Microwave‐Assisted Synthesis and Crystal Structures of 2‐Imidazolines and Imidazoles.

Hoz, António de la; Díaz‐Ortiz, Ángel; Mateo, María del Carmen; Moral, Mónica; Moreno, Andrés; Elguero, José; Foces‐Foces, Concepción; Rodríguez, Matías L.; Sánchez-Migallón, Ana

doi:10.1002/chin.200641111

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“…According to earlier structural studies on several similar bisimidazoles exemplified in Chart 2, coplanar and straight (symmetric) connection is often accompanied by symmetric locations of NH hydrogen atoms, so that the electric polarities of the two imidazolyl units cancel one another out. The molecular structures are symmetric and nonpolar for 1H,1′H-2,2′biimidazole (Bim), 27 1H,1′H-2,2′-bibenzimidazole (BBI), 28 several 1H,1′H-4,4′-biimidazole derivatives (R2-44Bim; R = H, Me, Et), 29−31 and two p-phenylene-bridged derivatives (s-44Im2P 32 and s-BI2P 33,34 ), whereas the o-phenylene-or methylene-bridged imidazoles Im2P 35 and 44Im2C 36 retain their polarity as a result of twisting of the two imidazolyl rings. The bridging spacers selected in the present study were ophenylene (BI2P (1), TMBI2P (2), and BI2X (3)), thien-2,5diyl (BI2T (4) and TMBI2T (5)), and 1H-imidazole-4,5-diyl units (BI2Im (6), TMBI2Im (7), BI2MIm (8), and TMBI2MIm (9)), which are expected to be bent, so as to eliminate inversion symmetry.…”

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confidence: 99%

Hydrogen-Bonded Architectures and Field-Induced Polarization Switching in Bridged Bis(benzimidazole) Crystals

Horiuchi

Ishibashi

Inada³

et al. 2018

Crystal Growth & Design

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The imidazole ring is chemically stable and forms an excellent building block for compounds that show externally switchable polarization in their crystalline states. We examined the structural properties of nine bridged bis-(benzimidazole)s, of which seven were new compounds, in an attempt to identify substances with highly polarizable dielectric properties arising from the multistability of their polar supramolecular architectures. Selected bridging ophenylene, thien-2,5-diyl, or 1H-imidazole-4,5-diyl units improved the thermal robustness as expected. Solution evaporation or vacuum sublimation of the bridged bis-(benzimidazole)s afforded single crystals, with or without solvent molecules, in which the molecules were hydrogen bonded to form either extended ribbons or cyclic oligomeric structures. 2,2′-(1,2-Phenylene)bis-1H-benzimidazole (BI2P) formed ladder-like ribbons that exist as low-or high-dipole configurations depending on the parallel or antiparallel orientation of the NH hydrogen atoms between the two benzimidazole rings. These two configurations were nearly degenerate in stability, permitting them to be electrically switched, as evidenced by their double (P−E) hysteresis curves. The switching process was ascribed to an order−disorder-type paraelectric-to-ferroelectric phase transition rather than to an antiferroelectric-toferroelectric phase transition. BI2P is also unique as a paraelectric crystal in which the ferroelectric state is field induced but is unexpectedly inaccessible by exclusively thermal stimulation.

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