Uniaxial Movements of a Metal-Cyanide Framework Switched by Weak Interactions through Dehydration and Rehydration

Room-Temperature Anisotropic Actuation Driven by a Synergistic Order-Disorder and Displacive Phase Transition in a Ferroelectric Crystal

Actuating materials convert different forms of energy into mechanical responses. To satisfy various application scenarios, they are desired to have rich categories, novel functionalities, clear structure-property relationships, fast responses, and, in particular, giant and reversible shape changes. Herein, we report a phase transition-driven ferroelectric crystal, (rac-3-HOPD)PbI3 (3-HOPD = 3-hydroxypiperidine cation), showing intriguingly large and anisotropic room-temperature actuating behaviors. The crystal consists of rigid one-dimensional [PbI3] anionic chains running along the a-axis and discrete disk-like cations loosely wrapping around the chains, leaving room for anisotropic shape changes in both the b- and c-axes. The shape change is switched by a ferroelectric phase transition occurring at around room temperature (294 K), driven by the exceptionally synergistic order-disorder and displacive phase transition. The rotation of the cations exerts internal pressure on the stacking structure to trigger an exceptionally large displacement of the inorganic chains, corresponding to a crystal lattice transformation with length changes of +24.6% and -17.5% along the b- and c-axis, respectively. Single crystal-based prototype devices of circuit switches and elevators have been fabricated by exploiting the unconventional negative temperature-dependent actuating behaviors. This work provides a new model for the development of multifunctional mechanically responsive materials.

Solvent-Induced Structural Transformation and Luminescence Response in a Dumbbell-Shaped Crystalline Molecular Rotor

Crystalline molecular rotors constitute a new class of stimuli-responsive molecular materials owing to inherent molecular dynamics. However, beyond the molecular level, the role of molecular packings on the bulk structures and related properties has yet to be fully understood. Herein, we report a crystalline molecular rotor showing solvent-induced structural transformation and luminescence response. The molecular rotor has a dumbbell shape with two plates as the stators and one axial bridging ligand as the rotator. The crystals adopt solvated and desolvated forms with strikingly different packing structures. The solvated forms can easily transform into the desolvated form. During the structure transformation, the butterfly-like conformation of the stator undergoes a drastic dihedral angle change of about 30°, resulting in a luminescent change of about 10 nm. These findings afford a new aspect for functional molecular rotor materials.

DCM self-trapping by the host deformation in flexible host–guest molecules

The desolvated structure can self-trap the DCM molecules to return to the 1·DCM state via ligand deformation even under weak host–guest interactions. The capture behavior of DCM is mostly due to the flexibility of the ligand.

Role of the B′-site metal ion in the framework structures and dielectric transitions in host–guest type cyanometalates (HIm)2[B′Co(CN)6] (HIm = imidazolium cation)

The B′-site alkali metal ion in (HIm)₂[B′Co(CN)₆] plays a key role in the change of the framework structures and the dynamic behaviours of the guest.

Phase transition in the extreme: a cubic-to-triclinic symmetry change in dielectrically switchable cyanide perovskites

Two novel three-dimensional metal–organic compounds of formula FA₂KM(CN)₆, where M = Co, Fe and FA = formamidinium (CH(NH₂)₂⁺), have been found to crystallize in a perovskite-like architecture.

[C7H14NO][ClO4]: order–disorder structural change induced sudden switchable dielectric behaviour at room temperature

Static-to-dynamic transition in organic–inorganic hybrid [C₇H₁₄NO][ClO₄] exhibits switch-type characteristics during the dielectric transitions between high- and low-dielectric states.

Flexible crystals of perovskite-like coordination polymers with a tunable and switchable organic guest: (CH3NH3)2[KFe(CN)6] and (CH3NH3)2[KCo(CN)6]

The crystal structure has been determined for (CH₃NH₃)₂[KCo(CN)₆] at temperatures 100 and 443 K.

Distinct room-temperature dielectric transition in a perchlorate-based organic–inorganic hybrid perovskite

Distinct room-temperature dielectric transition is realized in a perchlorate-based organic–inorganic hybrid perovskite with the introduction of a polar cationic guest.