Metal–Organic Frameworks as Versatile Platforms for Organometallic Chemistry

Transition Metal Chelation Effect in MOF-253 Materials: Guest Molecule Adsorption Dynamics and Proposed Formic Acid Synthesis Investigated by Atomistic Simulations

The dynamic characterization of guest molecules in the metal-organic frameworks (MOFs) can always provide the insightful and inspiring information to facilitate the synthetic design of MOF materials from the bottom-up design of perspective. Herein, we present a series of atomistic molecular dynamics simulation for investigating the bipyridine dicarboxylate (bpydc) linker rotation effect on guest molecule adsorption with and without considering the transition metal (TM) chelation in MOF-253 materials. The simulated PXRD patterns of the various linker orientations present the challenge of distinguishing these structural varieties by the conventional crystalline spectroscopic measurements. The observed short inter-TM stable structure may subsequently lead to the formation of a binuclear TM catalytic site, and a proposed formic acid generation mechanism from CO2 and H2 is derived based upon the density functional theory calculations for the application of CO2 reduction.

Halide mediated modulation of magnetic interaction and anisotropy in dimeric Co(II) complexes

The burgeoning interest in the field of molecular magnetism is to perceive the high magnetic anisotropy in different geometries of metal complexes and hence to draw a magneto-structural correlation. Despite a handful of examples to exemplify the magnetic anisotropy in various coordination geometries of mononuclear complexes, the magnetic anisotropies for two different coordination geometries are underexplored. Employing an appropriate synthetic strategy utilizing the ligand LH2 [2,2'-{(1E,1'E)-pyridine2,6-diyl-bis(methaneylylidine)}-bis(azaneylylidine)diphenol] and cobalt halide salts in a 1 : 2 stoichiometric ratio in the presence of triethylamine allowed us to report a new family of dinuclear cobalt complexes [CoII2X2(L)(P)(Q)]·S with varying terminal halides [X = Cl, P = CH3CN, Q = H2O, S = H2O (1), X = Br, P = CH3CN, Q = H2O, S = H2O (2), X = I, P = CH3CN, and Q = CH3CN (3)]. All these complexes are characterized through single crystal X-ray crystallography, which reveals their crystallization in the monoclinic system P21/n space group with nearly identical structural features. These complexes share vital components, including Co(II) centers, a fully deprotonated ligand [L]2-, halide ions, and solvent molecules. The [L]2- ligand contains two Co(II) centers, where phenolate oxygen atoms bridge the Co(II) centers, forming a Co2O2 four-membered ring. Co1 demonstrates a distorted pentagonal-bipyramidal geometry with axial positions for solvent molecules, while Co2 displays a distorted tetrahedral geometry involving phenolate oxygen atoms and halide ions. Temperature-dependent dc magnetic susceptibility measurements were conducted on 1-3 within a range of 2 to 300 K at 1 kOe. The χmT vs. T plots exhibit similar trends, with χmT values at 300 K higher than the spin-only value, signifying a significant orbital contribution. As the temperature decreases, χmT decreases smoothly in all the complexes; however, no clear saturation at low temperatures is observed. Field-dependent magnetization measurements indicate a rapid increase below 20 kOe, with no hysteresis and a low magnetic blocking temperature. DFT and CASSCF/NEVPT2 theoretical calculations were performed to perceive the magnetic interaction and single-ion anisotropies of Co(II) ions in various ligand-field environments.

Further Insight into the Conversion of a Ni-Fe Metal-Organic Framework during Water-Oxidation Reaction

Metal-organic frameworks (MOFs) are extensively investigated as catalysts in the oxygen-evolution reaction (OER). A Ni-Fe MOF with 2,5-dihydroxy terephthalate as a linker has been claimed to be among the most efficient catalysts for the oxygen-evolution reaction (OER) under alkaline conditions. Herein, the MOF stability under the OER was reinvestigated by electrochemical methods, X-ray diffraction, X-ray absorption spectroscopy, energy-dispersive spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy, nuclear magnetic resonance, operando visible spectroscopy, electrospray ionization mass spectroscopy, and Raman spectroscopy. The peaks corresponding to the carboxylate group are observed at 1420 and 1520 cm^-1 using Raman spectroscopy. The peaks disappear after the reaction, suggesting the removal of the carboxylate group. A drop in carbon content but growth in oxygen content after the OER was detected by energy-dispersive spectra. This shows that after the OER, the surface of MOF is oxidized. SEM images also show deep restructures in the surface morphology of this Ni-Fe MOF after the OER. Nuclear magnetic resonance and electrospray ionization mass spectrometry show the decomposition of the linker in alkaline conditions and even in the absence of potential. These experimental data indicate that during the OER, the synthesized MOF transforms to a Fe-Ni-layered double hydroxide, and the formed metal oxide is a candidate for the OER catalysis. Generalization is not true; however, taken together, these findings suggest that the stability of Ni-Fe MOFs under harsh oxidation conditions should be reconsidered.

Enhancing the Catalytic Activity of MOF-808 Towards Peptide Bond Hydrolysis through Synthetic Modulations

The performance of MOFs in catalysis is largely derived from structural features, and much work has focused on introducing structural changes such as defects or ligand functionalisation to boost the reactivity of the MOF. However, the effects of different parameters chosen for the synthesis on the catalytic reactivity of the resulting MOF remains poorly understood. Here, we evaluate the role of metal precursor on the reactivity of Zr-based MOF-808 towards hydrolysis of the peptide bond in the glycylglycine model substrate. In addition, the effect of synthesis temperature and duration has been investigated. Surprisingly, the metal precursor was found to have a large influence on the reactivity of the MOF, surpassing the effect of particle size or number of defects. Additionally, we show that by careful selection of the Zr-salt precursor and temperature used in MOF syntheses, equally active MOF catalysts could be obtained after a 20 minute synthesis compared to 24 h synthesis.

Editorial for Special Issue “Functional Coordination Polymers and Metal–Organic Frameworks”

Metal–Organic Frameworks (MOFs) and Coordination Polymers (CPs) are at the forefront of contemporary coordination chemistry research, as witnessed by the impressive (and ever-growing) number of publications appearing in the literature on this topic in the last 20 years (Figure 1), reaching almost 4000 papers in 2020 [...]

UiO-66-NH2 as an effective solid support for quinazoline derivatives for antibacterial agents against Gram-negative bacteria

UiO-66-NH2 is used as an effective drug carrier for the control of quinazoline release for antibacterial agents against Gram-negative bacteria.