Open Metal-organic Frameworks Research Articles

A Gas-Steamed Route to Mesoporous Open Metal-Organic Framework Cages Enhancing Flame Retardancy and Smoke Suppression of Polyurea.

Up to now, metal-organic frameworks (MOFs) with open nanostructures have shown outstanding capabilities in trapping smoke particles compared to the original MOFs. However, only a few MOF-based strategies have been reported to synthesize hierarchical porous cages thus far, which are mainly restricted to environmentally unfriendly wet-chemical liquid methods. Herein, as a proof-of-concept, a gas-steamed metal-organic framework approach was designed to fabricate a series of cheeselike open cages with hierarchical porosity. Briefly, zeolitic imidazolate framework-67 (ZIF-67) and phytic acid were employed as precursor and etchant, respectively. Abandoning the conventional wet-chemical method, the coordination bond of ZIF-67 was cleaved by acidic steam, forming an open framework with a high specific surface area and a hierarchical porous structure. The universality of this method was also confirmed by the selection of different etchants. Impressively, they also show outstanding fume-toxic adsorption capability and labyrinth effects based on abundant and complex porous channels. At only 5 wt % loading, Co3O4@open ZIF-67 cage-2 (Co3O4@OZC-2) imparted polyurea (PUA) composites with a 21.2% limiting oxygen index, and the peak of heat release rate, total heat release, and total smoke production were reduced by around 37.5, 25.5, and 40.4%, respectively, compared to neat PUA. This work will shed light on the advanced structural design of polymer composites with high fire safety, especially smoke suppression performance, so as to obtain more feasible applications.

Epitaxial Single-Domain Cu-BTC Metal-Organic Framework Thin Films and Foils by Electrochemical Conversion of Cuprous Oxide.

Metal-organic frameworks (MOFs) are an important class of crystalline porous materials with extensive chemical and structural merits. However, the fabrication of MOF thin films oriented along all crystallographic axes to achieve well-aligned nanopores and nanochannels with uniform apertures remains a challenge. Here, we achieved highly crystalline single-domain MOF thin films with the [111] out-of-plane orientation by electrochemical conversion of cuprous oxide. Copper(II)-benzene-1,3,5-tricarboxylate, Cu3(BTC)2 (referred to as Cu-BTC), is a well-known metal-organic open framework material with a cubic crystal system. Epitaxial Cu-BTC(111) thin films were manufactured by electrochemical oxidation of Cu2O(111) films electrodeposited on single-crystal Au(111). The Cu-BTC(111) shows an in-plane antiparallel relationship with the precursor Cu2O(111) with a -0.91% coincidence site lattice mismatch. A plausible mechanism was proposed for the electrochemical conversion of Cu2O into Cu-BTC, indicating formation of intermediate CuO, growth of Cu-BTC islands, and termination with coalesce into a dense film with a limiting thickness of about 740 nm. The Faradaic efficiency for the electrochemical conversion was 63%. In addition, epitaxial Cu-BTC(111) foils were fabricated by epitaxial lift-off following the electrochemical etching of residual Cu2O underneath the Cu-BTC. It was also demonstrated that Cu-BTC(111) films with two in-plane domains and textured Cu-BTC(111) films can be achieved on a large scale using electrodeposited Au/Si and Au-coated glass as low-cost substrates.

Polyoxometalate Metal-Organic Frameworks: Keggin Clusters Encapsulated into Silver-Triazole Nanocages and Open Frameworks with Supercapacitor Performance.

