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Structural polymorphism in new organic-inorganic hybrid:pyrazolium bromoantimonates(III) [C3N2H5]6Sb4Br18·2H2O (tetragonal and triclinic forms). Thermal, dielectric and proton magnetic resonance (1H NMR) studies on the tetragonal form.
Autorzy
Rok wydania
2008
Czasopismo
Numer woluminu
10
Strony
1469-1479
DOI
10.1016/j.solidstatesciences.2008.02.023
Kolekcja
Język
Angielski
Typ publikacji
Artykuł
Two polymorphic forms of pyrazolium bromoantimonates(III) - [C 3N 2H 5] 6Sb 4Br 18·2H 2O: α modification - tetragonal form and β modification - triclinic form, have been synthesized and structurally characterized at 100 K. The α-polymorph consists of a unique three-dimensional (3D) anionic substructure built up of cyclic tetramers and discrete chains linked to each other, three nonequivalent pyrazolium cations and water molecules. The β-polymorph is characterized by discrete cyclic anionic tetramers [Sb 4Br 18] -6, three nonequivalent cations and water molecules. The physical properties have been studied for the [C 3N 2H 5] 6Sb 4Br 18·2H 2O (α form). The differential scanning calorimetry (DSC) revealed a complex sequence of phase transitions above room temperature. The low-frequency dielectric relaxation process was found to appear at low temperatures, which was assigned to the dynamics of dipolar pyrazolium cations. The molecular motions of the pyrazolium cations in the α-polymorph were studied in a wide temperature range by means of a proton magnetic resonance ( 1H NMR) technique. Two minima of the spin-lattice relaxation time ( T1) are disclosed: at low temperatures a wide one attributed to a small-angle-libration of cations and motion of water molecules, whereas the high temperature one assigned to the reorientation of cation about its pseudo-fivefold axis.
Adres publiczny
https://doi.org/10.1016/j.solidstatesciences.2008.02.023
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