A three-dimensional organic–inorganic hybrid solid constructed from novel Mo–O–Zn bimetallic oxide networks linked via 3-amino-1,2,4-triazole

A novel three-dimensional organic–inorganic hybrid solid [Zn₃(3atrz)₂(H₂O)₂(MoO₄)₂]_n (1) (3atrz = 3-amino-1,2,4-triazole) constructed from two-dimensional Mo–O–Zn bimetallic oxide networks was prepared under hydrothermal condition and characterized. Unprecedented {Zn₆Mo₆} 12 metal central-membered inorganic rings together with novel {Zn₆(3atrz)₆} metal–organic coordination rings exist in this structure.     

Modification of Cu/Zn/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Catalyst by Activated Carbon Based Metal Organic Frameworks as Precursor for Hydrogen Production

In this study, Cu/Zn/Al₂O₃-AC (AC?=?activated carbon) catalyst was synthesized and evaluated for dimethoxymethane (DMM) reformation to hydrogen. The Cu/Zn/Al₂O₃-AC catalyst was prepared using high surface area metal organic frameworks (MOFs) consisting of Cu₃(BTC)₂ (MOF-199) and Zn₄O(BDC)₃ (MOF-5) for Cu(II) and Zn(II) sources respectively, as precursors while γ-Al₂O₃ was applied as support. The synthesized catalyst was investigated by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Brunauer–Emmett–Teller analysis (BET), Temperature programmed desorption (NH₃-TPD) and Energy-dispersive X-ray spectroscopy (EDX) techniques. Complete DMM conversion was observed over Cu/Zn/Al₂O₃-AC catalyst (Cu:Zn:Al mole ratio of 6:3:2) under atmospheric pressure, T?=?533 K, GHSV?=?20 NL h^?1 g_cat^?1, N₂/H₂O/DMM?=?24/5/1 volume percent (vol%) with hydrogen productivity of 12.8 L H₂ h^?1 g_cat^?1 and 64% hydrogen concentration. Application of MOFs as precursors and modified activated carbon as an acidic component provided the catalyst with the porous structure and high specific surface area for the hydrolysis of DMM, subsequently, high selectivity and productivity of hydrogen was obtained.     

Microwave enhanced synthesis of MOF-5 and its CO2 capture ability at moderate temperatures across multiple capture and release cycles

The metal-organic framework, MOF-5 (Zn₄O(BDC)₃), was prepared using solvothermal synthesis under microwave irradiation, followed by solvent exchange to improve molecular stability at high temperatures, and assessed for its ability to capture CO₂ at ambient pressure and temperatures up to 300 °C. The reaction product was characterised by X-ray diffraction, scanning electron microscope, N₂ physisorption, thermogravimetric analysis and CO₂ physisorption. Cyclic CO₂ physisorption showed the capacity of the MOF-5 crystals to be 3.61 wt% when cycled between 30 °C and 300 °C through 10 separate capture and release cycles. Above 400 °C MOF-5 underwent thermal decomposition and was no longer capable of capturing CO₂.     

Fabrication of nanosheets of a fluorescent metal–organic framework [Zn(BDC)(H2O)]n (BDC = 1,4-benzenedicarboxylate): Ultrasonic synthesis and sensing of ethylamine

A supramolecular metal–organic framework (MOF) constructed by two-dimensional (2D) infinite coordination polymers, [Zn(BDC)(H₂O)]_n (1, BDC = 1,4-benzenedicarboxylate), was synthesized by the reaction of zinc acetate with H₂BDC in dimethylformamide (DMF) under ultrasonic irradiation at ambient temperature and atmospheric pressure. Yield of 1 varied from 43.4% to 53.2% for the reaction time of 10–90 min. Samples with different morphologies, i.e. nanobelts, nanosheets, and microcrystals, were obtained under ultrasound irradiation for different reaction times. Fluorescence emission of nanosheets of [Zn(BDC)(H₂O)]_n was found to be highly sensitive to ethylamine, and solid state fluorescence intensity decreased with increasing contents of ethylamine in acetonitrile solution due to weak fluorescence quenching effect.     

