H/F Substitution Induced Large Increase of Tc in a 3D Hybrid Rare-Earth Double Perovskite Multifunctional Compound.

Invited for the cover of this issue are Le-Ping Miao, Chao Shi, Yi Zhang and co-workers at Jiangxi University of Science and Technology. The image depicts the structure diagrams of the 3D hybrid rare-earth double perovskite compounds. The phase transition temperatures of the two compounds were indicated by the "ice and fire", respectively. It implies the increase of the phase transition temperature of the compounds. Read the full text of the article at 10.1002/chem.202103913.

H/F Substitution Induced Large Increase of Tc in a 3D Hybrid Rare-Earth Double Perovskite Multifunctional Compound.

Increasing attention has been devoted to studying perovskite-type multifunctional stimuli-responsive materials with multiple channel physical characteristics. However, it remains challenging to simultaneously achieve multifunction and regulate structural phase transition temperature in hybrid perovskites. Here, we report two three-dimensional organic-inorganic hybrid rare-earth double perovskite compounds, (HQ)2 RbEu(NO3 )6 (1, HQ=quinuclidium) and (4FHQ)2 RbEu(NO3 )6 (2, 4FHQ=4-fluoro-quinuclidium), which exhibit ferroelasticity, dielectric switch, and excellent photoluminescence response. The phase transition temperature of 2 increases 169 K compared with 1 through H/F substitution. This result is attributed to the H/F substitution inducing the generation of the Rb-F coordination bond between cations and anions. Meanwhile, the photoluminescence emission intensity of 2 shows no quench with the increase of temperature, in particular, the emission spectrum achieves fine regulation at high temperatures. This work provides a new solution for the realization of multi-functions and regulations of the properties based on hybrid perovskite materials with high critical temperatures.

Structural phase transition in a charge-transfer compound: tropylium hexafluoridoantimonate(V)-1,4-dimethylnaphthalene (1/1).

Molecular motion in crystals has attracted much attention for the development of stimuli-responsive materials. The most studied are molecules with few atoms or highly symmetrical molecules. To develop molecules with new motion characteristics, we synthesized a charge-transfer compound, namely, tropylium hexafluoridoantimonate(V)-1,4-dimethylnaphthalene (1/1), (C7H7)[SbF6]·C12H12, and studied its structural phase transition. In this compound, the tropylium cation and the 1,4-dimethylnaphthalene molecule have planar geometry, but the latter has low symmetry. They are stacked as a one-dimensional chain structure through π-π charge-transfer interactions. Weak intermolecular interactions and planar molecular geometry result in a large degree of freedom of in-plane motion. Upon heating, due to the in-plane rotation of the molecules, the compound undergoes an order-disorder structural phase transition (phase-transition temperature = 334 K). The space group of the room-temperature phase is P21/m and the space group of the high-temperature phase is P4/mmm. This phase transition is accompanied by significant dielectric anomalies. The current investigation shows that the structural features of the title compound can be used to construct functional materials with phase transitions, such as molecular ferroelectrics.