Formation of a Syndiotactic Organic Polymer Inside a MOF by a [2+2] Photo‐Polymerization Reaction

Getting suitable crystals for single‐crystal X‐ray crystallographic analysis still remains an art. Obtaining single crystals of metal–organic frameworks (MOFs) containing organic polymers poses even greater challenges. Here we demonstrate the formation of a syndiotactic organic polymer ligand inside a MOF by quantitative [2+2] photopolymerization reaction in a single‐crystal‐to‐single‐crystal manner. The spacer ligands with trans,trans,trans‐conformation in the pillared‐layer MOF with guest water molecules in the channels, undergo pedal motion to trans,cis,trans‐conformation prior to [2+2] photo‐cycloaddition reaction and yield single crystals of MOF containing two‐dimensional coordination polymers fused with the organic polymer ligands. We also show that the organic polymer in the single crystals can be depolymerized reversibly by cleaving the cyclobutane rings upon heating. These MOFs also show interesting photoluminescent properties and sensing of small organic molecules.     

polyMOFs: A Class of Interconvertible Polymer‐Metal‐Organic‐Framework Hybrid Materials

Preparation of porous materials from one‐dimensional polymers is challenging because the packing of polymer chains results in a dense, non‐porous arrangement. Herein, we demonstrate the remarkable adaptation of an amorphous, linear, non‐porous, flexible organic polymer into a three‐dimensional, highly porous, crystalline solid, as the organic component of a metal–organic framework (MOF). A polymer with aromatic dicarboxylic acids in the backbone functioned as a polymer ligand upon annealing with Zn^II, generating a polymer–metal–organic framework (polyMOF). These materials break the dogma that MOFs must be prepared from small, rigid ligands. Similarly, polyMOFs contradict conventional polymer chemistry by demonstrating that linear and amorphous polymers can be readily coaxed into a highly crystalline, porous, three‐dimensional structure by coordination chemistry.     

A Dual‐Ligand Porous Coordination Polymer Chemiresistor with Modulated Conductivity and Porosity

Single‐ligand‐based electronically conductive porous coordination polymers/metal–organic frameworks (EC‐PCPs/MOFs) fail to meet the requirements of numerous electronic applications owing to their limited tunability in terms of both conductivity and topology. In this study, a new 2D π‐conjugated EC‐MOF containing copper units with mixed trigonal ligands was developed: Cu₃(HHTP)(THQ) (HHTP=2,3,6,7,10,11‐hexahydrotriphenylene, THQ=tetrahydroxy‐1,4‐quinone). The modulated conductivity (σ≈2.53×10^?5 S cm^?1 with an activation energy of 0.30 eV) and high porosity (ca. 441.2 m² g^?1) of the Cu₃(HHTP)(THQ) semiconductive nanowires provided an appropriate resistance baseline and highly accessible areas for the development of an excellent chemiresistive gas sensor.     

A Tale of Copper Coordination Frameworks: Controlled Single‐Crystal‐to‐Single‐Crystal Transformations and Their Catalytic CH Bond Activation Properties

Metal–organic frameworks (MOFs), as a class of microporous materials with well‐defined channels and rich functionalities, hold great promise for various applications. Yet the formation and crystallization processes of various MOFs with distinct topology, connectivity, and properties remain largely unclear, and the control of such processes is rather challenging. Starting from a 0D Cu coordination polyhedron, MOP‐1, we successfully unfolded it to give a new 1D‐MOF by a single‐crystal‐to‐single‐crystal (SCSC) transformation process at room temperature as confirmed by SXRD. We also monitored the continuous transformation states by FTIR and PXRD. Cu MOFs with 2D and 3D networks were also obtained from this 1D‐MOF by SCSC transformations. Furthermore, Cu MOFs with 0D, 1D, and 3D networks, MOP‐1, 1D‐MOF, and HKUST‐1, show unique performances in the kinetics of the C?H bond catalytic oxidation reaction.     