To investigate the relationship between the structures of polyoxometalate host-guest materials and their energy-storage performance, three novel polyoxometalate-based metal-organic compounds, [Ag10(C2H2N3)8][HVW12O40], [Ag10(C2H2N3)6][SiW12O40], and [Ag(C2H2N3)][Ag12(C2H2N3)9][H2BW12O40] are synthesized by a one-step hydrothermal method and further confirmed by single-crystal X-ray diffraction analyses and other numerous characterization techniques. In compound [Ag10(C2H2N3)8][HVW12O40], the Keggin clusters are intersected into channels formed by a 3D open metal-organic framework. In contrast, in compounds [Ag10(C2H2N3)6][SiW12O40] and [Ag(C2H2N3)][Ag12(C2H2N3)9][H2BW12O40], the Keggin clusters are encapsulated into silver-triazole metal-organic nanocages to construct core-shell structures, which are further fused together by covalent bonds to form 3D polyoxometalate-based metal-organic frameworks. The electrochemical properties of three compound-based electrodes are estimated by cyclic voltammetry, galvanostatic charge-discharge, electrochemically active surface area, and electrochemical impedance spectroscopy. The results of the electrochemical performance tests indicate that these compounds possess high specific capacitance and cycling stability, especially [Ag10(C2H2N3)8][HVW12O40], showing a specific capacitance of 93.5 F g-1, which is higher than that of many other polyoxometalate-based electrode materials. A possible mechanism of the electrochemical performance is explored, which is mainly related to the redox capacity of polyoxometalate, the electrochemically active surface area, the electrochemical impedance spectroscopy, and the microstructures of polyoxometalate-based metal-organic frameworks.

Understanding geology through crystal engineering: coordination complexes, coordination polymers and metal–organic frameworks as minerals

Recent structural studies of organic minerals, coupled with the intense search for new carbon-containing mineral species, have revealed naturally occurring structures analogous to those of advanced materials, such as coordination polymers and even open metal–organic frameworks exhibiting nanometre-sized channels. While classifying such `non-conventional' minerals represents a challenge to usual mineral definitions, which focus largely on inorganic structures, this overview highlights the striking similarity of organic minerals to artificial organic and metal–organic materials, and shows how they can be classified using the principles of coordination chemistry and crystal engineering.

Modification of the Electron Density in Prussian Blue Iron Sites to Improve the Charge Extraction at High Voltages in Sodium Ion Batteries

An interesting material for the cathode of Na-Ion battery is the metal-organic open framework called Prussian Blue AFe[Fe(CN)]6 (A= alkali metals), in which alkali ions occupy half of the empty cubic cavities created by a cubic network of alternating high spin Fe and low spin Fe in the vertices and -C≡N- ligands on the edges. These materials exhibit interesting properties such as low cost, easiness of synthesis and good stability. During the charge process this material exhibit two redox processes, the first associated to high spin Fe (coordinated to nitrogen) and the second to low spin Fe (coordinated to carbon); however, the extracted charge is mainly obtained during the discharge process at lower potentials (lower energy). Thus, in this work, in order to enhance the energy density, the high spin Fe in Prussian blue is partially replaced by Mn2+ and Co2+, i.e. samples NaxMnFe[Fe(CN)]6 and NaxCoFe[Fe(CN)]6. All materials were synthetized by precipitation method, the XRD revealed that materials crystallized in cubic cell, whereas the IR and Raman spectroscopy suggested that high spin Fe is in oxidation state 3+ and iron low spin is found in 2+. Mössbauer spectroscopy was used to confirm the oxidation state of the samples; moreover, the characterization indicates that the electronic density of the iron center is modified by the presence of Mn or Co in the structure. The electrochemical performance indicated that the charge extracted during the discharge process is similar in NaxCoFe[Fe(CN)]6 and NaxFe[Fe(CN)6] whereas in the NaxMnFe[Fe(CN)]6 the higher amount of extracted charge occurs in the second process at higher voltage. Thus, the incorporation of a second metal in the structure of the Prussian Blue cathode is capable to modify the electronic structure of the sites and lead to the possibility to control the extraction of charge at high voltages.

A Water-Stable Cl@Ag14 Cluster Based Metal-Organic Open Framework for Dichromate Trapping and Bacterial Inhibition.

