Planar Positive–Zero–Negative Thermal Expansion Transition in Crystalline Supramolecular Rotors

Abstract

Zero thermal expansion materials are crucial for manufacturing high-precision devices, but most of these materials discovered so far are inorganic. Organic zero thermal expansion materials are rare due to the need for precise control over the complex supramolecular interactions between organic groups in order to modulate their thermal expansion properties. Here, we report a novel organic crystalline supramolecular rotor, [(3-chloro-1-adamantylammonium)(18-crown-6)]ClO4, which exhibits planar positive–zero–negative thermal expansion along the a- and c-axes, with zero thermal expansion behavior in the range of 250–317 K. X-ray single-crystal structures, differential scanning calorimetry (DSC) measurements, and molecular dynamics simulations disclosed that such unique transition in thermal expansion results from the static–swing–rotation transition of 18-crown-6 in the crystal structure.

Dynamic Order–Disorder Reversible Phase Transition and Anisotropic Thermal Expansions in a Single-Component Organic Molecular Crystal

“…ZTE behavior in organic molecular materials is seldom due to the difficulty in controlling the ubiquitous complex supramolecular interactions. 30 Recently, we have reported a near ZTE characteristic along with anisotropic NTE and PTE characteristics in an imidazole-based single-component system. 12 Very recently, Nakamura et al have reported planar PTE-ZTE-NTE characteristics with reasonable CTEs in an 18crown-6 complex-based metal-free crystalline supramolecular rotor.…”

“…A very few cases of single-component organic materials with colossal PTE and NTE effects, i.e., coefficient of thermal expansion, CTE > ± 100 × 10 –6 K –1 , are reported in the literature. ,, Various inorganic systems such as oxides ,,,, and metal cyanide, , coordination polymers, , and metal–organic frameworks ,,, are known to exhibit NTE and ZTE characteristics. ZTE behavior in organic molecular materials is seldom due to the difficulty in controlling the ubiquitous complex supramolecular interactions . Recently, we have reported a near ZTE characteristic along with anisotropic NTE and PTE characteristics in an imidazole-based single-component system .…”

“…Very recently, Nakamura et al have reported planar PTE-ZTE-NTE characteristics with reasonable CTEs in an 18-crown-6 complex-based metal-free crystalline supramolecular rotor. Literature reports on inorganic systems suggest that the NTE and ZTE follow a similar mechanism. ,− However, in molecular systems, certain mechanisms have been reported for the NTE phenomenon, such as tilting of the molecule, , sliding of layers, steric hindrances of the molecules, transverse vibrations of atoms, − and scissor-jack-like motion. ,, …”

Negative to positive axial thermal expansion switching of an organic crystal: contribution to multistep photoactuation

“… 4 However, organic molecular crystals that switch from NTE to PTE or vice versa without a thermal phase transition have only rarely been reported. 5 …”

A confinement-regulated (H3C–NH3)+ ion as a smallest dual-wheel rotator showing bisected rotation dynamics

“…Among various types of supramolecular rotors, crown-ether-based rotors are of particular interest, which have been intensively studied from time to time. 29–40 In confined space, the conformationally flexible crown ethers are capable of forming stable supramolecular complexes with primary ammonium (R-NH 3 ) + ions through multiple O⋯H–N hydrogen bonds, which bind and/or semi-encapsulate the primary ammonium ions, providing a confined environment for their rotation. Following this strategy, a series of crown-ether-based supramolecular rotors had been prepared merely by a one pot self-assembly method, without intricate chemical processes.…”