Katarzyna Pogorzelec-Glaser

Structure, hydrogen bond network and proton conductivity of new benzimidazole compounds with dicarboxylic acids

Dicarboxylic acids are interesting for crystal engineering due to their ability of hydrogen bond formation. To find a relationship between the molecular structure and the properties of proton conducting materials, we synthesized two compounds of benzimidazole with dicarboxylic acids of different chain length: glutaric and pimelic acids. The structure of the compounds was determined by X-ray diffraction and compared with molecular arrangement studied by 13C CP/MAS NMR spectroscopy supported by Density Functional Theory computations for benzimidazole. Benzimidazole was found to form salt with glutaric acid in a 1 : 1 ratio and monoclinic layer-type structure with P21/n space group. Flat layers, parallel to (−102) plane, are built of glutaric acid molecules linked into rectangular-type chains by O–H⋯O bonds and benzimidazole molecules attached to the chains by N–H⋯O bonds. The molecule of the benzimidazole compound with pimelic acid contains two benzimidazole rings and one pimelic acid chain. The structure with alternating layers, built of two groups of benzimidazole dimers and layers of pimelic acid chains, belongs to P21/n space group. The acid layers are built of pimelic acid molecules linked by O–H⋯O hydrogen bonds into chains parallel to [30−1] direction and the benzimidazole dimers are linked to the acid layers by N–H⋯O bonds. Impedance spectroscopy studies in wide frequency and temperature range of pellets made of powdered compounds enabled to separate the contributions of crystalline and grain boundary parts to the electric conductivity. The conductivity (averaged over all directions) of the crystalline compounds of benzimidazole with glutaric and pimelic acid is characterized by activation energy of 2.5 eV and 1.6 eV, respectively, which is in an agreement with the hydrogen bond network in the materials.

The structural dynamics in the proton-conducting imidazolium oxalate

The 1H spin–lattice relaxation times and high-resolution solid-state nuclear magnetic resonance (NMR) under fast magic spinning were used to study the structural dynamics in the proton-conducting material imidazolium oxalate. The measurements provide evidence for the ordered and disordered domains within the studied material. The two components drastically differ in their 1H spin–lattice relaxation times and 1H–13C cross-polarization magic-angle-spinning (CP/MAS) spectra. The coalescence phenomenon of the resonances of the basal carbons of the imidazole ring undergoing a reorientation is observed only for mobile molecules in the disordered domains. Therefore, only these molecules can be responsible for proton conductivity allowing for the Grotthus mechanism.

Structure and phase transitions in Cu2P2O7

X-ray diffraction studies of the temperature variation of the Cu2P2O7 crystal structure were performed in the vicinity of the transition from the α-phase (C2/c space group) to the β-phase (C2/m space group). These results as well as those of Raman spectroscopy studies and temperature variation of the electric capacitance point to the existence of an intermediate phase in the temperature range 347–363 K.

The crystal structure and evidence of the phase transition in D-amphetamine sulfate, as studied by X-ray crystallography, DSC and NMR spectroscopy

X-Ray crystallography, DSC and NMR spectroscopy methods have been used to study the phase transition of D-amphetamine sulfate. The phase transition temperature occurs at about 325 K, and belongs to the discontinuous type with a large temperature hysteresis. A change in the space group is observed from monoclinic P21 in the low temperature phase to monoclinic C2 in the high temperature phase. The transformation from phase I to phase II is a result of the ordering of the SO42−groups, allowing a T-shape interaction between D-amphetamine molecules. Proton relaxation rate data obtained for the studied compound have been analysed by assuming two dynamically-inequivalent methyl groups below the phase transition and only one type of ammonium group above the phase transition. The activation energies for the C3 reorientation of the methyl groups have been determined to be 7.31 and 11.89 kJ mol−1, whereas for the ammonium group it is 27.29 kJ mol−1.

Morphology, molecular dynamics and electric conductivity of carbohydrate polymer films based on alginic acid and benzimidazole.

The present paper describes a preparation method and molecular investigations of new biodegradable proton-conducting carbohydrate polymer films based on alginic acid and benzimidazole. Electric conductivity was studied in a wide temperature range in order to check the potential application of these compounds as membranes for electrochemical devices. Compared to pure alginic acid powder or its film, the biodegradable film of alginic acid with an addition of benzimidazole exhibits considerably higher conductivity in the range above water boiling temperature (up to approximately 10(-3) S/cm at 473 K). Due to this important feature the obtained films can be considered as candidates for application in high-temperature electrochemical devices. The microscopic nature and mechanism of the conduction in alginate based materials were studied by proton nuclear magnetic resonance (NMR). The results show specific changes in morphology and molecular dynamics between pure alginate powders and the films obtained without and with the addition of benzimidazole molecules.