Decoding the principles of cluster-based framework assembly at the molecular level remains a persistent challenge. Herein, we isolated and characterized a novel water-stable three-dimensional (3D) metal-organic open framework [Cl@Ag14(cPrC≡C)10Cl2·(p-TOS)·1/3H2O]n (SD/Ag14, cPrC≡CH = cyclopropylacetylene; p-TOS = p-toluenesulfonate), which contains a chloride-templated Ag14 cluster as building block. For SD/Ag14, one chloride acts as the template to shape the Ag14 cluster and the other bridges the clusters to a 3D pcu-h open framework. As revealed by high resolution electrospray mass spectrometry (HRESI-MS), the Ag12-Ag14 species are potential cluster-based intermediates to the 3D pcu-h framework, which authenticates a preconceived idea that the 3D framework is hierarchically assembled from the silver clusters as observed in solid state. Interestingly, SD/Ag14 can be used effectively to remove the environmental pollutant Cr2O72- from wastewater through anion exchange in a single-crystal-to-single-crystal (SC-SC) transformation fashion. Furthermore, SD/Ag14 exhibits excellent antibacterial activity against Staphylococcus aureus, thus making it a potential antibacterial agent.

Carbon dioxide gas detection by open metal site metal organic frameworks and surface functionalized metal organic frameworks

Novel nanoporous materials known as Metal-Organic Frameworks (MOFs) are currently attracting wide attention due to their potential applications such as gas storage, gas separation and catalysis. Recently, MOF materials were also developed for chemical sensors. In this work, for the first time iso-structural MOFs M-MOF-74 (where M=Mg, Ni, Co and Zn) and ethylenediamine functionalized Mg-MOF-74 were investigated as selective CO2 gas sensing material for the work function read-out based method at ambient temperature and different humidity levels. M-MOF-74s are very interesting MOFs because they contain coordinatively unsaturated metal centers where adsorbates can interact strongly with their affinity towards gas molecules. Interaction of the CO2 molecules with open metal sites or amine-functional groups changes the work function (ΔΦ) of sensing layer which can serve as a signal for gas sensors. Results show that ethylenediamine functionalized Mg-MOF-74 exhibited enhanced CO2 gas sensing properties compared to other M-MOF-74 with respect to sensitivity, reversibility and stability.

Mimicking mineral neogenesis for the clean synthesis of metal–organic materials from mineral feedstocks: coordination polymers, MOFs and metal oxide separation

We present a systematic study of a mild approach for the activation of metal oxides, involving reactivity and self-assembly in the solid state, which enables their solvent-free chemical separation and direct solvent-free and low-energy conversion into coordination polymers and open metal–organic frameworks (MOFs). The approach is inspired by geological biomineralization processes known as mineral weathering, in which long-term exposure of oxide or sulfide minerals to molecules of biological origin leads to their conversion into simple coordination polymers. This proof-of-principle study shows how mineral neogenesis can be mimicked in the laboratory to provide coordination polymers directly from metal oxides without a significant input of either thermal or mechanical energy, or solvents. We show that such “aging” is accelerated by increased humidity, a mild temperature increase and/or brief mechanical activation, enabling the transformation of a variety of high-melting (800 °C–2800 °C) transition (MnII, CoII, NiII, CuII, and Zn) and main group (Mg and PbII) oxides at or near room temperature. Accelerated aging reactions are readily scaled to at least 10 grams and can be templated for the synthesis of two-dimensional and three-dimensional anionic frameworks of Zn, Ni(II) and Co(II). Finally, we demonstrate how this biomineralization-inspired approach provides an unprecedented opportunity for solvent-free chemical segregation of base metals, such as Cu, Zn and Pb, in their oxide form under mild conditions.

Two photoluminescent metal–organic frameworks based on a BODIPY-derived bipyridine ligand

Two new metal–organic open frameworks (MOFs) [Zn3L2(btc)2(H2O)]·(guests) (1), [CdL(bdc)]·(guests) (2), were successfully prepared by using a photoluminescent BODIPY-based bipyridine linker, L, and auxiliary ligands 1,4-benzenedicarboxylate (H2bdc) and 1,3,5-benzenetricarboxylate (H3btc), respectively. MOF 1 has a 2-fold interpenetrating three-dimensional (3D) framework with an 8-connecting body centered cubic (bcu) net, built upon a paddlewheel cluster [Zn2(O2CR)4], a tetrahedrally connecting Zn and a 3-connected btc3− ligand. MOF 2 has a highly open framework with a kagome-type net. It is a pillared layered structure made of 2D [Cd(bdc)] kagome sheets and L as pillars. MOF 1 was shown to exhibit permanent porosity and adsorption of N2, H2, CO2 and CH4. Both MOFs exhibited strong photoluminescent emissions at room temperature with peaks at 540 nm upon excitation, owing to a ligand L-based excited state.

