Vibration-reorientation dynamics, structural changes and its interrelation with the phase transition in polycrystalline [Cr(OC(NH2)2)6](BF4)3.

Polycrystalline hexakis(urea-O)chromium(III) tetrafluoroborate possesses in the temperature range of 295-105 K one solid-solid phase transition at T(C) ≈ 255 K. Analysis of the band shapes associated with the ν(as)(CN) and δ(as)(NH2) vibrational modes of the Fourier transform infrared absorption (FT-IR) spectra, registered in the temperature range of 295-10 K, indicated existence of fast (τ(R) ≈ 10(-12) s) reorientational motion of the protons from NH2 groups belonging to OC(NH2)2 (urea) ligands, which does not suddenly change at T(C). Moreover, splitting of the IR bands associated with the ν(as)(NH), ν(s)(NH) and ν(as)(BF)F2/ν(s)(CN) modes at T(C) indicated that this phase transition is associated with a change of crystal structure. Similar analysis of the Raman scattering bands (FT-RS), associated with the δ(s)(FBF)E, ν(s)(BF)A and ν(as)(BF)F2/ν(s)(CN) vibrational modes, indicated fast reorientation of the BF4(−) ions, which does not suddenly change at T(C), and additionally confirmed structural character of this phase transition. Results obtained from vibrational spectroscopy measurements are compatible with that obtained by electron paramagnetic resonance spectroscopy (EPR) measurements in function of temperature, where rapid narrowing of the EPR line in the vicinity of the T(C) was observed.

The relationship between reorientational molecular motions and phase transitions in [Mg(H2O)6](BF4)2, studied with the use of (1)H and (19)F NMR and FT-MIR.

A (1)H and (19)F nuclear magnetic resonance study of [Mg(H2O)6](BF4)2 has confirmed the existence of two phase transitions at Tc1 ≈ 257 K and Tc2 ≈ 142 K, detected earlier by the DSC method. These transitions were reflected by changes in the temperature dependences of both proton and fluorine of second moments M2 (H) and M2 (F) and of spin-lattice relaxation times T1 (H) and T1 (F). The study revealed anisotropic reorientations of whole [Mg(H2O)6](2+) cations, reorientations by 180° jumps of H2O ligands, and aniso- and isotropic reorientations of BF4 (-) anions. The activation parameters for these motions were obtained. It was found that the phase transition at Tc1 is associated with the reorientation of the cation as a whole unit around the C3 axis and that at Tc2 with isotropic reorientation of the BF4 (-) anions. The temperature dependence of the full width at half maximum value of the infrared band of ρt(H2O) mode (at ∼596 cm(-1)) indicated that in phases I and II, all H2O ligands in [Mg(H2O)6](2+) perform fast reorientational motions (180° jumps) with a mean value of activation energy equal to ca 10 kJ mole(-1), what is fully consistent with NMR results. The phase transition at Tc1 is associated with a sudden change of speed of fast (τR ≈ 10(-12) s) reorientational motions of H2O ligands. Below Tc2 (in phase III), the reorientations of certain part of the H2O ligands significantly slow down, while others continue their fast reorientation with an activation energy of ca 2 kJ mole(-1). This fast reorientation cannot be evidenced in NMR relaxation experiments. Splitting of certain IR bands connected with H2O ligands at the observed phase transitions suggests a reduction of the symmetry of the octahedral [Mg(H2O)6](2+) complex cation.

Polymorphism of resorcinol explored by complementary vibrational spectroscopy (FT-RS, THz-TDS, INS) and first-principles solid-state computations (plane-wave DFT).

The polymorphism of resorcinol has been complementary studied by combining Raman, time-domain terahertz, and inelastic neutron scattering spectroscopy with modern solid-state density functional theory (DFT) calculations. The spectral differences, emerging from the temperature-induced structural phase transition, have been successfully interpreted with an emphasis on the low-wavenumber range. The given interpretation is based on the plane-wave DFT computations, providing an excellent overall reproduction of both wavenumbers and intensities and revealing the source of the observed spectral differences. The performance of the generalized gradient approximation (GGA) functionals in prediction of the structural parameters and the vibrational spectra of the normal-pressure polymorphs of resorcinol has been extensively examined. The results show that the standard Perdew, Burke, and Ernzerhof (PBE) approach along with its "hard" revised form tends to be superior if compared to the "soft" GGA approximation.

