Effect of counter ions on physical properties of imidazole-based proton conductors

Helical model of compression and thermal expansion

A negative linear temperature expansion and a negative linear compressibility were observed for imidazolium benzoate salt. Its strongly anisotropic strain induced by the temperature and pressure changes has been explained by the mechanism of H-bonded helices deformed in the structure. X-ray diffraction and vibrational spectroscopy were used to analyze interactions in the crystal. The Quantum Theory of Atoms in Molecules (QTAiM) approach was applied to analyze the hydrogen bonds and other interactions. In the salt under study, the interactions within the helix are substantially higher in energy than between helices. With decreasing temperature and increasing pressure, the value of the helix pitch increases while the value of the semi-major axis decreases, which results in the negative linear expansion and negative linear compression, respectively.

A novel sensing platform for electrochemical detection of metronidazole antibiotic based on green-synthesized magnetic Fe3O4 nanoparticles

The spread of antibiotic resistant genes has become a serious global concern. Thus, the development of efficient antibiotic monitoring systems to reduce their environmental risks is of great importance. Here, a potent electrochemical sensor was fabricated to detect metronidazole (MNZ) on the basis of green synthesis of Fe₃O₄ nanoparticles (NPs) using Sambucus ebulus L. leaves alcoholic plant extract as a safe and impressive reducing and stabilizing agent. Several analyses such as X-ray diffraction (XRD), Fourier transform infrared spectrophotometer (FTIR), thermogravimetric analysis (TGA), field emission scanning electron microscope (FESEM), energy dispersive X-ray spectroscopy (EDX), and dynamic light scattering (DLS) confirmed the production of homogeneous, monodisperse, regular, and stable magnetite NPs with a spherical morphology. The as-prepared Fe₃O₄NPs were afterwards applied to evaluate the electrochemical activity of MNZ by merging them with graphene nanosheets (GR NSs) on the glassy carbon electrode (GCE). The GR/Fe₃O₄NPs/GCE represented extraordinary catalytic activity toward MNZ with two dynamic ranges of 0.05-5 μM and 5-120 μM, limit of detection (LOD) of 0.23 nM, limit of quantification (LOQ) of 0.76 nM, and sensitivity of 7.34 μA μM^-1 cm^-2. The fabricated sensor was further employed as a practical tool for electrochemical detection of MNZ in real aqueous samples.

Anhydrous proton-conducting imidazole triflate-SiO2 composite

ImidazoleTriflate (ITF)-SiO₂ composites xITF-(100-x)SiO₂ were prepared by planetary ball-milling method. The structure of the composites was studied by TG-DTA, XRD and FT-IR methods. The ionic conductivity was assessed by alternative current (AC) electrochemical impedance measurement. From XRD results, the crystal size of imidazole triflate became smaller as its loading in xITF-(100-x)SiO₂ decreased. With x = 40 weight percent, the calculated crystal size was about 7.3 nm. FT-IR spectra showed the existence of CF₃SO₃ ^-···H⁺ ion aggregates and imidazole-proton bonds. The electrical conductivity of sample x = 50 was about 6.3 × 10^-3 Scm^-1 at 130 °C under anhydrous condition and about 30 times higher than that of sample x = 100.

Spectroscopic and Structural Study of a New Conducting Pyrazolium Salt

The increase in conductivity with temperature in 1H-pyrazol-2-ium 2,6-dicarboxybenzoate monohydrate was analyzed, and the influence of the mobility of the water was discussed in this study. The electric properties of the salt were studied using the impedance spectroscopy method. WB97XD/6-311++G(d,p) calculations were performed, and the quantum theory of atoms in molecules (QTAiM) approach and the Hirshfeld surface method were applied to analyze the hydrogen bond interaction. It was found that temperature influences the spectroscopic properties of pyrazolium salt, particularly the carbonyl and hydroxyl frequencies. The influence of water molecules, connected by three-center hydrogen bonds with co-planar tetrameters, on the formation of structural defects is also discussed in this report.

Proton Conduction Mechanism for Anhydrous Imidazolium Hydrogen Succinate Based on Local Structures and Molecular Dynamics

Anhydrous organic crystalline materials incorporating imidazolium hydrogen succinate (Im-Suc), which exhibit high proton conduction even at temperatures above 100 °C, are attractive for elucidating proton conduction mechanisms toward the development of solid electrolytes for fuel cells. Herein, quantum chemical calculations were used to investigate the proton conduction mechanism in terms of hydrogen-bonding (H-bonding) changes and restricted molecular rotation in Im-Suc. The local H-bond structures for proton conduction were characterized by vibrational frequency analysis and compared with corresponding experimental data. The calculated potential energy surface involving proton transfer (PT) and imidazole (Im) rotational motion showed that PT between Im and succinic acid was a rate-limiting step for proton transport in Im-Suc and that proton conduction proceeded via the successive coupling of PT and Im rotational motion based on a Grotthuss-type mechanism. These findings provide molecular-level insights into proton conduction mechanisms for Im-based (or -incorporated) H-bonding organic proton conductors.

Investigation of the thermal and conductive properties of oxalic acid salts with planar and undulating proton-conducting layers

The physical properties of two proton conductors 1H-1,2,4-triazol-4-ium hydrogen oxalate (TriOX) and 1H-imidazol-3-ium hydrogen oxalate (ImiOX) were investigated.

Toward a new type of proton conductor based on imidazole and aromatic acids

A new approach towards achieving proton conducting materials based on aromatic acids and heterocyclic bases was proposed. It can lead to a new material in which all hydrogen bonding interactions are of medium or weak strength and rotations of the base and acid molecules are possible. If the above conditions are met, one can expect a high value of proton conductivity governed by the Grotthuss mechanism. Two salts of imidazole, one with benzoic acid having one carboxylic acid group and another with salicylic acid having a carboxylic and hydroxyl group located in the ortho position, were synthesized. Physical properties of these newly synthesized proton conducting salts were investigated using experimental and theoretical methods. The structures of these salts were studied by X-ray diffraction and ¹H and ¹³C NMR techniques. The intermolecular interactions in the salts were analyzed by DFT calculations, within the QTAiM theory, and by Hirshfeld surface analysis. The π-π interactions, the proton conduction pathways, and the transport mechanism are also discussed.