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The relationship between reorientational molecular motions and phase transitions in [Mg(H_{2}O)6](BF_{4})_{2}, studied with the use of ^{1}H and ^{19}F NMR and FT-MIR

The relationship between reorientational molecular ...

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dc.contributor.author Mikuli, Edward [SAP11006218] pl
dc.contributor.author Hetmańczyk, Joanna [SAP11019446] pl
dc.contributor.author Grad, Bartłomiej pl
dc.contributor.author Kozak, Asja pl
dc.contributor.author Wąsicki, Jan W. pl
dc.contributor.author Bilski, Paweł pl
dc.contributor.author Hołderna-Natkaniec, Krystyna pl
dc.contributor.author Medycki, Wojciech pl
dc.date.accessioned 2015-07-02T11:40:53Z
dc.date.available 2015-07-02T11:40:53Z
dc.date.issued 2015 pl
dc.identifier.issn 0021-9606 pl
dc.identifier.uri http://ruj.uj.edu.pl/xmlui/handle/item/11244
dc.language eng pl
dc.title The relationship between reorientational molecular motions and phase transitions in [Mg(H_{2}O)6](BF_{4})_{2}, studied with the use of ^{1}H and ^{19}F NMR and FT-MIR pl
dc.type JournalArticle pl
dc.abstract.en A 1H and 19F nuclear magnetic resonance study of [Mg(H2O)6](BF4)2 has confirmed the existence of two phase transitions at T c1 ≈ 257 K and T c2 ≈ 142 K, detected earlier by the DSC method. These transitions were reflected by changes in the temperature dependences of both proton and fluorine of second moments M2 H and M2 F and of spin-lattice relaxation times T1 H and T1 F. The study revealed anisotropic reorientations of whole [Mg(H2O)6]2+ cations, reorientations by 180° jumps of H2O ligands, and aniso- and isotropic reorientations of BF4 − anions. The activation parameters for these motions were obtained. It was found that the phase transition at T c1 is associated with the reorientation of the cation as a whole unit around the C3 axis and that at T c2 with isotropic reorientation of the BF4 − anions. The temperature dependence of the full width at half maximum value of the infrared band of ρt (H2O) mode (at ∼596 cm−1) indicated that in phases I and II, all H2O ligands in [Mg(H2O)6]2+ perform fast reorientational motions (180° jumps) with a mean value of activation energy equal to ca 10 kJ mole−1, what is fully consistent with NMR results. The phase transition at T c1 is associated with a sudden change of speed of fast (τR ≈ 10−12 s) reorientational motions of H2O ligands. Below T c2 (in phase III), the reorientations of certain part of the H2O ligands significantly slow down, while others continue their fast reorientation with an activation energy of ca 2 kJ mole−1. This fast reorientation cannot be evidenced in NMR relaxation experiments. Splitting of certain IR bands connected with H2O ligands at the observed phase transitions suggests a reduction of the symmetry of the octahedral [Mg(H2O)6]2+ complex cation. pl
dc.description.volume 142 pl
dc.description.number 6 pl
dc.identifier.doi 10.1063/1.4907372 pl
dc.identifier.eissn 1089-7690 pl
dc.identifier.eissn 1520-9032 pl
dc.title.journal The Journal of Chemical Physics pl
dc.language.container eng pl
dc.affiliation Wydział Chemii : Zakład Dydaktyki Chemii pl
dc.affiliation Wydział Chemii : Zakład Fizyki Chemicznej pl
dc.subtype Article pl
dc.identifier.articleid 064507 pl
dc.rights.original bez licencji pl
.pointsMNiSW [2015 A]: 35

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