Four-step thermosensitive dielectric response arising from motionable low-symmetry ammonium confined in deformable supramolecular cages

Abstract

Molecular dielectrics with temperature-tuned dipolar motion can function as thermosensitive electropolarized materials in smart devices. Up to now, most research was limited to the dipolar motion of simple and symmetric structures, yet more complicated dielectric responses for low-symmetry dipoles in deformable space were scarcely known but quite meaningful. Here we report such a crystalline dielectric with Me₂EtNH⁺ as a low-symmetry dipolar cation enclosed by host [Ni(NCS)₆]⁴⁻ anions, namely (Me₂EtNH)₄[Ni(NCS)₆]. Upon heating, it exhibits a rarely observed four-step thermosensitive dielectric response accompanying multiple structural phase transitions, owing to gradually enhanced rotation/jumping of the Me₂EtNH⁺ ions confined in deformable supramolecular cages. The motion dynamics of this low-symmetry cation is anisotropic and strongly affected by the flexible deformability of the host supramolecular cages, suggesting a complexity of molecular dynamics in such a simple crystalline salt.