The pillared layer framework DUT-8(Zn) (Zn<sub>2</sub>(2,6-ndc)<sub>2</sub>(dabco),
2,6-ndc = 2,6-naphthalenedicarboxylate, dabco =
1,4-diazabicyclo-[2.2.2]-octane, DUT = Dresden University of Technology) is a prototypical switchable MOF,
showing characteristic adsorption and desorption induced open phase (<i>op</i>) to closed phase (<i>cp</i>) transformation associated with huge
changes in cell volume. We demonstrate switchability strongly depends on a
framework-specific critical particle size (d<i><sub>crit</sub></i>).
The solvent removal process (pore desolvation stress contracting the framework)
significantly controls the <i>cp</i>/<i>op</i> ratio after desolvation and,
subsequently, the adsorption induced switchability characteristics of the
system. After desolvation, the dense <i>cp</i>
phase of DUT-8(Zn) shows no adsorption-induced reopening and therefore is
non-porous for N<sub>2</sub> at 77 K and CO<sub>2</sub> at 195 K. However,
polar molecules with a higher adsorption enthalpy, such as the polar molecules
such as chloromethane at 249 K and dichloromethane (DCM) at 298 K can reopen
the macro-sized crystals upon adsorption. For macro-sized particles, the outer
surface energy is negligible and only the type of metal (Zn, Co, Ni) controls
the DCM-induced gate opening pressure. The framework stiffness increases from
Zn to Ni as confirmed by DFT calculations, X-ray crystal structural analyses,
and low frequency Raman spectroscopy. The partial disintegration of the Zn
based node hinges produces an overall increased stabilization of<i> cp </i>vs. <i>op</i> phase shifts the critical particle size at which switchability
starts to become suppressed to even lower values (d<i><sub>crit</sub></i> < 200 nm) as compared to the Ni-based system (<i>d<sub>crit</sub></i> ≈ 500 nm). Hence, the
three factors affecting switchability (energetics of the empty host, (<i>E<sub>op</sub>-E<sub>cp</sub></i>) (I),
particle size (II), and desolvation stress (III)) appear to be of the same
order of magnitude and should be considered collectively, not individually.
Distribution Characteristics and Compressibility of Agglomerates as a Reflection of Granulation Parameters