M. Drozd

Perovskite metal formate framework of [NH2-CH(+)-NH2]Mn(HCOO)3]: phase transition, magnetic, dielectric, and phonon properties.

We report the synthesis, crystal structure, and thermal, dielectric, phonon, and magnetic properties of [NH2-CH(+)-NH2][Mn(HCOO)3] (FMDMn). The anionic framework of [(Mn(HCOO)3(-)] is counterbalanced by formamidinium (FMD(+)) cations located in the cavities of the framework. These cations form extensive N-H···O hydrogen bonding with the framework. The divalent manganese ions have octahedral geometry and are bridged by the formate in an anti-anti mode of coordination. We have found that FMDMn undergoes a structural phase transition around 335 K. According to the X-ray diffraction, the compound shows R3̅c symmetry at 355 K and C2/c symmetry at 295 and 110 K. The FMD(+) cations are dynamically disordered in the high-temperature phase, and the disorder leads to very large bandwidths of Raman and IR bands corresponding to vibrations of the NH2 groups. Temperature-dependent studies show that the phase transition in FMDMn is associated with ordering of the FMD(+) cations. Detailed analysis shows, however, that these cations still exhibit some reorientational motions down to about 200 K. The ordering of the FMD(+) cations is associated with significant distortion of the anionic framework. On the basis of the magnetic data, FMDMn is a weak ferromagnet with the critical temperature Tc = 8.0 K.

Crystal structure, phase transitions and vibrational spectra of bis(betaine) nitrate

Abstract The crystal structure of bis(betaine) nitrate (BBN) has been determined by X-ray diffraction as monoclinic, space group P2 1 / c , with a = 5.668(1), b = 11.259(2) and c = 23.073(5) A, β = 93.65(3)°, Z = 4. The crystal comprises nitrate ions, NO 3 − , and betaine dimers: two betaine moieties are joined by a very strong asymmetric hydrogen bond with an O···O distance of 2.449(2) A. Fist order type phase transitions at 394 K, 439 K and 460 K (melting and decomposition) and very likely second order type at about 448 K were discovered for the BBN sample by the Differential Scanning Calorimetry method. In the deuterated analogue they appear at 394 K, 434 K, 448 K and 459 K. The FTIR and FT-Raman spectra for the powder samples were measured at room temperature. Additionally the FTIR spectra were taken at low temperatures (till 10 K). A strong band at about 900 cm −1 arises from the ν a OHO vibration of the very strong hydrogen bond. The site symmetry of the NO 3 − anions is C 1 according to X-ray data and the vibrational spectra.

Structure and vibrational spectra of the tetra(betaine) selenate crystal

Abstract The crystal structure of tetra(betaine) selenate has been determined by X-ray diffraction as orthorhombic, space group Fddd, with a = 13.243(8), b = 19.077(9) and c = 21.96(2) A , Z = 8. The crystal comprises selenate ions, SeO2−4, and the betaine dimers: two betaine moieties are joined by a very strong symmetric (C2) hydrogen bond with the O…O distance of 2.424(6) A. Powder FTIR and FT-Raman spectra were measured and assignment of the observed bands to vibrations of the hydrogen bonds and internal vibrations of the betaine molecules and selenate ions is proposed.

First example of the ABC ν(OH) absorption structure for both gaseous and crystalline phase: infrared studies of dimethylphosphinic acid

Abstract Infrared spectra for both gaseous (4000-1000 cm −1 ) and polycrystalline (4000-400 cm −1 ) samples of dimethylphosphinic acid (CH 3 ) 2 POOH (DMPA) at various temperatures are reported and discussed. The main attention is focused on the hydrogen bond vibrations. For the first time, the characteristic ABC structure of the ν(OH) band, occurring in the spectra of solid samples of strongly hydrogen bonded complexes was observed in the gas phase spectra of DMPA dimers. In spite of different types of aggregates present in the solid state a similar shape of the ν(OH) absorption was found in the crystalline sample spectra. However, an inverse intensity distribution of the ABC subbands was observed. The presented results fully confirm the explanation of the ABC structure as being due to the Fermi resonances between ν(OH) and overtones of the deformation modes 2δ(OH) and 2γ(OH).

Structure, spectra and phase transition in p-nitroanilinium perchlorate crystal

Abstract The first X-ray diffraction and vibrational spectroscopic analysis of a novel complex between p -nitroaniline and perchloric acid is reported. The structure was solved in 295 K. Room temperature powder infrared and Raman measurements for the p -nitroanilinium perchlorate (1:1) crystals were carried out. The vibrational spectra in the region of internal vibrations of ions corroborates the X-ray data which show that p -nitroaniline molecule is monoprotonated. DSC measurements on powder sample indicate the phase transition point at about 213 and 208 K for heating and cooling, respectively. No detectable signal was observed during powder test for second harmonic generation.