A microporous metal–organic open framework containing uncoordinated carbonyl groups as postsynthetic modification sites for cation exchange and Tb3+ sensing

A novel 3D microporous compound [Zn3(Httca)2(4,4'-bpy)(H2O)2]n (MOF-COOH) containing uncoordinated carbonyl groups pointing to the pores was prepared. The uncoordinated carbonyl groups in the channels can act as postsynthetic modification sites for cation exchange. The MOF-COOH compound can effectively and selectively serve as an antenna for sensitizing the visible-emitting Tb(3+) cation.

Metallosupramolecular compounds based on Cu(ii)/oxalate/twisted NSSN ligands showing a new in situ S–C bond cleavage

Four new complexes, [Cu2(C2O4)2(SCS)]·3H2O (1), [Cu2(C2O4)3(SCSH)2]·H2O (2), [Cu(C2O4)(SS)2]·3H2O (3) and [Cu(C2O4)(SS)]·6H2O (4) [where SCS = bis(4-pyridylthio)methane and SS = 4,4′-dipyridyldisulfide], have been synthesized by the reaction of the SS and SCS ligands with the corresponding copper(II) oxalate salt. The different synthetic conditions allowed control of the preparation of a 3D open metal–organic framework in 1, a dinuclear zwitterionic molecular compound in 2 and one- and two-dimensional (1D and 2D) coordination polymers in 3 and 4, respectively. Compound 4 was also obtained by in situ transformation of the dithioether ligand (SCS) to the disulfide ligand (SS) under hydrothermal conditions at 150 °C. The topology of the structures has been studied and 1 is a new 3D MOF with a binodal 4-connected node in a scarcely known network topology. Different numbers and topologies of water molecules are hosted in the crystal lattices of the compounds. The integrity of the frameworks after dehydration has been validated and discussed. The magnetic properties of compounds 1, 2 and 4 have also been investigated. Strong antiferromagnetic behaviour was found in 1 and weak antiferromagnetic coupling was observed in 2 and 4. The magneto-structural correlations that govern these interactions are discussed in detail.

Selective Gas and Vapor Sorption and Magnetic Sensing by an Isoreticular Mixed-Metal–Organic Framework

A novel isoreticular oxamato-based manganese(II)-copper(II) open metal-organic framework H(2)O@iso1 featuring a pillared square/octagonal layer structure with alternating open and closed octagonal pores has been rationally prepared. The open-framework topology is responsible for a large selectivity in the separation of small gas (CO(2) over CH(4)) and vapor molecules (CH(3)OH over CH(3)CN and CH(3)CH(2)OH). H(2)O@iso1 displays a long-range three-dimensional ferromagnetic ordering with a drastic variation of the critical temperature as a function of the guest molecule [T(C) < 2.0 K (CO(2)@iso1 and CH(4)@iso1) and T(C) = 6.5 (CH(3)OH@iso1) and 21.0 K (H(2)O@iso1)].

Tuning the Adsorption Properties of Isoreticular Pyrazolate-Based Metal–Organic Frameworks through Ligand Modification

