Isomorphous Metal-organic Frameworks Research Articles

Two AIE-Ligand-Based 2-D Luminescent Metal-Organic Frameworks as Fe3+ Sensors.

The design and synthesis of high-performance sensors are very important but remain great challenges. In this work, a new aggregation-induced-emission (AIE) molecule 4,4'-(((9H-fluoren-9-ylidene)methylene)bis(4,1-phenylene))dipyridine (L) was successfully synthesized and first developed as a functional ligand to construct two isomorphic metal-organic frameworks (MOFs) [M(L)(OBBA)]n [M2+ = Cd2+ (1), Co2+ (2); H2OBBA = 4,4'-oxybisbenzoic acid]. They adopt [M2(COO)4] flywheel clusters, OBBA2- bridges, and terminal L ligands as building units to form isomorphic 2-D networks with Lewis base active cites (uncoordinated pyridyl N). Both 1 and 2 exhibit excellent water, pH, and thermal stabilities and extremely efficient Fe3+ sensing abilities in the water environment. The quenching constants and detection limits reach the best levels reported so far. The sensing mechanism of 1 and 2 toward Fe3+ is studied in depth, and the difference in their sensing performance is also explained.

Construction of new multi-cage-based MOFs using flexible triangular ligands for efficient gas adsorption and separation

Designing efficient absorbents for multi-gas adsorption and separation is of critical significance for gas purification in chemical engineering. Multi-cage structure enables sufficient interactions with multi-gas through the restriction effects, which is promising to achieve high multi-gas separation performance. In this work, two isomorphic metal-organic frameworks (MOFs) (SNNU-275, M ​= ​Cu, and SNNU-276, M ​= ​Ni) with three types of cages (octahedral M6L4, cuboctahedral M12L8, and M12L24), which are (3,4)-linked three-dimensional microporous structures formed by stacking M6(TPA)4 octahedral coordination molecular cages are synthesized by using tri(4-pyridyl) amine (TPA) ligands and Cu/Ni metals. TPA is selected as the central ligand due to the small size and flexible characteristics. The synthesized SNNU-275 exhibits a good combination of high C2H2/CO2 adsorption selectivity (28), while high C2H2 uptake capacity (68 ​cm3 ​g−1) is achieved for SNNU-276 with high stability. In addition, SNNU-275 and SNNU-276 exhibited superior uptake capacity for benzene and water vapor. Overall, this work not only provides new triangular tripyridine-based MOFs with multiple cages for efficient gas purification, but also demonstrated that the multicage engineering is a promising strategy for the multicomponent gas separation.

In(III) Metal–Organic Framework Incorporated with Enzyme-Mimicking Nickel Bis(dithiolene) Ligand for Highly Selective CO2 Electroreduction

Inspired by the exciting physical/chemical properties in metal-organic frameworks (MOFs) of the redox-active tetrathiafulvalene (TTF) ligands, nickel bis(dithiolene-dibenzoic acid), [Ni(C2S2(C6H4COOH)2)2], has been designed and developed as an inorganic analogue of the corresponding TTF-type donors (such as tetrathiafulvalene-tetrabenzoate, TTFTB), where a metal site (Ni) replaces the central C═C bond. In this work, [Ni(C2S2(C6H4COOH)2)2] and In3+ have been successfully assembled into a three-dimensional MOF, (Me2NH2+){InIII-[Ni(C2S2(C6H4COO)2)2]}·3DMF·1.5H2O (1, DMF = N,N-dimethylformamide), with satisfying chemical and thermal stabilities. With the combination of reversible redox activity and unsaturated metal sites originated from [Ni(C2S2(C6H4COOH)2)2], 1 showed a significantly enhanced performance in electrocatalytic CO2 reduction compared with the isomorphic MOF, (Me2NH2+)[InIII-(TTFTB)]·0.7C2H5OH·DMF (2, with TTFTB ligand). More importantly, by mimicking the active [NiS4] sites of formate dehydrogenase and CO-dehydrogenase, a prominently higher conversion rate and Faradaic efficiency (FE), with FEHCOO- increasing from 54.7% to 89.6% (at -1.3 V vs RHE, jHCOO- = 36.0 mA cm-2), were achieved in 1. Mechanistic investigations further confirm that [NiS4] can serve as a CO2 binding site and efficient catalytic center. This unprecedented effect of redox-active nickel dithiolene-based MOF catalysts on the performance of electroreduction of CO2 provides an important strategy for designing stable and efficient crystalline enzyme-mimicking catalysts for the conversion of CO2 into high-value chemical stocks.

