Chiral three-dimensional cadmium(II)-based coordination polymer constructed from a lactic acid derivative: synthesis, structure and properties

To obtain coordination polymers with nonlinear optical (NLO) activity, the lactic acid derivative (R)-5-(1-carboxyethoxy)isophthalic acid, or (R)-H₃cia, was selected as the chiral ligand. Through a solvothermal reaction with Cd²⁺ in the presence of pyrazine (pyr), the chiral complex poly[tetraaquabis[μ-(R)-5-(1-carboxylatoethoxy)isophthalato](μ-pyrazine)tricadmium(II)], {[Cd₃(C₁₁H₇O₇)₂(C₄H₄N₂)(H₂O)₄]n or [Cd₃{(R)-cia}₂(pyr)(H₂O)₄]n (abbreviated as HU32-R), was synthesized successfully. Single-crystal X-ray diffraction analysis reveals that HU32-R crystallizes in the monoclinic space group I2 and features a three-dimensional framework. The complex exhibits good phase purity and certain water stability. Solid-state circular dichroism (CD) spectroscopy confirms its macroscopic chirality. Fluorescence spectroscopy shows an emission peak at 487 nm upon excitation at 365 nm. Furthermore, second-harmonic generation (SHG) measurements indicate that HU32-R possesses significant second-order NLO activity, with an intensity approximately 0.72 times that of potassium dihydrogen phosphate (KDP).