Exceptional adsorption induced cluster and network deformation in the flexible metal organic framework DUT 8 Ni observed by in situ X ray diffraction and EXAFS

The gate opening mechanism in the highly flexible MOF Ni2 2,6 ndc 2dabco DUT 8 Ni , DUT Dresden University of Technology with unprecedented unit cell volume change was elucidated in detail using combined single crystal X ray diffraction, in situ XRD and EXAFS techniques. The analysis of the crystal structures of closed pore cp and large pore lp phases reveals a drastic and unique unit cell volume expansion of up to 254 , caused by adsorption of gases, surpassing other gas pressure switchable MOFs significantly. To a certain extent, the structural deformation is specific for the guest molecule triggering the transformation due to subtle differences in adsorption enthalpy, shape, and kinetic diameter of the guest. Combined adsorption and powder diffraction experiments using nitrogen 77 K , carbon dioxide 195 K , and n butane 272.5 K as a probe molecules reveal a one step structural transformation from cp to lp. In contrast, adsorption of ethane 185 K or ethylene 169 K results in a two step transformation with the formation of intermediate phases. In situ EXAFS during nitrogen adsorption was used for the first time to monitor the local coordination geometry of the metal atoms during the structural transformation in flexible MOFs revealing a unique local deformation of the nickel based paddle wheel nod

Metal-organic framework templated electrodeposition of functional gold nanostructures

Utilizing a pair of quick, scalable electrochemical processes, the permanently porous MOF HKUST-1 was electrochemically grown on a copper electrode and this HKUST-1-coated electrode was used to template electrodeposition of a gold nanostructure within the pore network of the MOF. Transmission electron microscopy demonstrates that a proportion of the gold nanostructures exhibit structural features replicating the pore space of this ∼1.4 nm maximum pore diameter MOF, as well as regions that are larger in size. Scanning electron microscopy shows that the electrodeposited gold nanostructure, produced under certain conditions of synthesis and template removal, is sufficiently inter-grown and mechanically robust to retain the octahedral morphology of the HKUST-1 template crystals. The functionality of the gold nanostructure within the crystalline HKUST-1 was demonstrated through the surface enhanced Raman spectroscopic (SERS) detection of 4-fluorothiophenol at concentrations as low as 1 μM. The reported process is confirmed as a viable electrodeposition method for obtaining functional, accessible metal nanostructures encapsulated within MOF crystals

Crystal Engineering of Phenylenebis azanetriyl tetrabenzoate Based Metal Organic Frameworks for Gas Storage Applications

The metal–organic framework (MOF) Cu₄(<i>m</i>pbatb)₂ (<i>m</i>pbatb-4,4′,4″,4‴-(1,3-phenylenebis­(azanetriyl))­tetrabenzoate), also known as DUT-71 (DUT – Dresden University of Technology), was functionalized via postsynthetic cross-linking of the copper paddle wheels by linear salen derivatives and dabco (1,4-diazabicyclo[2.2.2]­octane). This results in a series of porous MOFs, denoted as DUT-117­(M) (M – Cu, Ni, Pd). Besides significant improvement of the framework robustness, the influence of the metal coordinated by the salen ligand on the gas adsorption capacity (hydrogen –196 °C, methane 25 °C, and carbon dioxide 25 °C) was investigated. In this series DUT-117­(Ni) stands out as the best material for adsorptive methane storage with a high working capacity of 171 cm³·cm^–3 between 5 and 65 bar

Methane storage mechanism in the metal organic framework Cu 3 btc 2 An in situ neutron diffraction study

The adsorption of deutero-methane (CD<SUB>4</SUB>) in Cu<SUB>3</SUB>(btc)<SUB>2</SUB> (HKUST-1) was investigated at 77 K using high-resolution neutron powder diffraction. Rietveld refinement of the neutron data revealed a sequential filling of the rigid framework at distinct preferred adsorption sites, and showed the importance of open metal sites even for non-polar molecules such as methane. Four main adsorption sites were identified, located inside the small and two larger pores of the framework. The shorter distances between the CD<SUB>4</SUB> center and the pore wall atoms are covering a range from 3.07 to 3.547 Å. The maximum occupation of 170 CD<SUB>4 </SUB>molecules per unit cell, estimated from the refined occupancy of the adsorption sites, is close to the value estimated from volumetric adsorption isotherms at 77 K (176 molecules per cell). Molecular simulation gave further insight into the adsorption mechanism

Accurate model for predicting adsorption of olefins and paraffins on MOFs with open metal sites

Metal–organic frameworks (MOFs) have shown tremendous potential for challenging gas separation applications, an example of which is the separation of olefins from paraffins. Some of the most promising MOFs show enhanced selectivity for the olefins due to the presence of coordinatively unsaturated metal sites, but accurate predictive models for such systems are still lacking. In this paper, we present results of a combined experimental and theoretical study on adsorption of propane, propylene, ethane, and ethylene in CuBTC, a MOF with open metal sites. We first propose a simple procedure to correct for impurities present in real materials, which in most cases makes experimental data from different sources consistent with each other and with molecular simulation results. By applying a novel molecular modeling approach based on a combination of quantum mechanical density functional theory and classical grand canonical Monte Carlo simulations, we are able to achieve excellent predictions of olefin adsorption, in much better agreement with experiment than traditional, mostly empirical, molecular models. Such an improvement in predictive ability relies on a correct representation of the attractive energy of the unsaturated metal for the carbon–carbon double bond present in alkenes. This approach has the potential to be generally applicable to other gas separations that involve specific coordination-type bonds between adsorbates and adsorbents