Structural links beetween zeolite-type and clathrate hydrate-type materials synthesis and crystal structure of [NMe4]16[Si8O20][OH]8.116H2O

A novel crystalline tetramethylammonium silicate hydroxide polyhydrate has been obtained by fractional crystallization at room temperature from a highly alkaline aqueous NMe4OH-SiO2 solution. X-Ray single-crystal studies at 200 K revealed the trigonal crystal system, the unit-cell constants (hexagonal setting) a = 18.126(2) and c = 57.529(9) A°, the space group R3 and Z = 3 formula units of [NMe4]16[Si8O20][OH] 8·116H2O per unit cell. The crystal structure has been determined from 1416 unique Mo-Ka¯ data and refined to R = 0.104. The host-guest compound is of polyhedral clathrate type with a mixed three-dimensional, (mainly) four-connected tetrahedral network composed of oligomeric silicate anions [Si8O20]8-, OH- ions and H2O molecules linked via hydrogen bonds O-H?O. The silicate anions are each built up of eight SiO4 tetrahedra sharing corners to form a cube (double four-ring structure). Cationic guest species NMe4+ are enclosed in large polyhedral cavities [4668], [425865], [51264] and [425867] of the host structure; small [46] cages (i.e. the double-ring anions) and [4356] cages are unoccupied. Each silicate anion is the centre of a specific and probably very stable finite cluster [(NMe4)6(Si8O20)·24H 2O]2-. It is suggested that the polyhydrate may be taken as a crystalline model system for studies on the structures of aqueous tetramethylammonium silicate solutions

Metal-organic framework nanofibers via electrospinning

A hierarchical system of highly porous nanofibers has been prepared by electrospinning MOF (metal-organic framework) nanoparticles with suitable carrier polymers. Nitrogen adsorption proved the MOF nanoparticles to be fully accessible inside the polymeric fibers. © 2011 The Royal Society of Chemistry

In situ static and dynamic light scattering and scanning electron microscopy study on the crystallization of the dense zinc imidazolate framework ZIF-zni

The kinetics and mechanism of crystallization of the dense zinc imidazolate framework with zni topology, from comparatively dilute methanol solutions containing Zn(NO3)·6H2O and imidazole with variation of the zinc-to-imidazole ratio, were followed in situ by time-resolved static and dynamic light scattering. The light scattering data revealed that metastable primary particles of about 100 nm in diameter form rapidly upon mixing the component solutions. After a lag time that is dependent on the imidazole concentration, the primary particles aggregate into secondary particles by a monomer addition mechanism with the primary particles as the monomers. Complementary scanning electron microscopy revealed that further evolution of the secondary particles is a complex process involving polycrystalline intermediates, the non-spherical morphologies of which depend on the initial zinc-to-imidazole ratio. Time and location of the first appearance of crystalline order could so far not be established. The pure-phase ZIF-zni crystals obtained after 240 min are twins. The aspect ratio of the tetragonal crystals can be controlled via the zinc-to-imidazole ratio. © 2011 The Owner Societies

A zeolitic imidazolate framework with conformational variety

We show via structural considerations and DFT calculations that for a zeolitic imidazolate framework (ZIF) with sodalite (SOD) topology, [Zn(dcim)2]-SOD (dcim = 4,5-dichloroimidazolate), structural models of an infinite number of hypothetical conformational polymorphs with distinct linker orientations can be generated, which can be interconverted most likely only via reconstructive structural transitions. The relative total energies suggest that some of those polymorphs might be synthetically accessible. Efforts in that direction led to the synthesis of new trigonal 1 and previously known cubic 2 with improved crystallinity. According to structural analyses based on powder X-ray diffraction (PXRD) methods supported by NMR spectroscopy, 1 is the most stable of the theoretically predicted SOD-type framework conformers (isostructural to ZIF-7), whereas 2, at variance with a recent proposal, is a SOD-type material with a high degree of orientational disorder of the dcim linker units. The statistics of the linker orientations in 2 is close to that in 1, indicating that the disorder in 2 is not random. Rather, crystals of 2 are likely twins consisting of nanoscopic domains of trigonal 1 that are deformed to a cubic metric, with linker disorder located in the domain interfaces. As structural differences appear to be more related to characteristics of real as opposed to ideal crystal structures, we propose to not consider 1 and 2 as true conformational polymorphs. Systematic investigations of solvent mixtures led to the discovery of intermediate materials of 1 and 2. The PXRD patterns and SEM images indicate that they belong to a complete series of structural intermediates. Differences in the Ar adsorption/desorption behaviours reveal that 1, in contrast to 2, is a flexible ZIF framework.DFG/Priority Program/141

Conformationally Unambiguous Spin Labeling for Distance Measurements

Sajid M, Jeschke G, Wiebcke M, Godt A. Conformationally Unambiguous Spin Labeling for Distance Measurements. CHEMISTRY-A EUROPEAN JOURNAL. 2009;15(47):12960-12962

A zeolitic imidazolate framework with conformational variety: conformational polymorphs versus frameworks with static conformational disorder

