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

Adsorption of hydrogen sulphide on Metal-Organic Frameworks

Three new sets of interatomic potentials to model hydrogen sulphide (H2S) have been fitted. One of them is a 3-sites potential (which we named 3S) and the other two are 5-sites potentials (which we named 5S and 5Sd). The molecular dipole of the 3S and 5S potentials is 1.43 D, which is the value usually employed for H2S potentials, while the dipole of the 5Sd is the dipole measured experimentally for the H2S molecule, circa 0.974 D. The interatomic potentials parameters were obtained by fitting the experimental vapour-liquid equilibrium, vapour pressure and liquid density curves. The potential parameters fitted so far for H2S have been obtained applying long-range corrections to the Lennard-Jones energy. For that reason, when a cut and shift of the Lennard-Jones potentials is applied they do not yield the correct results. We employed a cut and shift of the Lennard-Jones potentials in the fitting procedure, which facilitates the use of the new potentials to model H2S adsorption on systems such as Metal-Organics Frameworks (MOFs). We have employed the newly developed potentials to study the adsorption of H2S on Cu-BTC, MIL-47 and IRMOF-1 and the results agree with the available electronic structures calculations. All calculations (both quantum and interatomic potential-based) predict that H2S does not bind to the Cu atoms in Cu-BTC

Crystallographic studies of gas sorption in metal-organic frameworks.

Metal-organic frameworks (MOFs) are a class of porous crystalline materials of modular design. One of the primary applications of these materials is in the adsorption and separation of gases, with potential benefits to the energy, transport and medical sectors. In situ crystallography of MOFs under gas atmospheres has enabled the behaviour of the frameworks under gas loading to be investigated and has established the precise location of adsorbed gas molecules in a significant number of MOFs. This article reviews progress in such crystallographic studies, which has taken place over the past decade, but has its origins in earlier studies of zeolites, clathrates etc. The review considers studies by single-crystal or powder diffraction using either X-rays or neutrons. Features of MOFs that strongly affect gas sorption behaviour are discussed in the context of in situ crystallographic studies, specifically framework flexibility, and the presence of (organic) functional groups and unsaturated (open) metal sites within pores that can form specific interactions with gas molecules

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

Crystallographic insights into (CH3NH3)3(Bi2I9): A new lead-free hybrid organic-inorganic material as a potential absorber for photovoltaics

The crystal structure of a new bismuth-based light-absorbing material for the application in solar cells was determined by single crystal X-ray diffraction for the first time. (CH3NH3)3(Bi2I9) (MBI) is a promising alternative to recently rapidly progressing hybrid organic–inorganic perovskites due to the higher tolerance against water and low toxicity. Single crystal X-ray diffraction provides detailed structural information as an essential prerequisite to gain a fundamental understanding of structure property relationships, while powder diffraction studies demonstrate a high degree of crystallinity in thin films

On the role of history-dependent adsorbate distribution and metastable states in switchable mesoporous metal-organic frameworks

Abstract A unique feature of metal-organic frameworks (MOFs) in contrast to rigid nanoporous materials is their structural switchabilty offering a wide range of functionality for sustainable energy storage, separation and sensing applications. This has initiated a series of experimental and theoretical studies predominantly aiming at understanding the thermodynamic conditions to transform and release gas, but the nature of sorption-induced switching transitions remains poorly understood. Here we report experimental evidence for fluid metastability and history-dependent states during sorption triggering the structural change of the framework and leading to the counterintuitive phenomenon of negative gas adsorption (NGA) in flexible MOFs. Preparation of two isoreticular MOFs differing by structural flexibility and performing direct in situ diffusion studies aided by in situ X-ray diffraction, scanning electron microscopy and computational modelling, allowed assessment of n-butane molecular dynamics, phase state, and the framework response to obtain a microscopic picture for each step of the sorption process