Vibrations and reorientations of NH3 molecules in [Mn(NH3)6](ClO4)2 studied by infrared spectroscopy and theoretical (DFT) calculations.

The vibrational and reorientational motions of NH3 ligands and ClO4(-) anions were investigated by Fourier transform middle-infrared spectroscopy (FT-IR) in the high- and low-temperature phases of [Mn(NH3)6](ClO4)2. The temperature dependencies of full width at half maximum (FWHM) of the infrared bands at: 591 and 3385cm(-1), associated with: ρr(NH3) and νas(N-H) modes, respectively, indicate that there exist fast (correlation times τR≈10(-12)-10(-13)s) reorientational motions of NH3 ligands, with a mean values of activation energies: 7.8 and 4.5kJmol(-1), in the phase I and II, respectively. These reorientational motions of NH3 ligands are only slightly disturbed in the phase transition region and do not significantly contribute to the phase transition mechanism. Fourier transform far-infrared and middle-infrared spectra with decreasing of temperature indicated characteristic changes at the vicinity of PT at TC(c)=137.6K (on cooling), which suggested lowering of the crystal structure symmetry. Infrared spectra of [Mn(NH3)6](ClO4)2 were recorded and interpreted by comparison with respective theoretical spectra calculated using DFT method (B3LYP functional, LANL2DZ ECP basis set (on Mn atom) and 6-311+G(d,p) basis set (on H, N, Cl, O atoms) for the isolated equilibrium two models (Model 1 - separate isolated [Mn(NH3)6](2+) cation and ClO4(-) anion and Model 2 - [Mn(NH3)6(ClO4)2] complex system). Calculated optical spectra show a good agreement with the experimental infrared spectra (FT-FIR and FT-MIR) for the both models.

Vibrations and reorientations of H2O molecules in [Sr(H2O)6]Cl2 studied by Raman light scattering, incoherent inelastic neutron scattering and proton magnetic resonance.

Vibrational-reorientational dynamics of H2O ligands in the high- and low-temperature phases of [Sr(H2O)6]Cl2 was investigated by Raman Spectroscopy (RS), proton magnetic resonance ((1)H NMR), quasielastic and inelastic incoherent Neutron Scattering (QENS and IINS) methods. Neutron powder diffraction (NPD) measurements, performed simultaneously with QENS, did not indicated a change of the crystal structure at the phase transition (detected earlier by differential scanning calorimetry (DSC) at TC(h)=252.9 K (on heating) and at TC(c)=226.5K (on cooling)). Temperature dependence of the full-width at half-maximum (FWHM) of νs(OH) band at ca. 3248 cm(-1) in the RS spectra indicated small discontinuity in the vicinity of phase transition temperature, what suggests that the observed phase transition may be associated with a change of the H2O reorientational dynamics. However, an activation energy value (Ea) for the reorientational motions of H2O ligands in both phases is nearly the same and equals to ca. 8 kJ mol(-1). The QENS peaks, registered for low temperature phase do not show any broadening. However, in the high temperature phase a small QENS broadening is clearly visible, what implies that the reorientational dynamics of H2O ligands undergoes a change at the phase transition. (1)H NMR line is a superposition of two powder Pake doublets, differentiated by a dipolar broadening, suggesting that there are two types of the water molecules in the crystal lattice of [Sr(H2O)6]Cl2 which are structurally not equivalent average distances between the interacting protons are: 1.39 and 1.18 Å. However, their reorientational dynamics is very similar (τc=3.3⋅10(-10) s). Activation energies for the reorientational motion of these both kinds of H2O ligands have nearly the same values in an experimental error limit: and equal to ca. 40 kJ mole(-1). The phase transition is not seen in the (1)H NMR spectra temperature dependencies. Infrared (IR), Raman (RS) and inelastic incoherent neutron scattering (IINS) spectra were calculated by the DFT method and quite a good agreement with the experimental data was obtained.

