Metal-organic Coordination Frameworks Research Articles

Polynuclear Cobalt Cluster-Based Coordination Polymers for Efficient Nitrate-to-Ammonia Electroreduction.

The electrocatalytic nitrate reduction reaction (NITRR) holds great promise for purifying wastewater and producing valuable ammonia (NH3). However, the lack of efficient electrocatalysts has impeded the achievement of highly selective NH3 synthesis from the NITRR. In this study, we report the design and synthesis of two polynuclear Co-cluster-based coordination polymers, {[Co2(TCPPDA)(H2O)5]·(H2O)9(DMF)} and {Co1.5(TCPPDA)[(CH3)2NH2]·(H2O)6(DMF)2} (namely, NJUZ-2 and NJUZ-3), which possess distinct coordination motifs with well-defined porosity, high-density catalytic sites, accessible mass transfer channels, and nanoconfined chemical environments. Benefitting from their intriguing multicore metal-organic coordination framework structures, NJUZ-2 and NJUZ-3 exhibit remarkable catalytic activities for the NITRR. At a potential of -0.8 V (vs. RHE) in an H-type cell, they achieve an optimal Faradaic efficiency of approximately 98.5% and high long-term durability for selective NH3 production. Furthermore, the electrocatalytic performance is well maintained even under strongly acidic conditions. When operated under an industrially relevant current density of 469.9 mA cm-2 in a flow cell, a high NH3 yield rate of up to 3370.6 mmol h-1 g-1cat. was observed at -0.5 V (vs. RHE), which is 20.1-fold higher than that obtained in H-type cells under the same conditions. Extensive experimental analyses, in combination with theoretical computations, reveal that the great enhancement of the NITRR activity is attributed to the preferential adsorption of NO3- and the reduction in energy input required for the hydrogenation of *NO3 and *NO2 intermediates.

Exclusive Coordination between Melem and Silver(I) Ions: From Irregular Aggregates to Nanofibers to Crystal Cubes.

There is growing focus on metal-free molecules and polymers owing to their potential applications in various energy and catalysis-related applications. Melem (2,5,8-triamino-s-heptazine, C6H6N10) has emerged as a metal-free material for solar-to-fuel conversion. However, its reactivity with metal ions or organic molecules has never been reported although it possesses multiple supramolecular interaction sites. In this work, we report on the synthesis of a novel metal-organic coordination framework (melem-Ag) by simply introducing Ag+ into the aqueous suspension of aggregated melem particles. Notably, as the reaction progresses, the melem disappears, and the morphology of the newly formed complex spontaneously evolves from nanofibers to single-crystalline blocks, which possess the same chemical structure, indicating that the morphology evolution is driven by Ostwald ripening. The structure of melem-Ag displays infinite nanocages of triangular pyramids consisting of melem molecules and Ag+, linked via Ag-N coordinate bonding and Ag-Ag argentophilic interactions. It is noteworthy that Ag+ is the only transition-metal cation that reacts with melem suspensions, even in the presence of other transition-metal cations (Co2+, Ni2+, Cu2+, and Zn2+). The coordination of Ag+ to melem results in metal-to-ligand charge transfer (MLCT), resulting in a quenched photoluminescence and enhanced light absorption. Exposing the melem-Ag crystals to UV light for varying time intervals results in the formation of colorful powders, which may be used for Ag-decorated photocatalysts.

