Multifunctional Triggering by Solid-Phase Molecular Motion: Relaxor Ferroelectricity, Modulation of Magnetic Exchange Interactions, and Enhancement of Negative Thermal Expansion

Abstract

Although the development of artificial molecular machines has garnered considerable attention in recent years, the construction of multifunctional solid-state molecular machines still faces several challenges. Herein, we report a supramolecular approach as an efficient strategy for building multifunctional trigger systems. In crystals composed of [Ni(dmit)2]− with a spin of S = 1/2 and supramolecular structures consisting of 4-aminopyridinium+ and benzo[18]crown-6, supramolecular cations with dynamic degrees of freedom affect the magnetic and dielectric properties and induce negative thermal expansion (NTE). The supramolecular cations in the crystals form one-dimensional columns. Two adjacent columns form a supramolecular ladder structure via π···π interactions between the phenylene groups of benzo[18]crown-6 and are arranged within a two-dimensional layer. A disorder between the two sites of the phenylene ring was observed in one of the crystallographically independent benzo[18]crown-6. Disordered benzo[18]crown-6 formed polar domains within the crystal, resulting in relaxor ferroelectricity. With increasing temperature, the supramolecular ladders elongated and the translational motion of benzo[18]crown-6 caused the molecular ladder to move closer to each other. Consequently, the crystals shrunk in the direction perpendicular to the ladder, exhibiting uniaxial NTE, and the magnetic exchange interaction between the [Ni(dmit)2]− crystals was disrupted.