Two Versatile N,N‘-Bipyridine-Type Ligands for Preparing Organic−Inorganic Coordination Polymers: New Cobalt- and Nickel-Containing Framework Materials

Water Content-Controlled Formation and Transformation of Concomitant Pseudopolymorph Coordination Polymers

Two concomitant pseudopolymorph coordination polymers {[Cd₂L₂(OAc)₄]·2DMSO} _n (1) and {[CdL(OAc)₂]·2.75H₂O} _n (2) were synthesized by self-assembly of 1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene (L) and cadmium acetate in DMSO. Single-crystal X-ray diffraction confirmed that 1D ladder structural motifs exist for pseudopolymorphs 1 and 2 which contain DMSO and water guest molecules, respectively. Our study illustrated the active role of solvent water content in obtaining compound 2. We find that the presence of water as an impurity in the DMSO solvent creates the possibility of formation of concomitant pseudopolymorph coordination polymers which is a unique event. Furthermore, our analyses showed the effect of environmental humidity on the transformation of unstable compound 1. 1D ladder pseudopolymorphic compound 1 could be transformed to guest-free 1D linear compound [CdL(OAc)₂(H₂O)] _n (3') (the powder form of single crystals of 3) through a scarce case of water absorption from air. Also, the crystalline material of coordination polymer 3 was transformed to coordination polymer 2 through the dissolution-recrystallization structural transformation process in DMF or DMSO. Our study clarified that the amount of water in the reaction container can control the formation of one of the compounds 2 or 3. In the presence of a significant amount of water, compound 3 (coordinated water) will be produced, whereas if a small amount of water is present, compound 2 (uncoordinated water) is prepared as an exclusive product.

Non-Calcined Layer-Pillared Mn0.5Zn0.5 Bimetallic-Organic Framework as a Promising Electrocatalyst for Oxygen Evolution Reaction

Electrocatalytic generation of oxygen is of great significance for sustainable, clean, and efficient energy production. Multiple electron transfer in oxygen evolution reaction (OER) and its slow kinetics represent a serious hedge for efficient water splitting, requiring the design and development of advanced electrocatalysts with porous structures, high surface areas, abundant electroactive sites, and low overpotentials. These requisites are common for metal-organic frameworks (MOFs) and derived materials that are promising electrocatalysts for OER. The present work reports on the synthesis and full characterization of a heteroleptic 3D MOF, [Zn₂(μ₄-odba)₂(μ-bpdh)]_n·nDMF (Zn-MUM-1), assembled from 4,4'-oxydibenzoic acid and 2,5-bis(4-pyridyl)-3,4-diaza-2,4-hexadiene (bpdh). Besides, a series of heterometallic MnZn-MUM-1 frameworks (abbreviated as Mn_0.5Zn_0.5-MUM-1, Mn_0.66Zn_0.33-MUM-1, and Mn_0.33Zn_0.66-MUM-1) was also prepared, characterized, and used for the fabrication of working electrodes based on Ni foam (NF), followed by their exploration in OER. These noble-metal-free and robust electrocatalysts are stable and do not require pyrolysis or calcination while exhibiting better electrocatalytic performance than the parent Zn-MUM-1/NF electrode. The experimental results show that the Mn_0.5Zn_0.5-MUM-1/NF electrocatalyst features the best OER activity with a low overpotential (253 mV at 10 mA cm^-2) and Tafel slope (73 mV dec^-1) as well as significant stability after 72 h or 6000 cycles. These excellent results are explained by a synergic effect of two different metals present in the Mn-Zn MOF as well as improved charge and ion transfer, conductivity, and stability characteristics. The present study thus widens the application of heterometallic MOFs as prospective and highly efficient electrocatalysts for OER.

Humidity-Induced Structural Transformation in Pseudopolymorph Coordination Polymers

Three cadmium coordination polymers, namely, {[CdL(OAc)₂](C₂H₅OH)}_n (1), {[CdL(OAc)₂](CH₃CN)}_n (2), and [CdL(OAc)₂(H₂O)]_n (3), were synthesized by an exoditopic 1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene Schiff base ligand (L) and cadmium acetate in the presence of different solvent systems. Single-crystal X-ray diffraction, powder X-ray diffraction, and thermogravimetric analysis showed that 1D ladder pseudopolymorphic compounds (1 and 2) transformed to the solvent-free 1D linear compound 3 through a rare case of water absorption from air at room temperature. Interestingly, compound 3 was transformed to compound 1 through a dissolution-recrystallization structural transformation process. The results illustrated that solvents and humidity have an important role in the formation of pseudopolymorphs with the same or different structural motifs.

