Molecular motion of halogenated ethylammonium/[18]crown-6 supramolecular ions in nickel dithiolate magnetic crystals

Abstract

Supramolecular cations, consisting of ethylammonium derivatives (X–CH₂CH₂–NH₃⁺) complexed with [18]crown-6, were incorporated into [Ni(dmit)₂]⁻ crystals in order to promote molecular motion. Crystals of (X–CH₂CH₂–NH₃⁺)([18]crown-6)[Ni(dmit)₂]⁻ (1: X = H, 2: X = F, 3: X = Cl and 4: X = Br) were prepared for this purpose. Although large amplitude molecular motions do not occur in crystal 1, dynamic disorder of F–CH₂ groups takes place between two sites in crystal 2. Similar disorder of Cl–CH₂ groups along with rotation of [18]crown-6 molecules also exists in crystal 3. Crystal 4 exhibits dynamic disorder of Br–CH₂–CH₂ groups between four sites. This is especially the case for crystal 4 which undergoes a distinct dielectric response with relaxer-like behavior in the temperature dependence of the dielectric loss tangent. Interactions between [Ni(dmit)₂]⁻ ions in all crystals are antiferromagnetic, and the magnitudes of the interactions are qualitatively consistent with the strength of intermolecular interactions estimated from transfer integrals, where interactions within [Ni(dmit)₂]⁻ dimers are the larger than the others in all crystals.