Zeolitic Boron Imidazolate Frameworks

B‐hive? A family of crystalline materials analogous to porous AlPO₄ but based on boron imidazolate frameworks (BIFs) can be formed by the crosslinking of various presynthesized boron imidazolates with monovalent cations (Li⁺ and Cu⁺, see picture). This synthetic method is capable of generating a large variety of open frameworks, ranging from the four‐connected zeolitic sodalite type to the three‐connected chiral (10,3)‐a type.

     

Alkali Metal Cation (K+, Cs+) Induced Dissolution/Reorganization of Porous Metal Carboxylate Coordination Networks in Water

Reversible structural transformations of porous metal–organic coordination networks based on Co or Ni and the benzene‐1,2,4,5‐tetracarboxylate tetraanion among 3D (4,8)‐connected nets and a 1D zigzag chain structure occur by an unexpected dissolution/reorganization process induced by alkali metal cations (K⁺, Cs⁺) in aqueous solution (see scheme).

     

An Unusual Porous Metal–Organic Framework that Demonstrates the Highly Efficient Exchange of Metal Ions and the Reversible Adsorption of Iodine

An exceedingly rare porous metal–organic framework that is based on cadmium ions and multi carboxylate ligands, namely, Na_0.25[(CH₃)₂NH₂]_1.75[Cd(L)₂] ? x solvent ( 1 , H₂L=2‐hydroxymethyl‐4,6‐bi(2′‐methoxyl‐4′‐(2′′‐1′′‐carboxyl)‐ethlene)‐1,3,5‐mesitylene), has been successfully synthesized under solvothermal conditions. Compound 1 exhibits a 2D network that is constructed from left‐ and right‐handed helical chains. Furthermore, neighboring 2D layers are stacked to give a porous motif. Strikingly, compound 1 exhibits the highly efficient exchange of metal ions from the main framework components whilst maintaining the structural integrity and the crystallinity of the network. In addition, Compound 1 also shows outstanding performance in the reversible adsorption of iodine.     

Guest‐Adaptable and Water‐Stable Peptide‐Based Porous Materials by Imidazolate Side Chain Control

The peptide‐based porous 3D framework, ZnCar, has been synthesized from Zn²⁺ and the natural dipeptide carnosine (β‐alanyl‐L ‐histidine). Unlike previous extended peptide networks, the imidazole side chain of the histidine residue is deprotonated to afford Zn–imidazolate chains, with bonding similar to the zeolitic imidazolate framework (ZIF) family of porous materials. ZnCar exhibits permanent microporosity with a surface area of 448 m² g^?1, and its pores are 1D channels with 5 Å openings and a characteristic chiral shape. This compound is chemically stable in organic solvents and water. Single‐crystal X‐ray diffraction (XRD) showed that the ZnCar framework adapts to MeOH and H₂O guests because of the torsional flexibility of the main His‐β‐Ala chain, while retaining the rigidity conferred by the Zn–imidazolate chains. The conformation adopted by carnosine is driven by the H bonds formed both to other dipeptides and to the guests, permitting the observed structural transformations.     

Bottom‐Up Synthesis of Porous Coordination Frameworks: Apical Substitution of a Pentanuclear Tetrahedral Precursor

Top down goes bottom up : A family of microporous interpenetrating diamond frameworks can be constructed from a pentanuclear tetrahedral complex with nitrate groups at the apical positions as an inorganic precursor. A “bottom‐up” methodology was used for substitution of the nitrate groups by linear ditopic carboxylate ligands (see picture). The Langmuir surface area of the resulting frameworks is higher than that of classical zeolites.

     

Catalytic Glucose Isomerization by Porous Coordination Polymers with Open Metal Sites

Highly efficient catalytic isomerization reactions from glucose to fructose in aqueous media using porous coordination polymers (PCPs) or metal–organic frameworks (MOFs) is reported for the first time. The catalytic activity of PCPs functionalized with ? NH₂, ? (CH₃)₂, ? NO₂, and ? SO₃H groups on the pore surface is systematically tested. The catalytic activity can be tuned by the acidity of open metal sites (OMSs) by modifying the organic linkers with the functional groups. As a result, it is demonstrated that MIL‐101 functionalized with ? SO₃H not only shows high conversion of glucose but also selectively produces fructose. Further, catalytic one‐pot conversion of amylose to fructose is achieved, thanks to the high stability of the framework in an acidic solution. These results show that MOF/PCP compounds having OMSs are promising materials for various useful heterogeneous catalytic reactions, in particular in the biomass field.     

