Mn(II)-Based Porous Metal–Organic Framework Showing Metamagnetic Properties and High Hydrogen Adsorption at Low Pressure

A Theoretical Perspective to Decipher the Origin of High Hydrogen Storage Capacity in Mn(II) Metal-Organic Framework

Herein, we report a detailed periodic DFT investigation of Mn(II)-based [(Mn₄ Cl)₃ (BTT)₈ ]^3- (BTT^3- =1,3,5-benzenetristetrazolate) metal-organic framework (MOF) to explore various hydrogen binding pockets, nature of MOF…H₂ interactions, magnetic coupling and, H₂ uptake capacity. Earlier experiments found an uptake capacity of 6.9 wt % of H_2, with the heat of adsorption estimated to be ∼10 kJ/mol, which is one among the highest for any MOFs reported. Our calculations unveil different binding sites with computed binding energy varying from -6 to -15 kJ/mol. The binding of H₂ at the Mn²⁺ site is found to be the strongest (site I), with H₂ found to bind Mn²⁺ ion in a η² fashion with a distance of 2.27 Å and binding energy of -15.4 kJ/mol. The bonding analysis performed using NBO and AIM reveal a strong donation of σ (H₂ ) to the d_z ² orbital of the Mn²⁺ ion responsible for such large binding energy. The other binding pockets, such as -Cl (site II) and BTT ligands (site III and IV) were found to be weaker, with the binding energy decreasing in the order I>II>III>IV. The average binding energy computed for these four sites put together is 9.6 kJ/mol, which is in excellent agreement with the experimental value of ∼10 kJ/mol. We have expanded our calculations to compute binding energy for multiple sites simultaneously, and in this model, the binding energy per site was found to decrease as we increased the number of H₂ molecules suggesting electronic and steric factors controlling the overall uptake capacity. The calculated adsorption isotherm using the GCMC method reproduces the experimental observations. Further, the magnetic coupling computed for the unbound MOF reveals moderate ferromagnetic and strong antiferromagnetic coupling within the tetrameric {Mn₄ } unit leading to a three-up-one-down spin configuration as the ground state. These were then coupled ferromagnetically to other tetrameric units in the MOF network. The magnetic coupling was found to alter only marginally upon gas binding, suggesting that both exchange interaction and the spin-states are unlikely to play a role in the H₂ uptake. This is contrary to the O₂ uptake studied lately, where strong dependence on exchange-coupling/spin state was witnessed, suggesting exchange-coupling/magnetic field dependent binding as a viable route for gas separation.

Magnetic Silica-Coated Picolylamine Copper Complex [Fe3O4@SiO2@GP/Picolylamine-Cu(II)]-Catalyzed Biginelli Annulation Reaction

An efficient and heterogeneous novel magnetic silica-coated picolylaminecopper complex [Fe₃O₄@SiO₂@GP/Picolylamine-Cu(II)] was synthesized, characterized, and employed as a magnetically recoverable nanocatalyst in Biginelli condensation for the preparation of biologically active 3,4-dihydropyrimidinones. Fe₃O₄@SiO₂@GP/Picolylamine-Cu(II) was synthesized easily using chemical attachment of the picolylaminecompound on Fe₃O₄@SiO₂@GP, followed by treatment with copper salt in ethanol under reflux conditions. Fe₃O₄@SiO₂@GP/Picolylamine-Cu(II) was affirmed by various analyses such as Fourier transform infrared, thermogravimetric analysis, X-ray diffraction, vibrating-sample magnetometry, field-emission scanning electron microscopy, transmission electron microscopy, DLS, inductively coupled plasma, energy-dispersive X-ray spectrometry, X-ray photoelectron spectroscopy, and Brunauer-Emmett-Teller. The resulting catalyst system was successfully used in the Biginelli reaction through a variety of compounds such as aromatic aldehyde, urea, and ethyl acetoacetate under solvent-free conditions or ethylene glycol at 80 °C and yielded the desired products with high conversions with powerful reusability. The current approach was convenient and clean, and only 0.01 g of the catalyst could be used to perform the reaction. The easy work-up procedure, gram-scale synthesis, usage of nontoxic solvent, improved yield, short reaction times, and high durability of the catalyst are several remarkable advantages of the current approach. Also, the Fe₃O₄@SiO₂@GP/Picolylamine-Cu(II) nanocatalyst could be recycled by an external magnet for eight runs with only a significant loss in the product yields.