Crystal structure and vibrational spectra of betaine hydrogen selenate monohydrate

Abstract The crystal structure of betaine hydrogen selenate monohydrate, (C5H12NO2)+·(HSeO4)−·(H2O), BHSeH2O, has been determined by X-ray diffraction as monoclinic, space group P2 1 c with a = 6.674(6), b = 11.912(9), c = 14.156(14) A, β = 100.61(4)° and Z = 4. It comprises protonated betaine moieties (betainium cations), hydrogen selenate anions and water molecules which are held together by a number of hydrogen bonds and form infinite chains. Two types of four-membered centrosymmetric rings are distinguished in the chain. The two rings share a common side. Powder FT-IR and FT-Raman spectra were measured for the title crystal, the dehydrated crystal (betaine hydrogen selenate, BHSe) and their deuterated analogues. Assignments of the observed bands to vibrations of the hydrogen bonds and internal vibrations of the hydrogen selenate anions and the betainium cations are proposed. DSC data are also presented.

Effect of encapsulation in MCM-41 type molecular sieves on vibrational spectra of liquid crystalline state

Abstract The paper deals with the investigation of IR absorption spectra of a pure 4- n -pentyl-4′-cyanobiphenyl (5CB) liquid crystal in nematic liquid crystalline (LC) state, pure aluminosilicate molecular sieves of MCM-41 type (with channels about 40 A in diameter) and their heterogeneous binary systems. It was shown that 5CB molecules are able to interact with active centers in the MCM-41 channels forming sufficiently strong hydrogen bonds of the —CN⋯H—O— type. This conclusion was confirmed by the data obtained from DSC measurements. Relative amount of the 5CB molecules interacting with the channel walls and that of the molecules retaining the LC state when encapsulated in molecular sieves MCM-41 and CuMCM-41 were estimated.

Structure formation and its influence on thermodynamic and optical properties of montmorillonite organoclay–5CB liquid crystal nanocomposites

Montmorillonite (MMT) clay modified with octadecylbenzyldimethylammonium chloride (OBDM), B2, and its composites with nematic liquid crystal (LC) 4‐pentyl‐4′‐cyanobiphenyl (5CB), 5CB–B2, with different concentration of the clay (3–8 wt %) were investigated by X‐ray diffraction, polarizing optical microscopy, differential scanning calorimetry, FTIR spectroscopy and atomic force microscopy. Modification of Na‐MMT with OBDM surfactant results in an increase of the chemical affinity of the clay for 5CB. This results in considerable increase of the basal spacings of the clay, giving a possibility for 5CB dimers to penetrate into the interlayer space. Better affinity of the clay for LC allows clay nanoparticles to disperse homogeneously in the LC, and affects thermodynamic and optical properties of the nanocomposites. For 5CB–B2 composites, the structure formation and the strength of the interface interactions were practically independent on B2 concentration. A comparison with 5CB–B3 composites (B3 is MMT modified with dioctadecyldimethylammonium chloride) revealed that the ability of the clay to form homogeneous structures in the LC and thermodynamic and optical properties of the composites are highly dependent on the chemical nature of the surfactant. Varying the type of the clay mineral modifier, it is possible to develop novel heterogeneous LC nanocomposites with desirable electro‐optical properties.

FT-IR, FT-Raman spectra and DFT calculations of melaminium perchlorate monohydrate.

Melaminium perchlorate monohydrate (MPM), an organic material has been synthesized by slow solvent evaporation method at room temperature. Powder X-ray diffraction analysis confirms that MPM crystal belongs to triclinic system with space group P-1. FTIR and FT Raman spectra are recorded at room temperature. Functional group assignment has been made for the melaminium cations and perchlorate anions. Vibrational spectra have also been discussed on the basis of quantum chemical density functional theory (DFT) calculations using Firefly (PC GAMESS) version 7.1 G. Vibrational frequencies are calculated and scaled values are compared with experimental values. The assignment of the bands has been made on the basis of the calculated PED. The Mulliken charges, HOMO-LUMO orbital energies are analyzed directly from Firefly program log files and graphically illustrated. HOMO-LUMO energy gap and other related molecular properties are also calculated. The theoretically constructed FT-IR and FT-Raman spectra of MPM coincide with the experimental one. The chemical structure of the compound has been established by (1)H and (13)C NMR spectra. No detectable signal was observed during powder test for second harmonic generation.

Guanidinium perchlorate ferroelectric crystal. Study of vibrational properties based on experimental measurements and theoretical calculations.

The infrared and Raman spectra of guanidinium perchlorate were measured at room temperature. The spectra are discussed with the framework of literature X-ray structure in relation to internal hydrogen bond network. For complete vibrational analysis the theoretical calculation of both infrared and Raman spectra in DFT approach were performed. The clear-cut assignment of observed bands was made on the basis of PED analysis. On the basis of theoretical studies the electrostatic charges and energies of HOMO and LUMO orbitals were obtained. Additionally the first order hyperpolarizability of investigated molecule was calculated. The obtained results are in good agreement with literature data, but according to performed calculation the specific damping of β hyperpolarizability in unit cell (comparable with isolated molecule) is observed. To explain in detail phase transitions phenomena (at ca. 452 and 454K) described in literature the temperature dependent infrared powder spectra were recorded. The temperature dependencies of bands position and intensities for titled crystal in the range 11-480K are analyzed.