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Raman light scattering, infrared absorption and DSC studies of the phase transition and vibrational and reorientational dynamics of H 2 O ligands and ClO 4 – anions in [Ba(H 2 O) 3 ](ClO 4 ) 2
Author(s) -
Hetmańczyk Joanna,
Hetmańczyk Łukasz,
MigdałMikuli Anna,
Mikuli Edward,
WesełuchaBirczyńska Aleksandra
Publication year - 2012
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.3130
Subject(s) - raman spectroscopy , chemistry , infrared , raman scattering , analytical chemistry (journal) , differential scanning calorimetry , phase transition , infrared spectroscopy , picosecond , molecular vibration , phase (matter) , molecule , thermodynamics , optics , laser , physics , organic chemistry , chromatography
[Ba(H 2 O) 3 ](ClO 4 ) 2 between 90 and 300 K possesses two solid phases. One phase transition of the first‐order type at: T C h = 211.3 K (on heating) and T C c = 204.6 K (on cooling) was determined by differential scanning calorimetry. The entropy change value (Δ S ≈ 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 H 2 O ligands and ClO 4 – 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 ρ w (H 2 O) 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 H 2 O reorientational motions. Ligands reorient fast, with correlation time of the order of several picoseconds, with a mean activation energy value E a = 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 δ d (OClO) E mode, and Raman band at ~1105 cm –1 , associated with ν as (ClO) F 2 mode, revealed the existence of a fast ClO 4 – reorientation in phase I and in phase II, with the E a (I) and E a (II) values equal to 8.0 and 6.5 kJ mol –1 , respectively. These reorientational motions of ClO 4 – are slightly distorted at the T C . Fourier transform far‐infrared and middle‐infrared spectra with decreasing of temperature indicated characteristic changes at the vicinity of PT at T C , which suggested lowering of the crystal structure symmetry. All these experimental facts suggest that the discovered phase transition is associated with small change of H 2 O ligands and somewhat major change of ClO 4 – anions reorientational dynamics, and with insignificant change of the crystal structure, too. Copyright © 2012 John Wiley & Sons, Ltd.