Nylon–MOF Composites through Postsynthetic Polymerization

Hybridization of metal–organic frameworks (MOFs) and polymers into composites yields materials that display the exceptional properties of MOFs with the robustness of polymers. However, the realization of MOF–polymer composites requires efficient dispersion and interactions of MOF particles with polymer matrices, which remains a significant challenge. Herein, we report a simple, scalable, bench‐top approach to covalently tethered nylon–MOF polymer composite materials through an interfacial polymerization technique. The copolymerization of a modified UiO‐66‐NH₂ MOF with a growing polyamide fiber (PA‐66) during an interfacial polymerization gave hybrid materials with up to around 29 weight percent MOF. The covalent hybrid material demonstrated nearly an order of magnitude higher catalytic activity for the breakdown of a chemical warfare simulant (dimethyl‐4‐nitrophenyl phosphate, DMNP) compared to MOFs that are non‐covalently, physically entrapped in nylon, thus highlighting the importance of MOF–polymer hybridization.     

Two‐in‐One: Inherent Anhydrous and Water‐Assisted High Proton Conduction in a 3D Metal–Organic Framework

The development of solid‐state proton‐conducting materials with high conductivity that operate under both anhydrous and humidified conditions is currently of great interest in fuel‐cell technology. A 3D metal–organic framework (MOF) with acid–base pairs in its coordination space that efficiently conducts protons under both anhydrous and humid conditions has now been developed. The anhydrous proton conductivity for this MOF is among the highest values that have been reported for MOF materials, whereas its water‐assisted proton conductivity is comparable to that of the organic polymer Nafion, which is currently used for practical applications. Unlike other MOFs, which conduct protons either under anhydrous or humid conditions, this compound should represent a considerable advance in the development of efficient solid‐state proton‐conducting materials that work under both anhydrous and humid conditions.     

Synergistically Directed Assembly of Aromatic Stacks Based Metal‐Organic Frameworks by Donor‐Acceptor and Coordination Interactions

A synergistically directed assembly approach to distinctive metal‐organic frameworks utilizing both donor‐acceptor (D‐A) interaction from aromatic systems and coordination interactions is presented. Based on such an approach, the coronene‐tpt (tpt = 2,4,6‐tri(4‐pyridyl)‐1,3,5‐triazine) stacks based coronene‐MOF‐1 — 4 have been successfully fabricated. Their structural discrepancies with coronene‐ absent control products, 1′ — 4′ , illustrate clearly the significance of coronene‐tpt based D‐A interactions in these architectures. All these coronene‐MOFs contain varied coronene‐tpt stacks as organic secondary building blocks (SBUs), which are closely interrelated with the coordination based framework structures. Moreover, porous coronene‐MOF‐1 and ‐2 exhibit high physicochemical stability and significant light hydrocarbons storage and separation performances.     

Hydrangea‐like NiCo‐based Bimetal‐organic Frameworks,and their Pros and Cons as Supercapacitor Electrode Materials in Aqueous Electrolytes

Hydrangea‐like NiCo‐based bimetal‐organic frameworks (NiCo‐MOF) are synthesized in DMF‐EtOH solution via a solvothermal method, using 4,4′‐biphenyldicarboxylic acid as a ligand. NiCo‐MOF having a highest capacity of 1056.6 F · g^–1 at 0.5 A · g^–1 and 457.7 F · g^–1 even at 10 A · g^–1 is achieved at a Ni/Co/BPDC molar ratio of 1:1:1, a temperature of 170 °C and a reaction time of 12 hours. It exhibits secondary 3D microsphere structures assembled by primary 2D nanosheet structures, good crystalline structure and good thermal stability below 350 °C in air. All the electrochemical data show that NiCo‐MOF has the pros and cons as supercapacitor electrode materials in aqueous electrolytes. On the one hand, NiCo‐MOF has a high capacity even at a high current density, low internal resistance, charge‐transfer resistance and ion diffusion impendence, owing to the ordered coordination structure, 2D nanosheet structure and 3D assembled microsphere structure of NiCo‐MOF. On the other hand, the cycling stability and rate capability are not ideal enough due to the hydrolysis of coordination bonds in aqueous electrolytes, especially, in alkaline solution. The good dispersion and high electrochemical activity of metal ions bring a high capacity for NiCo‐MOF, but they result in the poor stability of NiCo‐MOF. In the future work, finding a suitable organic electrolyte is an effective way to enhance the cycling stability of NiCo‐MOF as well as deriving more stable skeleton materials from NiCo‐MOF.     