Solvent directed assembly of two zinc(II)-2-(4-pyridyl)-4,5-imidazoledicarboxylate frameworks

Two zinc(II)-2-(4-pyridyl)-4,5-imidazoledicarboxylate frameworks, formulated as {[Zn₃(HPIDC)₃(DMF)₂](DMF)₂(H₂O)₂}_n (1) and {[Zn₄(HPIDC)₄(DMF)₄](DMF)₂(FMA)₂(H₂O)}_n (2) (H₃PIDC = 2-(4-pyridyl)-1H-4,5-imidazoledicarboxylic acid, DMF = N,N′-dimethylformamide, FMA = formamide) have been solvothermally synthesized depending on whatever solvents are used. In both structures, the HPIDC^2 − anions act as tripodal connectors to chelating with three zinc(II) cations while the zinc(II) cations coordinate with three HPIDC^2 − anions, to form the T-shape molecular building blocks [Zn_n(HPIDC)_n], which further connect in interdigitating or alternating fashion to result in the assembly of two different 3,3-connected networks. The luminescence behaviors and solvent effect were also discussed.     

Chemical Vapor Deposition of Pd(C<Subscript>3</Subscript>H<Subscript>5</Subscript>)(C<Subscript>5</Subscript>H<Subscript>5</Subscript>) to Synthesize Pd@MOF-5 Catalysts for Suzuki Coupling Reaction

Abstract  

The highly porous metal organic framework MOF-5 was loaded with the metal–organic compound [Pd(C₃H₅)(C₅H₅)] by metal–organic chemical vapor deposition (MOCVD) method. The inclusion compound [Pd(C₃H₅)(C₅H₅)]@MOF-5 was characterized by powder X-ray diffraction (PXRD), Fourier-transform infrared (FT-IR) spectroscopy, and solid-state nuclear magnetic resonance spectroscopy. It was found that the host lattice of MOF-5 remained intact upon precursor insertion. The –C₃H₅ ligand in the precursor is easier to lose due to the interaction between palladium and the benzenedicarboxylate linker in MOF-5, providing a possible explanation for the irreversibility of the precursor adsorption. Pd nanoparticles of about 2–5 nm in size was formed inside the cavities of MOF-5 by hydrogenolysis of the inclusion compound [Pd(C₃H₅)(C₅H₅)]@MOF-5 at room temperature. N₂ sorption of the obtained material confirmed that high surface area was retained. In the Suzuki coupling reaction the Pd@MOF-5 materials showed a good activity in the first catalytic run. However, the crystal structure of MOF-5 was completely destroyed during the following reaction runs, as confirmed by PXRD, which caused a big loss of the activity.     

A novel 3D zinc metal–organic framework based on the tetrazole-containing ligand and tricarboxylic acid

A novel zinc metal–organic framework (MOF) with the combination of 5,5′-(1,4-phenylene)bis(1H-tetrazole) (H₂BDT) and 1,3,5-benzenetricarboxylic acid (H₃BTC) as the mixed ligands, namely [Me₂NH₂]₄Zn₂(BDT)(BTC)₂ 2DMF (1), has been solvothermally synthesized and characterized. Single-crystal X-ray analysis reveals that the structure of 1 features a pillared-layered three-dimensional (3D) anionic framework of [Zn₂(BTC)₂(BDT)]_n⁴ⁿ⁻. The luminescent property studies indicated that 1 might be a potential blue-light material. It was found that the introduction of H₃BTC could exhibit an obvious influence on the luminescence of 1, which can help us in better designing luminescent MOF materials.     

Heterogeneous heck coupling in multivariate metal–organic frameworks for enhanced selectivity

Highly selective heterogeneous Heck coupling has been demonstrated inside a series of metal–organic frameworks (MOFs). These MOFs, Zn₄O(BDC-NH₂)_n(BDC)_(3 − n) (n = 3, 2.4, 1.8, 1.2, 0.9, 0.75, 0.6, 0.3, and 0.15), have been synthesized with different amounts of 1,4-benzenedicarboxylate (BDC) and 2-amino-1,4-benzenedicarboxylate (BDC-NH₂) incorporated into their structure. The BDC-NH₂ is functionalized by covalent postmodification with salicylic aldehyde for binding catalytically active Pd(II) ions. The catalytic activity of the embedded Pd(II) ions was tested via heterogeneous Heck coupling to produce resveratrol trimethyl ether, a pharmaceutically relevant precursor. It is also found during catalytic testing that a trade-off exists between amount of metalation and pore blocking.     