Two isoreticular series of pyrazolate-based 3D open metal-organic frameworks, MBDP_X, adopting the NiBDP and ZnBDP structure types [H(2)BDP = 1,4-bis(1H-pyrazol-4-yl)benzene], were synthesized with the new tagged organic linkers H(2)BDP_X (X = -NO(2), -NH(2), -OH). All of the MBDP_X materials have been characterized through a combination of techniques. IR spectroscopy proved the effective presence of tags, while X-ray powder diffraction (XRPD) witnessed their isoreticular nature. Simultaneous TG/DSC analyses (STA) demonstrated their remarkable thermal stability, while variable-temperature XRPD experiments highlighted their high degree of flexibility related to guest-induced fit processes of the solvent molecules included in the channels. A structural isomer of the parent NiBDP was obtained with a sulfonate tagged ligand, H(2)BDP_SO(3)H. Structure solution from powder diffraction data collected at three different temperatures (room temperature, 90, and 250 °C) allowed the determination of its structure and the comprehension of its solvent-related flexible behavior. Finally, the potential application of the tagged MOFs in selective adsorption processes for gas separation and purification purposes was investigated by conventional single component adsorption isotherms, as well as by advanced experiments of pulse gas chromatography and breakthrough curve measurements. Noteworthy, the results show that functionalization does not improve the adsorption selectivity (partition coefficients) for the resolution of gas mixtures characterized by similar high quadrupole moments (e.g., CO(2)/C(2)H(2)); however, the resolution of gas mixtures containing molecules with highly differentiated polarities (i.e., N(2)/CO(2) or CH(4)/CO(2)) is highly improved.

Decaaquabis(μ3-4-hydroxypyridine-2,6-dicarboxylato)bis(4-hydroxypyridine-2,6-dicarboxylato)tetramanganese(II) 3.34-hydrate: a new three-dimensional open metal–organic framework based on a tetranuclear MnIIcomplex of chelidamic acid and undecameric stitching water clusters

4-Hydroxypyridine-2,6-dicarboxylic acid (chelidamic acid, cdaH(3)) reacts with MnCl(2)·2H(2)O in the presence of 2-amino-4-methylpyrimidine in water to afford the tetranuclear title complex, [Mn(4)(C(8)H(3)NO(5))(4)(H(2)O)(10)]·3.34H(2)O, built through carboxylate bridging. The tetranuclear complex sits on a centre of inversion at (½, ½, ½). In the crystal, discrete undecameric (H(2)O)(10.34) water clusters (involving both coordinated and uncoordinated water molecules, with one site of an uncoordinated water molecule not fully occupied) assemble these tetranuclear Mn(II) complex units via an intricate array of hydrogen bonding into an overall three-dimensional network. The degree of structuring of the (H(2)O)(10.34) supramolecular association of water molecules observed in the present compound, imposed by its environment and vice versa, will be discussed in comparison to that observed for the (H(2)O)(14) supramolecular clusters in the case of the dinuclear complex [Mn(2)(cdaH)(2)(H(2)O)(4)]·4H(2)O [Ghosh et al. (2005). Inorg. Chem. 44, 3856-3862].

An open metal–organic framework based on Cu3-triad triangular units and templated by double Wells–Dawson anions

Abstract A novel double-Dawson-anion-templated, triangular trinuclear Cu-trz unit-based metal–organic framework [CuII8(trz)6(μ3-O)2(H2O)12][P2W18O62]·4H2O (1) (Htrz = 1,2,4-triazole), has been hydrothermally synthesized and characterized by routine methods. Compound 1 is the first example of the Cu3-triad triangular unit-based three-dimensional (3D) metal–organic framework templated by double [P2W18O62]6− polyoxoanions. Furthermore, the electrochemical property of compound 1 has been studied.

Cation‐Exchange Porosity Tuning in Anionic Metal–Organic Frameworks for the Selective Separation of Gases and Vapors and for Catalysis

