Dynamic Calcium Metal–Organic Framework Acts as a Selective Organic Solvent Sponge

Herein, we present a Ca‐based metal–organic framework named AEPF‐1, which is an active and selective catalyst in olefin hydrogenation reactions. AEPF‐1 exhibits a phase transition upon desorption of guest molecules. This structural transformation takes place by a crystal to crystal transformation accompanied by the loss of single‐crystal integrity. Powder diffraction methods and computational studies were applied to determine the structure of the guest‐free phase. This work also presents data on the exceptional adsorption behavior of this material, which is shown to be capable of separating polar from nonpolar organic solvents, and is a good candidate for selective solvent adsorption under mild conditions.     

Irreversible Amide‐Linked Covalent Organic Framework for Selective and Ultrafast Gold Recovery

Design of stable adsorbents for selective gold recovery with large capacity and fast adsorption kinetics is of great challenge, but significant for the economy and the environment. Herein, we show the design and preparation of an irreversible amide‐linked covalent organic framework (COF) JNU‐1 via a building block exchange strategy for efficient recovery of gold. JNU‐1 was synthesized through the exchange of 4,4′‐biphenyldicarboxaldehyde (BA) in mother COF TzBA consisting of 4,4′,4′′‐(1,3,5‐triazine‐2,4,6‐triyl)trianiline (Tz) and BA with terephthaloyl chloride. The irreversible amide linked JNU‐1 gave good stability, unprecedented fast kinetics, excellent selectivity and outstanding adsorption capacity for gold recovery. X‐ray photoelectron spectroscopy along with thermodynamic study and quantum mechanics calculation reveals that the excellent performance of JNU‐1 for gold recovery results from the formation of hydrogen bonds C(N)?H???Cl and coordinate interaction of O and Au. The rational design of irreversible bonds as both inherent linkage and functional groups in COFs is a promising way to prepare stable COFs for diverse applications.     

Efficient Fe‐Co‐N‐C Electrocatalyst Towards Oxygen Reduction Derived from a Cationic CoII‐based Metal–Organic Framework Modified by Anion‐Exchange with Potassium Ferricyanide

Fe‐Co‐N‐C electrocatalysts have proven superior to their counterparts (e.g. Fe‐N‐C or Co‐N‐C) for the oxygen reduction reaction (ORR). Herein, we report on a unique strategy to prepare Fe‐Co‐N‐C?x (x refers to the pyrolysis temperature) electrocatalysts which involves anion‐exchange of [Fe(CN)₆]^3? into a cationic Co^II‐based metal‐organic framework precursor prior to heat treatment. Fe‐Co‐N‐C‐900 exhibits an optimal ORR catalytic performance in an alkaline electrolyte with an onset potential (E_onset: 0.97 V) and half‐wave potential (E_1/2: 0.86 V) comparable to that of commercial Pt/C (E_onset=1.02 V; E_1/2=0.88 V), which outperforms the corresponding Co‐N‐C‐900 sample (E_onset=0.92 V; E_1/2=0.84 V) derived from the same MOF precursor without anion‐exchange modification. This is the first example of Fe‐Co‐N‐C electrocatalysts fabricated from a cationic Co^II‐based MOF precursor that dopes the Fe element via anion‐exchange, and our current work provides a new entrance towards MOF‐derived transition‐metal (e.g. Fe or Co) and nitrogen‐codoped carbon electrocatalysts with excellent ORR activity.     

Metal‐Ion Metathesis and Properties of Triarylboron‐Functionalized Metal–Organic Frameworks

An anionic metal–organic framework, H₃[(Mn₄Cl)₃ L ₈]?30 H₂O?2.5 DMF?5 Diox ( UPC‐15 ), was successfully prepared by the reaction of MnCl₂ with tris(p‐carboxylic acid)tridurylborane (H₃ L ) under solvothermal conditions. UPC‐15 with wide‐open pores (～18.8 Å) is constructed by packing of octahedral and cuboctahedral cages, and exhibits high gas‐sorption capabilities. Notably, UPC‐15 shows selective adsorption of cationic dyes due to the anion framework. Moreover, the catalytic and magnetic properties were investigated, and UPC‐15 can highly catalyze the cyanosilylation of aromatic aldehydes. UPC‐15 exhibits the exchange of metal ions from Mn to Cu in a single‐crystal‐to‐single‐crystal manner to generate UPC‐16 , which could not be obtained by the direct solvothermal reaction of CuCl₂ and H₃ L. UPC‐16 exhibits similar properties for gas sorption, dye separation, and catalytic activity. However, the magnetic behaviors for UPC‐15 and UPC‐16 are distinct due to the metal‐specific properties. Below 47 K, UPC‐15 exhibits a ferromagnetic coupling but UPC‐16 shows a dominant antiferromagnetic behavior.     