2D Coordination Polymer with a 1D Carboxylate‐Copper Chain Based on Rare Icosanuclear and Tetranuclear Clusters

The 2D coordination polymer {[Cu₃₂( pa )₂₄(μ₂‐OH)₈(μ₃‐OH)₈( bibp )₈] · (CH₃OH)₃(H₂O)₅}_∞ was prepared by the solvothermal reaction of Cu(NO₃)₂ · 3H₂O with phthalic acid (H₂ pa ) and 4, 4′‐bis(imidazol‐1‐yl)biphenyl ( bibp ). The Cu^II ions show five different kinds of coordination environments, which are all connected by the pa ^2– ion into an interesting 1D carboxylate‐copper chain with rare icosacopper and tetracopper clusters. The 1D chain is further bridged by the bibp ligand to form a 2D layer, which could be viewed as an unprecedented (4, 4) lattice based on rectangular and butterfly‐shaped tetracopper clusters with the ratio of 2:6. The magnetic properties were studied, and the results show antiferromagnetic interaction in the complicated 1D chain.     

A 3D Aluminoborate Open Framework Interpenetrated by 2D Zinc–Amine Coordination‐Polymer Networks in Its 11‐Ring Channels

A new inorganic–organic hybrid solid, [Zn(dap)₂][AlB₅O₁₀], combining the structural features of 3D open‐framework inorganic solids and 2D metal–organic coordination polymers has been synthesized under solvothermal conditions. The compound displays extensive luminescence and moderate second‐harmonic‐generation efficiency.     

Multielectron‐Transfer‐based Rechargeable Energy Storage of Two‐Dimensional Coordination Frameworks with Non‐Innocent Ligands

The metallically conductive bis(diimino)nickel framework (NiDI), an emerging class of metal–organic framework (MOF) analogues consisting of two‐dimensional (2D) coordination networks, was found to have an energy storage principle that uses both cation and anion insertion. This principle gives high energy led by a multielectron transfer reaction: Its specific capacity is one of the highest among MOF‐based cathode materials in rechargeable energy storage devices, with stable cycling performance up to 300 cycles. This mechanism was studied by a wide spectrum of electrochemical techniques combined with density‐functional calculations. This work shows that a rationally designed material system of conductive 2D coordination networks can be promising electrode materials for many types of energy devices.     

Muconato‐bridged Manganese Coordination Polymer exhibiting rare Distorted‐trigonal Prismatic Coordination Arrangement

Novel poly[Mn(H₂O)(dmb)(muco)] ( 1 ) (H₂muco = trans,trans‐muconic acid; dmb = 5,5′‐dimethyl‐2,2′‐bipyridine) was obtained by self‐assembly, one‐pot, solution reaction. 1 crystallizes in a monoclinic system with P2₁ space group and forms an infinite one‐dimensional (1D) polymer. Remarkably, the six‐coordinate Mn^II display a rare distorted trigonal prismatic configuration. This unusual coordination arrangement appears to be acquired due to the supramolecular interactions of the polymeric structure of 1 , mainly throughout hydrogen bonding, giving rise to a 2D framework. Magnetic properties measurements reveal that 1 possesses weak antiferromagnetic interactions with θ_(C–W) = –1.0 K and J = 458 cm^–1.     

A Novel 2‐D Copper(II) Complex with Paddlewheel‐like Building Block

By reaction of CuCl₂ with H₄btc (H₄btc = 1,2,4,5‐benzenetetracarboxylic acid) in mixed N,N‐dimethylformamide (DMF) and methanol solution, a new two‐dimensional (2‐D) copper(II) complex [Cu(btc)_0.5(DMF)]_n ( 1 ) based on the paddlewheel‐like [Cu₂(‐CO₂)₄(DMF)₂] building blocks has been synthesized, which is different from those previous Cu‐btc(II) coordination polymers obtained in water medium. Four carboxylate groups of (btc)^4? anion in 1 consistently exhibit bidentate bridging coordination mode, affording an unusual coordination mode of (btc)^4?. Further analysis indicates C–H···π weak interactions are the primary driving forces to assemble the 2‐D layers of 1 into a 3‐D packing structure.     