Metal–Organic Frameworks for Oxygen Storage

We present a systematic study of metal–organic frameworks (MOFs) for the storage of oxygen. The study starts with grand canonical Monte Carlo simulations on a suite of 10 000 MOFs for the adsorption of oxygen. From these data, the MOFs were down selected to the prime candidates of HKUST‐1 (Cu‐BTC) and NU‐125, both with coordinatively unsaturated Cu sites. Oxygen isotherms up to 30 bar were measured at multiple temperatures to determine the isosteric heat of adsorption for oxygen on each MOF by fitting to a Toth isotherm model. High pressure (up to 140 bar) oxygen isotherms were measured for HKUST‐1 and NU‐125 to determine the working capacity of each MOF. Compared to the zeolite NaX and Norit activated carbon, NU‐125 has an increased excess capacity for oxygen of 237 % and 98 %, respectively. These materials could ultimately prove useful for oxygen storage in medical, military, and aerospace applications.     

Enhancement of H2 Adsorption in Coordination Framework Materials by Use of Ligand Curvature

Curvy ligands for H ₂ storage? Enhancement of H₂ adsorption has been observed in coordination framework materials, an example of which is depicted, by the introduction of phenanthrene and 9,10‐dihydrophenanthrene groups into porous Cu^II–carboxylate framework materials of NbO topology.

     

Symmetry‐Guided Synthesis of Highly Porous Metal–Organic Frameworks with Fluorite Topology

Two stable, non‐interpenetrated MOFs, PCN‐521 and PCN‐523, were synthesized by a symmetry‐guided strategy. Augmentation of the 4‐connected nodes in the fluorite structure with a rigid tetrahedral ligand and substitution of the 8‐connected nodes by the Zr/Hf clusters yielded MOFs with large octahedral interstitial cavities. They are the first examples of Zr/Hf MOFs with tetrahedral linkers. PCN‐521 has the largest BET surface area (3411 m² g^‐1), pore size (20.5×20.5×37.4 Å) and void volume (78.5%) of MOFs formed from tetrahedral ligands. This work not only demonstrates a successful implementation of rational design of MOFs with desired topology, but also provides a systematic way of constructing non‐interpenetrated MOFs with high porosity.     

Electrochemical Synthesis and Catalytic Properties of Encapsulated Metal Clusters within Zeolitic Imidazolate Frameworks

It is very interesting and also a big challenge to encapsulate metal clusters within microporous solids to expand their application diversity. For this target, herein, we present an electrochemical synthesis strategy for the encapsulation of noble metals (Au, Pd, Pt) within ZIF‐8 cavities. In this method, metal precursors of AuCl₄^2?, PtCl₆^2?, and PdCl₄^2? are introduced into ZIF‐8 crystals during the concurrent crystallization of ZIF‐8 at the anode. As a consequence, very small metal clusters with sizes around 1.2 nm are obtained within ZIF‐8 crystals after hydrogen reduction; these clusters exhibit high thermal stability, as evident from the good maintenance of their original sizes after a high‐temperature test. The catalytic properties of the encapsulated metal clusters within ZIF‐8 are evaluated for CO oxidations. Because of the small pore window of ZIF‐8 (0.34 nm) and the confinement effect of small pores, about 80 % of the metal clusters (fractions of 0.74, 0.77, and 0.75 for Au, Pt, and Pd in ZIF‐8, respectively) retain their catalytic activity after exposure to the organosulfur poison thiophene (0.46 nm), which is in contrast to their counterparts (fractions of 0.22, 0.25, and 0.20 for Au, Pt, and Pd on the SiO₂ support). The excellent performances of metal clusters encapsulated within ZIF‐8 crystals give new opportunities for catalytic reactions.     

Controllable Syntheses of Porous Metal–Organic Frameworks: Encapsulation of LnIII Cations for Tunable Luminescence and Small Drug Molecules for Efficient Delivery

Two porous metal–organic frameworks (MOFs), [Zn₃(L)(H₂O)₂] ? 3 DMF ? 7 H₂O ( MOF‐1 ) and [(CH₃)₂NH₂]₆[Ni₃(L)₂(H₂O)₆] ? 3 DMF ? 15 H₂O ( MOF‐2 ), were synthesized solvothermally (H₆L=1,2,3,4,5,6‐hexakis(3‐carboxyphenyloxymethylene)benzene). In MOF ‐ 1 , neighboring Zn^II trimers are linked by the backbones of L ligands to form a fascinating 3D six‐connected framework with the point symbol (4¹².6³) (4¹².6³). In MOF‐2 , eight L ligands bridge six Ni^II atoms to generate a rhombic‐dodecahedral [Ni₆L₈] cage. Each cage is surrounded by eight adjacent ones through sharing of carboxylate groups to yield an unusual 3D porous framework. Encapsulation of Ln^III cations for tunable luminescence and small drug molecules for efficient delivery were investigated in detail for MOF‐1 .     

