Coordination polymers constructed from transition metal ions and organic N-containing heterocyclic ligands: Crystal structures and microporous properties

Metal Organic Frameworks: Current State and Analysis of Their Use as Modifiers of the Vulcanization Process and Properties of Rubber

The interest in and application of metal organic frameworks (MOF) is increasing every year. These substances are widely used in many places, including the separation and storage of gases and energy, catalysis, electrochemistry, optoelectronics, and medicine. Their use in polymer technology is also increasing, focusing mainly on the synthesis of MOF-polymer hybrid compounds. Due to the presence of metal ions in their structure, they can also serve as a component of the crosslinking system used for curing elastomers. This article presents the possibility of using zeolitic imidazolate framework ZIF-8 or MOF-5 as activators for sulfur vulcanization of styrene-butadiene rubber (SBR), replacing zinc oxide in conventional (CV) or effective (EF) curing systems to different extents. Their participation in the curing process and influence on the crosslinking density and structure, as well as the mechanical and thermal properties of the rubber vulcanizates, were examined.

Recent Advances in the Engineering of Single-Atom Catalysts Through Metal-Organic Frameworks

This mini-review highlights some recent progress in the engineering of single-atom catalysts (SACs) through metal-organic frameworks (MOFs) and derivatives. The inherent molecular and chemical specificities within the MOFs and derivatives can offer stabilisation of the SACs with high atomic isolation and dispersion. As MOFs are often considered an infinite array of self-assembled molecular catalysts, specifically designed structures can provide further functionalities to suit the needs of different catalytic applications. In brief, we can divide the preparation approaches into three main categories: (1) fabrication onto functional groups of the ligands, (2) fabrication onto Lewis acid sites of nodal centres, and (3) synthesis via a pyrolysis-mediated technique. Through these approaches, strong metal-support interactions can be established to aid the fine-tuning of the catalytic properties. We also discuss how recent progress in the development of state-of-the-art microscopic, spectroscopic, and crystallographic techniques has enabled scientists to elucidate the structure-activity relationship.

A rational study on the geometric and electronic properties of single-atom catalysts for enhanced catalytic performance

We investigate the geometric and electronic properties of single-atom catalysts (SACs) within metal-organic frameworks (MOFs) with respect to electrocatalytic CO2 reduction as a model reaction. A series of mid-to-late 3d transition metals have been immobilised within the microporous cavity of UiO-66-NH2. By employing Rietveld refinement of new-generation synchrotron diffraction, we not only identified the crystallographic and atomic parameters of the SACs that are stabilised with a robust MN(MOF) bonding of ca. 2.0 Å, but also elucidated the end-on coordination geometry with CO2. A volcano trend in the FEs of CO has been observed. In particular, the confinement effect within the rigid MOF can greatly facilitate redox hopping between the Cu SACs, rendering high FEs of CH4 and C2H4 at a current density of -100 mA cm-2. Although only demonstrated in selected SACs within UiO-66-NH2, this study sheds light on the rational engineering of molecular interactions(s) with SACs for the sustainable provision of fine chemicals.

Crystal structure of a novel one-dimensional zigzag chain-like cobalt(II) coordination polymer constructed from 4,4'-bi-pyridine and 2-hy-droxy-benzoate ligands

The synthesis, crystal structure and physical properties of a novel one-dimensional zigzag chain-like Co^II coordination polymer, [Co₂(2-OHbenz)₄(4,4′-bpy)_2.5(H₂O)]_n, constructed from 4,4′-bi­pyridine (4,4′-bpy) and 2-hy­droxy­benzoate (2-OHbenz) are reported.