High-throughput screening of synthesis parameters in the formation of the metal-organic frameworks MOF-5 and HKUST-1

High-throughput methods were employed to study the influence of reaction parameters on the synthesis of the metal-organic frameworks MOF-5 (Zn₄O[(OOC)₂ · C₆H₄]₃) and HKUST-1 (Cu₃[(OOC)₃C₆H₃]₂(H₂O)₃ · xH₂O). Thus, compositional parameters (metal salt, reagent concentrations, and pH) as well as process parameters (temperature, time) were investigated in order to establish reaction trends and fields of formation. A multiclave reaction block was used to perform the investigation of 24 different solvothermal reactions at a time. Attention was focused on the phase purity and the crystal morphology of the resulting compounds. The characterization of the samples was performed by X-ray powder diffraction and high resolution scanning electron microscopy. The experimental results show that the formation, phase purity, and morphology of MOF-5 and HKUST-1 are extremely sensitive to the synthesis parameters explored in this study.     

A novel adenine-based zinc(II) metal-organic framework featuring the Lewis basic sites for heterogeneous catalysis

Metal-organic frameworks (MOFs), as a new sort of crystalline materials, have attracted lots of interest in many applications during the past decades. Recently, many efforts have been focused on the development of MOFs as heterogeneous catalysis. In this communication, we selected adenine (ad) and tetracarboxylic acid, namely 5,5′-(1,3,6,8-tetraoxobenzo[Imn] Li et al. (1999), He et al. (2016) phenanthroline-2,7-diyl)bis-1,3-benzenedicarboxylic acid (H₄L), as organic linkers to assemble with Zn(II) ions to construct a novel adenine-based porous MOF. There are three different inorganic clusters in the framework, including ZnO₂N₂, Zn₂O₂N₆, and ZnO₅N clusters. Interesting, the resultant porous MOF, namely [H₂N(CH₃)₂]⋅[Zn₄(L)_1.5(ad)₃(H₂O)₂]⋅ 4DMF, retains free amino groups in the framework, which can be served as Lewis basic sites to catalyse Knoevenagel condensation reaction. The catalytic study exhibits that the as-synthesized MOF with free amino groups can be used as heterogeneous catalysis with remarkable catalytic efforts and good recycle.     

Unusual metal–organic network constructed from Zn(II), benzenetricarboxylate and bis(1,2,4-triazolyl)pyridine

Hydrothermal reaction of ZnSO₄ · 7H₂O with 1,3,5-benzenetricarboxylic acid (H₃btc) and 2,6-bis(1,2,4-triazolyl)pyridine (btp) afforded a novel metal–organic network {[Zn₃(btc)₂(btp)₂(H₂O)₂] · 4H₂O}_n (1) with a supramolecular cocrystal [H₃btc · btp · H₂O]_n (2). The complex 1 exhibits an unusual network containing two molecular squares and a rectangle. The networks interpenetrate to make a 3D metal–organic framework, which is quite thermal stable. Compound 2 shows a 2D supramolecular network assembled through strong hydrogen bonds.     

A pair of novel helical Zn(II) enantiomers constructed from l- and d-threonine Schiff bases: Synthesis,crystal structures and properties

Two novel homochiral helical Zn(II) coordination polymers, {[Zn₂(nap-l-thr)₂(H₂O)₂]·H₂O}_n (1) and {[Zn₂(nap-d-thr)₂(H₂O)₂]·H₂O}_n (2) (H₂nap-l-thr = N-(2-hydroxy-1-naphthylmethylidene)-l-threonine, H₂nap-d-thr = N-(2-hydroxy-1-naphthylmethylidene)-d-threonine) have been successfully synthesized and characterized by elemental analysis, IR, UV–visible and single-crystal X-ray diffraction. It is interesting to note that both complexes are a pair of enantiomers: 1 exhibits 1D right-handed helical chain of [Zn-COO⁻]_∞ and 2 is 1D left-handed helical chain of [Zn-COO⁻]_∞. There are various hydrogen bonds between the adjacent helical chains which result in a 2D homochiral supramolecular layer structure. Notably, under similar synthetic procedure by using the NO₃⁻, CH₃COO⁻, Cl⁻ salts of Zn^2 + ion as a starting reagent, and identical compounds were obtained. In addition, the chiral nature of complexes 1 and 2 are confirmed by the results of circular dichroism (CD) spectra measurements. Thermal stability and luminescence properties were also investigated.     

