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Abstract: [4-NH2C5H4NH][C4H3O4][C4H4O4] (APM) complex with rare stoichiometric ratio 1:2 has been synthesized and characterized by a single-crystal X-ray diffraction and powder X-ray diffraction in a wide temperature range (from 100K up to 338K), calorimetry and dielectric spectroscopy. The APM undergoes structural phase transition at 307/312K (cooling/heating) of first order type classified as an order–disorder. The crystal structure of APM below 307K consists of ordered 4-aminopyridinium cations, hydrogen maleate anions (HM) and neutral maleic acid molecules (MM) that interact via hydrogen bonds. The room temperature phase II and the high temperature phase one I is polar, space group P21, which is confirmed by the pyroelectric effect. The I → II phase transition is accompanied by a distinct electric permittivity anomaly (ε max ≈55 at 150kHz) that is characteristic of ferroelectric crystals. The infrared spectra of polycrystalline APM are presented and compared with other closely related analogs. [Copyright &y& Elsevier]

Abstract: (C5H5NH)3BiCl6 crystallizes at room temperature in the triclinic space group P . The crystal is built up of the separated octahedral anions and pyridinium cations. Differential scanning calorimetry (DSC) and dilatometric measurements disclose structural phase transition of first-order type at 265/302K (cooling/heating). The dielectric investigations reveal a step-wise change of the electric permittivity at Tc characteristic of the crystals with the high-temperature plastic-like phase. Temperature-dependent infrared spectra for polycrystalline samples have been taken between 20 and 306K to clarify the cation dynamics contribution to the mechanism of the phase transition. The modes assigned to the deformation vibration of the NH+ group in the pyridinium ring appear to be the most sensitive to the phase transition. The possible molecular motions of the C5H5NH+ cations are studied by the proton magnetic resonance (1H NMR). [Copyright &y& Elsevier]

Abstract: The di(n-pentylammonium) pentabromoantimonate(III) compound has been synthesized and studied by means of a single-crystal X-ray diffraction, differential scanning calorimetry, thermal expansion, dielectric and IR techniques. Two solid–solid phase transitions of first order: at 416/388K and 225/224K (heating/cooling) have been revealed. The crystal structure of [n-C5H11NH3]2[SbBr5] has been solved at 298K, Pna21 (phase II) and at 86K P212121 (phase III). The crystal structure is composed of the anions which form an infinite chain and four independent n-pentylammonium cations. The dielectric studies have been made in the frequency range 500Hz–1MHz between 160 and 430K. The dielectric relaxation process, taking place over the low temperature phase III, has a polydispersive character. The infrared measurements carried out between 11 and 300K indicate a significant role of the organic cations in the mechanism of the phase transition from the intermediate to the low temperature at 225K. [Copyright &y& Elsevier]

Abstract: [n-C4H9NH3]2[BiBr5] exhibits five solid–solid structural phase transitions; at 309 (1st order), 291 (1st), 240 (1st), 219 (close to 2nd) and at 166K (1st). The phase transitions at 291 and 240K are accompanied by distinct dielectric anomalies. The dielectric relaxation process was found to appear over the phases (III) and (I). The infrared spectra for [n-C4H9NH3]2[BiBr5] were measured in the region of the internal vibration of the n-butylammonium cation (4000–400cm−1) between 12 and 320K. The temperature changes of wavenumbers and of a width for many of the internal modes of the n-butylammonium clearly indicate the contribution of the organic sublattice to the phase transition mechanism. [Copyright &y& Elsevier]

Abstract: Infrared spectra (3500–500cm−1) of polycrystalline (C5H5NH)5Bi2Br11 samples were investigated within the temperature range 27–456K. The assignments of the observed bands in the spectra measured at 27, 310 and 456K are proposed. A temperature dependence of the wavenumbers and full width at half maximum (FWHM) of the bands arising from some internal vibrations of pyridinium cations are analysed in order to explain the role of cations in the mechanism of the phase transition at 118 (paraelectric–ferroelectric) and 403K. It was found that numerous bands arising from the internal modes of the cations exhibit the splitting in the vicinity of both phase transitions, that indicates a distinct changes in the motional state of the pyridinium moieties. [Copyright &y& Elsevier]

Differential scanning calorimetry and linear thermal expansion studies reveal seven phase transitions in [n-C4H9NH3]2[SbBr5] crystal. The phase transitions at 261, 280 and 292 K are accompanied by distinct dielectric anomalies. The dielectric relaxation processes were disclosed over the low temperature phases (VI, VII) and over the phase (III). The infrared spectra of powdered sample of [n-C4H9NH3]2[SbBr5] in Nujol were measured in the region of the internal vibration of the n-butylammonium cation (4000–400 cm-1) in the temperature range between 26 and 320 K. The temperature changes wavenumbers and width of most of the modes of the n-butylammonium cations were analysed. [Copyright &y& Elsevier]

Low frequency Raman spectroscopic studies (5–400 cm−1) were carried out for single crystal samples of (C5H5NH)6Bi4Cl18 within the temperature range 37–285 K to look for possible spectral changes resulting from the phase transitions at 122 and 154 K. A detailed analysis of frequencies, band widths and intensities of the bands was made for the (a(ba)c*) and (a(bb)c*) spectra through the phase transitions to understand their nature. It was shown that the transitions are not accompanied by any mode softening, thus indicating their order–disorder nature. However, the ordering of the pyridinium cations close to 122 and 154 K exerts a strong influence on the (Bi4Cl186−) anion. [Copyright &y& Elsevier]