A novel one-dimensional zigzag chain-like Co^II coordination polymer constructed from 4,4′-bi­pyridine (4,4′-bpy) and 2-hy­droxy­benzoate (2-OHbenz) ligands, namely, catena-poly[[(4,4′-bi­pyridine-κN)­(μ-2-hy­droxy­benzoato-κ²O:O′)(2-hy­droxy­benzoato-κ²O,O′)cobalt(II)]-μ-4,4′-bi­pyridine-κ²N:N′-[aquahemi(μ-4,4′-bi­pyridine-κ²N:N′)(2-hy­droxy­benzoato-κO(2-hy­droxy­benzoato-κ²O:O′)cobalt(II)], [Co₂(C₇H₅O₃)₄(C₁₀H₈N₂)_2.5(H₂O)]_n, has been synthesized by reacting cobalt(II) nitrate trihydrate, 4,4′-bpy and 2-hy­droxy­benzoic acid in a mixture of water and methanol at room temperature. There are two independent Co^II centers, Co1 and Co2, in the asymmetric unit, revealing a distorted octa­hedral geometry with chromophore types of [CoN₂O₄] and [CoN₂O₃O′], respectively. The Co1 ions are doubly bridged by 2-OHbenz ligands with syn–anti coordination mode, generating a dinuclear unit. The bridging 4,4′-bpy ligands connect these dinuclear units and the mononuclear Co2 chromophores, providing a one-dimensional alternating zigzag chain-like structure. In the crystal, inter­molecular hydrogen bonds, C—H⋯π and π–π stacking inter­actions are observed and these help to consolidate the packing. In addition, the physical properties of the title compound are reported.

Sb- and Bi-based coordination polymers with N-donor ligands with and without lone-pair effects and their photoluminescence properties

Fifteen new sublimable Sb- and Bi-based chlorido, bromido and iodido coordination polymers (CPs) with linear bispyridyl ligands are presented in this work and compared in terms of their crystal structures and photoluminescence properties. The Sb-CPs occur in two structural motifs: 1∞[Sb2X6(L)2] (X: Cl (a), Br (b), I (c); L: 1,2-bis(4-pyridyl)ethylene (bpe) (1), 1,2-bis(4-pyridyl)ethane (bpa) (2), 4,4'-bipyridine (bipy) (X: Br, I; 3)) with two polymorphs showing negligible stereochemical demand of the lone-pair and 1∞[SbCl3(bipy)] (3a) featuring a stereochemically active lone pair with significant 5p-contribution at SbIII. This is accompanied by differences in the coordination polyhedra being octahedral for high s-character, whereas a high p-character of the lone pair results in a square pyramid as the coordination sphere. The Bi-CPs are represented by the general formula 1∞[Bi2X6(L)2] (X: Cl (a), Br (b), I (c); L: 1,2-bis(4-pyridyl)ethylene (bpe) (4), 1,2-bis(4-pyridyl)ethane (bpa) (5)) and thus show no significant 6p-character of the lone pairs. For examining the parallels and differences between the SbIII- and BiIII-CPs, both are compared in terms of structures and luminescence properties, as well as with related literature known CPs. Altogether, this comparison of structures and properties allows for gaining new insights into the photoluminescence mechanisms of the Sb and Bi-containing CPs. For the first time, distinct hints on the participation of inter-valence charge transfer transitions in E3+-pairs (E: Sb, Bi) were observed for the Sb- and Bi-containing coordination polymers constructed from N-donor ligands.

Syntheses, supramolecular networks and Hirshfeld surface and thermal analyses of two new cadmium chloride coordination polymers with an N,O-chelating ligand

Two new coordination polymers, namely poly[[(3-aminopyrazin-4-ium-2-carboxylate-κ²N¹,O)di-μ-chlorido-cadmium(II)] monohydrate], {[CdCl₂(C₅H₅N₃O₂)]·H₂O}_n, (1), and poly[2-amino-3-carboxypyrazin-1-ium [(3-aminopyrazine-2-carboxylato-κ²N¹,O)di-μ-chlorido-cadmium(II)] monohydrate], {(C₅H₆N₃O₂)[Cd(C₅H₄N₃O₂)Cl₂]·H₂O}_n, (2), have been synthesized from the reaction of cadmium(II) chloride and 3-aminopyrazine-2-carboxylic acid (Hapca) under mild conditions in acidic media. The two coordination polymers have been characterized by single-crystal X-ray diffraction and show chloride-bridged zigzag chains with octahedrally coordinated metal ions, where Hapca acts as a bidentate ligand via the π-conjugated N atom and a carboxylate O atom. The chains are further interconnected via noncovalent interactions into three-dimensional supramolecular networks. The dominant H...O and H...Cl interactions for both compounds were quantified using Hirshfeld surface analysis. The thermal stability and topological analysis of the two-dimensional networks of (1) and (2) are also discussed.