The outperforming adsorptive properties of the so-called open metal–organic frameworks (MOFs) or porous coordination polymers (PCPs) rely on their fully accessible porous structure and the easy tuning of the shape, size, and chemical nature of their pores. The ability of some of these systems to mimic the structure and properties of zeolites has also been realized. There are, however, unsolved problems related to the general lower thermal and chemical stability (hydrolysissensitive nature) of MOFs compared to their zeolite counterparts. Consequently, the search for highly robust MOFs capable of withstanding the working conditions typically found in industrial processes is a highly desirable challenge. In this regard, the robustness of the metal–nitrogen(heterocycle) coordinative bonds leads to the formation of MOF materials with enhanced chemical and thermal stabilities. It should also be noted that, in contrast to the wellknown cation-exchange features of zeolites, the zeomimetic coordination polymers generally possess neutral or cationic frameworks and consequently do not usually give rise to cation-exchange processes. Herein, we report the synthesis, structural characterization, thermal/chemical stability, and adsorptive, separation, and catalytic properties of the anionic MOF NH4[Cu3(m3-OH)(m3-4-carboxypyrazolato)3] (NH4@1). In addition, we have examined the plausible modulation of its porous network by means of ion-exchange processes of the extraframework cations. The results show that the ion-exchange processes on these systems lead to profound changes in the textural properties of their porous surface and in the adsorption selectivity of different separation processes of gases and vapors. The crystal structure of NH4@1 [10] is based on an anionic 3D porous framework built up of trinuclear Cu3(m3-OH) clusters connected to another six through m3-4-carboxypyrazolato bridges (Figure 1). In this way, tetrahedral cages with

Metal–organic open frameworks with one-dimension channels assembled with pyridine 2,6-dicarboxylic acid and N-containing auxiliary ligands: Syntheses, crystal structures, and physical characterization

Four new complexes, {[Mn(imH) 2(pdc)]·H 2O} n ( 1), [Zn 2(pdc) 2(H 2O) 5]·2H 2O ( 2), [Zn(imH) 2(pdc)]·H 2O ( 3), {[Zn 2(pdc) 2(bpy)(H 2O) 2]·5H 2O} n ( 4) [imH = imidazole pdc = pyridine 2,6-dicarboxylate, bpy = 4,4′-bipyridine] have been synthesized under hydrothermal conditions and structurally characterized by elemental analysis, IR, PXRD, single-crystal X-ray diffraction and thermogravimetric analyses. All the four complexes display a three-dimensional (3D) open framework with one-dimensional (1D) channels that are filled with lattice water molecules. Particularly, in 4, the lattice water molecules form an infinite water chain. Both 1 and 4 consist of 1D polymeric chains. While 2 contains a dinuclear Zn(II) unit, and 3 is a mononuclear complex. Further, the result of thermal analysis of 1 and 2 shows the robustness of the overall supramolecular three-dimensional architecture. Complexes 1, 3, and 4 exhibit strong fluorescent emissions in the solid state at room temperature and could be significant in the field of photoactive materials.

A novel self-penetrating metal–organic open framework containing unusual triple-stranded molecular braid and septuple helices

Self-assembly of a long V-shaped 4,4′-oxydiphthalate (odpa) ligand and copper salt in the presence of a linear bidentate ligand affords a unique self-penetrating metal–organic open framework [Cu 2(odpa)(bpy) 2] ( 1) (bpy = 4,4′-bipyridine), exhibiting an unprecedented binodal four-connected (6 4.8 2) 2(6 2.8 4) topology. Its structure was determined by single-crystal X-ray diffraction analysis and further characterized by elemental analyses, IR spectrum, X-ray powder diffraction, and TG analysis. Compound 1 is a novel three-dimensional (3D) guest-free porous framework containing molecular braids and septuple helices, which are particularly rare in metal–organic coordination polymers.

Insights on Adsorption Characterization of Metal-Organic Frameworks: A Benchmark Study on the Novel soc-MOF

In order to explore the potential of novel open metal organic frameworks (MOFs) with soc topology for gas storage applications, we performed a systematic physical adsorption study with Hydrogen, Methane and Carbon dioxide as adsorptives over a wide range of temperatures (77–323 K) and pressures (0–5 MPa) by using a volumetric low pressure adsorption analyzer equipped with a cryostat, and a high pressure gravimetric system. The advanced interpretation of our systematic adsorption data in combination with the results from a comprehensive structural and surface characterization allows one assessing the potential of these novel MOFs for gas storage and separation applications.

Design of two 3D homochiral Co(II) metal–organic open frameworks by layered-pillar strategy: structure and properties

Two 3D homochiral metal–organic open frameworks were designed and fabricated in a layered-pillar fashion. They show considerable hydrogen storage property with a fairly high affinity to H2 and prove to be homochiral prous ferromagnet.