Inclusion of thiazyl radicals in porous crystalline materials

The incorporation of benzodithiazolyl (BDTA) and methylbenzodithiazolyl (MBDTA) radicals into porous hybrid frameworks via gas phase diffusion revealed that inclusion appeared selective for the MIL53(Al) framework against a range of other potential hosts. Both PXRD and EPR studies are consistent with retention of a π*-π* dimer motif for BDTA in MIL53(Al)@BDTA whereas MBDTA in MIL53(Al)@MBDTA appears to be monomeric. The guests are readily released by the addition of solvent (CH(2)Cl(2)).     

Advanced functional properties in nanoporous coordination framework materials

Coordination framework materials display a rich array of host-guest properties and are notable amongst porous media for their extreme chemical versatility. This article highlights a number of areas where specific function has been incorporated into these framework host lattices.     

Guest shape-responsive fitting of porous coordination polymer with shrinkable framework

In situ synchrotron X-ray powder diffraction patterns of porous coordination polymers [[Cu(2)(pzdc)(2)(bpy)].G] have been measured (pzdc = pyrazine-2,3-dicarboxylate, bpy = 4,4'-bipyridine) (where G = H(2)O for CPL-2 superset H(2)()O, G = benzene for CPL-2 superset benzene, and G = void for the apohost). The structures of apohost and CPL-2 superset benzene were determined from Rietveld analysis. Adsorption of benzene in the channels induced a remarkable contraction in the crystal (b axis; 6.8%, volume; 4.9%), although the channels were occupied by the benzene molecules. This crystal transformation provides a new pore structure that is well suited for benzene molecules, and we denote it as a "shape-responsive fitting" transformation. This type of pore gives rise to a new guideline: frameworks can be composed of flexible motifs that are linked via strong bond and/or stiff motifs that are connected via weaker bonds.     

Three-dimensional electron diffraction for porous crystalline materials: structural determination and beyond

Porous crystalline materials such as zeolites, metal–organic frameworks (MOFs) and covalent organic frameworks (COFs) have attracted great interest due to their well-defined pore structures in molecular dimensions. Knowing the atomic structures of porous materials is crucial for understanding their properties and exploring their applications. Many porous materials are synthesized as polycrystalline powders, which are too small for structure determination by X-ray diffraction. Three-dimensional electron diffraction (3DED) has been developed for studying such materials. In this Minireview, we summarize the recent developments of 3DED methods and demonstrate how 3DED revolutionized structural analysis of zeolites, MOFs, and COFs. Zeolites and MOFs whose structures remained unknown for decades could be solved. New approaches for design and targeted synthesis of novel zeolites could be developed. Moreover, we discuss the advances of structural analysis by 3DED in revealing the unique structural features and properties, such as heteroatom distributions, mixed-metal frameworks, structural flexibility, guest–host interactions, and structure transformation.

Three-dimensional electron diffraction is a powerful tool for accurate structure determination of zeolite, MOF, and COF crystals that are too small for X-ray diffraction. By revealing the structural details, the properties of the materials can be understood, and new materials and applications can be designed.     

Supramolecular isomerism of a metallocyclic dipyridyldiamide ligand metal halide system generating isostructural (Hg, Co and Zn) porous materials

We show how crystallisation of supramolecular isomers of a dynamic coordination system generates a series of isostructural porous materials. These mercury, cobalt and zinc metallocyclic materials show permanent porosity and exhibit single-crystal-to-single-crystal transformations.     

Ligand flexibility and framework rearrangement in a new family of porous metal-organic frameworks

Ligand flexibility permits framework rearrangement upon evacuation and gas uptake in a new family of porous MOFs.     

Intramolecular rearrangement of the imine-amide ligand within the nickel coordination sphere affected by carbon monoxide

The interactions of the nickel imine-amide allyl complex 1 with carbon monoxide and unsaturated hydrocarbons have been studied. It is shown that this complex reacts readily with carbon monoxide to form the nickel(0) diimine carbonyl complex [(2-(1-propenyl)-[1,10]phenanthroline)Ni(CO)₂] 2. During the process the ligand undergoes a deep transformation within the nickel coordination sphere. Specifically, the nickel-nitrogen σ-bond turns to an N-donor bond with aromatization of a ring in the nitrogen-containing ligand. This novel heteroaromatic ligand 2-(1-propenyl)-[1,10]phenanthroline has been isolated; the nickel(0) diimine carbonyl complex 2 has been studied with X-ray diffraction method. The comparative spectral studies of complexes 1, 2, and 2-(1-propenyl)-[1,10]phenanthroline have been carried out with UV/vis, IR-FT, and 2D NMR spectroscopy. It has been shown that the planar 16-electron nickel(II) imine-amide allyl complex 1 is indifferent to olefins and acetylenes. Based on the NMR data, this fact can be explained by the inability of the π-δ rearrangement into 1.     

