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

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 to 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 being located in the domain interfaces. As structural differences appear to be more related to characteristics of the real as opposed to the 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

Adsorption and diffusion of alkanes in CuBTC crystals investigated using infra-red microscopy and molecular simulations

The adsorption and intra-crystalline diffusion of n-butane (nC4), iso-butane (iC4), 2-methylbutane (2MB), and 2,2-dimethylpropane (neoP) in CuBTC (Cu-3(BTC)(2) where BTC = benzene-1,3,5-tricarboxylate) has been investigated using infrared microscopy (IRM), combined with molecular simulations. Both experiments and simulations show strong inflection characteristics in the adsorption isotherms. The primary cause of the inflection is due to the strong preference for adsorption within, and in the regions close to the mouths of tetrahedral pockets. The isotherm inflection has a significant influence on the dependence of the Maxwell-Stefan diffusivity, D-i, on the fractional occupancy, D-i. Both IRM experiments and simulations show that the D-i-theta(i) behavior appears to be influenced by the loading dependence of the inverse thermodynamic factor 1/Gamma(i) = dln theta(i)/dlnp(i). For nC4 and iC4, the D-i increase sharply by about one order of magnitude as the occupancy theta(i) increases from 0 to about 0.2. This increase is caused by the fact that the diffusion characteristics undergo a transition from being dominated by hops across narrow 4.6 A windows at low loadings to hops across large 9 A windows for loadings higher than 8 molecules per unit cell. For loadings higher than 8 molecules per unit cell the D-i-theta(i) dependence of nC4 and iC4 is dictated by 1/Gamma(i), characteristic of more open channel structures such as FAU zeolite. For 2MB and neoP, the IRM experiments show evidence of phase transition and except for the region in which this occurs the Di follows the occupancy dependence of 1/Gamma(i) for the entire range of loadings

Synthesis and characterization of some water soluble Zn(ii) complexes with (E)-N-(pyridin-2-ylmethylene)arylamines that regulate tumour cell death by interacting with DNA

The synthesis and spectroscopic properties of nine water soluble zinc(II) complexes of (E)-N-(pyridin- 2-ylmethylene)arylamines (Ln) with the general formula [Zn(X)2(Ln)] (X = Cl−, Br−, I−; (1–8)) and [Zn(μ-N3)- (N3)(L3)]2 (9) are reported. The complexes were characterized by elemental analysis and their spectroscopic properties were studied using UV-Visible, fluorescence, IR and 1H NMR spectroscopies. The solid state structures of zinc(II) complexes 2–4 and 6–9 were established by single crystal X-ray crystallography. The majority of the structures are mononuclear with tetra-coordinate zinc centres (2–4, 6 and 7) except where L carries an additional donor atom capable of coordinating zinc (8), in which case the zinc atom has a distorted square pyramidal geometry. The centrosymmetric molecule of [Zn(μ-N3)(N3)(L3)]2 (9) is binuclear with the zinc atoms in a trigonal bipyramidal coordination environment. In general, the dichlorozinc derivatives 1, 3–5 and 8 exhibited moderately elevated in vitro cytotoxic potency towards the human epithelial cervical carcinoma (HeLa) cell line, with 4 as the best performer (IC50 value of 18 μM). Apoptosis-inducing activity, assessed by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, showed that the zinc complexes interacted with DNA and thereby interfered the DNA binding of several transcription factors to its promoter sites, thus inhibiting gene transcription required for the biological activity of cells

Synthesis and structural characterization of an unprecedented nonmetal cation polyborate salt containing two different “isolated” polyborate anions: [H2en]2[B4O5(OH)4][B7O9(OH)5]·3H2O (en = H2NCH2CH2NH2)

The nonmetal cation polyborate salt of stoichiometry [H(2)en](2)[B11O18(OH)]center dot 7H(2)O is obtained from the reaction of 1,2-diaminoethane and boric acid (1:5 ratio) in H2O/MeOH. An X-ray crystallographic study of the product reveals that the polyborate moiety is composed of two isolated hydrated polyborate anions: [B4O5(OH)(4)](2-) and [B7O9(OH)(5)](2-). The structure is templated by the cations with the anions forming a supramolecular H-bonded network, augmented by additional H-bonds involving the waters of crystallization and the cations