Controlling the adsorption behavior of switchable porous materials is essential to pave the way for their successful implementation in highly selective separation and sensing applications. The switchable MOF M 2 (2,6-ndc) 2 (dabco) (DUT-8(M), where DUT = Dresden University of Technology, 2,6-ndc = naphthalene dicarboxylate, dabco = 1,4-diazabicyclo-[2.2.2]-octane, and M = Ni and Co) shows distinct differences in gating adsorption behavior depending on the transition metal of the node. Both DUT-8(Ni) and DUT-8(Co) transform into the closed pore phase after solvent removal. The nickel-containing compound shows high responsivity and gate opening in response to nitrogen adsorption, p/p 0 = 0.1 (77 K), resulting in a huge pore volume change, while the Co compound remains in a closed pore phase and is completely nonresponsive to nitrogen at 77 K. Herein, we demonstrate the gradual tuning of the gate opening pressure in DUT-8(M), upon nitrogen adsorption, by partially substituting nickel with cobalt in a series of mixed metal MOFs. The substitution mechanism was analyzed by powder X-ray diffraction (PXRD), solid-state UV/vis spectroscopy, inductively coupled plasma−optical emission spectroscopy elemental analysis, and energy-dispersive X-ray spectroscopy. In particular, continuous wave electron paramagnetic resonance (EPR) spectroscopy demonstrated the coexistence of Ni/Ni, Co/Ni, and Co/Co paddle wheel (PW) units. The gradual substitution of Ni in DUT-8(Ni) with Co allows continuous tuning of the gate opening pressure from p/p 0 0.1 to 0.75 (75% Co). The integration of Ni/Co-PWs into this pillared layer MOF has enabled, for the first time, in situ monitoring of this gating phenomenon via parallelized adsorption of N 2 (71 K) and EPR spectroscopy. These observations can be compared directly with in situ PXRD data collected during N 2 adsorption at 77 K. These complementary techniques reveal unique mechanistic insights into the structural changes of the PWs during the gating process. In addition, the experimental observations are supported by computational methods using density functional theory.

Although light is a prominent stimulus for smart materials, the application of photoswitches as light-responsive triggers for phase transitions of porous materials remains poorly explored. Here we incorporate an azobenzene photoswitch in the backbone of a metal-organic framework producing light-induced structural contraction of the porous network in parallel to gas adsorption. Light-stimulation enables non-invasive spatiotemporal control over the mechanical properties of the framework, which ultimately leads to pore contraction and subsequent guest release via negative gas adsorption. The complex mechanism of light-gated breathing is established by a series of in situ diffraction and spectroscopic experiments, supported by quantum mechanical and molecular dynamic simulations. Unexpectedly, this study identifies a novel light-induced deformation mechanism of constrained azobenzene photoswitches relevant to the future design of light-responsive materials.

In situ 1 H pulsed field gradient (PFG) NMR was used to investigate the molecular diffusion of n -butane in the pores of the flexible metal–organic framework DUT-49(Cu) at 298 K at different pore loadings, including pressure ranges below and above the negative gas adsorption (NGA) transition caused by structural contraction of the material. Supported by molecular dynamics simulations, the investigation provided crucial insight into confined diffusion within a highly flexible pore environment. The self-diffusion coefficients were derived from the experiment and compared with simulations, capturing the diffusion during n -butane adsorption and desorption. This complementary approach has yielded experimental characterization of molecular diffusion mechanisms during the unique process of NGA. This includes the observation of a 4-fold decrease of diffusivity within a less than 2 kPa gas pressure variation, corresponding to the NGA transition point.

Removal of the guest molecules from the pores of Metal-Organic Frameworks (MOFs) is one of the critical steps in particular for highly porous frameworks associated with high internal stress. In case of isostructural mesoporous (M= Cu, Ni, Mn, Fe, Co, Zn, Cd) frameworks, only and could be successfully desolvated so far and only by using supercritical activation. To get a deeper insight into the processes occurring upon the desorption of the solvent from the pores of DUT-49(M) the desolvation was monitored in situ by synchrotron PXRD. Analysis of the time-resolved PXRD data shows the full structural transformation pathway of the solid, which involves continuous and discontinuous phase transitions from open pore (op) to intermediate pore (ip) phase and from ip to contracted pore (cp) phase for and . For , the op to ip transition is directly followed by amorphization of the framework. All other frameworks show direct amorphization of the op phase.

Although light is a prominent stimulus for smart materials, the application of photoswitches as light-responsive triggers for phase transitions of porous materials remains poorly explored. Here we incorporate an azobenzene photoswitch in the backbone of a metal-organic framework producing light-induced structural contraction of the porous network in parallel to gas adsorption. Light-stimulation enables non-invasive spatiotemporal control over the mechanical properties of the framework, which ultimately leads to pore contraction and subsequent guest release via negative gas adsorption. The complex mechanism of light-gated breathing is established by a series of in situ diffraction and spectroscopic experiments, supported by quantum mechanical and molecular dynamic simulations. Unexpectedly, this study identifies a novel light-induced deformation mechanism of constrained azobenzene photoswitches relevant to the future design of light-responsive materials.