Directional Electron Transfer in Crystals of [CrCo] Dinuclear Complexes Achieved by Chirality-Assisted Preparative Method

The polarization
switching mechanism is used in various devices
such as pyroelectric sensors and memory devices. The change in polarization
mostly occurs by ion displacement. The development of materials whose
polarization switches via electron transfer in order to enhance operation
speed is a challenge. We devised a synthetic and crystal engineering
strategy that enables the selective synthesis of a [CrCo] heterometallic
dinuclear complex with a polar crystal structure, wherein polarization
changes stem from intramolecular charge transfer between Co and the
ligand. Polarization can be modulated both by visible-light irradiation
and temperature change. The introduction of chiral ligands was paramount
to the successful polarization switching in the valence tautomeric
compound. Mixing Cr and Co complexes with enantiopure chiral ligands
resulted in the selective formation of only pseudosymmetric [CrCo]
heterometallic complexes. Furthermore, the left-handed chiral ligands
preferentially interacted with their right-handed counterparts, enabling
molecules to form a polar crystal structure.