Two new coordination polymers with tetracarboxylate as photocatalysts for dye degradation

The removal of dyestuff wastewater is an important issue and project of environmental protection. Photocatalytic method is one of the most feasible strategies. Metal-organic frameworks (MOFs) have been extensively covered by in photocatalytic removal and degradation of dye molecules. Herein, we designed and prepared two isomorphic MOFs, including [Mn(L)0.5(H2O)] (1) and [Cd(L)0.5(H2O)] (2) (H4L = 1, 1′: 4′, 1′': 4′', 1′''-quterphenyl-2, 5, 2′'', 5′''-tetracarboxylic acid) to investigate and explore their photocatalytic activities. These metal centers are coordinated by four carboxylates to shape 1D assembled architecture with a paddlewheel unit, which was expanded and extended to provide a 3D supramolecular structure through the link of L. The results manifested that 1 and 2 could take as better candidate to catalyze the dye Rhodamine B (RhB) under UV irradiation. Compound 1 shows the good catalytic performance than that of compound 2. The degraded intermediates were traced using LC–MS technology and the conceivable ways of decomposition for the Rh B were supposed.

A serial of 2D Co‐Zn isomorphous metal–organic frameworks for photodegradation and luminescent detection properties

A series of 2D isomorphous MOFs [M (HBTC)(BMIOPE)·DMF·H2O]n (M = Zn (1), Zn0.7Co0.3 (2), Zn0.5Co0.5 (3), Zn0.3Co0.7 (4), Co (5), H3BTC = 1,3,5‐benzenetricarboxylic acid, BMIOPE = 4,4′‐bis(2‐methylimidazol‐1‐yl)diphenyl ether) were synthesized to investigate the correction between the center metal ions and the photocatalytic behaviors. The photocatalytic results show that with the increase of Co2+ content, the photodegradation properties are continuously improved from 1 to 5, which fully indicate that only changing metal ions could regulate the photodegradation properties. In detail, 1 is an inactive photocatalyst to degrade methylene blue (MB), while 5 exhibits preeminent photocatalytic properties under visible light irradiation. Moreover, 1 shows good selective sensing toward Fe3+, Cr3+, UO22+, CrO42− and Cr2O72− ions in aqueous solution. To the best of our knowledge, 1 is the first MOF example for the optical detection of Fe3+, Cr3+, UO22+, CrO42− and Cr2O72− ions in aqueous solution.

Solvatochromism and Selective Sorption of Volatile Organic Solvents in Pyridylbenzoate Metal-Organic Frameworks

Using cobalt(II) as a metal centre with different solvent systems afforded the crystallization of isomorphous metal-organic frameworks {[Co(34pba)(44pba)]·DMF}n (1) and {[Co(34pba)(44pba)]·(C3H6O)}n (2) from mixed 4-(4-pyridyl)benzoate (44pba) and 3-(4-pyridyl)benzoate (34pba) ligands. Zinc(II) under the same reaction conditions that led to the formation of 1 formed an isostructural {[Zn(34pba)(44pba)]·DMF}n framework (3). Crystal structures of all three MOFs were elucidated and their thermal stabilities were determined. The frameworks of 1, 2, and 3 were activated under vacuum to form the desolvated forms 1d, 2d, and 3d, respectively. PXRD results showed that 1d and 2d were identical, consequently, 1d and 3d were then investigated for sorption of volatile organic compounds (VOCs) containing either chloro or amine moieties. Thermogravimetric analysis (TGA) and nuclear magnetic resonance (NMR) were used to determine the sorption capacity and selectivity for the VOCs. Some sorption products of 1d with amines became amorphous, but the crystalline framework could be recovered on desorption of the amines. Investigation of the sorption of water (H2O) and ammonia (NH3) in 1d gave rise to new phases identifiable by means of a colour change (solvatochromism). The kinetics of desorption of DMF, water and ammonia from frameworks 1d and 3d were studied using non-isothermal TGA. Activation energies for both cobalt(II) and zinc(II) frameworks are in the order NH3 < H2O < DMF, with values for the 1d analogue always higher than those for 3d.