Rational engineering of metal–organic coordination networks into facet‐controlled phosphides for overall water splitting

AbstractAlthough transition metal phosphide electrocatalysts display unique electronic structure that serves as functional centers for hydrogen evolution reaction, the synthesis of this class of materials for oxygen evolution remains a challenge due to the complex multielectron transfer pathways and sluggish reaction kinetics. This study details an in‐situ modification and transformation of cyanide‐bridged nickel‐iron (CN‐NiFe) organometallic hybrid into the preferential Fe2P phase with prevailing exposed faceted active centers by leveraging on the facile coordinate cleavage dynamics and compound reactivity of labile metal organic coordination frameworks. The resultant transition metal phosphide attains high electrochemical surface area, low Tafel slope, and low overpotential for the oxygen evolution reaction, while also demonstrating bifunctional electrocatalytic performance for overall water splitting. Comprehensive experimental studies and density functional theory calculations reveal that the exceptional catalytic activity originates from the transformation of framework metallic sites into preferential active sites allows an optimal adsorption of oxygen evolution reaction intermediates.image

Naphthalene-tagged highly stable and reusable luminescent metal–organic probes for selective and fast detection of 4-nitroaniline in water

Four new Zn(ii) and Cd(ii) luminescent metal organic coordination frameworks with naphthalene tags have been synthesized, extensively characterized, and utilized for selective and fast sensing of 4-nitroaniline in water.

Proton conducting hybrid compounds based on CsH5(PO4)2 metal-organic coordination frameworks

The hybrid compounds based on CsH5(PO4)2 and metal-organic coordination framework, Cr-MIL-101 matrix, have been first synthesized. Proton conductivity, structural and thermal properties of (1-x)CsH5(PO4)2–xCr-MIL-101 nanocomposite electrolytes (x = 0.02–0.2) were investigated for the first time. The significant increase of proton conductivity has been shown due to the interface interaction of high dispersed mesoporous Cr-MIL-101 and CsH5(PO4)2. According to X-ray diffraction there is no chemical interaction between the components and no new compounds are formed. The data of X-ray diffraction, differential scanning calorimetry and electron microscopy show significant changes in structural and thermodynamic properties of CsH5(PO4)2 in nanocomposites due to dispersion and amorphization. As a result the proton conductivity of systems that increases by 1–3 orders of magnitude up to 10−2 S/cm at 130 °C in the low humidity conditions, depends on the composition and goes through maximum at x~0.07–0.11. The conductivity of nanocomposites significantly exceeds the ones for the initial salt and the dispersed matrix. Such new approach affords the solid materials with potent proton conducting properties at moderate temperatures.

Crystal structure of a low-spin poly[di-μ3-cyanido-di-μ2-cyanido-bis-(μ2-2-ethyl-pyrazine)-dicopper(I)iron(II)

In the title metal-organic framework, [Fe(C6H8N2)2{Cu(CN)2}2] n , the low-spin FeII ion lies at an inversion centre and displays an elongated octa-hedral [FeN6] coordination environment. The axial positions are occupied by two symmetry-related bridging 2-ethyl-pyrazine ligands, while the equatorial positions are occupied by four N atoms of two pairs of symmetry-related cyanide groups. The CuI centre is coordinated by three cyanide carbon atoms and one N atom of a bridging 2-ethyl-pyrazine mol-ecule, which form a tetra-hedral coordination environment. Two neighbouring Cu atoms have a short Cu⋯Cu contact [2.4662 (7) Å] and their coordination tetra-hedra are connected through a common edge between two C atoms of cyanide groups. Each Cu2(CN)2 unit, formed by two neighbouring Cu atoms bridged by two carbons from a pair of μ-CN groups, is connected to six FeII centres via two bridging 2-ethyl-pyrazine mol-ecules and four cyanide groups, resulting in the formation of a polymeric three-dimensional metal-organic coordination framework.

A new three-dimensional manganese(II) coordination polymer based on the 1,3,5-tris[(1H-imidazol-1-yl)methyl]benzene ligand.

