Łukasz Hetmańczyk

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 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.

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.

Phase transition, thermal dissociation and dynamics of NH3 ligands in [Cd(NH3)4](ReO4)2.

High temperature phase transition in [Cd(NH3)4](ReO4)2 at Tc=368.5K (on heating) was reported for the first time. Thermal stability was investigated by thermal analysis methods. The titled compound decomposes in three main stages. The first two are connected with deamination process whereas in the last step Re2O7 evaporates. The activation energy for NH3 lost processes was estimated from TG measurements. The dynamics of NH3 ligands in the low temperature phase was probed by various complementary techniques. Temperature dependent band shape analysis of properly chosen infrared and Raman scattering vibrational bands was performed. It was found that activation energy for NH3 reorientational motion (below 300K) is rather small and is equal to ca. 4kJmol(-1). The quasielastic neutron scattering measurements revealed that NH3 groups perform fast stochastic reorientational motion even in the low temperatures. The neutron and X-ray powder diffraction data do not revealed any drastic changes in the crystal structure in the wide temperature range.

Crystal structure, solid-solid phase transition and thermal properties of [Mn(H2O)2](ReO4)2

Abstract Using differential scanning calorimetry, one phase transition at = 285.0 K (on heating) and = 284.5 K (on cooling) was detected for [Mn(H2O)2](ReO4)2 in the temperature range 120–295 K. Sharpness of the heat flow anomaly and thermal hysteresis associated with this anomaly suggest that the detected phase transition is a first-order one. The following thermodynamic parameters for phase II ↔ phase I transition were obtained: ΔH ≈ 2.0 kJmol−1 and ΔS ≈ 6.9 Jmol-1 K−1. The latter quantity is close to Rln2, indicating some degree of molecular dynamical (configurational) disorder of the high temperature phase. X-ray single crystal diffraction and neutron powder diffraction results revealed that the phase transition discovered at is associated also with a change of the crystal structure from monoclinic (space group: I2/m, No. 12) to triclinic (P-1, No. 2). Moreover one hydrogen is disordered between two possible positions in the high temperature phase. Far infrared absorption spectra registered on cooling indicate at the vicinity of splitting of some degenerate vibrational modes. Additionally, one can observe a few new bands in the wavenumber ranges of 500–350 and 170–125 cm−1.