From 1D to 2D Cd(II) and Zn(II) Coordination Networks by Replacing Monocarboxylate with Dicarboxylates in Partnership with Azine Ligands: Synthesis, Crystal Structures, Inclusion, and Emission Properties

Eight mixed-ligand coordination networks, [Cd(2-aba)(NO₃)(4-bphz)_3/2]_n·n(dmf) (1), [Cd(2-aba)₂(4-bphz)]_n·0.75n(dmf) (2), [Cd(seb)(4-bphz)]_n·n(H₂O) (3), [Cd(seb)(4-bpmhz)]_n·n(H₂O) (4), [Cd(hpa)(3-bphz)]_n (5), [Zn(1,3-bdc)(3-bpmhz)]_n·n(MeOH) (6), [Cd(1,3-bdc)(3-bpmhz)]_n ·0.5n(H₂O)·0.5n(EtOH) (7), and [Cd(NO₃)₂(3-bphz)(bpe)]_n·n(3-bphz) (8) were obtained by interplay of cadmium nitrate tetrahydrate or zinc nitrate hexahydrate with 2-aminobenzenecarboxylic acid (H(2-aba)), three dicarboxylic acids, sebacic (decanedioic acid, H₂seb), homophthalic (2-(carboxymethyl)benzoic acid, H₂hpa), isophthalic (1,3-benzenedicarboxylic acid, H₂(1,3-bdc)) acids, bis(4-pyridyl)ethane (bpe) and with four azine ligands, 1,2-bis(pyridin-4-ylmethylene)hydrazine (4-bphz), 1,2-bis(1-(pyridin-4-yl)ethylidene) hydrazine (4-bpmhz), 1,2-bis(pyridin-3-ylmethylene)hydrazine (3-bphz), and 1,2-bis(1-(pyridin-3-yl) ethylidene)hydrazine (3-bpmhz). Compounds 1 and 2 are 1D coordination polymers, while compounds 3–8 are 2D coordination polymers. All compounds were characterized by spectroscopic and X-ray diffraction methods of analysis. The solvent uptakes and stabilities to the guest evacuation were studied and compared for 1D and 2D coordination networks. The de-solvated forms revealed a significant increase of emission in comparison with the as-synthesized crystals.

Template effect of innocent and coordinating anions on the formation of interpenetrated 2D and 3D networks: methyl orange and iodine sorption studies

A pyridyl based Schiff base resulted in a 2D staircase network (CP1) with Cd(ii) when ClO₄⁻ is the counter anion while the use of benzene-1,3-disulphonate counter anion resulted in a novel 3D Cd(ii) coordination polymer with threefold interpenetration (CP2).

Ultrasound-assisted preparation of a nanostructured zinc(II) amine pillar metal-organic framework as a potential sorbent for 2,4-dichlorophenol adsorption from aqueous solution

Using a green and simple route with ultrasound illumination under atmospheric pressure and at room temperature, the nanosized preparation of a Zn(II) metal-organic framework, [Zn(ATA)(BPD)]_∞ (ATA = 2-aminoterephthalic acid), BPD = 1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene), having nano-plate shape and 3D channel framework, was considered and the product was named as compound 1. The X-ray diffraction (XRD), scanning electron microscopy (SEM), IR spectroscopy, Brunauer-Emmett-Teller (BET), and thermogravimetric analysis (TGA) were used for characterization of the synthesized micro/nano-structures. Further, impact of different sonication times and initial reagent contents on the shape and size of the micro/nano-structures was investigated. The results show that under ultrasound irradiation non-aggregated plates with uniform morphology can be obtained with content of [0.0125] M of the initial reagents in the presence of triethylamine (TEA) at 120 min. Moreover, through N₂ adsorption, effect of the preparation route on the porosity was explored. The bulk and nano-plates of compound 1 were also studied for adsorption of 2,4-dichlorophenol as a pollutant sample. Kinetic studies indicated that 2,4-dichlorophenol adsorption via MOF nano-plates are of first-order kinetics. Also, MOF nano-plates have significantly been reutilized for five times while their adsorption properties have remained unchanged.

Cd(ii) and Cu(ii) coordination polymers constructed from the expanded 1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene ligand: conventional and ultrasound-assisted synthesis, crystal structure, luminescence and magnetic properties

Metal nodes in extend 1D and 3D structures with N,N′-donor linker: the co-ligands decides!

