P. Ławniczak

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.

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.

The proton conductivity in benzimidazolium azelate under moderate pressure

Abstract The kinetic Monte Carlo method is applied to examine effects of hydrostatic pressure on the benzimidazolium azelate (BenAze) proton conductivity. Following the experimental indications the recently proposed model has been modified to simulate the transport phenomena under moderate pressure, resulting in a very good agreement between numerical and experimental results. We demonstrate that the pressure-induced changes in the proton conductivity can be attributed to solely two parameters: the length of the hydrogen bond and the amplitude of lattice vibrations while other processes play a minor role. Furthermore, in high-pressure regime we anticipate the crossover from the increasing to decreasing temperature dependence of the proton conductivity arising from the changes in the hydrogen-bond activation barrier with increased pressure.

Numerical modeling of the heterocycle intercalated proton-conducting polymers at various mole ratios

Abstract The kinetic Monte Carlo simulations are employed to study the proton conductivity for anhydrous heterocyclic based polymers. The proton transport is based on a two-step process called the Grotthuss mechanism. In the referring system the proton concentration depends on the relative molar ratio, x , of the benzimidazole and the polystyrene sulfonic acid. Available experimental data with contrasting behavior are fitted and interpreted in terms of our microscopic model. Moreover, it has been shown that the current behavior similar to the Vogel–Tamman–Fulcher law can be reproduced with high precision on the basis of the Grotthuss mechanism.

Comparison of structural, thermal and proton conductivity properties of micro- and nanocelluloses

Our search for a cellulose-based proton conducting material is continued. This paper presents selected physicochemical properties of cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs) together with cellulose microcrystals (CMCs) and cellulose microfibrils (CMFs), determined by X-ray diffraction (XRD), thermogravimetric analysis (TGA + DTA), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FT-IR), and electrical impedance spectroscopy (EIS). The CNCs and CNFs were studied in the forms of powder and film. They were produced in the process of transition metal catalyzed oxidative process or by TEMPO-mediated oxidation. It has been shown that regardless of the production method and the form of the sample the celluloses retained the cellulose Iβ crystalline structure, the cellulose films showed similar thermal properties in the relevant temperature range from room temperature to about 200 °C, and the TEMPO-oxidized CNF film showed the highest proton conductivity when compared with those of the other samples studied.