Dynamics of a caged imidazolium cation-toward understanding the order-disorder phase transition and the switchable dielectric constant.

A molecular compass-like behaviour is found in a perovskite-type cage compound (HIm)2[KCo(CN)6] (HIm = imidazolium cation). The dynamic changes in the HIm cation from the static to rotating state along with the rearrangement of the host cage result in switchable and anisotropic dielectric constants.

Switching Dielectric Constant Near Room Temperature in a Molecular Crystal.

The organic salt bis(2-chloroethyl)amine hydrochloride shows a sharp switching of its dielectric constant at 320 K. The switching property originates from the dynamic changes of the (2-chloroethyl)ammonium cation between frozen and motional states, corresponding to a structural phase transition.

An organic-inorganic hybrid compound containing imidazolium cations and a one-dimensional lithium hexacyanidocobaltate-based anionic framework.

An organic-inorganic hybrid compound, catena-poly[bis(3H-imidazol-1-ium) [[tetracyanido-κ(4)C-cobalt(III)]-µ-cyanido-κ(2)C:N-[diaqualithium(I)]-µ-cyanido-κ(2)N:C]], {(C3H5N2)2[CoLi(CN)6(H2O)2]}n, was synthesized by the reaction of Li3[Co(CN)6] with imidazolium chloride in aqueous solution. The compound crystallizes in the monoclinic space group C2/c (data collected at 273 K). In the crystal structure, neighbouring [Co(CN)6](3-) anionic units are linked by Li(+) cations through the cyanide groups in a trans mode, forming a one-dimensional zigzag chain structure extending along the c axis. A three-dimensional supramolecular network is formed through hydrogen-bonding interactions and is further stabilized by weak CN···π interactions between the cyanide groups and the imidazolium cations.

Uniaxial movements of a metal-cyanide framework switched by weak interactions through dehydration and rehydration.

A metal-cyanide framework undergoes a dehydration-rehydration triggered reversible single-crystal-to-single-crystal transformation. The resulting accordion-like contraction-expansion corresponds to a size change along the c axis as much as 24 %. This anisotropic response arises from the cooperativity among the water molecules, K ions, and CN groups between the unique two-dimensional bimetallic layers through weak interactions of hydrogen bonds and electrostatic (ionic) interactions. The key role of the water molecules in the dehydration-rehydration process is revealed by solid-state (1)H NMR spectroscopy and dielectric measurements.