Hydrothermal Syntheses and Crystal Structures of Three Zn(II) Coordination Compounds Constructed with 3,5-Pyrazoledicarboxylic Acid

Three novel metal–organic coordination compounds, [Zn(Hdcp)(H₂O)₄]·1.5H₂O (1), [Zn(Hdcp)(H₂O)₂]_∞ (2) and [Zn₃(dcp)₂(H₂O)₅]_∞ (3) with the ligand 3,5-pyrazoledicarboxylic acid were prepared by the hydrothermal method. The complexes were structurally characterized by elemental analysis, IR spectroscopy and X-ray single-crystal diffraction. Compound 1 is a mononuclear molecule that is linked into a 3D supramolecular framework via N–H···O and O–H···O hydrogen bonds. In 2, two types of carboxylic bridges were found between Zn^II ions to form a 1D double-chain. The 1D chains were further construct into a 3D structure by hydrogen bonds. Trinuclear 3 consists of 1D bi-infinite parallelogram chains of [Zn₃(dcp)₂(H₂O)₃] trimers. In the basic trinuclear unit a further bridging mode of the ligand is seen where two dcp^3? ligands chelate three Zn^II ions by utilizing five donors of the dcp^3? ligand. The photoluminescent properties of 1, 2 and 3 were investigated.     

Enhancement of orientation of rigid polymer blocks by incorporating rod–coil block copolymer chains into metal–organic frameworks

Incorporation of polymer chains into metal–organic frameworks (MOFs) is a simple yet efficient method for improving the orientation of the polymer chains. However, due to their rigidity and high molecular weight, many rigid polymer chains are either not easily loaded into MOFs, or not easily aligned within the MOF channels. In this paper, we propose a strategy for enhancing the orientation of rigid blocks by incorporating rod–coil block copolymer chains into MOFs. In this strategy, on the one hand, the rigid blocks have a low molecular weight, so that the steric hindrance effect from the MOF channels could align the rigid blocks more efficiently. On the other hand, because the covalent bonds between the repeat units of the flexible blocks can rotate relatively easily, the steric hindrance effect from the flexible blocks can further help the rigid blocks to be oriented within the MOF channels. In confirmatory simulations, two all‐atom MOF models, [Zn₂(BDC)₂(TED)]_n and [Zn₂(BPDC)₂(TED)]_n (TED = triethylenediamine, BDC = 1,4‐benzenedicarboxylate, BPDC = 4,4′‐biphenyldicarboxylate), are established. With these MOF models, molecular dynamics simulations are performed for the rigid poly(phenylene vinylene) (PPV) chain and the rod–coil block copolymer PPV‐block‐polystyrene (PSt). Further, their respective degrees of orientation (DoOs) are calculated. Within [Zn₂(BDC)₂(TED)]_n and [Zn₂(BPDC)₂(TED)]_n, the DoOs of the rigid PPV blocks of PPV‐block‐PSt are 0.968 and 0.902, respectively, while the DoOs of the rigid PPV chains are 0.865 and 0.711, respectively. These calculation results prove the feasibility of our proposed strategy. © 2019 Society of Chemical Industry     

Pillar-layered Zn–triazolate–carboxylate frameworks tuned by the bend angles of ditopic ligands

In the utilization of three ditopic ligands with different bend angles as pillars, we reported herein three pillar-layered Zn–triazolate–carboxylate frameworks, namely, [Zn₂(ATRZ)₂(BDC)]_n (1), [Zn₂(ATRZ)₂(TPDC)]_n·2nDMF (2) and [Zn₂(ATRZ)₂(ADDC)]_n (3) (ATRZ = 3-amino-1,2,4-triazole, H₂BDC = 1,4-benzenedicarboxylic acid, H₂TPDC = 2,5-thiophenedicarboxylic acid, and H₂ADDC = 1,3-adamantanedicarboxylic acid). Single crystal structural analyses demonstrate that different geometries of ditopic carboxylate pillars not only result in Zn–ATRZ layers adopting various corrugated configurations, but also give rise to 3,4-connected self-interpenetrated net of 1 and non-interpenetrated nets of 2 and 3. All these compounds exhibit high thermal stability and blue photoluminescence.     