Syntheses,Structures and Sorption Properties of Three Isoreticular Trinuclear Indium‐Based Amide‐Functionalized Metal–Organic Frameworks

Amide‐functionalized metal–organic frameworks (AFMOFs) as a subclass of MOF materials have received great interest recently because of their intriguing structures and diverse potential applications. In this work, solvothermal reactions between indium nitrate and two mixed‐linkers afforded two new isoreticular 8‐connected trinuclear indium‐based AFMOFs of [(In₃O)(OH)(L2)₂(IN)₂]?(solv)_x ( 2‐In ) and [(In₃O)(OH)(L2)₂(AIN)₂]?(solv)_x ( NH₂‐2‐In ) (H₂L2=4,4′‐(carbonylimino)dibenzoic acid and HIN=isonicotinic acid or HAIN=3‐aminoisonicotinic acid), respectively. Moreover, by means of reticular chemistry, an extended network of [(In₃O)(OH)(L3)₂(PB)₂]?(solv)_x (3‐In) (H₂L3=4,4′‐(terephthaloylbis(azanediyl))dibenzoic acid, HPB=4‐(4‐pyridyl)benzoic acid) was also successfully realized after prolongation of the former dicarboxylate linker and HIN, resulting in a truly 8‐connected isoreticular AFMOF platform. These frameworks were structurally determined by single‐crystal X‐ray diffraction (SCXRD). Sorption studies further demonstrate that 2‐In and NH₂‐2‐In exhibit not only high surface areas and pore volumes but also relatively high carbon capture capabilities (the CO₂ uptakes reach 60.0 and 75.5 cm³ g^?1 at 298 K and 760 torr, respectively) due to the presences of amide and/or amine functional groups. The selectivity of CO₂/N₂ and CO₂/CH₄ calculated by IAST are 10.18 and 12.43, 4.20 and 4.23 for 2‐In and NH₂‐2‐In , respectively, which were additionally evaluated by mixed‐gases dynamic breakthrough experiments. In addition, high‐pressure gas sorption measurements show that both materials could take up moderate amounts of natural gas.     

Guest‐Responsive Function of a Dynamic Metal–Organic Framework with a π Lewis Acidic Pore Surface

A 3D dynamic coordination framework with an electron‐deficient pore surface has been synthesized by using Zn^II (having a variable coordination number) and a predesigned flexible π‐electron‐deficient core‐based ligand, exhibiting chemical separations based on pore surface functionalization (π Lewis acidic pore surfaces and open metal sites) and framework flexibility, giving rise to a unique smart guest‐responsive material.     

Solvent‐Dependent Cation Exchange in Metal–Organic Frameworks

We investigated which factors govern the critical steps of cation exchange in metal–organic frameworks by studying the effect of various solvents on the insertion of Ni²⁺ into MOF‐5 and Co²⁺ into MFU‐4l. After plotting the extent of cation insertion versus different solvent parameters, trends emerge that offer insight into the exchange processes for both systems. This approach establishes a method for understanding critical aspects of cation exchange in different MOFs and other materials.     

New Mechanistic Insight into Stepwise Metal‐Center Exchange in a Metal–Organic Framework Based on Asymmetric Zn4 Clusters

