Tailoring adsorption induced phase transitions in the pillared-layer type metal–organic framework DUT-8(Ni)

Abstract

Tailoring the characteristics of gating transitions in the porous network, Ni(ndc)dabco (ndc = 2,6-naphthalenedicarboxylate, dabco = 1,4-diazabicyclo[2.2.2]octane), also termed DUT-8(Ni) (DUT = Dresden University of Technology), was achieved by systematically adjusting the critical synthesis parameters. The impact of the starting composition and solvent mixtures in the synthesis was found to critically affect the guest-response properties of the obtained materials. A comprehensive set of physical characterization methods, namely thermal analysis, H NMR of digested crystals, solid stateC NMR, PXRD, SEM, IR and Raman spectroscopy shows that the crystallite size is a crucial factor, determining the differing characteristics such as "gate pressure" and adsorption capacity in the guest-responsive switching behaviour of DUT-8. Crystallites smaller than 500 nm in size retain the open form after removal of the guest molecules resulting in typical "Type Ia" isotherm, whereas crystallites larger than 1 μm transform into the "closed pore" form and therefore can show a characteristic "gate opening" behaviour during gas adsorption. The particle size distribution of DUT-8(Ni) can be tailored by changing the synthesis conditions and consequently the slope of the isotherm at the "gating step" is affected. The in depth analysis of synthesis conditions and switching behaviour is an important step towards a better understanding of the fundamental principles responsible for guest responsive porosity switching in the solid state.

Mechanical Properties in Metal–Organic Frameworks: Emerging Opportunities and Challenges for Device Functionality and Technological Applications

“…While such effects have only been studied in a limited number of MOFs, the impacts can be significant. For instance, when confined to a thin film or synthesized below a critical particle size, significant alterations to MOF phase transition behaviors have been observed. Overall, the complexity of the many open questions that remain in this field and their direct connection to important opportunity areas and challenges for MOF applications suggests that investigations into MOF mechanical properties will continue to be a rich area of research moving forward.…”

Pillared-layered metal–organic frameworks for mechanical energy storage applications

“…For instance, the crystal size has shown to modify the hysteresis behavior and corresponding threshold values in exible MOFs in different ways. [93][94][95]…”

Raman spectroscopy studies of the terahertz vibrational modes of a DUT-8 (Ni) metal–organic framework

“…24 X-ray powder diffraction patterns were measured to prove the sample's phase purity (Fig. S4, ESI †).…”

“…22,23 The peculiarity of this MOF is that it can be synthesized in ''rigid'' and ''flexible'' forms, depending on the synthetic conditions. 24 The rigid version (DUT-8(Ni)_rigid), consisting of nano sized crystallites, can be desolvated without any phase transition and shows a typical ''Type Ia'' nitrogen physisorption isotherm at 77 K. In contrast, the flexible form (DUT-8(Ni)_flex), crystalized as macro crystals, undergoes a transformation into a closed phase (cp) upon desolvation and can be reversibly transformed into the open phase (op) by adsorption of gases or liquids. Both modifications were investigated in their ''as made'' as well as desolvated forms to probe the terahertz vibrational modes which are jointly responsible for flexibility.…”