Spray‐Coating of Catalytically Active MOF–Polythiourea through Postsynthetic Polymerization

A UiO‐66‐NCS MOF was formed by postsynthetic modification of UiO‐66‐NH₂. The UiO‐66‐NCS MOFs displays a circa 20‐fold increase in activity against the chemical warfare agent simulant dimethyl‐4‐nitrophenyl phosphate (DMNP) compared to UiO‐66‐NH₂, making it the most active MOF materials using a validated high‐throughput screening. The ?NCS functional groups provide reactive handles for postsynthetic polymerization of the MOFs into functional materials. These MOFs can be tethered to amine‐terminated polypropylene polymers (Jeffamines) through a facile room‐temperature synthesis with no byproducts. The MOFs are then crosslinked into a MOF–polythiourea (MOF–PTU) composite material, maintaining the catalytic properties of the MOF and the flexibility of the polymer. This MOF–PTU hybrid material was spray‐coated onto Nyco textile fibers, displaying excellent adhesion to the fiber surface. The spray‐coated fibers were screened for the degradation of DMNP and showed durable catalytic reactivity.     

Solvo‐thermal Preparation of One Novel Cadmium(II) Coordination Polymer with 1‐(4‐Aminobenzyl)‐1,2,4‐Triazole and Bi‐functional Photo‐Luminescent Sensing for Acetone and Dichromate

In this work a 1,2,4‐triazole derivative 1‐(4‐aminobenzyl)‐1,2,4‐triazole (abtz) was utilized, one new cadmium(II) coordination polymer, namely [Cd(abtz)I₂]_n ( 1 ) was prepared through the powerful solvo‐thermal synthetic strategy. In compound 1 , the abtz building blocks are interlinked through the central Cd^II ions forming the two‐dimensional (2D) layer coordination framework. Powder X‐ray diffraction (PXRD) characterization also reveals that we have prepared the pure phases of coordination polymer 1 . Optical properties have been determined, which can behave the excellent photo‐luminescent emission of coordination polymer 1 . Photo‐luminescent experiment also reveals that coordination polymer 1 can behave the highly sensitive detection for acetone molecules with high K_sv value (K_sv = 4.12 ×10⁴ L · mol^–1) in the recyclable detection fashion. Additionally, coordination polymer 1 also can behave the highly sensitive detection for pollutant dichromate with excellent quenching efficiency K_sv (K_sv = 2.12 × 10⁴ L · mol^–1) and low detection limit [38 × 10^–3 mM (S/N = 3)]. UV/Vis, photo‐luminescent lifetime, and PXRD patterns also have been determined to analyze the detection mechanism.     

Controlled Synthesis of Porous Coordination‐Polymer Microcrystals with Definite Morphologies and Sizes under Mild Conditions

Herein, we report a facile and convenient method for the synthesis of the porous coordination polymer MOF‐14 [Cu₃(BTB)₂] (H₃BTB=4,4′,4′′‐benzene‐1,3,5‐triyl‐tribenzoic acid) as microcrystals with definite shapes and crystal facets controlled by the reaction medium at room temperature. The amount of sodium acetate added to the reaction system plays a crucial role in the shape evolution of MOF‐14 from rhombic dodecahedrons to truncated rhombic dodecahedrons and cubes with truncated edges and then to cubes. The addition of a base could accelerate the formation rate of crystal growth and increase the supersaturation of crystal growth, thus resulting in the formation of MOF‐14 cube crystals with high‐energy crystal facets. The morphological evolution was also observed for HKUST‐1 [Cu₃(BTC)₂] (H₃BTC=1,3,5‐benzenetricarbocylic acid) from octahedrons to cubes, thus verifying the probable mechanism of the morphological transformation. The gas‐adsorption properties of MOF‐14 with different shapes were studied and reveal that the porous coordination‐polymer microcrystals display excellent and morphology‐dependent sorption properties.     

