Correlation between crystal structures and polar (ferroelectric) properties of hybrids of haloantimonates(iii) and halobismuthates(iii)

Halogenoantimonates(iii) and halogenobismuthates(iii) are a highly versatile class of organic–inorganic hybrid materials, applicable in optoelectronics and switchable dielectric devices.

Isostructural phase transition, quasielastic neutron scattering and magnetic resonance studies of a bistable dielectric ion-pair crystal [(CH3)2NH2]2KCr(CN)6

We have synthesised and characterised a novel organic-inorganic hybrid crystal, [(CH3)2NH2]2KCr(CN)6. The thermal DSC, TMA, DTG and DTA analyses indicate two solid-to-solid structural phase transitions (PTs). According to the X-ray diffraction experiments, the first PT at 220 K is isostructural, since it does not involve a change of the space group. This transition occurs between the states, where the (CH3)2NH2+ cations are orientationally disordered and ordered (frozen). The other reversible PT at 481 K leads to a melt-like phase similar to the one observed in plastic crystals or polar liquids. Dielectric spectroscopy has been used to characterise the switching properties of the dipole moments in the vicinity of the PTs. Continuous-wave electron paramagnetic resonance spectroscopy was employed to investigate the effect of ordering on the local environment of the Cr3+ ions. We have also applied the quasielastic neutron scattering (QENS) technique as well as 1H NMR spectroscopy to measure the dynamics of the (CH3)2NH2+ cations residing in the inorganic framework.

Multifunctional materials based on the double-perovskite organic–inorganic hybrid (CH3NH3)2[KCr(CN)6] showing switchable dielectric, magnetic, and semiconducting behaviour

Herein, we have synthesised and characterised a novel organic–inorganic hybrid crystal, [CH₃NH₃]₂KCr(CN)₆ (MACr).

Reorientational dynamics of organic cations in perovskite-like coordination polymers

Here we report the dynamics of organic cations as guest molecules in a perovskite host-framework. The molecular motion of CH₃NH₃⁺ (MAFe), (CH₃)₂NH₂⁺ (DMAFe) and (CH₃)₃NH⁺ (TrMAFe) in the cage formed by KFe(CN)₆^3- units was studied using a combination of experimental methods: (i) thermal analysis, (ii) dielectric and electric studies, (iii) optical observations, (iv) EPR and ¹H NMR spectroscopy and (v) quasielastic neutron scattering (QENS). In the case of MAFe and TrMAFe, the thermal analysis reveals one solid-to-solid phase transition (PT) and two PTs for the DMAFe crystal. A markedly temperature-dependent dielectric constant indicates the tunable and switchable properties of the complexes. Also, their semiconducting properties are confirmed by a dc conductivity measurement. The broadband dielectric relaxation is analyzed for the TrMAFe sample in the frequency range of 100 Hz-1 GHz. QENS shows that we deal rather with the localized motion of the cation than a diffusive one. Three models, which concern the simultaneous rotation of the CH₃ and/or NH₃ group, π-flips and free rotations of the organic cation, are used to fit the elastic incoherent structure factor. The ¹H NMR spin-lattice relaxation time for all compounds under study, as well as the second moments, has been measured in a wide temperature range. In all studied samples, the temperature dependence of the second moment of the proton NMR line indicated the gradual evolution of the molecular movements from the rigid state up to a highly disordered one.

Widely used hardly known. An insight into electric and dynamic properties of formamidinium iodide

The simple organic crystal formamidinium iodide (FAI) appeared to be a novel semiconducting material in a wide temperature range. The electric properties of FAI and the role of formamidinium cation (FA⁺) in the molecular mechanism of the solid-to-solid phase transitions (at 345 K (III → II) and 388 K (II → I)) were analysed. The creation of the ferroelastic domain structure in phases III and II was proved on the basis of observation under a polarizing microscope. Moreover, the molecular arrangement of dipolar organic FA⁺ was studied by ¹H NMR (spin-lattice relaxation time) and vibrational spectroscopy supported by density functional theory. The theoretical results show a good agreement with the experimental data. The infrared spectrum in a harmonic approximation was calculated and a comparative vibrational analysis was performed. All used techniques showed that the prototypic phase I exhibits the feature of plastic phase.

The simple organic crystal formamidinium iodide (FAI) appeared to be a novel semiconducting material in a wide temperature range.

Crystal structural analysis of methyl-substituted pyrazines with anilic acids: a combined diffraction, inelastic neutron scattering,1H-NMR study and theoretical approach

The molecular complexes of the pyrazine derivatives with anilic acids were analyzed in terms of the structure of molecules, the vibrational spectra, INS,¹HNMR and theoretical approach.

Structures and phase transitions in molecular complexes containing tetrafluoroboric acid and tetramethylpyrazine

Crystals of tetrafluoroboric acid with tetramethylpyrazine, TMP + HBF₄ + H₂O (1 : 1 : 2, A), TMP + HBF₄ (1 : 1, B) and TMP + HBF₄ (1 : 2, C) were synthesized and characterized by physicochemical experimental methods.

Flexible crystals of perovskite-like coordination polymers with a tunable and switchable organic guest: (CH3NH3)2[KFe(CN)6] and (CH3NH3)2[KCo(CN)6]

The crystal structure has been determined for (CH₃NH₃)₂[KCo(CN)₆] at temperatures 100 and 443 K.

Structures and phase transitions in neat 4,4′-di-tert-butyl-2,2′-bipyridyl and in its molecular complexes with either bromanilic or iodanilic acid

Using the DSC method, structural phase transitions (PTs) have been found at 165 and 219 K for 4,4′-di-tert-butyl-2,2′-bipyridyl (dtBBP), whereas for its complex with iodanilic acid (dtBBP·IA) PT is found at 331 K.

Serum leptin in systemic lupus erythematosus

Leptin, a peptide hormone, plays an essential role in the regulation of body weight, the endocrine function, reproduction, the immune response and inflammation. The immune system, in turn, modifies leptin's production. Systemic lupus erythematosus (SLE) is an autoimmunological disease characterized by widespread inflammation with possible involvement of each body organ and system. In this study, we assessed serum leptin levels in SLE patients and the control group in search for correlations between leptin concentrations and other markers' level, the activity of the disease, its duration, the age of the patients and their bone mineral density. Blood samples were collected from 30 SLE and 30 control group women. Each SLE patient was matched with one from the control for age (+/-1 year) and the body mass index (BMI; +/-1). Serum leptin levels were determined using the DRG Leptin ELISA Kit. Serum leptin levels in SLE patients ranged from 1.8 to 66.3 ng/ml (median value 7.5), and in control group it was 8.8 ng/ml (0.7-39.2) (NS). In SLE, serum leptin levels (after the logarithmic transformation) correlated with BMI (r = 0.89, P < 0.0001), the age (r = 0.34, P < 0.01) and the patients' disease duration (r = 0.59, P < 0.0005). Serum leptin levels in SLE patients with arthritis (P < 0.05) and central nervous system (CNS) involvement (P = 0.05) were significantly lower in comparison with serum leptin levels in SLE patients without arthritis and CNS involvement. No correlation was found between serum leptin levels and the T-score. In the control group, the logarithmic transformation of serum leptin levels positively correlated with BMI (r = 0.52, P < 0.05). No differences in serum leptin levels were shown between SLE patients and the control group. However, we found correlation between BMI and serum leptin levels in both groups. Furthermore, serum leptin levels in SLE patients with arthritis and CNS involvement were significantly lower in comparison with SLE patients without arthritis and CNS involvement, which suggests that active chronic inflammation may lower plasma leptin concentrations.