Soft secondary building unit: dynamic bond rearrangement on multinuclear core of porous coordination polymers in gas media

A new synthetic approach to prepare flexible porous coordination polymers (PCPs) by the use of soft secondary building units (SBUs) which can undergo multiple reversible metal-ligand bonds breaking is reported. We have prepared a zinc paddle-wheel-based two-fold interpenetrated PCP, {[Zn(2)(tp)(2)(L(2))]·2.5DMF·0.5water}(n) (2a, H(2)tp = terephthanlic acid; L(2) = 2,3-difluoro-1,4-bis(4-pyridyl)benzene), showing dynamic structural transformations upon the removal and rebinding of guest molecules. The X-ray structures at different degrees of desolvation indicate the highly flexible nature of the framework. The framework deformations involve slippage of the layers and movement of the two interpenetrated frameworks with respect to each other. Interestingly, the coordination geometry of a zinc paddle-wheel unit (one of the popular SBUs) is considerably changed by bond breaking between zinc and oxygen atoms during the drying process. Two zinc atoms in the dried form 2d reside in a distorted tetrahedral geometry. Compound 2d has no void volume and favors the uptake of O(2) over Ar and N(2) at 77 K. The O(2) and Ar adsorption isotherms of 2d show gate-opening-type adsorption behaviors corroborating the structure determination. The CO(2) adsorption isotherm at 195 K exhibits multiple steps originating from the flexibility of the framework. The structural transformations of the zinc clusters in the framework upon sorption of guest molecules are also characterized by Raman spectroscopy in which the characteristic bands corresponding to ν(sym)(COO(-)) vibration were used.     

Glucoamylase covalently coupled to porous glass

Glucoamylase (EC 3.2.1.3) was immobilized to alkylamine porous glass with glutaraldehyde. The choice and pretreatment of carrier and conditions for immobilization have been investigated. The immobilized enzyme contained about 4.0–8.0% protein and its activity was about 1000–1700 U/g. Some characteristics of the immobilized enzyme and the native enzyme have been comparatively investigated. The optimum temperature and the pH stability of the preparation were almost identical to the native one. However, the optimum pH of bound glucoamylase shifted 1.3 pH units toward the alkaline side compared to the native one. The Michaelis constant(K _m ) of bound glucoamylase for soluble starch was about four times higher than that of the native enzyme, whileK _m values for maltose approached those of the native material. At 45‡C the half-life of IMG was 104 days under operational conditions. Alkaline protease, α-amylase, asparaginase, and penicillin acylase were also chemically coupled to porous glass by the same method and high relative activities were obtained.     

Quest for highly porous metal-metalloporphyrin framework based upon a custom-designed octatopic porphyrin ligand

A porous metal-metalloporphyrin framework, MMPF-2, has been constructed from a custom-designed octatopic porphyrin ligand, tetrakis(3,5-dicarboxyphenyl)porphine, that links a distorted cobalt trigonal prism secondary building unit. MMPF-2 possesses permanent microporosity with the highest surface area of 2037 m(2) g(-1) among reported porphyrin-based MOFs, and demonstrates a high uptake capacity of 170 cm(3) g(-1) CO(2) at 273 K and 1 bar.     

Temperature-dependent supramolecular stereoisomerism in porous copper coordination networks based on a designed carboxylate ligand

Two novel temperature-controlled supramolecular stereoisomers of porous copper coordination networks have been synthesized and characterized.     