Ionothermal synthesis of a 3D Zn–BTC metal-organic framework with distorted tetranuclear [Zn4(μ4-O)] subunits

A zinc metal-organic framework (MOF), [Zn₄(BTC)₂(μ₄-O)(H₂O)₂], was synthesized with Zn(NO₃)₂ · 6H₂O and H₃BTC ligand (H₃BTC = 1,3,5-benzenetricarboxylic acid) by ionothermal synthesis in 1-ethyl-3-methylimidazolium bromide ionic liquid as solvent. The compound features a 3-D architecture constructed by linking [Zn₄(μ₄-O)] subunits with BTC³⁻ ligands. They are composed of two five-coordinated and two four-coordinated Zn ions, different from the [Zn₄(μ₄-O)] units of other MOFs. The effect of reaction conditions to the MOF structure is discussed.     

One novel polynuclear complex [Cu2(bpc)2(N3)4Ca(H2O)2Na2(H2O)2]n having three different transition and non-transition metal centres

The complex [Cu₂(bpc)₂(N₃)₄Ca(H₂O)₂Na₂(H₂O)₂]_n (1) (bpc²⁻=2,2^′-bipyridyl-3,3^′-dicarboxylate) has been prepared and characterised by elemental analyses, spectroscopic and single crystal X-ray diffraction study. Single crystal X-ray analysis revealed a novel polynuclear complex containing three different metal centres such as an alkali metal (sodium), an alkaline earth metal (calcium) and a transition metal atom (copper) connected together by azide and carboxylato groups.     

Asymmetric Solvation of the Zinc Dimer Cation Revealed by Infrared Multiple Photon Dissociation Spectroscopy of Zn2+(H2O)n (n = 1–20)

Investigating metal-ion solvation—in particular, the fundamental binding interactions—enhances the understanding of many processes, including hydrogen production via catalysis at metal centers and metal corrosion. Infrared spectra of the hydrated zinc dimer (Zn₂⁺(H₂O)_n; n = 1–20) were measured in the O–H stretching region, using infrared multiple photon dissociation (IRMPD) spectroscopy. These spectra were then compared with those calculated by using density functional theory. For all cluster sizes, calculated structures adopting asymmetric solvation to one Zn atom in the dimer were found to lie lower in energy than structures adopting symmetric solvation to both Zn atoms. Combining experiment and theory, the spectra show that water molecules preferentially bind to one Zn atom, adopting water binding motifs similar to the Zn⁺(H₂O)_n complexes studied previously. A lower coordination number of 2 was observed for Zn₂⁺(H₂O)₃, evident from the highly red-shifted band in the hydrogen bonding region. Photodissociation leading to loss of a neutral Zn atom was observed only for n = 3, attributed to a particularly low calculated Zn binding energy for this cluster size.     

Syntheses,crystal structures of two coordination polymers constructed from imidazole-based dicarboxylate ligands containing alkyl group

Two new coordination polymers, |DMF|[Zn₂(C₇N₂O₄H₆)₂(C₁₀N₂H₈)] (1) and |(H₂O)₃|[Co(C₈N₂O₄H₉)₂(H₂O)₂] (2) have been synthesized based on 2-ethyl-1H-imidazole-4,5-dicarboxylic acid (H₃EtImDC) and 2-propyl-1H-imidazole-4,5-dicarboxylic acid (H₃PrImDC) as organic ligands, respectively. Single-crystal X-ray diffraction analysis reveals that compound 1 is a two dimensional layered structure constructed from two types of six-membered metallocycle, and the layers are stacked in an –ABCABC– sequence. For 2, the mononuclear [Co(C₈N₂O₄H₉)₂(H₂O)₂] molecules are connected with each other through hydrogen bonds forming a three dimensional supermolecular structure. Further characterizations including elemental analyses, IR spectra, and thermogravimetric analyses have been studied.     

Two new pH-controlled coordination polymers constructed from an asymmetrical tricarboxylate ligand and Zn-based rod-shaped SBUs

Two new 3D coordination polymers, [Zn₃(L)₂(H₂O)₄]·H₂O (1) and [Zn₅(μ₃-OH)₄(L)₂(H₂O)₂] (2) (H₃L = 3-(2′,5′-dicarboxylphenyl)benzoic acid), have been synthesized under hydrothermal conditions by adding different amounts of NaOH. Structural analyses show that both of them contain 1D inorganic Zn(II)-chains as rod-shaped secondary building units (SBUs) but they are in different forms. The rod-shaped Zn(II)-chain of 1 is only Zn-carboxylate chain, while the one in 2 is formed by the independent Zn₅(COO)₆ clusters connected by hydroxyl oxygen. Furthermore, the thermal and luminescent properties of both compounds have been studied.