Order-Disorder Phase Transition, Anisotropic and Switchable Dielectric Constants Induced by Freeze of the Wheel-Like Motion in a Hexafluorosilicate-Based Crystal

Abstract

An order-disorder phase transition is found in a hexafluorosilicate-based crystal, bis(betainium) hexafluorosilicate bis (betaine) (1). At room temperature, 1 crystallizes in an orthorhombic space group Fddd and the hexafluorosilicate moiety exhibits partial disorder which originates from a uniaxial wheellike rotation. As temperature decreases, a total freeze of this wheel-like motion results in a second-order phase transition at 250 K and the low temperature phase of 1 belongs to a monoclinic space group C/2c. Thermal measurements and variable-temperature single-crystal X-ray diffractions confirm that distinctive order-disorder transformation of the anionic rotor is the main driving force for the solid-state phase transition. Further, theoretical computation of potential energies for the wheel-like motion elucidates the dynamic changes in the anion from rotating to static state. Moreover, dynamic changes of the crystalline in-plane rotor give rise to anisotropic and switchable dielectric constants.[a] S.

Synthesis, Structure, and Dielectric Properties of (3-Nitroanilinium) (18-Crown) (PF6)

“…Novel organic-inorganic hybrid complexes have the potential of combining the distinct properties of their components and, therefore, exhibit appealing features (e.g., dielectric anisotropy, uniaxial polarity ferroelectricity, and strongly non-linear properties) and diverse structures (e.g., zero-dimensional molecular motors, one-dimensional chains, two-dimensional layers, and three-dimensional networks) [6][7][8][9][10]. From the viewpoint of crystal engineering, the assembly of molecular complexes with motional or flexible components is an effective and rational strategy [11][12][13][14][15][16].…”

Phase transition and switchable dielectric behaviours in an organic–inorganic hybrid compound: (3-nitroanilinium) 2 (18-crown-6) 2 (H 2 PO 4 ) 2 (H 3 PO 4 ) 3 (H 2 O)

“…We have previously reported molecular rotators based on supramolecules formed by crown ether and anilinium derivatives that showed reversible phase transitions via hydrogen bonding. For example, a layered crystal of (2-nitroanilinium)(18-crown-6)(IO 4 ) showed a pair of reversible peaks at 260.5 K (cooling) and 264.5 K (heating) with heat hysteresis of approximately 4 K. Structural analysis and potential energy calculations indicated that the dielectric anomaly and phase transition occur because of intra-and intermolecular proton transfer of -NH þ 3 in 2-nitroanilinium as a consequence of -NO 2 motion in the cation [53][54][55]. It was suggested that hydrogen-bonding interactions and/or molecular motion give rise to symmetry breaking, thus leading to the dielectric anomaly behaviour as well as the phase transition.…”

Revealing the order–disorder type phase transition mechanism in two new supramolecular clathrates

“…4,5 Recently, diverse methods were used to construct and design new hybrid molecular-based materials with high-temperature reversible phase transition. [6][7][8][9][10][11] Crown ether is a kind of a typical host molecule, and acts as a stator and then can be widely used as a building block to create supramolecular host-guest compounds, while the guests, protonated organic amine cations R-NH 3 + , are easily anchored in the cavity of crown ethers via strong hydrogen bonds. [12][13][14][15][16][17] This assembled architecture with large intermolecular and intramolecular spaces is beneficial to molecular rotation and molecular group motion of host-guest supramolecular compounds.…”