Synthetic, spectral, structural and catalytic activity of infinite 3-D and 2-D copper(ii) coordination polymers for substrate size-dependent catalysis for CO2 conversion

Two copper(ii) coordination polymers have been synthesized and used as substrate size-dependent catalyst for CO₂ cycloaddition with epoxides.

Design and fabrication of energetic metal-organic framework [Cu(ntz)]n films with high energy-density and stability

In this work, for the first time, we have successfully prepared energetic metal-organic framework [Cu(ntz)]_n films by integrating electrochemical deposition and solvothermal growth. With its excellent energy, stability and ignition performances, the [Cu(ntz)]_n film has potential application in microelectromechanical systems (MEMS) to achieve functional nanoenergetics-on-a-chip.

2D networks of metallo-capsules and other coordination polymers from a hexapodal ligand

2D M₃L₂ coordination polymers (M = Re(i), Cu(ii), Co(ii), Ni(ii)) feature metal-linked M₆L₂-cages, and the Re(i) material absorbs iodine.

Structural Diversity of Three Pyrazoyl-Carboxyl Bifunctional Ligand-Based Metal-Organic Frameworks: Luminescence and Magnetic Properties

Three metal-organic frameworks (MOFs), [Cd(Hpzbpdc)(H₂ O)]⋅H₂ O (1), [Mn₂ (Hpzbpdc)₂ (dmf)₂ ] (2), and [H₂ N(CH₃ )₂ ]_0.5 [Eu(Hpzbpdc)_1.5 (HCOO)_0.5 (dmf)_0.5 ]⋅DMF⋅0.5 H₂ O (3) (H₃ pzbpdc=4'-(2 H-pyrazol-3-yl)biphenyl-3,5-dicarboxylic acid), have been solvothermally synthesized from one pyrazoyl-carboxyl bifunctional ligand and characterized by single-crystal structures. The H₃ pzbpdc ligand in 1-3 displays various coordination modes through the pyrazoyl and carboxyl groups. Both 1 and 3 contain dinuclear cluster building units and reveal a four-connected gismondine (gis) zeolite 3D framework and a 2D grid layer structure, respectively. Compound 1 shows blue luminescence, compound 3 reveals red luminescence that arises from efficient energy transfer from the organic ligand to the europium(III) ion, and compound 2 reveals an uncommon (3,8)-connected tfz-d; UO₃ net with a rare Mn₄ (COO)₆ cluster and shows antiferromagnetic interactions between the manganese(II) ions.

Micropore Formation of [Zn2(Oxac) (Taz)2]·(H2O)2.5 via CO2 Adsorption

As-synthesized [Zn₂(Oxac) (Taz)₂]·(H₂O)_2.5, referred to as ZOTW_2.5, was prepared from aqueous methanol solutions of Zn₅(CO₃)₂(OH)₆ and two kinds of ligands of 1,2,4-triazole (Taz) and oxalic acid (Oxac) at 453 K for 12 h. The crystal structure was determined by the Rietveld method. As-synthesized ZOTW_2.5 was pretreated at 383 K and 1 mPa for t_pt h, ZOTW_x(t_pth). ZOTW_x(≥3h) showed a type I adsorption isotherm for N₂ at 77 K having a saturation amount (V_s) of 180 mg/g, but that pretreated shortly showed only 1/10 in V_s. CO₂ was adsorbed at 303 K in sigmoid on nonporous ZOTW_x(≤2h) and in Langmuir-type on ZOTW_x(≥3h) to reach the adsorption amount of 120 mg/g at 700 Torr. N₂ adsorption on ZOTW_x(≤2h)deCO₂, degassed after CO₂ adsorption on ZOTW_x(≤2h), was promoted 5-fold from 180 mg/g on ZOTW_x(t_pth) and ZOTW_x(≥3h)deCO₂ up to ca. 1000 mg/g. The interaction of CO₂ and H₂O molecules in micropores may lead to a new route for micropore formation.