Supramolecular Cu(ii)–dipyridyl frameworks featuring weakly coordinating dodecaborate dianions for selective gas separation

Several novel weakly coordinating dodecaborate anion hybrid supramolecular Cu(ii)–dipyridyl frameworks were synthesized and characterized by single crystal analysis with one potential for selective C₂H₂/C₂H₄ and C₂H₂/CO₂ separation.

Substitution Effects Regulate the Formation of Butterfly-Shaped Tetranuclear Dy(III) Cluster and Dy-Based Hydrogen-Bonded Helix Frameworks: Structure and Magnetic Properties

The generation of two types of complexes with different topological connections and completely different structural types merely via the substitution effect is extremely rare, especially for -CH₃ and -C₂H₅ substituents with similar physical and chemical properties. Herein, we used 3-methoxysalicylaldehyde, 1,2-cyclohexanediamine, and Dy(NO₃)₃·6H₂O to react under solvothermal conditions (CH₃OH:CH₃CN = 1:1) at 80 °C to obtain the butterfly-shaped tetranuclear Dy^III cluster [Dy₄(L¹)₄(μ₃-O)₂(NO₃)₂] (Dy₄, H₂L¹ = 6,6'-((1E,1'E)-(cyclohexane-1,3-diylbis(azanylylidene))bis(methanylylidene))bis(2-methoxyphenol)). The ligand H₂L¹ was obtained by the Schiff base in situ reaction of 3-methoxysalicylaldehyde and 1,2-cyclohexanediamine. In the Dy₄ structure, (L¹)^2- has two different coordination modes: μ₂-η¹:η²:η¹:η¹ and μ₄-η¹:η²:η¹:η¹:η²:η¹. The four Dy^III ions are in two coordination environments: N₂O₆ (Dy1) and O₉ (Dy2). The magnetic testing of cluster Dy₄ without the addition of an external field revealed that it exhibited a clear frequency-dependent behavior. We changed 3-methoxysalicylaldehyde to 3-ethoxysalicylaldehyde and obtained one case of a hydrogen-bonded helix framework, [DyL²(NO₃)₃]_n·2CH₃CN (Dy-HHFs, H₂L² = 6,6'-((1E,1'E)-(cyclohexane-1,3-diylbis(azanylylidene))bis(methanylylidene))bis(2-ethoxyphenol)), under the same reaction conditions. The ligand H₂L² was formed by the Schiff base in situ reaction of 3-ethoxysalicylaldehyde and 1,2-cyclohexanediamine. All Dy^III ions in the Dy-HHFs structure are in the same coordination environment (O₉). The twisted S-shaped (L²)^2- ligand is linked by a Dy(III) ion to form a spiral chain. The spiral chain is one of the independent units that is interconnected to form Dy-HHFs through three strong hydrogen-bonding interactions. Magnetic studies show that Dy-HHFs exhibits single-ion-magnet behavior (U_eff = 68.59 K and τ₀ = 1.10 × 10^-7 s, 0 Oe DC field; U_eff = 131.5 K and τ₀ = 1.22 × 10^-7 s, 800 Oe DC field). Ab initio calculations were performed to interpret the dynamic magnetic performance of Dy-HHFs, and a satisfactory consistency between theory and experiment exists.