Acid- and base-stable porous mechanically interlocked 2D metal–organic polyrotaxane forin situorganochlorine insecticide encapsulation, sensing and removal

The encapsulation and removal of extremely toxic dieldrin by compound1.

Four Mixed-Ligand Zn(II) Three-Dimensional Metal-Organic Frameworks: Synthesis, Structural Diversity, and Photoluminescent Property

Assemblies of four three-dimensional (3D) mixed-ligand coordination polymers (CPs) having formulas, {[Zn₂(bdc)₂(4-bpdh)]·C₂H₅OH·2H₂O}_n (1), [Zn(bdc)(4-bpdh)]_n (2), {[Zn₂(bdc)₂(4-bpdh)₂]·(4-bpdh)}_n (3), and {[Zn(bdc)(4-bpdh)]·C₂H₅OH}_n (4) (bdc²⁻ = dianion of 1,4-benzenedicarboxylic acid, 4-bpdh = 2,5-bis(4-pyridyl)-3,4-diaza-2,4-hexadiene) have been synthesized and structurally characterized by single-crystal X-ray diffraction method. Structural determination reveals that the coordination numbers (geometry) of Zn(II) ions in 1, 2, 3, and 4 are five (distorted square-pyramidal (SP)), six (distorted octahedral (O_h)), five (trigonal-bipyramidal (TBP)), and four (tetrahedral (T_d)), respectively, and are bridged by 4-bpdh with bis-monodentate coordination mode and bdc²⁻ ligands with bis-bidentate in 1, chelating/bidentate in 2, bis-monodentate and bis-bidentate in 3, and bis-monodentate in 4, to generate two-fold interpenetrating 3D cube-like metal-organic framework (MOF) with pcu topology, non-interpenetrating 3D MOF, two-fold interpenetrating 3D rectangular-box-like MOF with pcu topology and five-fold interpenetrating diamondoid-like MOF with dia topology, respectively. These different intriguing architectures indicate that the coordination numbers and geometries of Zn(II) ions, coordination modes of bdc²⁻ ligand, and guest molecules play important roles in the construction of MOFs and the formation of the structural topologies and interpenetrations. Thermal stabilities, and photoluminescence study of 1–4 were also studied in detail. The complexes exhibit ligands based photoluminescence properties at room temperature.

Sonochemical synthesis and structural characterization of a new nanostructured Co(II) supramolecular coordination polymer with Lewis base sites as a new catalyst for Knoevenagel condensation

A new Co(II) mixed-ligand coordination supramolecular polymer with composition [Co₂(ppda)(4-bpdh)₂(NO₃)₂]_n (1) (where, ppda=p-phenylenediacrylic acid, 4-bpdh=2,5-bis(4-pyridyl)-3,4-diaza-2,4-hexadiene) was synthesized using solvothermal, mechanochemical and sonochemical methods. Compound 1 and the new nanostructure have been characterized by single-crystal X-ray, infrared spectroscopy (IR), powder X-ray diffraction (PXRD) analysis and scanning electron microscopy (SEM). The thermal stability of compound 1 was also studied by thermal gravimetric analysis (TGA). The surface area of these compounds was determined by BET. The single-crystal X-ray data shows a new interesting two-dimensional coordination polymer (CP). In addition, the effect of various sonication concentrations of initial reagents, power of ultrasound irradiation and also the time on the size and morphology of nano-structured coordination polymer 1 were evaluated. Moreover, it has been demonstrated that the nanostructure of the CP1 can be used as a catalyst in Knoevenagel condensation reaction.

Porosity and dye adsorption enhancement by ultrasonic synthesized Cd(II) based metal-organic framework

A Cd(II) based metal-organic framework, TMU-7, was synthesized by incorporation of V-shaped flexible dicarboxylate ligand and the N-donor pillar ligand using sonochemical method while morphology and size of particles were investigated and characterized by scanning electron microscopy and X-ray powder diffraction. Moreover, N₂ adsorption was applied to examine the effect of synthesis method on porosity. Also TMU-7 was evaluated for its Congo red adsorption.

Enhancement of photocatalytic performance in two zinc-based metal–organic frameworks by solvent assisted linker exchange

Solvent-assisted linker exchange (SALE) was performed on two pillared metal–organic frameworks (MOFs), [Zn₂(oba)₂(4-bpdb)]_n·(DMF)₂ (TMU-4) and [Zn(oba)(4-bpmb)_0.5]_n·(DMF)_1.5 (TMU-6), to tune their photocatalytic properties.