Vibrational and reorientational motions of H2O ligands, phase transition and thermal properties of [Sr(H2O)6]Cl2.

One phase transition (PT) at TC(h)=252.9K (on heating) and at TC(c)=226.5K (on cooling) was detected by DSC for [Sr(H2O)6]Cl2 in 123-295K range. Thermal hysteresis of this PT equals to 26.4K. Entropy change (ΔS) value at this first-order type phase transition equals to ca. 1.5Jmol(-1)K(-1). The temperature dependences of the full width at half maximum (FWHM) values of the infrared bands associated with ρt(H2O)E and δas(HOH)E modes (at ca. 417 and 1628cm(-1), respectively) suggest that the observed phase transition is associated with a sudden change of a speed of the H2O reorientational motions. The H2O ligands in the high temperature phase reorientate quickly (correlation times 10(-11)-10(-13)s) with the activation energy of ca. 2kJmol(-1). Below TC(c) probably a part of the H2O ligands stop their reorientation, while the remainders continue their fast reorientation but with the activation energy of ca. 8kJmol(-1). Far and middle infrared spectra indicated characteristic changes at the vicinity of PT with decreasing of temperature, which suggested lowering of the crystal structure symmetry. Splitting of the band (at 3601cm(-1)) connected with vas(OH) mode near the TC(c) suggests lowering of the crystal lattice symmetry. All these facts suggest that the discovered PT is connected both with a change of the reorientational dynamics of the H2O ligands and with the change of the crystal structure.

Dynamics and the mesomorphic properties of a novel antiferroelectric liquid crystalline thiobenzoate MHPSBO10: thermal, optical and dielectric spectroscopy study.

The complementary studies of the mesomorphic properties of a novel antiferroelectric liquid crystal (AFLC) (S)-2-octile 4-S-(4'decyloxybiphenyl-4-tiocarboxy)benzoate, known under MHPSBO10 acronym have been undertaken. The polymorphism has been complementary studied in details by Differential Scanning Calorimetry (DSC), Transmitted Light Intensity (TLI) and Polarization Microscopy (POM). The switching characteristics along with multiple macroscopic parameters describing the mesomorphic properties were determined by using electro-optic measurements, both upon cooling and heating. Frequency domain dielectric spectroscopy (DS), covering a wide frequency range, has been applied to characterize the molecular motions. Several collective modes, including the low frequency processes in the condensed hexatic phase were detected, analyzed in details and followed with the temperature. The presented studies deliver a wide report of the phase transitions, molecular dynamics and the macroscopic properties of the novel antiferroelectric thiobenzoate.

Experimental (FT-IR and FT-RS) and theoretical (QC-DFT) studies of vibrational modes and molecular structure of new low-temperature phases of [Ru(NH3)6](BF4)3 and [Ru(NH3)6](ClO4)3.

Vibrational spectra of [Ru(NH(3))(6)](BF(4))(3) and [Ru(NH(3))(6)](ClO(4))(3) in their novel low-temperature solid phases were recorded using FT-IR and FT-RS. Quantum chemical calculations of molecular structure and vibrational modes were made separately for BF(4)(-),ClO(4)(-)and[Ru(NH(3))(6)](3+) ions. The harmonic vibrational frequencies and the related IR and RS bands intensities and activities, respectively, were simulated at the B3LYP/6-311+G(d) and B3LYP/LANL2TZ(f)/6-311+G(d,p) levels of the DFT. Full interpretation of the vibrational spectra has been carried out with the aid of the normal coordinate analysis. The assignments of the vibrational modes were based on the potential energy distribution data, using the MOLVIB program. The calculated Ru-N stretching frequencies are too low, in comparison to experiment, which indicates that B3LYP method underestimates the Ru-N bond strength. Some values of calculated and measured (obtained from X-ray) bond lengths and angles were also compared. Conclusions about possible interactions inside and between the complex ions were drawn.

Temperature-dependent infrared spectroscopy studies of a novel antiferroelectric liquid-crystalline thiobenzoate.

