A novel style of 2D Hofmann-type coordination polymer incorporated trigonal prismatic coordination geometry with bidentate co-ligands

A novel 2D Hofmann-type framework was prepared with a bidentate co-ligand, 5,5'-dimethyl-2,2'-bipyridyl (dmbpy), which forces the curvature of the layer. X-ray diffraction analysis demonstrated that the coordination polymers, MnII(dmbpy)[MVN(CN)4] (MV = Mn (1) and Cr (2)), formed a considerably corrugated 2D cyanide-bridged network with a quasi C4v symmetric building unit, [CrVN(CN)4]2-, and trigonal prismatic coordination geometry around MnII. Compound 2 demonstrated a metamagnetic-like ordering at 14.4 K, caused by the intra- and inter-layer antiferromagnetic interactions between CrV (S = 1/2) and MnII (S = 5/2), and a weak ferromagnetic behaviour at 2 K reflecting the single-ion anisotropy of CrV and structural anisotropy.

Principles of Design and Synthesis of Metal Derivatives from MOFs

Materials derived from metal-organic frameworks (MOFs) have demonstrated exceptional structural variety and complexity and can be synthesized using low-cost scalable methods. Although the inherent instability and low electrical conductivity of MOFs are largely responsible for their low uptake for catalysis and energy storage, a superior alternative is MOF-derived metal-based derivatives (MDs) as these can retain the complex nanostructures of MOFs while exhibiting stability and electrical conductivities of several orders of magnitude higher. The present work comprehensively reviews MDs in terms of synthesis and their nanostructural design, including oxides, sulfides, phosphides, nitrides, carbides, transition metals, and other minor species. The focal point of the approach is the identification and rationalization of the design parameters that lead to the generation of optimal compositions, structures, nanostructures, and resultant performance parameters. The aim of this approach is to provide an inclusive platform for the strategies to design and process these materials for specific applications. This work is complemented by detailed figures that both summarize the design and processing approaches that have been reported and indicate potential trajectories for development. The work is also supported by comprehensive and up-to-date tabular coverage of the reported studies.

Highly Selective MOF-Based Turn-Off Luminescence Detection of Hg2+ Ions in an Aqueous Medium and Its Dual Functional Catalytic Activity toward Aldol Condensation and β-Enamination Reactions

A new organic ligand, 5-(carboxyformamido)isophthalic acid (5-CFIA), was prepared and employed for the synthesis of two compounds [M₃(C₁₀H₄O₇N₁)₂(8H₂O)]·H₂O (M = Cd, Mn). The compounds have three-dimensionally extended structures. Both the compounds were found to be luminescent at room temperature. The luminescence nature was exploited for the detection of Hg²⁺ ions in an aqueous medium with good selectivity. The interactions between Hg²⁺ ions and the compounds quench the luminescence intensity and act as a turn-off sensor. Both the compounds exhibited low limits for the detection of Hg²⁺ ions and in the range mandated by the WHO. The interactions between Hg²⁺ ions and the compound involve the -NH group, which was probed using Raman and IR spectroscopic techniques. These studies provide important pointers toward the mechanism of this turn-off luminescence behavior. The compounds were explored for base-catalyzed aldol condensation and Lewis acid-promoted β-enaminoester formation reactions. The aldol condensation reaction uses the -NH functionality as a base. The studies indicate that the electron-withdrawing group produces products with higher yields. The β-enaminoester reaction uses the Lewis acid centers, and the studies reveal that the electron-withdrawing groups produce lesser yields of the products. The catalytic nature of the reaction and recyclability of the catalysts were also established. The catalytic reactions employ ethanol (aldol condensation) and no solvent (β-enaminoester), which suggests that the reactions are green and environmentally friendly. The Mn compound was observed to be anti-ferromagnetic.

Gas-solid two-phase flow (GSF) mechanochemical synthesis of dual-metal-organic frameworks and research on electrochemical properties

As an alternative approach for conventional mechanochemical synthesis, a novel gas-solid two-phase flow (GSF) synthetic technique for the mechanochemical synthesis of dual metal-organic frameworks (DMOFs) was reported for the first time. The prepared CoMn₂(BTC)₂ was characterized by FT-IR, DTA, TG/DTG, and XRD studies. The results indicated that CoMn₂(BTC)₂ (BTC = 1,3,5-benzenetricarboxylate) was successfully synthesized after 10 min at a rate of 60 kg h^-1. CoMn₂O₄ microspheres were also prepared via the CoMn₂(BTC)₂ precursor method and characterized using FT-IR, XPS, XRD, SEM, EDS, and BET methods. The electrochemical properties of the as-prepared CoMn₂O₄ were investigated, and the GSF results showed that the microsphere electrodes of CoMn₂O₄ had a high specific capacitance (969 F g^-1) at a current density of 1 A g^-1 in 3 M aqueous KOH solution.

