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

Using a lactic acid derivative, ( R )-3-(1-carboxyethoxy)benzoic acid [( R )-H 2 cea] as the chiral synthon, two chiral coordination polymers (CPs), namely, poly[[[μ 2 -2,5-bis(1 H -imidazol-1-yl)pyridine][μ 2 -( R )-3-(1-carboxylatoethoxy)benzoato]cadmium(II)] monohydrate], {[Cd(C 10 H 8 O 5 )(C 11 H 9 N 5 )]·H 2 O} n or [Cd{( R )-cea}(2,5-dip)]·H 2 O (HCU37- R ), and poly[[μ 2 -2,5-bis(2-methyl-1 H -imidazol-1-yl)pyridine][μ 2 -( R )-3-(1-carboxylatoethoxy)benzoato]cadmium(II)], {[Co(C 10 H 8 O 5 )(C 13 H 13 N 5 )]} n or [Co{( R )-cea}(2,5-dmip)] (HCU38- R ), were obtained via hydrothermal self-assembly with Cd 2+ and Co 2+ ions, respectively, in the presence of 2,5-bis(1 H -imidazol-1-yl)pyridine (2,5-dip) or 2,5-bis(2-methyl-1 H -imidazol-1-yl)pyridine (2,5-dmip). Single-crystal structure analysis reveals that both complexes crystallize in the space group P 2 1 . However, the replacement of Cd 2+ with Co 2+ 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.