The self-assembly of coordination polymers and the crystal engineering of metal-organic coordination frameworks have attracted great interest, but it is still a challenge to predict and control the compositions and structures of the complexes. Employing multidentate organic ligands and suitable metal ions to construct inorganic-organic hybrid materials through metal-ligand coordination and hydrogen-bonding interactions has become a major strategy. Recently, imidazole-containing multidentate ligands that contain an aromatic core have received much attention. A new three-dimensional MnII coordination polymer based on 1,3,5-tris[(1H-imidazol-1-yl)methyl]benzene, namely poly[(ethane-1,2-diol-κO)(μ-sulfato-κ2O:O'){μ3-1,3,5-tris[(1H-imidazol-1-yl)methyl]benzene-κ3N:N':N''}manganese(II)], [Mn(SO4)(C18H18N6)(C2H6O2)]n, was synthesized and characterized by elemental analysis, IR spectroscopy and single-crystal X-ray diffraction. Crystal structural analysis shows that there are two kinds of crystallographically independent MnII centres, each lying on a centrosymmetric position and having a similar six-coordinated octahedral structure. One is coordinated by four N atoms from four 1,3,5-tris[(1H-imidazol-1-yl)methyl]benzene (timb) ligands and two O atoms from two different bridging sulfate anions. The second is surrounded by two timb N atoms and four O atoms, two from sulfate anions and two from two ethane-1,2-diol ligands. The tripodal timb ligand bridges neighbouring MnII centres to generate a two-dimensional layered structure running parallel to the ab plane. Adjacent layers are further bridged by sulfate anions, resulting in a three-dimensional structure with 3,4,6-c topology. Thermogravimetric analysis of the title polymer shows that it is stable up to 533 K. The first weight loss between 533 and 573 K corresponds to the release of coordinated ethane-1,2-diol molecules, and further decomposition occurred at 648 K.

Shape assisted fabrication of fluorescent cages of squarate based metal–organic coordination frameworks

Micronic cage structures of squarate based metal-organic coordination frameworks (MOCFs) have been fabricated for the first time by specific anion selective etching of metal squarate cubes. Time and stoichiometry dependent synthesis and the corresponding microscopic studies have provided mechanistic insight into the cage formation. Furthermore, a non-covalent post-synthetic strategy has been adopted to functionalize the micronic cubes or cages with chromophores rendering the resulting hybrids green fluorescent.

A new POM-templated metal–organic complex based on the flexible bis-pyridyl-bis-amide ligand

A new POM-templated metal–organic complex [Cu4(L)7(H2O)12(SiMo12O40)2]·7H2O [L = N,N′-bis(3-pyridinecarboxamide)-1,6-hexane], has been hydrothermally synthesized and characterized by elemental analysis, IR, TG and single-crystal X-ray diffraction analysis. The results reveal that the complex is a 2D metal–organic coordination framework of [Cu4(L)7(H2O)12]n8n+ cations containing decanuclear cycles with dimensions of ca. 17.55 × 57.42 A, in which the SiMo12O404− anions act as non-coordinated anionic templates. The electrochemical properties of a bulk-modified carbon paste electrode of the complex have been investigated, and the results indicate that the complex-modified CPE has good electrocatalytic activity toward the reduction of nitrite in aqueous 1 M H2SO4 solution.

Novel 3D lanthanum oxalate metal-organic-framework: Synthetic, structural, luminescence and adsorption properties

The hydrothermal reaction of La(NO3)3 with 2-pyrimidinecarbonitrile in water yields a 3D metal-organic coordination framework [La2(ox)3(H2ox)(H2O)2](H2O)8 (1) (ox=oxalate). This compound has channels with hosted water molecules inside and shows an intense photoluminescence emission at room temperature in the solid state. Due to the great channels that this compound possesses we have analyzed the experimental and simulated adsorption properties. This is one of the few examples of three-dimensional lanthanum polymers based only on oxalate ligand.