Facile Fabrication of a Multifunctional Metal-Organic Framework-based Sensor Exhibiting Exclusive Solvochromic Behaviors toward Ketone Molecules

To probe the efficient strategy for preparing a multifunctional sensing material, the facile synthesis strategies and successful examples are urgently required. Through the utilization of a hexadentate ligand derived from cyclotriphosphazene, which displays spiral configurations and multiple connection modes, a novel metal-organic framework (MOF) was constructed via one-step synthesis from low-cost raw materials. The presence of multiple interaction sites decorating the helical channels of the reported MOF gives rise to exclusive solvochromic-sensing behavior for small ketone molecules such as acetone, acetophenone, and 2,5-diketohexane. Additionally, the helical structure of a manganese-carboxylate chain allows for the pore volume not only be available for the adsorption of large organic molecules but also enables the enantiopure selective separation of 1-phenylethanol (ee 35.99 %). Furthermore, the structural analysis of the acetophenone-encapsulated sample allowed the solvochromic mechanism to be elucidated, which should be ascribed to the strong hydrogen-bonding interaction between the guest molecules and specific sites on a host matrix. The experimental results have not only clearly manifested the vital role of starting materials of MOFs, including the connection modes and spatial configuration, but also have provided very valuable insight for the future assembly of novel multifunctional sensing materials.

Enhanced hydrogen adsorption on graphene by manganese and manganese vanadium alloy decoration

In this work, two kinds of novel manganese decorated (G + Mn) and manganese-vanadium co-decorated (G + MnV) graphene composites are synthesized by in situ wet chemical reduction, and their hydrogen storage properties and microstructures are characterized by Sievert-type adsorption apparatus, BET, SEM, TEM/STEM, EDX and EELS. Compared with pristine graphene, Mn decoration marginally increases the hydrogen adsorption capacity of graphene at room temperature and 4 MPa hydrogen pressure from 0.25 wt% to 0.36 wt%. On the other hand, the co-decoration of Mn and V increases the room temperature hydrogen storage capacity of graphene significantly to 1.81 wt% under 4 MPa hydrogen pressure, which is 1.56 wt% higher than the capacity of pristine graphene. The microstructures and valence states of the decorated Mn and Mn-V nanoparticles are investigated by TEM, EDX and EELS analyses, and strong interactions between the decorated nanoparticles and graphene are observed. Based on the results from structural analyses, potential enhancement mechanisms are suggested in terms of the catalytic effects of nanoparticles on graphene hydrogen adsorption. Given the relatively low cost of Mn and V metals compared to noble metals such as Pd, Pt and Au, these results demonstrate a low cost and effective way to significantly enhance the room temperature hydrogen adsorption properties of graphene for potential hydrogen storage applications.

Incorporation of Pyrazine and Bipyridine Linkers with High-Spin Fe(II) and Co(II) in a Metal-Organic Framework

A series of isoreticular metal-organic frameworks (MOFs) of the formula M(BDC)(L) (M = Fe(II) or Co(II), BDC = 1,4-benzenedicarboxylate, L = pyrazine (pyz) or 4,4'-bipyridine (bipy)) has been synthesized and characterized by N₂ gas uptake measurements, single crystal and powder X-ray diffraction, magnetometry, X-ray absorption spectroscopy, and Mössbauer spectroscopy. These studies indicate the formation of a permanently porous solid with high-spin Fe(II) and Co(II) centers that are weakly coupled, consistent with first-principles density functional theory calculations. This family of materials represents unusual examples of paramagnetic metal centers coordinated by linkers capable of mediating magnetic or electronic coupling in a porous framework. While only weak interactions are observed, the rigid 3D framework of the MOF dramatically impacts the properties of these materials when compared with close structural analogues.

A series of transition metal coordination polymers based on a rigid bi-functional carboxylate–triazolate tecton

By utilizing a pre-designed bi-functional ligand, five new transition-metal-based coordination polymers have been constructed and structurally characterized, along with their luminescence or magnetic properties.

A Zn(ii) complex with large channels based on 3′-nitro-biphenyl-3,5,4′-tricarboxylic acid: synthesis, crystal structure, fluorescence sensing of ATP, ADP, GTP, and UTP in aqueous solution and drug delivery

A 3D Zn(ii)–MOF with large cubic channels was synthesized. It showed fluorescence sensing of ATP, ADP, GTP, and UTP. Furthermore, it exhibited a remarkable capacity for and controlled release of 5-fluorouracil.

