. 33 This suggests that the influence of particle size and metal node characteristics are interconnected and both aspects change the characteristics at a similar order of magnitude.…”

Tailoring Adsorption Induced Switchability of a Pillared Layer MOF by Crystal Size Engineering

“…According to the crystallographic data, Zn…Zn distance in 1_op is 2.966 Å, which is significantly longer than in DUT-8(Ni) and DUT-8(Co) (2.653 and 2.691 Å). 33 Figure S1, ESI), indicating that all samples are phase pure.…”

Structural‐Deformation‐Energy‐Modulation Strategy in a Soft Porous Coordination Polymer with an Interpenetrated Framework

“…[14] This finding differs from the reported selective recognition of CH 2 Cl 2 by soft PCP DTU-8(Co), which is primarily a consequence of the smaller molecule size of CH 2 Cl 2 . [15] Interestingly, the slopes of the CH 2 Cl 2 adsorption isotherms at low pressures indicate that PCP-NH 2 -bdc exhibits stronger CH 2 Cl 2 -framework interactions than PCP-bdc (Figure S10), probably due to the presence of hydrogen-bonding interactions between the amino moieties and CH 2 Cl 2 molecules. Similar adsorption behaviors were also observed for CS 2 , which has a slightly larger kinetic diameter (3.7 ) [14] ( Figure S11).…”