Prussian Blue Nanocontainers: Selectively Permeable Hollow Metal–Organic Capsules from Block Ionomer Emulsion-Induced Assembly

Hollow polymer-based particles are useful for the encapsulation, protection, and release of active compounds. Adding a metal-organic coordination framework shell to nanocontainers is an attractive goal because it should help control their stability and permeability while yielding new properties and functions. We have discovered that polymer capsules with a Prussian blue analogue inner shell can be synthesized by emulsion-induced assembly of a metal-containing amphiphilic block ionomer. The capsules are selectively permeable and were used as nanocontainers to encapsulate and release a model compound. Further, these nanomaterials are tunable in size and organize into 2-D close-packed arrays in the solid state. Potential applications for these materials include the encapsulation and nanopatterning of pharmaceutical, biological, and catalytic compounds.

A new 2D cadmium chloride network with 2-aminopyrimidine displaying long lifetime photoluminescence emission

The hydrothermal reaction of CdCl 2 with 2-aminopyrimidine in water yields a 2D metal–organic coordination framework [CdCl 2(PymNH 2)] ( 1) (PymNH 2 = 2-aminopyrimidine). This compound consists of Cd 2( μ-Cl) 2 corner-sharing chains bridged by PymNH 2 through the endocyclic ring nitrogen atoms. Interestingly, this polymer exhibits long lifetime photoluminescence emission at room temperature in the solid state with long lifetimes decay.

Synthesis, structures and luminescence properties of two new Zn(II) coordination compounds incorporating the 5-(4-pyridyl)tetrazolate spacer ligand

The hydrothermal reaction of ZnCl 2 with 5-(4-pyridyl)tetrazole afforded the 2D metal–organic coordination framework [Zn(OH)(4-ptz)] ( 1) and the mononuclear complex [Zn(4-ptz) 2(H 2O) 4]∙2(H 2O) ( 2) [4-ptz = 5-(4-pyridyl)-tetrazolate]. Compound 1 consists of a zig-zag bidimensional network formed by rectangular (4,4) grid sheets. Molecules of 2 form a 3D extended network of hydrogen bonding involving water molecules and the tetrazolate ligand. In addition, compound 1 exhibits strong fluorescence at room temperature in the solid state.

Nanoporous metal–organic framework comprising of 1D cobalt oxalate chains and flexible ligands exhibiting both dynamic gas adsorption and antiferromagnetic chain behaviours

A novel three-dimensional (3D) nanoporous metal–organic framework with moganite topology, [Co2(ox)2(dchtpy)]n·9nH2O (1·9H2O), has been obtained from the hydrothermal reaction of CoCl2, oxalic acid, NaOH and 1a,4a-dihydroxy-1e,2e,4e,5e-tetra(4-pyridyl)cyclohexane (dchtpy). X-ray analysis reveals that the bulky dchtpy ligands link four adjacent metal oxalate chains and form a 3D hybrid network with both moganite topology and 3D channels in various sizes. The largest pores (channel A) are the ones viewed along the a-axis, which are composed of two [Co(ox)]n chains and two bulky ligands in the dimensions of 10.76 × 10.67 A excluding the van der Waals radii. Along the {101} direction there was found the second large channels (channel B) in the size of 10.51 × 4.66 A. Notably the hydroxyl groups of dchtpy extend towards the channels on the middle of the walls, dividing the pores with two small channels in approximately 4.50 × 4.66 A. Besides, small pores in dimensions of 7.07 × 8.24 A and 6.98 × 6.06 A can also be found along the a- and c-axes, respectively. The potential solvent accessible void of the framework, calculated by PLATON, is 46.1% of the total volume and is occupied with disordered aqua molecules. Variable-temperature powder X-ray diffraction experiments confirmed that the crystallinity and network integrity of 1 can be retained up to 375 °C upon the removal of guest aqua molecules, in which thermal stability is among the most stable metal organic coordination frameworks. The framework shows guest-induced dynamic flexibility and elasticity and has a gating effect on the sorption of small gas molecules. The hydroxyl groups from the ligands functionalize the walls of the channels and have strong hydrogen bonds with adsorbents, leading to high sorption capacity at ambient temperature. Magnetic studies revealed significant antiferromagnetic interaction between the Co(II) ions in 1·9H2O with J = −12.4(1) cm−1 and g = 2.450(4).