Isomorphous Lanthanide Metal–Organic Frameworks Based on Biphenyldicarboxylate: Synthesis, Structure, and Photoluminescent Properties

We report the structures of six anionic, isomorphous metal–organic frameworks [Ln(bpdc)2–][NH2(CH3)2+], where Ln = La, Ce, Nd, Eu, Gd, Er, and bpdc2– = biphenyl-4,4′-dicarboxylate = –O2C(C6H4)2CO2–...

Isomorphic MOF-derived porous carbon materials as electrochemical sensor for simultaneous determination of hydroquinone and catechol

It is needed to speed up the development of a sensitive detection platform for simultaneous determination of dihydroxybenzene isomers with harmful properties. Here, two isomorphic Metal–organic frameworks (MOFs) [Zn(Trz)(R-BDC)1/2] (FJU-40-R, R = H or NH2; Trz = 1,2,4-Triazole; H-BDC = terephthalic acid) were selected to derive two N-doping porous carbon (NPC) materials. Further, a strategy for constructing electrochemical sensors for simultaneous determination of hydroquinone (HQ) and catechol (CT) was proposed by the MOF-derived NPC modifying glass carbon electrode (GCE). It was found that HQ and CT had good responses on NPC-FJU-40-H/GCE, but had no obvious responses on NPC-FJU-40-NH2/GCE. NPC-FJU-40-H/GCE displayed excellent reproducibility, stability, and anti-interference. Under the optimal conditions, the linear ranges of HQ and CT on NPC-FJU-40-H/GCE were 1 ~ 70 µmol L−1 and 1 ~ 100 µmol L−1 with the detection limits of 0.18 µmol L−1 for HQ and 0.31 µmol L−1 for CT, respectively. Although the porous carbon (PC) derived from MOFs has been applied in electrochemical sensing, the effect of the ligand functional groups of isomorphic MOFs on the electrochemical properties of the derived PC materials is still lack of relevant research. Our research provided an idea that the electrocatalysis properties of MOF-derived porous carbon materials could be tuned by changing the functional groups in ligands of isomorphic MOFs in electrochemical sensing field. A feasible strategy was proposed by changing the ligands of the two isomorphic MOFs (FJU-40-H and FJU-40-NH2) to tune the electrocatalysis properties of MOF-derived N-doped porous carbon materials for the simultaneous determination of dihydroxybenzene isomer.

Effect of Functional Groups on the Adsorption of Light Hydrocarbons in fmj-type Metal–Organic Frameworks

The functionalized modification of targeted porous metal–organic frameworks (MOFs) is important to improve the adsorption capacity of light hydrocarbon gases. Five isomorphic MOFs with different functional groups (F, Cl, NH2, CH3, and OCH3) are successfully synthesized by systematic functional modification of UMCM-151. By studying the adsorption properties of C2 and C3 hydrocarbons (C2H2, C2H4, C2H6, C3H6, and C3H8), it is found that the electron-withdrawing group functional UMCM-151-F and UMCM-151-Cl exhibit strong affinity for C2H2 (98.71 cm3 g–1 for UMCM-151-F and 90.29 cm3 g–1 for UMCM-151-Cl), while the electron-donating group functional UMCM-151-NH2, UMCM-151-CH3, and UMCM-151-OCH3 have strong affinity for C2H4 (97.89 cm3 g–1 for UMCM-151-NH2, 90.22 cm3 g–1 for UMCM-151-CH3 and 94.13 cm3 g–1 for UMCM-151-OCH3). The differences in affinity of electron effects for light hydrocarbon provide an experimental basis for porous MOFs to improve their light hydrocarbon storage capacity.

