Structural transformation of copper coordination complexes accompanied with chiral transformation

Abstract

Four copper coordination complexes [CuL(CH₃OH)]_n (1), [CuL(C₂H₅OH)]_n (2), [(CuL)·0.5H₂O]_n (3), and [CuL(H₂O)·0.5H₂O]_n (4) with a tridentate Schiff base ligand (NaHL = sodium (E)-2-((4-fluoro-2-hydroxybenzylidene)amino)acetate) were obtained in different solvents and reaction times. Structural analysis reveals that 1 and 2 are isomorphic 2D honeycomb network coordination polymers, while 3 and 4 are 1D polymers with helical chains and zigzag chains, respectively. Both metal ions and ligands show multiple coordination modes due to the influence of the solvent, resulting in huge differences in the crystal structure. Interestingly, as time passes, achiral 1 and 2 undergo recrystallization and are transformed into the chiral M-helix structure 3. Moreover, 1, 2, and 3 can transform into 4 just by soaking in water. The mechanism of structural transformation as well as the optical and chiral properties were studied based on single-crystal structure analysis. The results indicate that the tridentate Schiff base ligand can provide flexible coordination environments to construct versatile structures and help with structural transformation.