Metal-organic coordination frameworks based on mixed methylmalonate and 4,4′-bipiridine ligands: synthesis, crystal structure and magnetic properties

Five new complexes of formulae [M2(4,4′-bpy)(Memal)2X2]n [M = Fe(III) (2), Mn(II) (3), Co(II) (4), Ni(II) (5) and Zn(II) (6), and X = Cl−/OH− (2) and H2O (3–6); 4,4′-bpy = 4,4′-bipyridine and Memal = methylmalonate dianion] have been synthesized by following the previously reported procedure for [Cu2(4,4′-bpy)(Memal)2(H2O)2]n (1). Moreover, two new phases of the Cu(II)/Memal/4,4′-bpy system, namely {[Cu(4,4′-bpy)2][Cu(4,4′-bpy)2(Memal)(NO3)(H2O)]}n·nNO3·3.5nH2O (7) and [Cu(4,4′-bpy)2(Memal)(H2O)]n·nH2O (8), were obtained by varying the synthetic conditions. They were all structurally characterized by single crystal X-ray diffraction, and the magnetic properties of 2–5, 7 and 8 were investigated in the temperature range 1.9–295 K. 1–6 are isomorphous compounds whose structure consists of square grids of metal ions linked through anti–syn carboxylate bridges that grow in the crystallographic ac plane. These layers are pillared along the b axis by bis-monodentate 4,4′-bpy ligands to afford a [4466]-sqp three-dimensional net. Ferro- (1 and 5) and antiferromagnetic (2–4) interactions between the metal ions are mediated by the carboxylate bridge in the anti–syn conformation, the bis-monodentate 4,4′-bpy ligand being unable to transmit a significant magnetic coupling. The values of the magnetic coupling (J) for 2–5 are −0.269(3), −0.225(2), −0.05 and +0.272(3) cm−1 respectively, the isotropic spin Hamiltonian being . Complexes 7 and 8 exhibit quite a different structure, as driven by the 4,4′-bpy groups. A square-grid of [Cu(4,4′-bpy)2]2n+n occurs in 7, which grows in the ab plane and is pillared through anti–syn carboxylate bridges from [Cu(Memal)(4,4′-bpy)2(NO3)(H2O)] units along the c axis to build up a [41263]-pcu net. Analysis of the magnetic data for this compound shows an overall antiferromagnetic behaviour with the coexistence of ferro- and antiferromagnetic interactions. The structure of 8 consists of linear chains of copper(II) running along the c axis, where aquabis(4,4′-bipyridine)copper(II) units are connected by bis(monodentate) methylmalonate ligands. A significant intrachain antiferromagnetic interaction is observed in 8 through the extended Cu–OCCCO–Cu exchange pathway [J = −1.38(1) cm−1]. The assembling role of the 4,4′-bpy coligand in 1–8 and in previous malonate-containing complexes is analyzed and discussed.

Structural Flexibility and Selective Guest Accommodation in Two CuII Metal–Organic Coordination Frameworks

