Unprecedented transformation of [I−·I3−] to [I42−] polyiodides in the solid state: structures, phase transitions and characterization of dipyrazolium iodide triiodideElectronic supplementary information (ESI) available: Details of the crystal structure, thermal, optical and dielectric properties as well as proton magnetic resonance studies (1H NMR). CCDC 1022215 and 1022217. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c5dt02265g

• Main Authors: W c awik, M, Szklarz, P, Medycki, W, Janicki, R, Piecha-Bisiorek, A, Zieli ski, P, Jakubas, R
• Format: Article
• Language: English
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c5dt02265g

Dipyrazolium iodide triiodide, [C 3 N 2 H 5 + ] 2 [I − ·I 3 − ], 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 − ·I 3 − ] to [I 4 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 [C 3 N 2 H 5 + ] 2 [I − ·I 3 − ] 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. Dipyrazolium iodide triiodide, [C 3 N 2 H 5 + ] 2 [I − ·I 3 − ], has been synthesized and studied by means of X-ray diffraction, differential scanning calorimetry, dielectric measurements, and UV-Vis spectroscopy.