Cadmium(ii) coordination polymers based on substituted malonic acid: synthesis, characterization and photoluminescence properties

The influence of the chain length on the topology and luminescence of four new cadmium(ii) R-malonate coordination polymers is analysed herein.

Amino-functionalized metal–organic framework for adsorption and separation of dichloromethane and trichloromethane

MOF functionalized with –NH₂ exhibits improved adsorption capacity and selectivity for the adsorption and separation of dichloromethane and trichloromethane.

Spectral, morphological, linear and nonlinear optical properties of nanostructured benzimidazole metal complex thin films

Metal organic materials are widely investigated to find their suitability for nonlinear optical applications due to the advantage of combined organic and inorganic properties. In this work benzimidazole based metal organic thin films of dichlorobis (1H-Benzimidazole) Co(II) and dichlorobis (1H-Benzimidazole) Cu(II) were deposited by chemical bath deposition method. The deposited films were annealed at 100, 150 and 200 °C to investigate the effect of annealing on the properties of thin films. Surface homogeneity of the films was increased with the annealing temperature due to the surface diffusion of the films and the same was evidently shown by Raman spectroscopy and Atomic Force Microscopy studies. But annealing the films at 200 °C yielded bulk patches on the surface due to the distortion of molecules. Linear and nonlinear optical properties of the films annealed at 150 °C showed relatively higher transmittance and improved nonlinear optical properties than the other as prepared and annealed samples.

Copper coordination polymers from cavitand ligands: hierarchical spaces from cage and capsule motifs, and other topologies

Copper coordination polymers from cavitand ligands are reported including networked cage-motif structures, one of which takes up C₆₀ from solution.

The cyclotriveratrylene-type ligands (±)-tris(iso-nicotinoyl)cyclotriguaiacylene L1 (±)-tris(4-pyridylmethyl)cyclotriguaiacylene L2 and (±)-tris{4-(4-pyridyl)benzyl}cyclotriguaiacylene L3 all feature 4-pyridyl donor groups and all form coordination polymers with Cu^I and/or Cu^II cations that show a remarkable range of framework topologies and structures. Complex [Cu^I₄Cu^II_1.5(L1)₃(CN)₆]·CN·n(DMF) 1 features a novel 3,4-connected framework of cyano-linked hexagonal metallo-cages. In complexes [Cu₃(L2)₄(H₂O)₃]·6(OTf)·n(DMSO) 2 and [Cu₂(L3)₂Br₂(H₂O)(DMSO)]·2Br·n(DMSO) 3 capsule-like metallo-cryptophane motifs are formed which linked through their metal vertices into a hexagonal 2D network of (4³.12³)(4².12²) topology or a coordination chain. Complex [Cu₂(L1)₂(OTf)₂(NMP)₂(H₂O)₂]·2(OTf)·2NMP 4 has an interpenetrating 2D 3,4-connected framework of (4.6².8)(6².8)(4.6².8²) topology with tubular channels. Complex [Cu(L1)(NCMe)]·BF₄·2(CH₃CN)·H₂O 5 features a 2D network of 6³ topology while the Cu^II analogue [Cu₂(L1)₂(NMP)(H₂O)]·4BF₄·12NMP·1.5H₂O 6 has an interpenetrating (10,3)-b type structure and complex [Cu₂(L2)₂Br₃(DMSO)]·Br·n(DMSO) 7 has a 2D network of 4.8² topology. Strategies for formation of coordination polymers with hierarchical spaces emerge in this work and complex 2 is shown to absorb fullerene-C₆₀ through soaking the crystals in a toluene solution.