AbstractTwo metal–organic coordination frameworks of CuII, [Na2Cu(2,4‐pyrdc)(H2O)(μ‐OH2)2]n (1) and {[Cu(2,5‐pyrdc) (NH3)](2H2O)}n (2) (2,4‐pyrdc = pyridine‐2,4‐dicarboxylate; 2,5‐pyrdc = pyridine‐2,5‐dicarboxylate), were synthesized and structurally characterized. The structure of compound 1 was known and shows that Cu(2,4‐pyrdc)2(H2O) functions as a metalloligand and is linked to two different NaI atoms to form a 3D heterometallic CuII–NaI framework. The single crystals of compound 2 were obtained from aqueous ammoniacal solution and crystallize in the triclinic (P$\bar {1}$) crystal system. Compound 2 is a 2D sheet consisting of two different CuII 1D chains bridged by a 2,5‐pyrdc ligand. Stacking of the 2D sheets results in a 3D supramolecular host with 1D water‐filled channels. Both frameworks are highly thermally stable and exhibit reversible structural transformation upon removal of the metal‐bound water and NH3 molecules for 1 and 2, respectively. Sorption studies reveal that desolvated frameworks 1′ and 2′ both behave nonporous to N2. However, 1′ exhibits structural transformation and hysteretic stepwise sorption of H2O and MeOH molecules, but THF and C6H6 molecules are not adsorbed. Similarly, H2O and MeOH molecules are easily adsorbed in 2′, but THF and C6H6 molecules are not. Such high selectivity in 1′ and 2′ was correlated to the smaller pore aperture and specific host–guest interaction conferred by the unsaturated Lewis acidic sites on the pore surfaces and the Lewis basic adsorbates. Low‐temperature magnetic study of 2 revealed that theCuII atoms are antiferromagnetically coupled, with J = –1.45 cm–1 and g = 2.01.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

A bimetallic pillared-layer metal–organic coordination framework with a 3D biporous structure

A novel bimetallic [Mn(ii)-Fe(iii)] 3D biporous pillared-layer metal-organic coordination framework constructed by a cyanometallate anion ([Fe(CN)(6)](3-)) and an organic linker (4,4'-bipy) is found to exhibit permanent porosity with excellent size selective vapour sorption properties and H(2)-storage capability.

Structural diversity and modulation of metal–organic coordination frameworks with a flexible V-shaped dicarboxyl building block

A family of new coordination polymers based on a V-shaped flexible dicarboxyl building block 4,4′-(hexafluoroisopropylidene)bis(benzoic acid) and familiar metal ions (MnII, CoII, NiII, CuII, ZnII, and AgI) have been prepared and structurally characterized. Their thermal stability and solid state luminescent properties of the ZnII and AgI complexes have also been investigated. Single-crystal X-ray diffraction analysis reveals a significant structural diversity of these coordination frameworks, such as the 1-D zigzag chain, 2-fold interpenetrating layer composed of 21 helical arrays, and 3-D open network with 42 helicity and pcu topology based on the rod-shaped secondary building units (SBUs). Additionally, hydrogen bonding interactions are found in these structures to further extend or stabilize the coordination motifs. A comprehensive analysis of the coordination systems based on this dicarboxyl tecton also demonstrates that it is an excellent candidate for the design and construction of multiform metal–organic frameworks (especially helical arrays), which can be dominated by metal ions and/or synthetic conditions.

Chemistry of porous coordination polymers

Abstract Remarkable advances in the recent development of porous compounds based upon coordination polymers have paved the way toward functional chemistry having potential applications such as gas storage, separation, and catalysis. From the synthetic point of view, the advantage is a designable framework, which can readily be constructed from building blocks, the so-called bottom-up assembly. Compared with conventional porous materials such as zeolites and activated carbons, porous inorganic-organic hybrid frameworks have higher potential for adsorption of small molecules because of their designability with respect to the coordination geometry around the central metal ion as well as size and probable multifunctionality of bridging organic ligands. Although rigidity and robustness of porous framework with different degree of adsorption are the most studied properties of metal-organic coordination frameworks, there are few studies on dynamic porous frameworks, which could open up a new dimension in materials chemistry.

4-(4-Pyridyl)benzoic Acid (PybenH) Dimer: An Efficient and Reasonable Design for a Long Linear Bidentate Building Block Employed in Metal–Organic Coordination Framework

Abstract Self-assembly of 4-(4-pyridyl)benzoic acid (pybenH), Ni2+, SCN− and an aromatic guest (naphthalene or dibenz[a,h]anthracene) gave two isostructural inclusion compounds, in which pybenH ligands form the corresponding dimers acting as bidentate building blocks with a length of ca. 20.86 Å.