Tuning helical chirality and physical properties in chiral lactate-based coordination polymers by varying metal...

Using a lactic acid derivative, (R)-3-(1-carboxyethoxy)benzoic acid [(R)-H₂cea] as the chiral synthon, two chiral coordination polymers (CPs), namely, poly[[[μ₂-2,5-bis(1H-imidazol-1-yl)pyridine][μ₂-(R)-3-(1-carboxylatoethoxy)benzoato]cadmium(II)] monohydrate], {[Cd(C₁₀H₈O₅)(C₁₁H₉N₅)]·H₂O}_n or [Cd{(R)-cea}(2,5-dip)]·H₂O (HCU37-R), and poly[[μ₂-2,5-bis(2-methyl-1H-imidazol-1-yl)pyridine][μ₂-(R)-3-(1-carboxylatoethoxy)benzoato]cadmium(II)], {[Co(C₁₀H₈O₅)(C₁₃H₁₃N₅)]}_n or [Co{(R)-cea}(2,5-dmip)] (HCU38-R), were obtained via hydrothermal self-assembly with Cd²⁺ and Co²⁺ ions, respectively, in the presence of 2,5-bis(1H-imidazol-1-yl)pyridine (2,5-dip) or 2,5-bis(2-methyl-1H-imidazol-1-yl)pyridine (2,5-dmip). Single-crystal structure analysis reveals that both complexes crystallize in the space group P2₁. However, the replacement of Cd²⁺ with Co²⁺ and the change of auxiliary ligand from 2,5-dip to 2,5-dmip not only alter the coordination geometry of the metal centre and the bridging mode of the (R)-cea^2- ligand, but also significantly affect the expression of helical chirality: HCU37-R simultaneously contains left-handed and right-handed helical chains, forming a helical two-dimensional (2D) layer, whereas HCU38-R generates only a single right-handed helical chain. In addition, HCU37-R contains guest water molecules, which extend the helical layers into the final framework via hydrogen bonding, resulting in a twofold interpenetrating structure, while HCU38-R is directly stacked from 2D layers without guest molecules. HCU37-R exhibits a significant second harmonic generation (SHG) response and HCU38-R shows antiferromagnetic behaviour.