Herein, a mechanism of stepwise metal‐center exchange for a specific metal–organic framework, namely, [Zn₄(dcpp)₂(DMF)₃(H₂O)₂]_n (H₄dcpp=4,5‐bis(4′‐carboxylphenyl)phthalic acid), is disclosed for the first time. The coordination stabilities between the central metal atoms and the ligands as well as the coordination geometry are considered to be dominant factors in this stepwise exchange mechanism. A new magnetic analytical method and a theoretical model confirmed that the exchange mechanism is reasonable. When the metathesis reaction occurs between Cu^II ions and framework Zn^II ions, the magnetic exchange interaction of each pair of Cu^II centers gradually strengthens with increasing amount of framework Cu^II ions. By analyzing the changes of coupling constants in the Cu‐exchanged products, it was deduced that Zn4 and Zn3 are initially replaced, and then Zn1 and Zn2 are replaced later. The theoretical calculation further verified that Zn4 is replaced first, Zn3 next, then Zn1 and Zn2 last, and the coordination stability dominates the Cu/Zn exchange process. For the Ni/Zn and Co/Zn exchange processes, besides the coordination stability, the preferred coordination geometry was also considered in the stepwise‐exchange behavior. As Ni^II and Co^II ions especially favor octahedral coordination geometry in oxygen‐ligand fields, Ni^II ions and Co^II ions could only selectively exchange with the octahedral Zn^II ions, as was also confirmed by the experimental results. The stepwise metal‐exchange process occurs in a single crystal‐to‐single crystal fashion.     

Framework Cationization by Preemptive Coordination of Open Metal Sites for Anion‐Exchange Encapsulation of Nucleotides and Coenzymes

Cationic frameworks can selectively trap anions through ion exchange, and have applications in ion chromatography and drug delivery. However, cationic frameworks are much rarer than anionic or neutral ones. Herein, we propose a concept, preemptive coordination (PC), for targeting positively charged metal–organic frameworks (P‐MOFs). PC refers to proactive blocking of metal coordination sites to preclude their occupation by neutralizing ligands such as OH^?. We use 20 MOFs to show that this PC concept is an effective approach for developing P‐MOFs whose high stability, porosity, and anion‐exchange capability allow immobilization of anionic nucleotides and coenzymes, in addition to charge‐ and size‐selective capture or separation of organic dyes. The CO₂ and C₂H₂ uptake capacity of 117.9 cm³ g^?1 and 148.5 cm³ g^?1, respectively, at 273 K and 1 atm, is exceptionally high among cationic framework materials.     

Selective and Sensitive Aqueous‐Phase Detection of 2,4,6‐Trinitrophenol (TNP) by an Amine‐Functionalized Metal–Organic Framework

Highly selective and sensitive aqueous‐phase detection of nitro explosive 2,4,6‐trinitrophenol (TNP) by a hydrolytically stable 3D luminescent metal–organic framework is reported. The compound senses TNP exclusively even in the presence of other nitro‐compounds, with an unprecedented sensitivity in the MOF regime by means of strategic deployment of its free amine groups. Such an accurate sensing of TNP, widely recognized as a harmful environmental contaminant in water media, establishes this new strategic approach as one of the frontiers to tackle present‐day security and health concerns in a real‐time scenario.     

A Spiderweb‐Like Metal–Organic Framework Multifunctional Foam

Processing metal–organic frameworks (MOFs) into hierarchical macroscopic materials can greatly extend their practical applications. However, current strategies suffer from severe aggregation of MOFs and limited tuning of the hierarchical porous network. Now, a strategy is presented that can simultaneously tune the MOF loading, composition, spatial distribution, and confinement within various bio‐originated macroscopic supports, as well as control the accessibility, robustness, and formability of the support itself. This method enables the good dispersion of individual MOF nanoparticles on a spiderweb‐like network within each macrovoid even at high loadings (up to 86 wt %), ensuring the foam pores are highly accessible for excellent adsorption and catalytic capacity. Additionally, this approach allows the direct pre‐incorporation of other functional components into the framework. This strategy provides precise control over the properties of both the hierarchical support and MOF.     

A Calixarene‐Based Metal–Organic Framework for Highly Selective NO2 Detection

A calixarene‐based metal–organic framework (Zr‐cal, [Zr₆O₄(OH)₄(FA)₆]₂(cal)₃], FA=formate, cal=1,3‐alt‐25,26,27,28‐tetrakis[(carboxy)methoxy]calixarene) was synthesized and characterized by single‐crystal X‐ray diffraction. The three‐dimensional framework is a 4,6‐connected network of gar topology and exhibits two equal but nonintersecting three‐dimensional pore systems. It has a specific BET surface area of 670 m² g^?1, and the calixarene cavities are accessible through the pore systems. The exposed calixarenes can be used for the visual detection and encapsulation of NO₂ through the formation of deeply colored charge–transfer complexes inside the MOF. The highly selective complexation was analyzed by UV/Vis and IR spectroscopy, and the stability of the material was confirmed by powder X‐ray diffraction and ¹H NMR spectroscopy. Finally, the MOF was used as a sensor material in a home‐made sensor cell and showed high sensitivity for NO₂.     

