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Mikuli, Edward; Migdał-Mikuli, Anna; Mayer, J.

doi:10.1023/a:1010112801504

Cited by 17 publications

(15 citation statements)

References 35 publications

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“…Further support for this conclusion comes from the fact that the I → II transition is associated with a change of perchlorate dynamics ͑MgHP; 12 NiHP; 28 MgHP, NiHP; 34 MgHP; 36 MnHP, FeHP͒. 37 This would involve breaking the hydrogen bonds and a corresponding change in E a at this transition, contrary to our observation.…”

Section: The Hindering Potential In Phase I and Iicontrasting

confidence: 89%

Hydrogen dynamics in [Me(H2O)6](ClO4)2 with Me=Mg, Mn, Fe, Ni, and Zn investigated with quasielastic neutron scattering

Nöldeke

Asmussen

Press

et al. 2000

The Journal of Chemical Physics

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The hydrogen dynamics in the metalhexahydrateperchlorates with Mg, Mn, Fe, Ni, and Zn as metal ions has been investigated with quasielastic neutron scattering. The water molecules perform 180°-flip motions on a picosecond time scale through a series of solid–solid phase transitions. In the highest temperature phase I and the subsequent phase II, rotational barriers of typically Ea=50 meV are found. These values are surprisingly small in view of the low symmetry of H2O molecules. The I → II phase transition has only very small effects on the hydrogen dynamics. At the transition into phase III an increase of the rotational barriers to typically Ea=250 meV is found. This is interpreted as the formation of weak hydrogen bonds. In phase I 180°-flip motions provide a complete description of the observed data. In phases II and III an extension of the dynamical model toward a stronger localization of hydrogen is required. A preference is given to a mechanism leading to a temporary blockade of the flip motions. In phase III of the Fe compound, the existence of crystallographically different sites for water molecules is inferred.

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Section: The Hindering Potential In Phase I and Iicontrasting

confidence: 89%

Hydrogen dynamics in [Me(H2O)6](ClO4)2 with Me=Mg, Mn, Fe, Ni, and Zn investigated with quasielastic neutron scattering

Nöldeke

Asmussen

Press

et al. 2000

The Journal of Chemical Physics

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“…, where M ¼ Mn, Fe, Co Ni or Zn, we also discovered characteristic and similar dependences of the phase transition temperature T C1 upon lattice parameters or crystal density[6]. Thus the main aim of this paper was to determine the values of phase transition parameters and to check whether [were filtered off and washed with cold water.…”

mentioning

confidence: 76%

“…For sharp peaks the values were calculated to a high accuracy (4%), whereas for the diffuse peak the estimate was less accurate. Other experimental details were the same as those published in our previous paper [7]. Subsequent cooling of melted sample leads to a peak associated with its crystallization at T cr ¼ 345 K. For this sample DSC measurements were performed also with the scanning rates: 10 K min À1 , 20 K min À1 and 30 K min À1 .…”

Section: Heat Flow Measurementsmentioning

confidence: 99%

“…These crystals form a primitive crystallographic lattice with the number of molecules in an elementary cell Z ¼ 2 and with lattice parameters: a ¼ 15.36 Å and c ¼ 5.38 Å [1][2][3]. The [Mg(H 2 O) 6 ] 2þ cation is a slightly deformed octahedron, where Mg 2þ is surrounded by six oxygen atoms coming from H 2 O ligands and the BF À 4 anion is a nearly regular tetrahedron. The compound is isomorphic with hexaaquametal(II) tetrafluoroborates, hexaaquametal(II) chlorates(VII) and hexaaquametal(II) manganates(VII), if metal(II) is manganese, iron, cobalt, nickel or zinc.…”

Section: Introductionmentioning

confidence: 99%

“…The list of band positions of the Raman (FT-RS) and infrared (FT-MIR and FT-FIR) spectra of [Mg(H 2 O)6 ](BF 4 ) 2 at room temperature (vw -very weak, w -weak, shshoulder, m -medium, s -strong, vs -very strong, br -broad) and the comparison with the literature data. MgA 6 ¼…”

mentioning

confidence: 99%

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Phase transitions in [Mg(H₂O)₆](BF₄)₂studied by differential scanning calorimetry§

