Helical Cd‐Based Frameworks Based on Lactic Acid Derivatives and Their Second‐Order Nonlinear Optical Responses

Chiral coordination polymers (CPs) have attracted considerable attention for their unique structures and potential applications. In this study, using enantiomeric lactic acid derivatives ( R )‐4‐(1‐carboxyethoxy)‐2‐methylbenzoic acid (( R )‐H ₂ cmba) and ( S )‐H ₂ cmba as ligands, a pair of chiral CPs, [Cd(( R )‐cmba)(1,4‐bmb)]·H ₂ O (HCU34‐ R ) and [Cd(( S )‐cmba)(1,4‐bmb)]·H ₂ O (HCU34‐ S ), were successfully synthesized via hydrothermal reaction in the presence of 1,4‐bis(4‐methyl‐1H‐imidazol‐1‐yl)benzene (1,4‐bmb). Single‐crystal X‐ray diffraction analysis revealed that HCU34‐ R and HCU34‐ S crystallize in the tetragonal crystal system with space groups P 4 ₃ and P 4 ₁ , respectively. Their structures feature multiple types of helical chains along the c ‐axis, including left‐handed and right‐handed chains formed by the chiral ligands and Cd(II), helical chains formed by 1,4‐bmb and Cd(II), as well as composite helical chains constructed from all three components. These helical structures further assemble into three‐dimensional helical frameworks with fourfold interpenetrated structures exhibiting dia topological network. Solid‐state UV–vis absorption spectra indicate that the absorption intensity of both complexes increases with decreasing incident light wavelength, showing strong absorption in the ultraviolet region. Second‐order nonlinear optical (NLO) measurements demonstrate that the relative second‐harmonic generation intensities of HCU34‐ R and HCU34‐ S are 0.26 and 0.24 times that of KDP, respectively, revealing significant NLO activity.