Switchable pillared layer metal–organic frameworks M2(2,6-ndc)2(dabco) (DUT-8(M), M ¼ Ni, Co, 2,6-ndc ¼ 2,6-
naphthalenedicarboxylate, 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 N2 at 77 K, CO2 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 DUT8(Ni), 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 DUT8(Co) compared to DUT-8(Ni) explaining the different flexibility behaviour of these isomorphous MOFs.