Methylamine Separations Enabled by Cooperative Ligand Insertion in Copper-Carboxylate Metal-Organic Frameworks

Monomethylamine (NH2CH3), dimethylamine (NH(CH3)2), and trimethylamine (N(CH3)3) are important chemical feedstocks that are produced industrially as an azeotropic mixture and must be separated using an energy-intensive thermal distillation. While solid adsorbents have been proposed as alternatives to distillation for separating various industrial gas mixtures, methylamine separations remain largely unexplored in this context. Here, we investigate two isoreticular frameworks Cu(cyhdc) (cyhdc2- = trans-1,4-cyclohexanedicarboxylate) and Cu(bdc) (bdc2- = 1,4-benzenedicarboxylate) as prospective candidates for this challenging separation, motivated by the recent discovery that Cu(cyhdc) reversibly captures ammonia through a unique framework-to-coordination polymer phase change. Through a combination of gas adsorption and powder X-ray diffraction analyses, we find that Cu(cyhdc) and Cu(bdc) reversibly bind large quantities of mono- and dimethylamine through framework-to-coordination polymer phase change mechanisms, although both frameworks adsorb only moderate amounts of trimethylamine via physisorption. Single-crystal X-ray diffraction analysis of select mono- and dimethylamine containing phases suggests that the number of hydrogen bond donors available and the linker donor strength are key factors influencing amine uptake. Finally, investigation of the tricomponent adsorption behavior of both materials reveals that Cu(cyhdc) is selective for the capture of monomethylamine from a range of mono-, di-, and trimethylamine mixtures.

An Interesting Conversion Route of Mononuclear Zinc Complex to Zinc Mixed Carboxylate Coordination Polymer

A complex [Zn(bpy)(acr)₂]·H₂O (1) was converted in a DMF medium (DMF = N,N'-dimethylformamide) into a coordination polymer [Zn(bpy)(acr)(HCOO)]_n (1a) (bpy = 2,2'-bipyridine, and Hacr = acrylic acid), and the species was fully characterized through a single crystal X-ray diffraction. Additional data were obtained by IR and thermogravimetric analysis. Complex (1a) crystalized the coordination polymer in the space group Pca2₁ of an orthorhombic system. Structural characterization revealed that Zn(II) adopted a square pyramidal stereochemistry generated by bpy molecules, coordinated by chelate, acrylate, and formate ions as unidentate and bridged, respectively. The presence of both the formate and the acrylate with different coordination modes generated two bands in ranges that were characteristic for the carboxylate vibration modes. Thermal decomposition occurs in two complex steps: it first happens via a bpy release, which is followed by an overlapped process that is associated with acrylate and formate decomposition. The obtained complex is of present interest due to the presence of two different carboxylates in its composition and situation, which is rarely reported in the literature.

Photoactive Metal-Organic Frameworks for the Selective Synthesis of Thioethers: Coupled with Phosphine to Modulate Thiyl Radical Generation

Metal-organic framework (MOF) materials are intriguing photocatalysts to trigger radical-mediated chemical transformations. We report herein the synthesis and characterization of a series of isomorphic MOFs which show a novel structure, wide visible-light absorption, high chemical stability, and specific redox potential. The prepared MOFs were explored for the photoinduced single-electron oxidation of thiol compounds, generating reactive thiyl radicals to afford thioethers via a convenient thiol-olefin reaction. Importantly, we provide a widely applicable strategy by combing a photoactive MOF with phosphine to modulate the generation of thiyl radical in the reaction, thereby producing a single product of the thioether without the formation of a disulfide byproduct due to the dimerization of thiyl radicals. The photocatalytic reaction takes advantage of this strategy, showing great generality where tens of thiols and olefins have been examined as coupling partners. In addition, the strategy has also been demonstrated to be effective for the reactions catalyzed by other MOFs. Mechanism studies reveal that the selective synthesis of C-S products relies on a synergy between the photoinduced generation of a thiyl radical over the MOF and the in situ cleavage of S-S bond into a S-H bond by phosphine. It is notable that the synthesized MOFs show advanced performance in comparison with classical MOFs. The work not only provides a series of novel MOF photocatalysts that are capable of photoinduced thiol-olefin coupling but also indicates the great potential of MOFs for photochemical transformations mediated by reactive radicals.