2007

Self Cite

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Three solid phases of [Mg(H 2 O) 6 ](BF 4 ) 2 have been detected by differential scanning calorimetry (DSC). The phase transition temperatures: T h C1 ¼ 259.0 AE 1.5 K and T h C2 ¼ 143.3 AE 2.0 K on heating, and at: T c C1 ¼ 255.3 AE 0.3 K and T c C2 ¼ 140.6 AE 0.2 K on cooling, were determined as the mean values from results obtained for two samples independently synthetized in different ways. The presence of ca 3.7 K and 2.7 K wide hysteresis of the phase transition temperatures: T C1 and T C2 , respectively, suggests that both detected phase transitions are of the first order type. Mean values of entropy changes at the phase transitions: ÁS 1 ¼ 17.9 AE 1.3 kJ mol À1 K À1 and ÁS 2 ¼ 8.3 AE 0.2 kJ mol À1 K À1 indicate that both phase transitions are of order-disorder type. At ca T m ¼ 370.2 AE 3.1 K [Mg(H 2 O) 6 ](BF 4 ) 2 partially melts (dissolves in water). Temperature of the sample crystallization depends on the scanning rate of the cooling.

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Raman light scattering, infrared absorption and DSC studies of the phase transition and vibrational and reorientational dynamics of H₂O ligands and ClO₄^– anions in [Ba(H₂O)₃](ClO₄)₂

Hetmańczyk

Migdał-Mikuli

et al. 2012

J Raman Spectroscopy

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[Ba(H2O)3](ClO4)2 between 90 and 300 K possesses two solid phases. One phase transition of the first‐order type at: TCh = 211.3 K (on heating) and TCc = 204.6 K (on cooling) was determined by differential scanning calorimetry. The entropy change value (ΔS ≈ 15 Jmol–1 K–1), associated with the observed phase transition, indicates a moderate degree of molecular dynamical disorder. Both, vibrational and reorientational motions of H2O ligands and ClO4– anions, in the high‐temperature and low‐temperature phases, were investigated by Fourier transform far‐infrared and middle‐infrared and Raman light scattering spectroscopies. The temperature dependences of the full‐width at half‐maximum values of the bands associated with ρw(H2O) mode, in both infrared (~570 cm–1) and Raman light scattering (~535 cm–1) spectra, suggest that the observed phase transition is not associated with a sudden change of a speed of the H2O reorientational motions. Ligands reorient fast, with correlation time of the order of several picoseconds, with a mean activation energy value Ea = 5.1 kJ mol–1 in both high and low temperature phases. On the other hand, measurements of temperature dependences of full‐width at half‐maximum values of the infrared band at ~460 cm–1, associated with δd(OClO)E mode, and Raman band at ~1105 cm–1, associated with νas(ClO)F2 mode, revealed the existence of a fast ClO4– reorientation in phase I and in phase II, with the Ea(I) and Ea(II) values equal to 8.0 and 6.5 kJ mol–1, respectively. These reorientational motions of ClO4– are slightly distorted at the TC. Fourier transform far‐infrared and middle‐infrared spectra with decreasing of temperature indicated characteristic changes at the vicinity of PT at TC, which suggested lowering of the crystal structure symmetry. All these experimental facts suggest that the discovered phase transition is associated with small change of H2O ligands and somewhat major change of ClO4– anions reorientational dynamics, and with insignificant change of the crystal structure, too. Copyright © 2012 John Wiley & Sons, Ltd.

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Cited by 17 publications

References 35 publications

Hydrogen dynamics in [Me(H2O)6](ClO4)2 with Me=Mg, Mn, Fe, Ni, and Zn investigated with quasielastic neutron scattering

Hydrogen dynamics in [Me(H2O)6](ClO4)2 with Me=Mg, Mn, Fe, Ni, and Zn investigated with quasielastic neutron scattering

Phase transitions in [Mg(H₂O)₆](BF₄)₂studied by differential scanning calorimetry§

Raman light scattering, infrared absorption and DSC studies of the phase transition and vibrational and reorientational dynamics of H₂O ligands and ClO₄^– anions in [Ba(H₂O)₃](ClO₄)₂

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Untitled

Cited by 17 publications

References 35 publications

Hydrogen dynamics in [Me(H2O)6](ClO4)2 with Me=Mg, Mn, Fe, Ni, and Zn investigated with quasielastic neutron scattering

Hydrogen dynamics in [Me(H2O)6](ClO4)2 with Me=Mg, Mn, Fe, Ni, and Zn investigated with quasielastic neutron scattering

Phase transitions in [Mg(H2O)6](BF4)2studied by differential scanning calorimetry§

Raman light scattering, infrared absorption and DSC studies of the phase transition and vibrational and reorientational dynamics of H2O ligands and ClO4– anions in [Ba(H2O)3](ClO4)2

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Product

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About

Phase transitions in [Mg(H₂O)₆](BF₄)₂studied by differential scanning calorimetry§

Raman light scattering, infrared absorption and DSC studies of the phase transition and vibrational and reorientational dynamics of H₂O ligands and ClO₄^– anions in [Ba(H₂O)₃](ClO₄)₂