Enhanced Gas Adsorption on Cu3(BTC)2 Metal-Organic Framework by Post-Synthetic Cation Exchange and Computational Analysis

Increased gas adsorption in a series of post-synthetically modified metal-organic frameworks (MOFs) of the type HKUST-1 was achieved by the partial cation exchange process. Manipulation of post-synthetic conditions demonstrates high tunability in the site substitution and gas adsorption properties during the dynamic equilibrium process. In this work, post-synthetic modification of Cu₃(BTC)₂ is carried on by exposure to TM²⁺ solutions (TM = Mn, Fe, Co, Ni) at different time intervals. The crystal structure, composition, and morphology were studied by powder X-ray diffraction, Fourier-transform infrared spectroscopy, inductively coupled plasma optical emission spectroscopy, and scanning electron microscopy. Structural analysis supports the retention of the crystal structure and partial substitution of the Cu metal nodes within the framework. A linear increase in the transmetalation process is observed with Fe and Co with a maximum percentage of 39 and 18%, respectively. Conversely, relatively low cation exchange is observed with Mn having a maximum percentage of 2.40% and Ni with only 2.02%. Gas adsorption measurements and surface area analysis were determined for each species. Interestingly, (Cu/Mn)₃(BTC)₂ revealed the highest CO₂ adsorption capacity of 5.47 mmol/g, compared to 3.08 mmol/g for Cu₃(BTC)₂. The overall increased gas adsorption can be attributed to the formation of defects in the crystal structure during the cation exchange process. These results demonstrate the outstanding potential of post-synthetic ion exchange as a general approach to fine-tuning the physical properties of existing MOF architectures.

Coupling Postsynthetic High-Temperature Oxidative Thermolysis and Thermal Rearrangements in Isoreticular Zinc MOFs

Herein, we report coupling in situ high temperature postsynthetic modifications (PSMs) in metal-organic frameworks (MOFs). Thermo-reactive propargyloxy-functionalized zinc IRMOFs (isoreticular metal-organic frameworks) prepared from 2-(prop-2-yn-1-yloxy)-[1,1'-biphenyl]-4,4'-dicarboxylic acid (H₂bpdcOCH₂CCH) were investigated for their high-temperature postsynthetic rearrangement (PSR) chemistry to heterocyclic chromenes and benzofurans and then coupled to solid-gas reactions with molecular oxygen. The selectivity for the initial molecular rearrangements was found to be inverted in the porous MOF environment compared to conventional melt reactions of the ester compound Me₂bpdcOCH₂CCH and proceeded far more easily than the solid-state transformation from H₂bpdcOCH₂CCH, showing the potential of MOFs to give rise to different chemistry. The major oxidative process was thermolysis of the chromene ring with a minor pathway of allylic-type oxidation to give heterocyclic chromenone functionality. The sequence was also successful on a series of two-component multivariate IRMOF frameworks prepared from thermo-reactive H₂bpdcOCH₂CCH and thermo-resistant H₂bpdcOMe linkers, demonstrating that these reactions can be used with known crystal engineering strategies. All transformations were fully compatible with the requirements to maintain MOF crystallinity and porosity as evidenced by surface area analysis and X-ray powder diffraction measurements. This work contributes to establishing the feasibility of high-temperature solid-gas manifolds for MOF PSM.

Hypervalent organoiodine(v) metal-organic frameworks: syntheses, thermal studies and stoichiometric oxidants

Iodinated analogues of the highly porous IRMOF-9 and UiO-67 frameworks were prepared and post-synthetically oxidised with dimethyldioxirane (DMDO). Analysis by X-ray photoelectron spectroscopy (XPS) confirmed promotion to the iodine(v) state and detailed differential scanning calorimetry-thermal gravimetric analysis (DSC-TGA) showed the hypervalent metal-organic frameworks (MOFs) undergo exothermic elimination at ∼200 °C with XPS showing hypervalency is maintained. The hypervalent MOFs are active heterogeneous reagents in sulfoxidation and alcohol oxidation reactions. The crystallinity and porosity of the MOFs were maintained following post-synthetic oxidation, thermolysis and after the heterogeneous reactions, as shown by powder X-ray diffraction (PXRD) and gas adsorption analyses. This work showcases the unique ability MOFs hold for studying chemical reactions and the potential for hypervalent organoiodine MOFs as reuseable oxidants.

A post-synthetically reduced borane-functionalised metal–organic framework with oxidation-inhibiting reactivity

Highly porous boron-loaded MOFs with novel auto-oxidation inhibiting reactivity are achieved via post-synthetic ketone reduction and alcohol reactions with H₃B·THF.

Tritopic Triazatruxene Ligands for Multicomponent Metal-Organic Frameworks

Multicomponent metal-organic frameworks (MOFs) are built up from multiple ligands that are geometrically distinct. These ligands occupy specific positions in the MOF lattice. Installing different functionalities at precise locations in the framework is an important step in making MOFs for specific applications. This can be achieved by designing functionalized ligands for multicomponent MOFs. Here, we report a simple synthetic procedure for a new tritopic triazatruxene based tricarboxylic acid, H₃ tat. We show that this ligand can be symmetrically derivatized with various substituents on its nitrogen centres. We report a new isoreticular series of well-ordered quaternary MOFs based on these new triazatruxene ligands together with two linear carboxylate ligands and Zn₄ O clusters. These MOFs are isostructural to the previously reported MUF-77 series and show similar high surface areas and large pore volumes. Furthermore, H-bonding between the NH sites of the incorporated triazatruxene ligands and guest molecules is employed to modify their fluorescence behavior.

High temperature expulsion of thermolabile groups for pore-space expansion in metal–organic frameworks

Direct radiative heating at 200 °C quantitatively converts sulfoxide-tags to desirable vinyl groups on a porous zinc(ii) metal–organic framework analogue of IRMOF-9.

Hydrogen Storage Materials for Mobile and Stationary Applications: Current State of the Art

One of the limitations to the widespread use of hydrogen as an energy carrier is its storage in a safe and compact form. Herein, recent developments in effective high-capacity hydrogen storage materials are reviewed, with a special emphasis on light compounds, including those based on organic porous structures, boron, nitrogen, and aluminum. These elements and their related compounds hold the promise of high, reversible, and practical hydrogen storage capacity for mobile applications, including vehicles and portable power equipment, but also for the large scale and distributed storage of energy for stationary applications. Current understanding of the fundamental principles that govern the interaction of hydrogen with these light compounds is summarized, as well as basic strategies to meet practical targets of hydrogen uptake and release. The limitation of these strategies and current understanding is also discussed and new directions proposed.

The synthesis and characterisation of coordination and hydrogen-bonded networks based on 4-(3,5-dimethyl-1H-pyrazol-4-yl)benzoic acid

A variety of coordination materials are formed from the heteroditopic ligand 4-(3,5-dimethyl-1H-pyrazol-4-yl)benzoate.