Metal–organic ferroelectric complexes: enantiomer directional induction achieved above-room-temperature homochiral molecular ferroelectrics

Abstract

Ferroelectrics as a class of technically important materials have been eagerly pursued, similarly to the gold rush. In particular, in recent years, molecular ferroelectrics have stood out because of their variable structures and excellent properties. However, the discovery of new ferroelectrics is often random rather than strategically designed. Homochirality provides an important bridging effect between structure and properties, in which homochiral crystals tend to crystallize in polar space groups, increasing the possibility of the integration of homochirality with ferroelectricity. In this study, the strategy of homochirality was utilized to realize ferroelectricity in enantiomorphic metal–organic complex crystals based on a nonferroelectric racemic mixture. Unlike the nonferroelectric racemic mixture, both Cu(1,10-phenanthroline)₂SeO₄·(R-1,2-propanediol) and Cu(1,10-phenanthroline)₂SeO₄·(S-1,2-propanediol) adopted the enantiomorphic-polar point group 1 (C₁) at ambient temperature and display mirror images, as verified by the crystal structure analysis and vibrational circular dichroism (VCD) spectra. The enantiomers show 2F1-type ferroelectric phase transitions, including a similar phase transition temperature (T_c) and other ferroelectric properties. This finding reveals that the introduction of homochiral molecules provides significant structure-related physical properties crucial for the effective design of homochiral molecular ferroelectrics.