MOF based engineered materials in water remediation: Recent trends

The significant upsurge in the demand for freshwater has prompted various developments towards water sustainability. In this context, several materials have gained remarkable interest for the removal of emerging contaminants from various freshwater sources. Among the currently investigated materials for water treatment, metal organic frameworks (MOFs), a developing class of porous materials, have provided excellent platforms for the separation of several pollutants from water. The structural modularity and the striking chemical/physical properties of MOFs have provided more room for target-specific environmental applications. However, MOFs limit their practical applications in water treatment due to poor processability issues of the intrinsically fragile and powdered crystalline forms. Nevertheless, growing efforts are recognized to impart macroscopic shapability to render easy handling shapes for real-time industrial applications. Furthermore, efforts have been devoted to improve the stabilities of MOFs that are subjected to fragile collapse in aqueous environments expanding their use in water treatment. Advances made in MOF based material design have headed towards the use of MOF based aerogels/hydrogels, MOF derived carbons (MDCs), hydrophobic MOFs and magnetic framework composites (MFCs) to remediate water from contaminants and for the separation of oils from water. This review is intended to highlight some of the recent trends followed in MOF based material engineering towards effective water regeneration.

Visible-light-responsive lanthanide coordination polymers for highly efficient photocatalytic aerobic oxidation of amines and thiols

Photoinduced activation of oxygen by visible-light-responsive CPs via electron/energy transfer and its roles on aerobic oxidation of amines and thiols.

Unpaired Electron-Induced Wide-Range Light Absorption within Zn (or Cu) MOFs Containing Electron-Withdrawing Ligands: A Theoretical and Experimental Study

In photocatalysis, it is of general interest to understand and design wide-range light-absorbing inorganic/organic hybrid materials with an excellent photo-induced intramolecular charge-transfer (ICT) effect. To verify the role of unpaired electrons in enhancing ICT within electron-withdrawing ligand-based metal-organic frameworks (MOFs), the molecular structure, density of states (DOS), and electronic structure of strong electron-deficient pyridine-diketopyrrolopyrrole (P-DPP)-based Zn (or Cu) MOFs were calculated in Gaussian package to validate the unpaired electron ICT. The electron spin resonance technique has detected the unpaired electrons for the coordination systems containing Zn-O or Cu-O clusters and P-DPP ligand on photoexcitation. The estimated band gaps from the DOS calculation for P-DPP-Cu and P-DPP-Zn are 1.4 and 2.4 eV, respectively, showing a good agreement with the experimental UV-vis optical spectra. The partial DOS, dipole moment, and frontier orbital analysis prove that the ICT should happen from Zn-O or Cu-O clusters to P-DPP ligands. This research may contribute to a comprehensive understanding of electron-withdrawing ligand-induced ICT within MOFs and shed light on the design of light-absorbing MOFs with excellent ICT or conductivity.

Plasma-catalysed reaction Mn+ + L–H → MOFs: facile and tunable construction of metal–organic frameworks in dielectric barrier discharge

A fast, energy-saving and green strategy was proposed for preparing diverse and fine-tuned metal–organic frameworks in either DMF or ethanol, catalyzed by liquid-phase plasma generated via dielectric barrier discharge.

Solvent-dependent selective cation exchange in anionic frameworks based on cobalt(ii) and triphenylamine linkers: reactor-dependent synthesis and sorption properties

Two anionic cobalt(ii) MOFs were obtained dependent on the reactor design and show a solvent-dependent cation exchange leading to a remarkable increase in the surface area of post-synthetic modified materials.

Two new Cu(ii) and La(iii) 2D coordination polymers, synthesis and in situ structural analysis by X-ray diffraction

