title: Unprecedented transformation of [I(-)·I3(-)] to [I4(2-)] polyiodides in the solid state: structures, phase transitions and characterization of dipyrazolium iodide triiodide.
abstract: Dipyrazolium iodide triiodide, [C3N2H5(+)]2[I(-)·I3(-)], has been synthesized and studied by means of X-ray diffraction, differential scanning calorimetry, dielectric measurements, and UV-Vis spectroscopy. Two reversible, solid-solid phase transitions (Imma (I) ↔ (II) ↔Pbam (III)) at 254 K and 182/188 K respectively have been revealed. The anionic network experiences spectacular changes associated with a huge rebuilding of the inorganic network from [I(-)·I3(-)] to [I4(2-)]. The low frequency dielectric relaxation process occurs in phase II with the activation energy of ca. 34 kJ mol(-1). The molecular motion of the pyrazolium cations in [C3N2H5(+)]2[I(-)·I3(-)] has been studied by means of proton magnetic resonance studies ((1)H NMR). The ferroelastic properties of all phases have been confirmed by polarizing microscopy observations. The molecular mechanism of the phase transitions in the compound is proposed.
authors.affiliation: Faculty of Chemistry, University of Wrocław, F. Joliot-Curie 14, 50-383 Wrocław, Poland. anna.piecha@chem.uni.wroc.pl.
authors.forename: M
authors.initials: M
authors.lastname: Węcławik
authors.forename: P
authors.initials: P
authors.lastname: Szklarz
authors.forename: W
authors.initials: W
authors.lastname: Medycki
authors.forename: R
authors.initials: R
authors.lastname: Janicki
authors.forename: A
authors.initials: A
authors.lastname: Piecha-Bisiorek
authors.forename: P
authors.initials: P
authors.lastname: Zieliński
authors.forename: R
authors.initials: R
authors.lastname: Jakubas