Polarity and ferromagnetism in two-dimensional hybrid copper perovskites with chlorinated aromatic spacers

Abstract

Two-dimensional (2D) organic−inorganichybrid copper perovskites have drawn tremendous attention as promisingmultifunctional materials. Herein, by incorporating ortho, metaand para-chlorine substitution in the benzylamine structure, we firstlyreport theinfluence of positional isomerism on the crystal structures of chlorobenzylammonium copper (II) chloride perovskites A2CuCl4. 2Dpolar ferromagnets (3-ClbaH)2CuCl4 and (4-ClbaH)2CuCl4(ClbaH+ = chlorobenzylammonium) are successfully obtained. They bothadopt a polar monoclinic space group Cc at room temperature, displayingsignificant differences in crystal structures. In contrast, (2-ClbaH)2CuCl4adopts a centrosymmetric space group P21/c at roomtemperature. This associated structural evolution successfullyenhances the physical properties of the two polar compounds with high thermalstability, discernible second harmonic generation (SHG) signals, ferromagnetism,and narrowoptical band gaps.These findings demonstrate that theintroduction of chlorine atoms into the inter-layer organicspecies is a powerful tool to tune crystalsymmetries and physical properties, and this inspires further exploration of designinghigh-performance multifunctional copper-based materials.