Two new coordination polymers were synthesized solvothermally using 4,4'-dimethoxy-3,3'-biphenyldicarboxylic acid (H2dmbpdc), and di- and trivalent metal salts (Cu(NO3)2·2.5H2O and La(NO3)3·6H2O). Their structures were determined by single-crystal X-ray diffraction analysis, and their thermal stability was evaluated by thermogravimetric analysis. The copper compound Cu(dmbpdc)(DMF; N,N-dimethylformamide), CPO-71-Cu, is based on the well known copper acetate paddlewheel secondary building unit. The asymmetric unit comprises one copper cation with one DMF molecule and one linker molecule coordinated. The lanthanum compound La2(dmbpdc)3(DMF)(H2O)3, CPO-72-La, is formed from a dimer of nine-coordinate, edge sharing lanthanum cations. To this dimer, three water molecules and one DMF molecule are coordinated in an ordered fashion. In addition, the asymmetric unit contains three crystallographically unique linker molecules. Both CPO-71-Cu and CPO-72-La form two-dimensional layered structures, and topological analyses reveal sql topologies with point symbol 4(4)·6(2) and vertex symbol 4·4·4·4·6(2)·6(2). The thermal behavior of CPO-71-Cu was investigated in an in situ structural analysis by variable temperature powder- and single-crystal X-ray diffraction.

Facile Synthesis of Fe2O3 Nano-Dots@Nitrogen-Doped Graphene for Supercapacitor Electrode with Ultralong Cycle Life in KOH Electrolyte

Fe2O3 nanodots supported on nitrogen-doped graphene sheets (denoted as Fe2O3 NDs@NG) with different loading masses are prepared through a facile one-pot solvothermal method. The resulting Fe2O3 NDs@NG composites exhibit outstanding electrochemical properties in aqueous KOH electrolyte. Among them, with the optimal loading mass of Fe2O3 NDs, the corresponding Fe2O3 NDs@NG-0.75 sample is able to deliver a high specific capacitance of 274 F g(-1) at 1 A g(-1) and the capacitance is still as high as 140 F g(-1) even at a ultrahigh current density of 50 A g(-1), indicating excellent rate capability. More remarkably, it displays superior capacitance retention after 100,000 cycles (about 75.3% at 5 A g(-1)), providing the best reported long-term cycling stability for iron oxides in alkaline electrolytes to date. Such excellent electrochemical performance is attributed to the right combination of highly dispersed Fe2O3 NDs and appropriately nitrogen-doped graphene sheets, which enable the Fe2O3 NDs@NG-0.75 to offer plenty of accessible redox active sites, facilitate the electron transfer and electrolyte diffusion, as well as effectively alleviate the volume change of Fe2O3 NDs during the charge-discharge process.

Three novel d7/d10 metal complexes with N-heterocyclic ligand of 2,6-bis(3-pyrazolyl)pyridine: synthesis, structure, surface photovoltage spectroscopy and photocatalytic activity

We synthesized three novel d⁷/d¹⁰ metal complexes with 2,6-bis(3-pyrazolyl)pyridine and studied their surface photovoltage spectra and photocatalytic activities.

Anionic zinc-trimesic acid MOFs with unusual topologies: reversible hydration studies

The reaction of 1,3,5-benzenetricarboxylic acid (H(3)BTC) with ZnSO(4).6H(2)O in a DMF-water solution afforded two new metal-organic frameworks [Zn(6)(mu(3)-OH)(2)(BTC)(4)(DMF)(2.5)(H(2)O)(2)].[Zn(H(2)O)(3)(DMF)(3)].3.1H(2)O (1) and Zn(2)(HBTC)(BTC)(H(2)O)(3)].DMA.3H(2)O (2). Both compounds are thermally stable and can be prepared reproducibly. Rehydration experiments on compound 2 demonstrate reversible dehydration and rehydration while 1 rehydrates to a different crystalline material. Network analysis revealed a binodal (3,6)-net for 1 and a (3,5)-net for 2, both rare topologies.

Hydrothermal Synthesis of a Novel Uranium Oxalate/Glycolate via In-Situ Ligand Formation

A novel templated uranium oxalate/glycolate, (UO2)4(O)2(C2O4)(H2C2O3)2.2[(C8H20)N] (a = 7.9230(8) A, b = 13.3793(13) A, c = 17.4141(18) A, beta = 96.006(2) degrees , monoclinic, P21/n, Z = 2), has been synthesized under hydrothermal conditions via in-situ ligand synthesis. The oxalate and glycolate anions have been formed through the oxidation of 1,4-diazabicyclo[2.2.2]octane, which proceeds through intermediates such as piperazine and ethylene glycol. Reported herein is the synthesis of this compound, crystal structure, and mechanistic information regarding the oxidation pathway.