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Title: Phase transitions and molecular motions in [Cd(H{sub 2}O){sub 6}](BF{sub 4}){sub 2} studied by DSC, {sup 1}H and {sup 19}F NMR and FT-MIR

Two solid phase transitions of [Cd(H{sub 2}O){sub 6}](BF{sub 4}){sub 2} occurring on heating at T{sub C2}=183.3K and T{sub C1}=325.3K, with 2K and 5K hysteresis, respectively, were detected by differential scanning calorimetry (DSC). High value of entropy changes indicated large orientational disorder of the high temperature and intermediate phase. Nuclear magnetic resonance ({sup 1}H NMR and {sup 19}F NMR) relaxation measurements revealed that the phase transitions at T{sub C1} and T{sub C2} were associated with a drastic and small change, respectively, of the both spin-lattice relaxation times: T{sub 1}({sup 1}H) and T{sub 1}({sup 19}F). These relaxation processes were connected with the 'tumbling' motions of the [Cd(H{sub 2}O){sub 6}]{sup 2+}, reorientational motions of the H{sub 2}O ligands, and with the iso- and anisotropic reorientation of the BF{sub 4}{sup -} anions. The cross-relaxation effect was observed in phase III. The line width and the second moment of the {sup 1}H and {sup 19}F NMR line measurements revealed that the H{sub 2}O reorientate in all three phases of the title compound. On heating the onset of the reorientation of 3 H{sub 2}O in the [Cd(H{sub 2}O){sub 6}]{sup +2}, around the three-fold symmetry axis of these octahedron, causes the isotropic reorientation of the whole cation.more » The BF{sub 4}{sup -} reorientate isotropically in the phases I and II, but in the phase III they perform slow reorientation only about three- or two-fold axes. A small distortion in the structure of BF{sub 4}{sup -} as well as of [Cd(H{sub 2}O){sub 6}]{sup 2+} is postulated. The temperature dependence of the bandwidth of the O-H stretching mode measured by Fourier transform middle infrared spectroscopy (FT-MIR) indicated that the activation energy for the reorientation of the H{sub 2}O did not change much at the T{sub C2} phase transition.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4]
  1. Department of Chemical Physics, Faculty of Chemistry, Jagiellonian University, Ulica Ingardena 3, 30-060 Cracow (Poland). E-mail: mikuli@chemia.uj.edu.pl
  2. Department of Chemical Physics, Faculty of Chemistry, Jagiellonian University, Ulica Ingardena 3, 30-060 Cracow (Poland)
  3. Institute of Molecular Physics, Polish Academy of Sciences, ul. Smoluchowskiego 17, 60-179 Poznan (Poland)
  4. Institute of Physics, A. Mickiewicz University, Umultowska 85, 61-606 Poznan (Poland)
Publication Date:
OSTI Identifier:
20653400
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Solid State Chemistry; Journal Volume: 177; Journal Issue: 10; Other Information: DOI: 10.1016/j.jssc.2004.07.008; PII: S0022-4596(04)00387-1; Copyright (c) 2004 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ABSORPTION SPECTROSCOPY; ACTIVATION ENERGY; ANIONS; CALORIMETRY; ENTROPY; FLUORINE 19; FOURIER TRANSFORMATION; HEATING; HYDROGEN 1; HYSTERESIS; INFRARED SPECTRA; LIGANDS; LINE WIDTHS; NUCLEAR MAGNETIC RESONANCE; PHASE TRANSFORMATIONS; SPIN-LATTICE RELAXATION; TEMPERATURE DEPENDENCE; TEMPERATURE RANGE 0273-0400 K; WATER