Magnetic properties of BiFeO3 micro-cubes synthesized by microwave agitation

In this article, we present results of field cooled (FC) and zero field cooled (ZFC) magnetization measurements and investigation of aging and memory effect in bismuth ferrite (BFO) multiferroic micro-cubes obtained by means of simple microwave synthesis procedure. It is found that difference between FC and ZFC magnetizations appear at the temperature of freezing of ferromagnetic domain walls. The decay of the magnetic moment versus time described by power-law relation and the absence of memory effect are caused by domain growth mechanism rather than by the spin-glass phase. The negligible value of remnant magnetic moment indicates that BFO compound exhibits low concentration of ferromagnetic domains and can be close to ferromagnetic to spin-glass transition.

Structure and molecular dynamics of bis-1H-1,2,4-triazole succinic acid complex crystals

Bis-1,2,4-triazole succinic acid (1H-1,2,4-triazole butanedioic acid (2 : 1)) belongs to the family of dicarboxylic acid compounds of nitrogen containing heterocyclic molecules which are expected to exhibit proton conductivity. We determined the crystal structure of the bis-1,2,4-triazole succinic acid complex by X-ray diffraction and compared it with that obtained by semi-empirical molecular orbital calculations. Wave-like layer structure with layers parallel to the (10) plane of the P21/c monoclinic space group was ascribed to the compound and we consider the structure to be formed as a result of a competition between strong specific interaction within a single layer and weak interlayer interactions of the N–H⋯π type hydrogen bond. The calculated distributions of the charge density as well as the electrostatic potential in the plane parallel to the triazole pentagon are in good agreement with those obtained from XRD data. The powder IR and Raman spectra of the title crystal and additionally of the 1H-1,2,4-triazole and β-succinic acid crystal were measured. The relation between these vibrational spectra and their relationship with the crystal structures are discussed. Particular attention is paid to the vibrations arising from the hydrogen bonds formed in these crystals.

Magnetic Relaxation in Bismuth Ferrite Micro-Cubes

The process of magnetic relaxation was studied in bismuth ferrite BiFeO3 multiferroic micro-cubes obtained by means of microwave assisted Pechini process. Two different mechanisms of relaxation were found. The first one is a rapid magnetic relaxation driven by the domain reorientations and/or pinning and motion of domain walls. This mechanism is also responsible for the irreversible properties at low temperatures. The power-law decay of the magnetic moment confirms that this relaxation takes place in the system of weakly interacting ferromagnetic or superferromagnetic domains. The second mechanism is a long-term weak magnetic relaxation due to spin glass-phase.

Dielectric Relaxation in Confined Ferroelectric Polymer

The dynamics of segmental and chain motions in poly(vinylidene fluoride) confined to anodized aluminum oxide nanopores by melt-wetting was studied by broad-band dielectric spectroscopy. Molecular structure of the confined polymer was studied by means of wide-angle X-ray scattering in the transmission mode with ψ scanning. The confined polymer was found to form multilayered cylindrical mesostructure containing three polymorphs with the <020> direction of nonpolar polymorph II aligned along the pore channels. The relaxation rates of segmental motions in the amorphous phase of the polymer were found to be shorter in confined geometry than in the bulk, whereas the relaxation of the local mode was found to be broadened due to inhomogeneous relaxation times in the pores.

Properties of PVDF-MCM41 Nanocomposites Studied by Dielectric, Raman and NMR Spectroscopy

To obtain information on the polymer-inorganic filler interactions and on the confinement effect of polymer chains we studied the properties of solution-cast poly(vinylidene fluoride)-MCM41 molecular sieve nanocomposites. The dielectric response of the nanocomposites was found to be determined generally by the response of the polymer matrix, whereas the polymer-filler interactions resulted in an increase of the relaxation rates of the local mode and segmental motions in the amorphous phase of the poly(vinylidene fluoride) matrix. The effect has been related to a reduction of intermolecular correlations between the segments and was confirmed by the dispersion of 1H spin-lattice relaxation times in PVDF-MCM41 composites. Moreover, the relaxometry experiments have shown that the dynamics of poly(vinylidene fluoride) chains confined to MCM41 molecular sieve channels can be described by tube/reptation model proposed by De Gennes, Doi and Edwards.