Hydrogen‐Bonding/Steric‐Effect Competition Drives Symmetry Differentiation Toward Antiferroelectric and Ferroelectric States in Homologous 1D Hybrid Lead Bromides

ABSTRACT Molecular hybrid materials often show competing dipole arrangements, making macroscopic polarity difficult to control. Parallel dipole ordering favors ferroelectricity, whereas antiparallel ordering can cancel macroscopic polarity and potentially give rise to antiferroelectric behavior. Herein, we employ stepwise N‐ethylation as a molecular‐design strategy to regulate interaction networks and symmetry evolution in a homologous series of 1D lead bromides. The structures evolve from chiral nonpolar (MTP)PbBr 3 ( 1 , MTP = thiomorpholinium , P 2 1 2 1 2 1 ) to centrosymmetric antiferroelectric (EtMTP)PbBr 3 ( 2 , EtMTP = N‐ethylthiomorpholinium , Pbca ), and finally to polar ferroelectric (Et 2 MTP)PbBr 3 ( 3 , Et 2 MTP = N, N‐diethylthiomorpholinium , P 3 c 1 ). Structural analyses show that ethyl substitution progressively weakens directional N─H···Br hydrogen bonding while increasing the steric demand of the organic cations, thereby shifting the balance between hydrogen bonding and steric effects. In 2 , antiparallel ordering of organic dipoles produces a compensated antipolar structure, while double P–E hysteresis loops confirm antiferroelectric behavior. In 3 , diethyl substitution removes the dipole‐canceling packing mode and promotes parallel ordering, giving rise to macroscopic polarity. Compound 3 exhibits T c ≈ 400 K, P s ≈ 3.20 µC cm − 2 , and d 33 ≈ 15 pC N − 1 . This work demonstrates that hydrogen‐bonding/steric‐effect competition provides a molecular basis for regulating symmetry, dipole ordering, and multifunctionality in low‐dimensional hybrid materials.