Encoding Metal-Cation Arrangements in Metal-Organic Frameworks for Programming the Composition of Electrocatalytically Active Multimetal Oxides

In the present contribution, we report how through the use of metal-organic frameworks (MOFs) composed of addressable combinations of up to four different metal elements it is possible to program the composition of multimetal oxides, which are not attainable by other synthetic methodologies. Thus, due to the ability to distribute multiple metal cations at specific locations in the MOF secondary building units it is possible to code and transfer selected metal ratios to multimetal oxides with novel, desired compositions through a simple calcination process. The demonstration of an enhancement in the electrocatalytic activity of new oxides by preadjusting the metal ratios is here reported for the oxygen reduction reaction, for which activity values comparable to commercial Pt/C catalysts are reached, while showing long stability and methanol tolerance.

A remarkable annealing time effect on the magnetic properties of single-source coordination polymer precursor-derived CoFe2O4 nanoparticles

The diversity in the magnetocrystalline anisotropy of nano-sized CoFe₂O₄ samples has been derived from coordination polymers through differential occupancy of Co²⁺ in octahedral sites.

Coordination polymer-derived nano-sized zinc ferrite with excellent performance in nitro-explosive detection

Herein, a mixed metal coordination polymer, {(H₂pip)[Zn_1/3Fe_2/3(pydc-2,5)₂(H₂O)]·2H₂O} 1 {where H₂pip = piperazinediium and pydc-2,5 = pyridine-2,5-dicarboxylate}, was successfully synthesized using a hydrothermal technique. To confirm the structure and phase purity of 1, single crystals of an isomorphous pure Fe compound, {(H₂pip)[Fe(pydc-2,5)₂(H₂O)]·2H₂O} 1a, were synthesized based on similar synthetic conditions. Single crystal X-ray data of 1a confirmed the one-dimensional anionic metal-organic coordination polymer hydrogen bonded with protonated piprazine (piperazinediium) and lattice water molecules. The phase purity of 1 and 1a were confirmed via powder X-ray diffraction. Compound 1 was systematically characterized using IR, TGA, SEM, and EDX elemental mapping analysis. Compound 1 was used as a single source precursor for the preparation of nano-sized ZnFe₂O₄via thermal decomposition. The as-obtained ZnFe₂O₄ was fully characterized using PXRD, SEM, TEM, and EDX elemental mapping analysis. It was found that ZnFe₂O₄ was formed in its pure form with particle size in the nano-dimension. The aqueous dispersion of nano-sized ZnFe₂O₄ exhibits a strong emission at 402 nm upon excitation at 310 nm. This emissive property was employed for luminescence-based detection of nitroaromatic explosives in an aqueous medium through luminescence quenching for the first time. Importantly, selective detections have been observed for phenolic nitroaromatics based on differential luminescence quenching behaviour along with a detection limit of 57 ppb for 2,4,6-trinitrophenol (TNP) in water.

Metal-Organic Framework-Derived Materials for Sodium Energy Storage

Recently, sodium-ion batteries (SIBs) are extensively explored and are regarded as one of the most promising alternatives to lithium-ion batteries for electrochemical energy conversion and storage, owing to the abundant raw material resources, low cost, and similar electrochemical behavior of elemental sodium compared to lithium. Metal-organic frameworks (MOFs) have attracted enormous attention due to their high surface areas, tunable structures, and diverse applications in drug delivery, gas storage, and catalysis. Recently, there has been an escalating interest in exploiting MOF-derived materials as anodes for sodium energy storage due to their fast mass transport resulting from their highly porous structures and relatively simple preparation methods originating from in situ thermal treatment processes. In this Review, the recent progress of the sodium-ion storage performances of MOF-derived materials, including MOF-derived porous carbons, metal oxides, metal oxide/carbon nanocomposites, and other materials (e.g., metal phosphides, metal sulfides, and metal selenides), as SIB anodes is systematically and completely presented and discussed. Moreover, the current challenges and perspectives of MOF-derived materials in electrochemical energy storage are discussed.