Three-dimensional porous coordination polymer functionalized with amide groups based on tridentate ligand: selective sorption and catalysis

To create a functionalized porous compound, amide group is used in porous framework to produce attractive interactions with guest molecules. To avoid hydrogen-bond formation between these amide groups our strategy was to build a three-dimensional (3D) coordination network using a tridentate amide ligand as the three-connector part. From Cd(NO3)2.4H2O and a three-connector ligand with amide groups a 3D porous coordination polymer (PCP) based on octahedral Cd(II) centers, {[Cd(4-btapa)2(NO3)2].6H2O.2DMF}n (1a), was obtained (4-btapa = 1,3,5-benzene tricarboxylic acid tris[N-(4-pyridyl)amide]). The amide groups, which act as guest interaction sites, occur on the surfaces of channels with dimensions of 4.7 x 7.3 A2. X-ray powder diffraction measurements showed that the desolvated compound (1b) selectively includes guests with a concurrent flexible structural (amorphous-to-crystalline) transformation. The highly ordered amide groups in the channels play an important role in the interaction with the guest molecules, which was confirmed by thermogravimetric analysis, adsorption/desorption measurements, and X-ray crystallography. We also performed a Knoevenagel condensation reaction catalyzed by 1a to demonstrate its selective heterogeneous base catalytic properties, which depend on the sizes of the reactants. The solid catalyst 1a maintains its crystalline framework after the reaction and is easily recycled.     

Corrections to coupled Hartree–Fock theory: the rearrangement effect

In this communication we discuss a method of incorporating corrections to the coupled Hartree–Fock (CHF ) formalism by introducing the so-called “rearrangement effect.” In this we take account of the relaxation of the core orbitals when excitations from a starting Hartree–Fock wave function occur. The magnitude of this correction numerically is found to be quite significant for the polarizabilities of two-electron atomic systems, results for which are reported.     

Extending framework based on the linear coordination polymers: Alternative chains containing lanthanum ion and acrylic acid ligand

One-dimensional alternative chains of two lanthanum complexes: [La(L¹)₃(CH₃OH)(H₂O)₂]·5H₂O (L¹=anion of α-cyano-4-hydroxycinnamic acid ) 1 and [La(L²)₃(H₂O)₂]·3H₂O (L²=anion of trans-3-(4-methyl-benzoyl)-acrylic acid) 2 were synthesized and structurally characterized by single-crystal X-ray diffraction, element analysis, IR and thermogravimetric analysis. The crystal structure data are as follows for 1: C₃₁H₃₆LaN₃O₁₇, triclinic, P-1, , , , α=72.7960(10)°, β=83.3820(10)°, γ=67.1650(10)º, Z=2, R₁=0.0377, wR₂=0.0746; for 2: C₃₃H₃₇LaO₁₄, triclinic, P-1, , , , α=81.145(2)°, β=87.591(2)°, γ=67.345(5)°, Z=2, R₁=0.0869, wR₂=0.220. 1 is a rare example of the alternative chain constructed by syn-syn and anti-syn coordination mode of carboxylato ligand arranged along the chain alternatively. La(III) ions in 2 are linked by two η³-O bridges and four bridges (two η²-O and two η³-O) alternatively. Both of the linear coordination polymers grow into two- and three-dimensional networks by packing through extending hydrogen-bond network directed by ligands.     

Optimizing luminescence sensitivity and moisture stability of porous coordination frameworks by varying ligand side groups

Hydrophobic ethyl, butyl or hexyl groups were introduced into the dicarboxylate ligand in the fluorescent porous coordination framework [Zn_2(fda)_2(bpy)](LMOF-202, H_2fda=9H-fluorene-2,7-dicarboxylic acid, bpy=4,4′-bipyridine) for improving water stability and tuning oxygen sensitivity. The long hexyl groups gave satisfactory water stability but its oxygen sensitivity is low(70.8% fluorescence quenched at 1 bar O_2(1 bar=105 Pa)). In contrast, the shorter side groups gave high oxygen sensitivity(93.9% fluorescence quenched at 1 bar O_2) and low water stability. The derivation of the Stern-Volmer curves of the O_2 luminescence quenching data from the linear form can be used for detecting trace impurities in the luminescent framework, being much more sensitive than conventional methods such as powder X-ray diffraction. Mixing the ethyl and hexyl groups in the solid-solution manner brought high oxygen sensitivity(96.4% fluorescence quenched at 1 bar O_2) and high water stability simultaneously in the same coordination framework.     

Functional materials: from hard to soft porous frameworks

This Review aims to give an overview of recent research in the area of porous, organic-inorganic and purely organic, functional materials. Possibilities for introducing organic groups that exhibit chemical and/or physical functions into porous materials will be described, with a focus on the incorporation of such functional groups as a supporting part of the pore walls. The number of organic groups in the network can be increased such that porous, purely organic materials are obtained.