Unprecedented transformation of [I⁻·I₃⁻] to [I₄²⁻] 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.

Crystal structure of bis(1,3-phenylenedimethanaminium) bis(triiodide) tetraiodide – water (1/2) , C8H16I5N2O

“…The formal I4 2− anion in the title structure looks like a snapshot of an intermediate between the well known centrosymmetric arrangement [20] and two discrete anions [I − • I 3 − ] [24,25] and may lead to a better understanding of the bonding schemes of short-chain polyiodides.…”

“…The formal I4 2− anion is of particular interest as, depending on the interpretation of the iodide-iodine bonds, an alternative description as two iodide anions weakly attached to one I 2 molecule is possible [20,21]. Another distortion of the formal I4 2− may lead to the adduct of two anions [I − • I 3 − ] [24,25]. This contribution is part of a long term project, which focuses on polyiodides designed and trapped in hydrogen-bonded surroundings [16-21, 26, 27].…”

Effects of All‐Organic Interlayer Surface Modifiers on the Efficiency and Stability of Perovskite Solar Cells

“…For example, iodide ion readily transforms to the elemental iodine, capable of forming triiodide complex both in solution and solid states. [46][47][48][49][50] Such reaction is typically difficult to control and it can be induced by both light and oxygen, accentuating the susceptibility of the species towards ambient condition. As the resulting oxidized products could further introduce trap centers within HPs, which are potentially harmful to the performance and durability of the final materials as well as the photovoltaic devices, this highlights the need for alternative passivating agents that can function as effectively as the halides, but with much more robust stability profile.…”

“…However, they are also known to be relatively reactive. For example, iodide ion readily transforms to the elemental iodine, capable of forming triiodide complex both in solution and solid states [46–50] . Such reaction is typically difficult to control and it can be induced by both light and oxygen, accentuating the susceptibility of the species towards ambient condition.…”

Structures and phase transitions in neat 4,4′-di-tert-butyl-2,2′-bipyridyl and in its molecular complexes with either bromanilic or iodanilic acid

“…We have attempted to fit these single minima taking into account the interactions of protons with neighbouring quadrupolar halogen nuclei (Cl, Br). 39,40 The interactions are probably the main reason of the visible characteristic flattening of the spin-lattice relaxations time runs at low temperature. The obtained theoretical fit curves were drawn with the quadrupolar spin-lattice rates of each halogen (R Cl Q = 5.7 × 10 −9 s and R Br Q = 4.0 × 10 −9 s) and with suitable relaxation constants C HCl = 3.1 × 10 6 s −2 and C HBr = 5.9 × 10 6 s −2 .…”