Thermal Conversion of MOF@MOF: Synthesis of an N-Doped Carbon Material with Excellent ORR Performance.

Here we propose a new strategy in which two isomorphic metal-organic frameworks (MOFs) [FJU-40-H (a) and FJU-40-NH2 (b)] are used to construct the core-shell material MOF@MOF. This strategy based on nitrogen doping and specific surface has resulted in an N-doped porous carbon (NPC) material in a one-step thermal treatment in N2 atmosphere; this material displays high catalytic activity for the oxygen reduction reaction (ORR). The materials were analyzed by SEM, XPS, Raman, specific surface area, pore size distribution and electrochemical measurements. It was found that NPC derived from the core-shell MOF@MOF can provide excellent catalytic ORR performance exceeding that of the single MOF. The onset potential is NPC-b@a-4h (-0.068 V)>NPC-a@b-4h (-0.075 V)>NPC-a-4h (-0.109 V)>NPC-b-4h (-0.113 V). Moreover, the results also show that the performance of NPC-b@a (n=4.15) is better than that of NPC-a@b (n=3.32), which means the different nitrogen content of ligands inside and outside of the core affects the ORR properties.

Metal–Organic Frameworks with Extended Viologen Units: Metal-Dependent Photochromism, Photomodulable Fluorescence, and Sensing Properties

The photoresponsive viologen unit has been widely used to endow metal–organic materials with photochromic and other photomodulable properties. Herein we report the first examples of the metal–organic materials functionalized by extended viologens (ExVs), of general formula [ML]·2H2O (M = Zn for 1, M = Mn for 2, M = Co for 3, and L is a tetracarboxylate ligand with the p-phenylene-extended viologen spacer). Of the three isomorphic metal–organic frameworks, only 1 is photochromic owing to formation of extended viologen radicals through photoinduced electron transfer (PET). The incapability of 2 and 3 to undergo photochromism can be ascribed to longer intermolecular donor–acceptor contacts, emphasizing the sensitivity of solid-state PET to structural changes. 1 also shows strong fluorescence owing to interligand charge transfer, and the fluorescence can be reversibly modulated and switched on/off in the photochromic process. Furthermore, 1 shows excellent hydrolytic stability and can be used as a sensitive, ...

Six Isomorphous Window-Beam MOFs: Explore the Effects of Metal Ions on MOF-Derived Carbon for Supercapacitors.

Six isomorphous metal-organic frameworks (MOFs) with a 3D window-beam architecture have been synthesized from solvothermal reactions, and are named Zn, Cd, Ni, Co, Mn and Cu-MOF, respectively. The series of MOFs was utilized as precursors to synthesize MOF-derived carbon with different morphologies. Zn and Cd-MOFs lead to the derivation of porous carbons (PCs), which exhibit remarkable BET specific surface areas. For derivates of Ni, Co and Mn-MOFs, graphitized carbons (GCs) show some carbon graphitization, but their BET specific surface areas are relatively small. C-Cu has the smallest BET specific surface area, and there is no carbon graphitization. Therefore, the metal ion of the parent MOF exerts a crucial effect on the preparation of MOF-derived carbon, such as the pore-forming effect of Zn and Cd species, and catalytic graphitization of Ni, Co, and Mn species. The capacitances of MOF-derived carbon follow the sequence of PCs>GCs>C-Cu, which reveals that the specific surface area plays a dominant role in the capacitive performance of electrical double layer capacitors (EDLCs), and that the graphitization could improve the capacitance. Significantly, PC-Zn exhibits the best specific capacitance (138 F g-1 at 0.5 Ag-1 ), and excellent life cycle, which can be applied as an electrode material in supercapacitors.

Ni(II)/Zn(II)-triazolate clusters based MOFs constructed from a V-shaped dicarboxylate ligand: Magnetic properties and phosphate sensing

Two isomorphous metal-organic frameworks (MOFs) {[M2(μ3-OH)(trz)(sdba)(H2O)]·3H2O}∞ (M = Ni for 1, Zn for 2, Htrz = 1,2,4-triazole, H2sdba = 4,4′-sulfonyldibenzoate) were obtained under the same reaction condition. Both of complexes present a three dimensional 8-c framework with whc1 topology based on M4-(μ3-OH) units. Moreover, the magnetic properties of 1 and anion sensing of 2 were investigated. The magnetic study show that the domain antiferromagnetic interactions exist in 1. However, complex 2 can be considered as a promising chemical sensor for detecting PO43¯by means of fluorescence enhancement among various anions in aqueous solutions.

