ABSTRACT
The synthesis and crystal structure of the perfluorinated metal-organic framework CFA-15 (Coordination Framework Augsburg University-15), CuII3(tfpc)2(OH)2·DMF, as well as the crystal structure of its ligand (H2-tfpc = 3,5-bis(trifluoromethyl)-1H-pyrazole-4-carboxylic acid) are described. The MOF crystallizes in the monoclinic crystal system within the chiral space group C2 (no. 5). It features a 3-D microporous framework with rhombic channels along the c-axis. The MOF is formed by 1-D chains of Cu(ii) ions expanding in the c-direction, bridged by OH- groups, DMF molecules and tfpc2- ligands. Two different Cu(ii) species are located within the structure, bridged in a {Cu1-Cu1-Cu2-Cu1-Cu1-Cu2} mode. By thermal treatment, it was possible to remove coordinated solvent molecules and generate free accessible, unsaturated and reactive metal centres. The structure of activated CFA-15 was refined via Rietveld method. DRIFT measurements, which were used to study adsorption of CO2 and NO in the MOF, showed a formation of a stable NO-CFA-15 complex. CFA-15 was further characterized by thermogravimetric analysis, variable temperature powder X-ray diffraction measurements, IR spectroscopy, as well as photoluminescence and gas sorption measurements. The isosteric heats of adsorption for CO, CO2, H2 and O2 were determined, and compared to DFT calculated sorption energies as well as to data reported in literature for similar materials.
ABSTRACT
In the present work, we employ broadband dielectric spectroscopy to study the molecular dynamics of the prototypical glass former glycerol confined in two microporous zeolitic imidazolate frameworks (ZIF-8 and ZIF-11) with well-defined pore diameters of 1.16 and 1.46 nm, respectively. The spectra reveal information on the modified α relaxation of the confined supercooled liquid, whose temperature dependence exhibits clear deviations from the typical super-Arrhenius temperature dependence of the bulk material, depending on the temperature and pore size. This allows assigning well-defined cooperativity length scales of molecular motion to certain temperatures above the glass transition. We relate these and previous results on glycerol confined in other host systems to the temperature-dependent length scale deduced from nonlinear dielectric measurements. The combined experimental data can be consistently described by a critical divergence of this correlation length as expected within theoretical approaches assuming that the glass transition is due to an underlying phase transition.
ABSTRACT
Quinones are well known as redox-active compounds. In this work bistriazole-p-benzoquinone was prepared and its electrochemical behaviour in aqueous alkaline solutions was studied by cyclic voltammetry. Two successive one-electron reduction steps were observed - the first step was reversible and the second quasireversible. Based on the nature of the alkali cation, the potential of the cathodic peak minimum and the anodic peak maximum was shifted towards positive direction as follows Li+ > Na+ > K+. In order to know more about the chemical structure of the alkali salts, the lithium, sodium and potassium salts of bistriazole-p-benzoquinone were crystallized and their structure could be revealed by single crystal X-ray analysis. Additionally, the thermal stability of the compounds was investigated by thermogravimetric analysis and variable temperature X-ray powder diffraction analysis.