Synthesis of CrOx/C catalysts for low temperature NH3-SCR with enhanced regeneration ability in the presence of SO2

Chromium oxide nano-particles with an average diameter of 3 nm covered by amorphous carbon (CrO_x/C) were successfully synthesized. The synthesized CrO_x/C materials were used for the selective catalytic reduction of NO_x by NH₃ (NH₃-SCR), which shows superb NH₃-SCR activity and in particular, satisfactory regeneration ability in the presence of SO₂ compared with Mn-based catalysts. The as-prepared catalysts were characterized by XRD, HRTEM, Raman, FTIR, BET, TPD, TPR, XPS and in situ FTIR techniques. The results indicated presence of certain amounts of unstable lattice oxygen exposed on the surface of CrO_x nano-particles with an average size of 3 nm in the CrO_x/C samples, which led to NO being conveniently oxidized to NO₂. The formed NO₂ participated in NH₃-SCR activity, reacting with catalysts via a “fast NH₃-SCR” pathway, which enhanced th NH₃-SCR performance of the CrO_x/C catalysts. Furthermore, the stable lattice of the CrO_x species made the catalyst immune to the sulfation process, which was inferred to be the cause of its superior regeneration ability in the presence of SO₂. This study provides a simple way to synthesize stable CrO_x nano-particles with active oxygen, and sheds light on designing NH₃-SCR catalysts with highly efficient low temperature activity, SO₂ tolerance, and regeneration ability.

Novel CrO_x@C catalyst with both remarkable NH₃-SCR activity and satisfactory regeneration ability in the presence of SO₂.

Magnetic diversity in three-dimensional two-fold-interpenetrated structures: a story of two compounds

A two-fold-interpenetrated three-dimensional nickel-based hybrid structure exhibited canted-antiferromagnetic and field-induced spin-flop transitions.

Magnetic properties of manganese based one-dimensional spin chains

Magnetic susceptibility and heat capacity of three manganese based structures are measured and modeled with one-dimensional antiferromagnetic chains.

Porous ZnCo2O4 nanoparticles derived from a new mixed-metal organic framework for supercapacitors

ZnCo₂O₄ nanoparticles were synthesized by thermal annealing of a new mixed-metal MOF and show high capacitance for electrochemical capacitors.

Metal/metal oxide nanostructures derived from metal–organic frameworks

MOFs-derived micro/nanostructures have important potential applications. In this review, we describe the use of MOFs as templates in the synthesis of metal/metal oxide micro/nanostructures and composite materials. The applications of the derived materials are also reviewed.

A 3D oxalate-based network as a precursor for the CoMn₂O₄ spinel: synthesis and structural and magnetic studies

A novel heterometallic oxalate-based compound of the formula {[Co(bpy)3][Mn2(C2O4)3]·H2O}n (1; bpy = 2,2'-bipyridine) was synthesized and characterized by elemental analysis, IR spectroscopy, single-crystal X-ray diffraction (XRD), and magnetization measurement. The molecular structure of 1 is made of a three-dimensional (3D) anionic network, [Mn2(C2O4)3]n(2n-), and tris-chelated cations [Co(bpy)3](2+) occupying the vacancies of the framework. Splitting between the zero-field-cooled (ZFC) and field-cooled (FC) branches of susceptibility below the small peak at 13 K indicates magnetic ordering. Compound 1 was used as a single-source precursor for the formation of the mixed-metal oxide CoMn2O4. This conversion via thermal decomposition was explored by thermal analysis (TGA and DTA), IR spectroscopy, powder XRD, and magnetic susceptibility measurement. From refined structural parameters, it could be seen that the spinel obtained by the thermal treatment of 1 at 800 °C is characterized by the inversion parameter δ = 21%, and therefore the structural formula at room temperature can be written as (tet)[Co(0.79)Mn(0.21)](oct)[Co(0.105)Mn(0.895)]2O4. The temperature dependence of magnetization for CoMn2O4 points to at least three magnetic phases: the ferrimagnetic state is observed below 83 K, and up to 180 K blocking of the magnetic moments of nanocrystallites of 31 nm appears, transforming to paramagnetic-like behavior above 180 K. Microstructural characterization of the CoMn2O4 sample was carried out by means of XRD line-broadening analysis.