The First Example of Hetero-Triple-Walled Metal-Organic Frameworks with High Chemical Stability Constructed via Flexible Integration of Mixed Molecular Building Blocks

An unprecedented 3D hetero-triple-walled metal-organic framework is obtained by straightforward elaboration of the mixed molecular building block (MBB) strategy. In this approach, multiple individual flexible and rigid MBBs are integrated into one composite building block as separate layers, which are of the same shape but different sizes. This MOF shows exceptional water stability and the application of Li-ion battery electrodes.

The ionothermal synthesis, structure, and magnetism-structure relationship of two biphenyl tetracarboxylic acid-based metal-organic frameworks

Two new metal-organic frameworks (1-2) were ionothermally obtained by the reaction of a biphenyltetracarboxylic sodium (Na4BPTC) ligand and M(OOCCH3)2 (M = Co(1) and Mn(2)). Crystal structure analysis reveals that 1 is a Co3Na6 unit-based three dimensional heterometallic MOF, while 2 exhibits a {Mn(COO)n} chain-based three-dimensional framework. Furthermore, the magnetic measurement shows that both of them have anti-ferromagnetic properties. A combination of Density Functional Theory (DFT) and Quantum Monte Carlo (QMC) simulation uncovers that in 2 the coupling parameters between two adjacent Mn(II) ions are J1 = -2.0 cm(-1) and J2 = -1.6 cm(-1), and the magnetism mainly originates from the propagation of Mn(II) ions by the super-exchange of carboxylates. Interestingly, the superexchange modes of J1 and J2 are different. Two spin nets of -/+/- dominate in the coupling for J1, while for J2 there are two spin nets of -/+/- and one spin net of +/-/+.

Three 3D coordination polymers based on [1,1′:4′,1′′-terphenyl]-2′,4,4′′,5′-tetracarboxylate demonstrating magnetic properties and selective sensing of Al3+/Fe3+over mixed ions

Three 3D coordination polymers have been synthesized by using the 1,1′:4′,1′′-terphenyl]-2′,4,4′′,5′-tetracarboxylate acid and Cd(ii),Co(ii) and Mn(ii), the Cd(ii) complex shows selective sensing Al³⁺/Fe³⁺ over the mixed metal ions.

Porous materials based on metal–nucleobase systems sustained by coordination bonds and base pairing interactions

Two approaches to metal–nucleobase porous materials: coordination bond sustained MOFs and hydrogen bond pairing based SMOFs.

Solvent modulated assembly of two Zn metal–organic frameworks: syntheses, luminescence, and gas adsorption properties

Two new MOFs based on H₂btca and zinc – [Zn(btca)(2,2′-bipy)]_n (1) and [Zn₂(btca)₂(bpy)(H₂O)]_n·n(DMA) (2) – have been designed and synthesized by modulating the solvent.

Postsynthetic ligand exchange for the synthesis of benzotriazole-containing zeolitic imidazolate framework

A postsynthetic ligand exchange strategy is used for introducing benzotriazole to ZIF-7 without changing its framework, high stability and morphology.

Dinuclear Cd(ii), Mn(ii) and Cu(ii) complexes derived from (anthraquinone-1-diyl) benzoate: DNA binding and cleavage studies

Three dinuclear Cd(ii), Mn(ii) and Cu(ii) complexes have been successfully synthesized under solvothermal conditions. Among them, only the Cu(ii) complex has the activity for DNA cleavage.

Tuning the magnetic behaviors in [FeIII12LnIII4] clusters with aromatic carboxylate ligands

Six new Fe–Ln clusters composed of a Fe₁₂Ln₄ core derived from two monocarboxylate ligands have been successfully obtained with a step-by-step strategy. Magnetic analyses suggest that 1–6 show different magnetic properties, and 2 and 6 display SMM-like behaviors.

Two three-dimensional cadmium(ii) coordination polymers based on 5-amino-tetrazolate and 1,2,4,5-benzenetetracarboxylate: the pH value controlled syntheses, crystal structures and luminescent properties

Two 3D cadmium(ii) coordination polymers have been prepared by controlling the pH values of the reaction mixture.