Silver(I) 2,2'-(1,2-Phenylenedisulfanediyl)diacetic Acid as a Molecular Building Block for a Silver(I)-Cadmium(II) Coordination Polymer

Starting from heterotopic multidentate ligand 2,2'-(1,2-phenylenedisulfanediyl)diacetic acid, (R_S,R_S,R_S,R_S/S_S,S_S,S_S,S_S)-[Ag{1,2-C₆H₄(SCH₂COOH)₂-κ²S,S'}₂]BF₄ (1) was prepared and further used as a building block for the synthesis of heterobimetallic Ag-Cd coordination polymer [Ag₂Cd₂{1,2-(OOCCH₂S)₂C₆H₄}₃(H₂O)₃ 5H₂O]_n (2). Both complexes were characterized by X-ray structure analysis and conventional spectroscopic techniques.

Structural diversities in Cu(i) and Ag(i) sulfonate coordination polymers and their anion exchange properties

Cu(i)/Ag(i) sulfonate CPs have been synthesized and characterized. One of the CPs exhibits a reversible anion exchange for perchlorate and permanganate.

Anion-dependent host-guest properties of porous assemblies of coordination complexes (PACs), [Cu(A)₂(py)₄] (A = PF₆, BF₄, CF₃SO₃, and CH₃SO₃; py = pyridine), based on Werner-type copper(II) complexes in the solid state

We report the syntheses and crystal structures of novel porous assemblies of coordination complexes (PACs) with/without guest molecules, α-[Cu(A)₂(py)₄] (α-PAC-2-A (A = PF₆, BF₄, CF₃SO₃, and CH₃SO₃); py = pyridine), γ-{[Cu(PF₆)₂(py)₄]·2guest} (γ-PAC-2-PF₆ ⊃ 2guest (guest = acetone and py)), γ-{[Cu(BF₄)₂(py)₄]·2acetone} (γ-PAC-2-BF₄ ⊃ 2acetone), and β-{[Cu(CH₃SO₃)₂(py)₄]·2.67H₂O} (β-PAC-2-CH₃SO₃ ⊃ 2.67H₂O). The single-crystal X-ray diffraction analyses of α-PAC-2-A show that α-PAC-2-A have dense packing structures, in which anions of the discrete coordination complexes form weak hydrogen-bonding and anion-π interactions. In contrast, γ-PAC-2-PF₆ ⊃ 2guest, γ-PAC-2-BF₄ ⊃ 2acetone, and β-PAC-2-CH₃SO₃ ⊃ 2.67H₂O form guest-including structures with coordination environments around the Cu(II) atoms similar to the α-forms. The vapour adsorption measurements for MeCN and acetone in α-PAC-2-A suggest that the adsorption associated with structural transformations is induced by weak Lewis-base PF₆⁻ and BF₄⁻ anions covered only with fluorine atoms, which weaken the host-host interactions.

Synthesis and characterization of coordination polymer nanoparticles as radioisotope tracers

Coordination polymer nanoparticles (NPs) with gamma-emitting nuclide (Au-198), 411keV, 675keV, 822keV and 1087keV were prepared by coordination polymerization of the radioisotope Au(3+) ions and 1,4-bis(imidazole-1-ylmethyl)benzene in an aqueous solution at room temperature for 3h. Here, the radioisotope Au(3+) ions were prepared by dissolution of Au-198 foil, which was prepared by neutron irradiation from the HANARO reactor, in KCN aqueous solution. The successful synthesis of the radioisotope coordination polymer NPs with 5±0.5nm was confirmed via UV-vis spectroscopy, Transmission Electron Microscopy (TEM), Energy Dispersive X-ray Spectrometry (EDXS), Thermogravimetric analysis (TGA), and Gamma spectroscopy analysis. The synthesized radioisotope coordination polymer NPs can be used as radiotracers in science, engineering, and industrial fields.