Postsynthetic Tuning of Metal-Organic Frameworks for Targeted Applications

Dual-Emitting Dye@MOF Composite as a Self-Calibrating Sensor for 2,4,6-Trinitrophenol

An anionic metal-organic framework (MOF) {(NH₂Me₂)[Zn₃(μ₃-OH)(tpt)(TZB)₃](DMF)₁₂}_n (1, tpt = 2,4,6-tri(4-pyridyl)-1,3,5-triazine, H₂TZB = 4-(1H-tetrazol-5-yl)benzoic acid and DMF = N,N-dimethylformamide), with both nanosized cages and partitions, has been solvothermally synthesized, which can serve as a crystalline vessel to encapsulate the fluorescent dye rhodamine 6G (Rh6G) via a "bottle around ship" approach. As a result, the obtained dye@MOF composite system features a blue emission of the ligand at 373 nm and a red emission of Rh6G at 570 nm when dispersed in solution, which could be used for decoding the trace amount of 2,4,6-trinitrophenol (TNP) by referring the peak-height ratio of each emission, even in coexistence with other potentially competitive nitroaromatic analytes. Furthermore, the observed fluorescence responses of the composite toward TNP are highly stable and reversible after recycling experiments. To the best of our knowledge, this is the first example of an MOF-implicated self-calibrated sensor for TNP detection.

Detoxification of a Sulfur Mustard Simulant Using a BODIPY-Functionalized Zirconium-Based Metal-Organic Framework

Effective detoxification of chemical warfare agents is a global necessity. As a powerful photosensitizer, a halogenated BODIPY ligand is postsynthetically appended to the Zr₆ nodes of the metal-organic framework (MOF), NU-1000, to enhance singlet oxygen generation from the MOF. The BODIPY/MOF material is then used as a heterogeneous photocatalyst to produce singlet oxygen under green LED irradiation. The singlet oxygen selectively detoxifies the sulfur mustard simulant, 2-chloroethyl ethyl sulfide (CEES), to the less toxic sulfoxide derivative (2-chloroethyl ethyl sulfoxide, CEESO) with a half-life of approximately 2 min.

Competitive Coordination Strategy to Finely Tune Pore Environment of Zirconium-Based Metal-Organic Frameworks

Metal-organic frameworks (MOFs) are a class of crystalline porous materials with reticular architectures. Precisely tuning pore environment of MOFs has drawn tremendous attention but remains a great challenge. In this work, we demonstrate a competitive coordination approach to synthesize a series of zirconium-metalloporphyrinic MOFs through introducing H₂O and monocarboxylic acid as modulating reagents, in which well-ordered mesoporous channels could be observed clearly under conventional transmission electron microscopy. Owing to plenty of unsaturated Lewis acid catalytic sites exposed in the visualized mesoporous channels, these structures exhibit outstanding catalytic activity and excellent stability in the chemical fixation of carbon dioxide to cyclic carbonates. The zirconium-based MOFs with ordered channel structures are expected to pave the way to expand the potential applications of MOFs.

Solid-State Gas Adsorption Studies with Discrete Palladium(II) [Pd2 (L)4 ]4+ Cages

The need for effective CO₂ capture systems remains high, and due to their tunability, metallosupramolecular architectures are an attractive option for gas sorption. While the use of extended metal organic frameworks for gas adsorption has been extensively explored, the exploitation of discrete metallocage architectures to bind gases remains in its infancy. Herein the solid state gas adsorption properties of a series of [Pd₂ (L)₄ ]⁴⁺ lantern shaped coordination cages (L = variants of 2,6-bis(pyridin-3-ylethynyl)pyridine), which had solvent accessible internal cavities suitable for gas binding, have been investigated. The cages showed little interaction with dinitrogen gas but were able to take up CO₂ . The best performing cage reversibly sorbed 1.4 mol CO₂ per mol cage at 298 K, and 2.3 mol CO₂ per mol cage at 258 K (1 bar). The enthalpy of binding was calculated to be 25-35 kJ mol^-1 , across the number of equivalents bound, while DFT calculations on the CO₂ binding in the cage gave ΔE for the cage-CO₂ interaction of 23-28 kJ mol^-1 , across the same range. DFT modelling suggested that the binding mode is a hydrogen bond between the carbonyl oxygen of CO₂ and the internally directed hydrogen atoms of the cage.

Atomistic Approach toward Selective Photocatalytic Oxidation of a Mustard-Gas Simulant: A Case Study with Heavy-Chalcogen-Containing PCN-57 Analogues

Here we describe the synthesis of two Zr-based benzothiadiazole- and benzoselenadiazole-containing metal-organic frameworks (MOFs) for the selective photocatalytic oxidation of the mustard gas simulant, 2-chloroethyl ethyl sulfide (CEES). The photophysical properties of the linkers and MOFs are characterized by steady-state absorption and emission, time-resolved emission, and ultrafast transient absorption spectroscopy. The benzoselenadiazole-containing MOF shows superior catalytic activity compared to that containing benzothiadiazole with a half-life of 3.5 min for CEES oxidation to nontoxic 2-chloroethyl ethyl sulfoxide (CEESO). Transient absorption spectroscopy performed on the benzoselenadiazole linker reveals the presence of a triplet excited state, which decays with a lifetime of 9.4 μs, resulting in the generation of singlet oxygen for photocatalysis. This study demonstrates the effect of heavy chalcogen substitution within a porous framework for the modulation of photocatalytic activity.

Metal–organic framework catalysis

Welcome to this CrystEngComm themed issue entitled “Metal–organic framework catalysis.”

Coordination change, lability and hemilability in metal–organic frameworks

Deformation or cleavage/reformation of metal–ligand bonds in MOFs lies at the heart of chemical/thermal stability and dynamic/flexible behaviour, provides avenues for post-synthetic modification, and can enable novel or improved performance for a variety of applications.

Low-cost CuNi@MIL-101 as an excellent catalyst toward cascade reaction: integration of ammonia borane dehydrogenation with nitroarene hydrogenation

Nitroarene hydrogenation is greatly boosted on coupling with ammonia borane dehydrogenation over low-cost CuNi@MIL-101 with bimetallic CuNi nanoparticles with size of ca. 3 nm.