RESUMO
Plastic crystals functioning with rotatable components offer new opportunities in areas such as modern optoelectronic materials. Here, by taking advantage of controllable rotation of the polar component within the ion-pair plastic-crystal system, we present two such crystals, namely, (Et4N)(CrO3X) (X = Cl or Br), which are unusual examples exhibiting two-staged thermosensitive dielectric responses above room temperature. The frequency-dependent response in the first stage is due to the structural phase transitions, whereas that in the second stage is induced by dynamic rotation of the polar halochromate anions in their NaCl-type plastic-crystal phases. The intrinsic mechanisms were also explicated by molecular dynamics simulations, providing a direct insight into the dynamic characteristics of these two compounds. These studies show that ionic plastic crystals functioning with polar groups are an attractive candidate as sensitive thermoresponsive dielectric materials.
RESUMO
The molecular dynamics of encapsulated cations within perovskite-like coordination polymers [(CH3)3NH][M(N3)3] (M = Mn, Cd) are investigated, which are well controlled by the confined space of a deformable azido framework. The Mn-based compound provides a rare example that features an unvaried/varied rotational energy barrier during its two different structural phase transitions.