Unusual crystal structure and chirality of uridine 5′-monophosphate coordination polymer

The auxiliary ligand effect in the structure and charility of uridine 5′-monophosphate coordination polymer was investigated.

Ultrasound-assisted oxidative desulfurization process of liquid fuel by phosphotungstic acid encapsulated in a interpenetrating amine-functionalized Zn(II)-based MOF as catalyst

In this work, ultrasound-assisted oxidative desulfurization (UAOD) of liquid fuels performed with a novel heterogeneous highly dispersed Keggin-type phosphotungstic acid (H₃PW₁₂O₄₀, PTA) catalyst that encapsulated into an amino-functionalized MOF (TMU-17-NH₂). The prepared composite exhibits high catalytic activity and reusability in oxidative desulfurization of model fuel. Ultrasound-assisted oxidative desulfurization (UAOD) is a new way to performed oxidation reaction of sulfur-contain compounds rapidly, economically, environment-friendly and safely, under mild conditions. Ultrasound waves can be apply as an efficient tool to decrease the reaction time and improves oxidative desulfurization system performance. PTA@TMU-17-NH₂ could be completely performed desulfurization of the model oil by 20mg of catalyst, O/S molar ratio of 1:1 in presence of MeCN as extraction solvent. The obtained results indicated that the conversions of DBT to DBTO₂ achieve 98% after 15min in ambient temperature. In this work, we prepared TMU-17-NH₂ and PTA/TMU-17-NH₂ composite by ultrasound irradiation for first time and employed in UAOD process. Prepared catalyst exhibit an excellent reusability without PTA leaching and loss of activity.

High adsorption capacity of two Zn-based metal-organic frameworks by ultrasound assisted synthesis

Micro- and nano-rods and plates of two 3D, porous Zn(II)-based metal-organic frameworks [Zn(oba)(4-bpdh)0.5]n·(DMF)1.5 (TMU-5) and [Zn(oba)(4-bpmb)0.5]n (DMF)1.5 (TMU-6) were prepared by sonochemical process and characterized by scanning electron microscopy, X-ray powder diffraction and IR spectroscopy. These MOFs were synthesized using a non-linear dicarboxylate (H2oba=4,4-oxybisbenzoic acid) and two linear N-donor (4-bpdh=2,5-bis(4-pyridyl)-3,4-diaza-2,4-hexadiene and 4-bpmb=N(1),N(4)-bis((pyridin-4-yl)methylene)benzene-1,4-diamine) ligands by ultrasonic irradiation. Sonication time and concentration of initial reagents influencing size and morphology of nano-structured MOFs, were also studied. Calcination of TMU-5 and TMU-6 at 550°C under air atmosphere yields ZnO nanoparticles. TMU-5 and TMU-6 exhibited maximum percent adsorption of 96.2% and 92.8% of 100ppm rhodamine B dye, respectively, which obeys first order reaction kinetics.

Synthesis and crystal structure of 4-(2-ammonio-eth-yl)morpholin-4-ium di-chlorido-diiodido-cadmate/chlorido-tri-iodido-cadmate (0.90/0.10)

The crystal structure of the title compound, (C6H16N2O)[CdCl1.90I2.10], a new organic-inorganic hybrid salt synthesized in the form of single crystals, consists of discrete statistically distributed di-chlorido-diiodido-cadmate/chlorido-tri-iodido-cadmate anions (occupancy ratio 0.90:0.10) and 4-(2-ammonio-eth-yl)morpholin-4-ium cations, [NH3(CH2)2NH(CH2)4O]2+. The cations are linked by inter-molecular N-H⋯O hydrogen bonds, forming corrugated chains extending parallel to the c axis. The [CdCl1.90I2.10]2- tetra-halidocadmate anions lie between the chains to maximize the electrostatic inter-actions and are connected with the organic cations via N-H⋯Cl and C-H⋯Cl(I) hydrogen bonds developing in the ab plane and leading to the formation of a three-dimensional network structure. The tetra-coordinate CdII atom has a distorted tetra-hedral conformation, with a τ4 index of 0.87.

Crystal structure of 1,2-bis-[(1H-imidazol-2-yl)methylidene]hydrazine and its one-dimensional hydrogen-bonding network

In the title compound, C8H8N6, two imidazolyl groups are separated by a zigzag -CH=N-N=CH- linkage. An inversion center is located at the mid-point of the N-N single bond and the complete molecule is generated by symmetry. In the crystal, each mol-ecule forms four N-H⋯N hydrogen bonds with two neighbouring mol-ecules to constitute a one-dimensional ladder-like structure propagating along the a-axis direction.