Random mixed-metal Co1-xNix single-chain magnets with simultaneous azide, carboxylate and tetrazolate bridges.

This paper reports the magnetic properties of a series of isomorphous metal-organic frameworks based on random heterometallic Co1-xNix chains with simultaneous azide, carboxylate and tetrazolate bridges. All the mixed-metal compounds show intrachain FM interactions, field-induced metamagnetism, and SCM-like slow magnetic relaxation. These behaviors are quite different from the parent Co(ii) and Ni(ii) materials, and even a small amount of metal replacement can cause significant magnetic changes. The static properties such as AF ordering, metamagnetic critical field and the hysteresis parameters show complicated composition dependence. Most interestingly, the mixed-metal systems can show a higher blocking temperature than the Co(ii) compound, suggesting that the randomly distributed metal ions have synergistic effects on slow relaxation of magnetization. This is phenomenologically associated with the competitive effects of Δτ and τo.

Crystal structure, magnetism, and luminescent properties of two isostructural pcu MOFs based on a triangular ligand

Two isomorphous metal-organic frameworks, {[M(TIPA) (btec)½]H2O}n, [M = Co (1) or Zn (2)] were synthesized hydrothermally based on a semi-rigid N-center triangular ligand TIPA, where TIPA = tris(4-(1H-imidazol-1-yl)-phenyl)amine, H4btec = 1,2,4,5-benzenetetracarboxylic acid. Single crystal structural analyses show that complexes 1 and 2 are isostructural and both feature a twofold interpenetrated pcu topology. In 1 and 2, the btec4− ligand adopting μ2-η2:η1 and μ1-η1:η0 coordination modes connect adjacent dinuclear Co/Zn units to form a 1D straight polymeric chain. Then these chains arranged in parallel/parallel fashion were further extended to a 3D network by exo-tridentate ligand TIPA with μ2-κ2N:N′ coordination mode. The magnetic property of 1 and the luminescent property of 2 were investigated. Furthermore, the structure and spectroscopic property of 2 were further investigated by DFT and TD-DFT calculations.

New Zinc functionalized metal organic Framework for selective sensing of chromate ion

A modified metal organic framework have been prepared by the solvothermal process of 2-(4-carboxyphenyl)-1, 3-dioxoisoindoline-5-carboxylic acid with Zn(OAc)2.2H2O. The framework has a PtS − type net. The obtained porous material has been characterized by X-ray diffraction, Scanning electron microscopy, UV–vis spectroscopy, FTIR spectroscopy and BET surface area analysis. The BET surface area was 757m2/g−1. The synthesized MOF exhibits reasonably good fluorescence characteristics. The luminescent studies indicates that the obtained Zn-MOF could be an efficient material for selectively sensing anion especially CrO42−. The mechanism of sensing is also studied in detail. The Zn-MOF senses the anion without altering its structural integrity. This post-synthesis route can be used for synthesis of isomorphous metal–organic frameworks that cannot be obtained by direct synthesis.

Flexible Bipyridinium Constructed Porous Frameworks with Superior Broad-Spectrum Adsorption toward Organic Pollutants

A flexible bipyridinium ligand has been introduced into a series of isomorphous metal–organic frameworks to yield porous materials with subtriangular 1D channel and cagelike pore space. The introduction of bipyridinium molecules into the porous frameworks leads to the formation of 1D channel with positively charged surface, which shows high affinities to polar molecules such as methanol, ethanol, and water vapor. Additionally, the bipyridinium molecules possess conjugated pyridyl rings connected by carbon–carbon single bonds, which can rotate freely to keep twisted or large-conjugated planar configuration by controlling coordination condition during the self-assembly process. The cagelike pore space formed by these flexible bipyridinium molecules contains arene–arene stacked pyridyl rings and thus renders abundant π–π interaction sites for efficient adsorption of benzene and toluene molecules, and is also large enough to accommodate cyclohexane molecules. These metal–organic frameworks show efficient adso...

