Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
1411543 | Journal of Molecular Structure | 2009 | 7 Pages |
Abstract
Fourier transform middle infrared spectroscopy, inelastic/quasielastic incoherent neutron scattering and proton magnetic resonance data for [Ca(H2O)4](ClO4)2 in the temperature range of 20-300 K and 110-300 K, respectively, are reported. Lack of infrared bands broadening with increasing temperature indicated that molecular reorientational correlation time is longer than 10â12 s. The elastic peak of neutron inelastic scattering registered in the high temperature phase shows broadening, which can be well described by a model of 180° instantaneous stochastic jumps of protons around the two-fold axis formed by the CaO bond, assuming that only two out of four H2O ligands per [Ca(H2O)4]2+ formula unit undergoes fast reorientation with reorientational correlation time ÏR(H2O) of an order of 10â11 s. The analysis of the second moment M2 of 1H NMR line in the low temperature phase of [Ca(H2O)4](ClO4)2 revealed that the reorientation via 180° flips (jumps) of water molecules causes a very small changes of M2. It confirms that reorientation of H2O is fast even at 110 K. The reason for the first plateau of M2 â 9.5 Ã 10â8 T2, which was observed at ca. 110-190 K range, is the anisotropic reorientation of whole [Ca(H2O)4]2+ cations around the two-fold symmetry axis going through two calcium atoms of the neighbouring [Ca(H2O)4]2+ cations. Above the phase transition at TC4h, the anisotropic reorientation of [Ca(H2O)4]2+ (around the pseudo three-fold symmetry axis formed by the Caâ¦O direction between [Ca(H2O)4]2+ cation and ClO4â anion, lying along the hydrogen bridge bond OHâ¦O) is setting on with a frequency of the order of a few kHz, consequently above TC1h one can observe next plateau of M2 â 2.5 Ã 10â8 T2.
Related Topics
Physical Sciences and Engineering
Chemistry
Organic Chemistry
Authors
Joanna HetmaÅczyk, Anna MigdaÅ-Mikuli, Edward Mikuli, Krystyna HoÅderna-Natkaniec, Åukasz HetmaÅczyk, Ireneusz Natkaniec,