Versatile Tailoring of Paddle‐Wheel ZnII Metal–Organic Frameworks through Single‐Crystal‐to‐Single‐Crystal Transformations

A new tetracarboxylate ligand having short and long arms formed 2D layer Zn^II coordination polymer 1 with paddle‐wheel secondary building units under solvothermal conditions. The framework undergoes solvent‐specific single crystal‐to‐single crystal (SC‐SC) transmetalation to produce 1_Cu . With a sterically encumbered dipyridyl linker, the same ligand forms non‐interpenetrated, 3D, pillared‐layer Zn^II metal–organic framework (MOF) 2 , which takes part in SC‐SC linker‐exchange reactions to produce three daughter frameworks. The parent MOF 2 shows preferential incorporation of the longest linker in competitive linker‐exchange experiments. All the 3D MOFs undergo complete SC‐SC transmetalation with Cu^II, whereby metal exchange in different solvents and monitoring of X‐ray structures revealed that bulky solvated metal ions lead to ordering of the shortest linker in the framework, which confirms that the solvated metal ions enter through the pores along the linker axis.     

Aryl acrylate based high‐internal‐phase emulsions as precursors for reactive monolithic polymer supports

Water‐in‐oil high‐internal‐phase emulsions (HIPEs), containing 4‐nitrophenyl acrylate and 2,4,6‐trichlorophenyl acrylate as reactive monomers, were prepared and polymerized, and highly porous monolithic materials resulted. The novel materials were studied by combustion analysis, Fourier transform infrared spectroscopy scanning electron microscopy, mercury porosimetry, and N₂ adsorption/desorption analysis. With both esters, cellular macroporous monolithic polymers were obtained; the use of 4‐nitrophenyl acrylate resulted in a cellular material with void diameters between 3 and 7 μm and approximately 3‐μm interconnects, whereas the use of 2,4,6‐trichlorophenyl acrylate yielded a foam with void diameters between 2 and 5 μm, most interconnects being around 1 μm. The resulting monoliths proved to be very reactive toward nucleophiles, and possibilities of functionalizing the novel polymer supports were demonstrated via reactions with amines bearing additional functional groups and via the synthesis of an acid chloride derivative. Tris(hydroxymethyl)aminomethane and tris(2‐aminoethyl)amine derivatives were obtained. The hydrolysis of 4‐nitrophenylacrylate removed the nitrophenyl group, yielding a monolithic acrylic acid polymer. Furthermore, functionalization to immobilized acid chloride was performed very efficiently, with more than 95% of the acid groups reacting. The measurement of the nitrogen content in 4‐nitrophenyl acrylate poly(HIPE)s after various times of hydrolysis showed the influence of the total pore volume of the monolithic polymers on the velocity of the reaction, which was faster with the more porous polymer. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 296–303, 2005     

High Resolution Scanning Tunneling Microscopy of a 1D Coordination Polymer with Imidazole‐Based N,N,O Ligands on HOPG

Novel κ³‐N,N,O ligands tend to form 1D coordination polymer strands. Deposition of 1D structures on highly oriented pyrolytic graphite (HOPG) was achieved from diluted solutions and polymer strands have been studied on HOPG by AFM/STM. Single strands were mapped by STM and their electronic properties were subsequently characterized by current imaging tunneling spectroscopy (CITS). Periodic density functional calculations simulating a polymer strand deposited on a HOPG surface are in agreement with the zig‐zag structure indicated by experimental findings. Both the observed periodicity and the Zn–Zn distances can be reproduced in the simulations. Van der Waals interactions were found to play a major role for the geometry of the isolated polymer strand, for the adsorption geometry on HOPG, as well as for the adsorption energy.     

A Three‐Dimensional Porous Organic Semiconductor Based on Fully sp2‐Hybridized Graphitic Polymer

Dimensionality plays an important role in the charge transport properties of organic semiconductors. Although three‐dimensional semiconductors, such as Si, are common in inorganic materials, imparting electrical conductivity to covalent three‐dimensional organic polymers is challenging. Now, the synthesis of a three‐dimensional π‐conjugated porous organic polymer (3D p‐POP) using catalyst‐free Diels–Alder cycloaddition polymerization followed by acid‐promoted aromatization is presented. With a surface area of 801 m² g^?1, full conjugation throughout the carbon backbone, and an electrical conductivity of 6(2)×10^?4 S cm^?1 upon treatment with I₂ vapor, the 3D p‐POP is the first member of a new class of permanently porous 3D organic semiconductors.