Paddle Wheel Based Triazolyl Isophthalate MOFs: Impact of Linker Modification on Crystal Structure and Gas Sorption Properties.

Syntheses and comprehensive characterization of two closely related series of isomorphous metal-organic frameworks (MOFs) based on triazolyl isophthalate linkers with the general formula ∞(3)[M2(R(1)-R(2)-trz-ia)2] (M = Cu, Zn) are presented. Using solvothermal synthesis and synthesis of microcrystalline materials on the gram scale by refluxing a solution of the starting materials, 11 MOFs are readily available for a systematic investigation of structure-property relationships. The networks of the two series are assigned to rutile (rtl) (1-4) and α-PbO2 (apo) (5-9) topology, respectively. Due to the orientation of the triazole substituents toward the cavities, both the pore volume and the pore diameter can be adjusted by choice of the alkyl substituents. Compounds 1-9 exhibit pronounced microporosity with calculated porosities of 31-53% and show thermal stability up to 390 °C as confirmed by simultaneous thermal analysis. Systematic investigation of adsorption properties by CO2 (298 K) and N2 (77 K) adsorption studies reveal remarkable network flexibility induced by alkyl substituents on the linker. Fine-tuning of the gate opening pressure and of the hysteresis shape is possible by adjusting the substitution pattern and by choice of the metal ion.

Two novel metal-organic frameworks based on linear dicarboxylic acid and 5-(4-pyridyl)tetrazole

Two isomorphic metal-organic frameworks, [Co2(4-Ptz)2(BDC)(DMA)]n (1) and [Co2(4-Ptz)2(2-NH2-BDC)(DMA)]n (2) (4-Ptz=5-(4-Pyridyl)tetrazole, H2BDC=Terephthalic Acid, 2-NH2-H2BDC=2-Aminoterephthalic Acid, DMA=N,N-dimethylacetamide), have been successfully constructed through solvothermal reactions. Crystallographic data analysis reveals a binuclear Co(II) cluster-based structure for 1 and 2, which were constructed by bridging two neighboring Co(II) ions with teterazole rings of 4-Ptz ligand together with one DMA oxygen atom. Simplifying Co2 cluster as a 6-connecting node, complexes 1 and 2 reveal bcu-6 net. The CO2 adsorption isotherms measurement at 273K manifests higher adsorption quantities for 2 (33.8cm3/g) than 1 (26.2cm3/g), which was attributed to the introduction of NH2-group in 2.

A series of isomorphous Metal-Organic Frameworks with rtl topology – Metal distribution and tunable sorption capacity via substitution of metal ions

The formation and analysis of ten microporous triazolyl isophthalate based MOFs, including nine isomorphous and one isostructural compound is presented. The compounds 1M–3M with the general formula [M(R1-R2-trz-ia)]∞3 ·x H2O (M2+ = Co2+, Cu2+, Zn2+, Cd2+; R1 = H, Me; R2 = 2py, 2pym, prz (2py = 2-pyridinyle; 2pym = 2-pyrimidinyle; prz = pyrazinyle)) crystallize with rtl topology. They are available as single crystals and also easily accessible in a multi-gram scale via refluxing the metal salts and the protonated ligands in a solvent. Their isomorphous structures facilitate the synthesis of heteronuclear MOFs; in case of 2M, Co2+ ions could be gradually substituted by Cu2+ ions. The Co2+:Cu2+ ratios were determined by ICP-OES spectroscopy, the distribution of Co2+ and Cu2+ in the crystalline samples are investigated by SEM-EDX analysis leading to the conclusions that Cu2+ is more favorably incorporated into the framework compared to Co2+ and, moreover, that the distribution of the two metal ions between the crystals and within the crystals is inhomogeneous if the crystals were grown slowly. The various compositions of the heteronuclear materials lead to different colors and the sorption properties for CO2 and N2 are dependent on the integrated metal ions.