Chiral Effect on the Spin Crossover Behavior in a Pair of Co(II) Enantiomers and their Racemic Complex

The combination of spin crossover (SCO) with chirality has caught increasing research interest owing to its potential applications in the fields of multifunctional magnetic molecular materials and devices. In this work, we synthesized a pair of homochiral Co(II) SCO complexes and their racemic complex by applying chiral Schiff base terimine ligands modified by naphthyl group. Single-crystal X-ray diffraction results showed that the chiral ligands retained chirality after coordination with Co(II) ion, giving rise to a pair of enantiomeric Co(II) complexes in the RR and SS configurations, respectively. The circular dichroism spectroscopy demonstrated the enantiomeric nature of the homochiral complexes. The enantiomers exhibited similar thermally induced SCO, while the racemate was trapped in the high spin state. The differences in SCO behavior between the homochiral and racemic complexes are attributed to different supramolecular interactions. This work provides a feasible approach to constructing new chiral SCO materials and offers perspectives in developing switchable nonlinear optical magnetic materials.