Design and Synthesis of a Water‐Stable Anionic Uranium‐Based Metal–Organic Framework (MOF) with Ultra Large Pores

Ionic metal–organic frameworks (MOFs) are a subclass of porous materials that have the ability to incorporate different charged species in confined nanospace by ion‐exchange. To date, however, very few examples combining mesoporosity and water stability have been realized in ionic MOF chemistry. Herein, we report the rational design and synthesis of a water‐stable anionic mesoporous MOF based on uranium and featuring tbo‐type topology. The resulting tbo MOF exhibits exceptionally large open cavities (3.9 nm) exceeding those of all known anionic MOFs. By supercritical CO₂ activation, a record‐high Brunauer‐Emmett‐Teller (BET) surface area (2100 m² g^?1) for actinide‐based MOFs has been obtained. Most importantly, however, this new uranium‐based MOF is water‐stable and able to absorb positively charged ions selectively over negatively charged ones, enabling the efficient separation of organic dyes and biomolecules.     

Switch‐On Fluorescence of a Perylene‐Dye‐Functionalized Metal–Organic Framework through Postsynthetic Modification

A perylene dye was introduced directly as a linker into a metal–organic framework (MOF) during synthesis. Depending on the dye concentration in the MOF synthesis mixture, different fluorescent materials were generated. The successful incorporation of the dye was proven by using ¹³C and ²⁷Al MAS NMR spectroscopy, by solution NMR spectroscopy after digestion of the MOF sample, and by synthesizing a reference dye without connecting groups, which could coordinate on the metal–oxo cluster inside the MOF. Fluorescence quenching effects of the MOF linker, 2‐aminoterephthalate, were observed and overcome by postsynthetic modification with acetic anhydride. We show here for the first time that amino groups, which can be used as anchoring points for covalent attachment of other molecules, are responsible for fluorescence quenching. Thus, a very promising strategy to implement switchable fluorescence into MOFs is shown here.     

Chiral Metal–Organic Framework Hollow Nanospheres for High‐Efficiency Enantiomer Separation

Chiral ZIF‐8 hollow nanospheres with d ‐histidine as part of chiral ligands (denoted as H‐d ‐his‐ZIF‐8) were prepared for separation of (±)‐amine acids. Compared to bulk d ‐his‐ZIF‐8 without a hollow cavity, the prepared H‐d ‐his‐ZIF‐8 showed 15 times higher separation capacity and higher ee values of 90.5 % for alanine, 95.2 % for glutamic acid and 92.6 % for lysine, respectively.     

Preparation and Gas Separation Properties of Metal‐Organic Framework Membranes

Continuous and intergrown metal‐organic framework (MOF) membranes, MIL‐100(In) (MIL represents Materials Institute Lavoisier), were prepared directly on porous anodic alumina oxide (AAO) membranes using an in situ crystallization method. The pore surface of MIL‐100(In) is conferred with polarity due to the presence of the 1, 3,5‐benzenetricarboxylic acid. The thickness of MIL‐100(In) membranes was tuned by varying the reactant concentration of indium chloride and 1, 3,5‐benzenetricarboxylic acid. Single gas permeation measurements on this MOF membrane indicate the large permeances of 0.90 × 10^–6 and 0.81 × 10^–6 mol · m^–2·s^–1·Pa^–1 for CO₂ and CH₄, and relatively high ideal selective factors of 3.75 and 3.38 for CO₂/N₂ and CH₄/N₂, respectively.     

Site‐Selective Synthesis of Janus‐type Metal‐Organic Framework Composites

Herein, bipolar electrochemistry is applied in a straightforward way to the site‐selective in situ synthesis of metal–organic framework (MOF) structures, which have attracted tremendous interest in recent years because of their significant application potential, ranging from sensing to gas storage and catalysis. The novelty of the presented work is that the deposit can be intentionally confined to a defined area of a substrate without using masks or templates. The intrinsic site‐selectivity of bipolar electrochemistry makes it a method of choice to generate, in a highly controlled way, hybrid particles that may have different functionalities combined on the same particle. The wireless nature of electrodeposition allows the potential for mass production of such Janus‐type objects.