The temperature-dependent infrared spectroscopy studies of one novel antiferroelectric liquid crystal (AFLC), known under the MHPSBO10 acronym, have been undertaken. The FT-IR measurements have been performed for homeotropic and planar heterogeneous sample geometries. The main order parameters have been determined and followed with temperature. The presented study delivers complex insight into the evolution of the vibrational spectrum upon phase transitions, covering the whole mesophase range. The experimental studies have been supported by theoretical studies of MHPSBO10 in confined geometries.

Complex vibrational analysis of an antiferroelectric liquid crystal based on solid-state oriented quantum chemical calculations and experimental molecular spectroscopy.

The experimental and theoretical vibrational spectroscopic study of one of a novel antiferroelectric liquid crystals (AFLC), known under the MHPSBO10 acronym, have been undertaken. The interpretation of both FT-IR and FT-Raman spectra was focused mainly on the solid-state data. To analyze the experimental results along with the molecular properties, density functional theory (DFT) computations were performed using several modern theoretical approaches. The presented calculations were performed within the isolated molecule model, probing the performance of modern exchange-correlations functionals, as well as going beyond, i.e., within hybrid (ONIOM) and periodic boundary conditions (PBC) methodologies. A detailed band assignment was supported by the normal-mode analysis with SQM ab initio force field scaling. The results are supplemented by the noncovalent interactions analysis (NCI). The relatively noticeable spectral differences observed upon Crystal to AFLC phase transition have also been reported. For the most prominent vibrational modes, the geometries of the transition dipole moments along with the main components of vibrational polarizability were analyzed in terms of the molecular frame. One of the goals of the paper was to optimize the procedure of solid-state calculations to obtain the results comparable with the all electron calculations, performed routinely for isolated molecules, and to test their performance. The presented study delivers a complex insight into the vibrational spectrum with a noticeable improvement of the theoretical results obtained for significantly attracting mesogens using modern molecular modeling approaches. The presented modeling conditions are very promising for further description of similar large molecular crystals.

Experimental (FT-IR and FT-RS) and theoretical (DFT) studies of molecular structure and internal modes of [Mn(NH3)6](NO3)2.

Fourier-transform Raman and infrared spectra of [Mn(NH(3))(6)](NO(3))(2) were recorded and interpreted by comparison with respective theoretical spectra calculated using DFT method. The [Mn(NH(3))(6)](2+) cation equilibrium geometry with C(1) symmetry, harmonic vibrational frequencies, infrared and Raman scattering intensities were determined using B3LYP/LAN2LTZ+/6-311+G(d,p) level of theory. The band assignment was based on potential energy distribution (PED) of normal modes. The computations of NO(3)(-) anion frequencies were performed under assumption of D(3h) symmetry, using 6-311+G(d,p) basis set. In order do draw a comparison, additional calculations were performed separately for the [Cd(NH(3))(6)](NO(3))(2) and [Ni(NH(3))(6)](NO(3))(2). The computations were also carried out using selected modern exchange-correlation functionals. A sufficient general agreement between the theoretical and the experimental spectra has been achieved.

Vibrations and reorientations of H2O molecules and NO3(-) anions in [Ca(H2O)4](NO3)2 studied by incoherent inelastic neutron scattering, Raman light scattering, and infrared absorption spectroscopy.

The vibrational and reorientational motions of H(2)O ligands and NO(3)(-) anions were investigated by Fourier transform middle-infrared Raman scattering (RS) spectroscopy and phonon density of states, calculated from incoherent inelastic neutron scattering, in the high- and low-temperature phases of [Ca(H(2)O)(4)](NO(3))(2). The theoretical IR and RS spectra were also calculated by means of the quantum chemistry method using density functional theory with PBE1PBE functional at 6-311++G(2d,2p) basis set level. The temperature dependences of the full width at half maximum values of nu(s)(H(2)O) bands in both the infrared absorption and the RS spectroscopy suggest that the observed phase transitions (at T(C1) and T(C2)) are not connected with a drastic change in the speed of H(2)O reorientational motions. However, similar Raman nu(4)(NO(3)(-)) band shape measurements as a function of temperature revealed the existence of a fast NO(3)(-) reorientation in phase I, which is abruptly slowed at the phase transition at T(C1). Activation energy values for the reorientational motions of H(2)O ligands and NO(3)(-) anions were calculated.