We show via structural considerations and DFT calculations that for a zeolitic imidazolate framework (ZIF) with sodalite (SOD) topology, [Zn(dcim)2]-SOD (dcim = 4,5-dichloroimidazolate), structural models of an infinite number of hypothetical conformational polymorphs with distinct linker orientations can be generated, which can be interconverted most likely only via reconstructive structural transitions. The relative total energies suggest that some of those polymorphs might be synthetically accessible. Efforts in that direction led to the synthesis of new trigonal 1 and previously known cubic 2 with improved crystallinity. According to structural analyses based on powder X-ray diffraction (PXRD) methods supported by NMR spectroscopy, 1 is the most stable of the theoretically predicted SOD-type framework conformers (isostructural to ZIF-7), whereas 2, at variance with a recent proposal, is a SOD-type material with a high degree of orientational disorder of the dcim linker units. The statistics of the linker orientations in 2 is close to that in 1, indicating that the disorder in 2 is not random. Rather, crystals of 2 are likely twins consisting of nanoscopic domains of trigonal 1 that are deformed to a cubic metric, with linker disorder located in the domain interfaces. As structural differences appear to be more related to characteristics of real as opposed to ideal crystal structures, we propose to not consider 1 and 2 as true conformational polymorphs. Systematic investigations of solvent mixtures led to the discovery of intermediate materials of 1 and 2. The PXRD patterns and SEM images indicate that they belong to a complete series of structural intermediates. Differences in the Ar adsorption/desorption behaviours reveal that 1, in contrast to 2, is a flexible ZIF framework

Insight into Fast Nucleation and Growth of Zeolitic Imidazolate Framework-71 by In Situ Static Light Scattering at Variable Temperature and Kinetic Modeling

Zeolitic imidazolate frameworks (ZIFs) represent an important subclass of porous metal organic frameworks (MOFs). The present work continues a previous study on ZIF-71 nanocrystal formation at room temperature (<i>Cryst. Growth Des.</i> <b>2016</b>, 16, 2002–2010), which proposed a four-step formation process. It introduces a kinetic nucleation and growth model, which satisfactorily reproduces in situ time-resolved static light scattering data measured at room temperature in the previous work and at variable temperatures in the present work. Successful fitting can only be achieved with a precursor reaction being put before particle nucleation. The kinetic analysis provides rate constants for the precursor reaction, for particle nucleation, and for particle growth via monomer addition, and the equilibrium concentration of nonconsumed matter at the end of reaction. The rate constants of the precursor reaction and the nucleation process increase with temperature, which is counterintuitive if compared to classical nucleation theory as it suggests a decrease of the nucleation rate with temperature. In fact, ZIF-71 formation deviates from classical nucleation in that a precursor reaction to produce active “monomers” precedes the formation of amorphous particles that subsequently transform into the crystalline ZIF phase

One-dimensional Zn(II) oligo(phenyleneethynylene)dicarboxylate coordination polymers: Synthesis, crystal structures, thermal and photoluminescent properties

Schaate A, Schulte M, Wiebcke M, Godt A, Behrens P. One-dimensional Zn(II) oligo(phenyleneethynylene)dicarboxylate coordination polymers: Synthesis, crystal structures, thermal and photoluminescent properties. INORGANICA CHIMICA ACTA. 2009;362(10):3600-3606.The rigid, p-conjugated dicarboxylic acid 1,4-bis-[2-(4-carboxyphenyl)ethynyl]-2,5-dihexylbenzene {HO2C[PEP(hexyl)(2)EP]CO2H} has been used to synthesise the new crystalline coordination polymers {Zn(O2C[PEP(hexyl)(2)EP]CO2)(DMF)(2)} (1) and {Zn(O2C[PEP(hexyl)(2)EP]CO2)(DEF)(2)} (2) in N, N-dimethylformamide (DMF) and N, N-diethylformamide (DEF), respectively, under mild conditions. Single-crystal X-ray crystallography revealed that 1 and 2 are isostructural and consist of uncharged zigzag coordination chains in which [Zn(formamide)(2)](2+) fragments are bridged by (O2C[PEP(hexyl)(2)EP] CO2)(2) ligands. The zigzag chains possess different intra-chain Zn center dot center dot center dot Zn center dot center dot center dot Zn angles due to the different volumes of the coordinating formamide molecules and subtle differences in the hydrophobic inter-chain interactions. Upon heating 1 and 2 to 200 degrees C, removal of the coordinating formamide molecules occurs, yielding the formamide-free compounds 1-DMF and 2-DEF of composition {Zn(O2C[PEP(hexyl)(2)EP] CO2)}. According to powder X-ray diffraction and FT-IR spectroscopy studies, these materials are not crystalline but still possess partial ordering of intact, yet modified coordination chains in a structural arrangement which appears to be related to the respective parent compounds. Compounds 1, 2, 1-DMF and 2-DEF exhibit blue photoluminescence. The emission maxima of 1-DMF and 2-DEF are red-shifted by ca. 25 nm with respect to lambda(max) of 1 and 2, respectively. (C) 2009 Elsevier B. V. All rights reserved

Metastable metal imidazolates: development of targeted syntheses by combining experimental and theoretical investigations of the formation mechanisms

Abstract In this report, we summarize our experimental and theoretical investigations in the zinc(II) imidazolate, [Zn(im)2], and zinc(II) 4,5-dichloroimidazolate, [Zn(dcim)2], systems that have been published previously. This comprises a study on the thermodynamic stabilities of the two densest phases with coi and zni framework structures in the [Zn(im)2] system including the discovery and characterization of a new [Zn(im)2·0.5py]-neb phase (py = pyridine), a study on the mechanism of formation of the [Zn(im)2]-zni phase as well as a study on the discovery and characterization of a new [Zn(dcim)2]-SOD phase. In addition, we present as yet unpublished work. This concerns the discovery and characterization of a new [Zn(im)2·0.5mor]-neb phase (mor = morpholine) and investigations of the mechanisms of crystallization of [Zn(im)2·0.5py]-neb and [Zn(im)2·0.5mor]-neb as well as an evalutation of time-resolved SAXS/WAXS data recorded in-situ during the formation of [Zn(im)2]-zni.</jats:p