Halogen Substitution Dual Regulation of Structure and Symmetry in an Edge-Shared ABX₃ Hybrid Ferroelectric

Organic-inorganic hybrid ABX₃-type ferroelectric materials with their structural versatility hold broad application prospects in optoelectronics, data storage, sensing, and other advanced fields. Despite chemical strategies targeting organic motifs that have proven effective for the rational design of novel hybrid molecular ferroelectrics, studies on halogen substitution receiving dual regulation of structure and symmetry in an edge-shared ABX₃ hybrid ferroelectrics remain scarce. Herein, we synthesized a new one-dimensional ABX₃ hybrid ferroelectric DMEIM-CdCl₃ (DMEIM = N-(iodomethyl)-N,N-dimethylethylamine) by employing a halogen substitution strategy. This approach precisely tuned the crystal space group of the parent compound (centrosymmetric Pbca) to the ferroelectric Cc space group. Structurally, DMEIM-CdCl₃ features one-dimensional [CdCl₅]^-_n pyramidal chains composed of edge-shared CdCl₅ hexahedra, deviating from the conventional ABX₃ framework built from face- or corner-sharing polyhedra. DMEIM-CdCl₃ undergoes a characteristic ferroelectric phase transition above room temperature (T_c = 379 K) with an Aizu notation of 2/mFm. This work offers insights into expanding the family of hybrid ferroelectric materials through rational chemical design.