Carbon Dioxide Sensitivity of Zeolitic Imidazolate Frameworks

Zeolitic imidazolate frameworks of zinc, cobalt, and cadmium, including the framework ZIF‐8 commercially sold as Basolite Z1200, exhibit surprising sensitivity to carbon dioxide under mild conditions. The frameworks chemically react with CO₂ in the presence of moisture or liquid water to form carbonates. This effect, which has been previously not reported in metal–organic framework chemistry, provides an explanation for conflicting reports on ZIF‐8 stability to water and is of outstanding significance for evaluating the potential applications of metal–organic frameworks, especially for CO₂ sequestration.     

Metal–Organic Frameworks Constructed from Versatile [WS4Cux]x−2 Units: Micropores in Highly Interpenetrated Systems

Five metal–organic frameworks (MOFs) formed by [WS₄Cu_x]^x?2 secondary building units (SBUs) and multi‐pyridyl ligands are presented. The [WS₄Cu_x]^x?2 SBUs function as network vertexes showing various geometries and connectivities. Compound 1 contains one‐dimensional channels formed in fourfold interpenetrating diamondoid networks with a hexanuclear [WS₄Cu₅]³⁺ unit as SBU, which shows square‐pyramidal geometry and acts as a tetrahedral node. Compound 2 contains brick‐wall‐like layer also with a hexanuclear [WS₄Cu₅]³⁺ unit as SBU. The [WS₄Cu₅]³⁺ unit in 2 is a new type of [WS₄Cu_x]^x?2 cluster unit in which the five Cu⁺ ions are in one plane with the W atom, forming a planar unit. Compound 3 shows a nanotubular structure with a pentanuclear [WS₄Cu₄]²⁺ unit as SBU, which is saddle‐shaped and acts as a tetrahedral node. Compound 4 contains large cages formed between two interpenetrated (10,3)‐a networks also with a pentanuclear [WS₄Cu₄]²⁺ unit acting as a triangular node. The [WS₄Cu₄]²⁺ unit in 4 is isomeric to that in 3 and first observed in a MOF. Compound 5 contains zigzag chains with a tetrahedral [WS₄Cu₃]⁺ unit as SBU, which acts as a V‐shaped connector. The influence of synthesis conditions including temperature, ligand, anions of Cu^I salts, and the ratio of [NH₄]₂WS₄ to Cu^I salt on the formation of these [WS₄Cu_x]^x?2‐based MOFs were also studied. Porous MOF 3 is stable upon removal and exchange of the solvent guests, and when accommodating different solvent molecules, it exhibits specific colors depending on the polarity of incorporated solvent, that is, it shows a rare solvatochromic effect and has interesting prospects in sensing applications.     

Electrically Conductive Porous Metal–Organic Frameworks

Owing to their outstanding structural, chemical, and functional diversity, metal–organic frameworks (MOFs) have attracted considerable attention over the last two decades in a variety of energy‐related applications. Notably missing among these, until recently, were applications that required good charge transport coexisting with porosity and high surface area. Although most MOFs are electrical insulators, several materials in this class have recently demonstrated excellent electrical conductivity and high charge mobility. Herein we review the synthetic and electronic design strategies that have been employed thus far for producing frameworks with permanent porosity and long‐range charge transport properties. In addition, key experiments that have been employed to demonstrate electrical transport, as well as selected applications for this subclass of MOFs, will be discussed.     

Microporous Metal–Organic Frameworks for Gas Separation

Microporous metal–organic frameworks (MOFs) are comparatively new porous materials. Because the pores within such MOFs can be readily tuned through the interplay of both metal‐containing clusters and organic linkers to induce their size‐selective sieving effects, while the pore surfaces can be straightforwardly functionalized to enforce their different interactions with gas molecules, MOF materials are very promising for gas separation. Furthermore, the high porosities of such materials can enable microporous MOFs with optimized gas separation selectivity and capacity to be targeted. This Focus Review highlights recent significant advances in microporous MOFs for gas separation.     

The First One‐Pot Synthesis of Metal–Organic Frameworks Functionalised with Two Transition‐Metal Complexes

The synthesis of a metal–organic framework (UiO‐67) functionalised simultaneously with two different transition metal complexes (Ir and Pd or Rh) through a one‐pot procedure is reported for the first time. This has been achieved by an iterative modification of the synthesis parameters combined with characterisation of the resulting materials using different techniques, including X‐ray absorption spectroscopy (XAS). The method also allows the first synthesis of UiO‐67 with a very wide range of loadings (from 4 to 43 mol %) of an iridium complex ([IrCp*(bpydc)(Cl)Cl]^2?; bpydc=2,2′‐bipyridine‐5,5′‐dicarboxylate, Cp*=pentamethylcyclopentadienyl) through a pre‐functionalisation methodology.