Reversible Phase Transition, Switchable Second‐Order Nonlinear Optical and Dielectric Properties in a Bismuth(III)‐Based Compound: (R)‐3‐(Fluoropyrrolidinium) 2 BiBr 5

A new Bi(III)‐based hybrid organic‐inorganic compound, (R)‐3‐(fluoropyrrolidinium) 2 BiBr 5 ( 1 ), has been synthesized by solution evaporation. It undergoes a drastic reversible phase transition that appears above the room temperature centered at 407 K, exhibiting a recognizable second‐order nonlinear optical response and noteworthy dielectric anomaly. Variable‐temperature single‐crystal structural analyses exhibit its structure consists of one‐dimensional zigzag chains of [BiBr 5 ] ∞ containing cis‐connected anionic octahedra and (R)‐3‐(Fluoropyrrolidinium) cations. We speculate, the existence of phase transition properties of 1 triggered by thermal stimulus probably originates from the deformation of anions and order‐disorder transition of the cations in the crystal lattice. All of those findings will provide a new way to design and fabricate of hybrid organic‐inorganic multifunctional stimuli‐responsive materials.