Syntheses and Structures of Four Pairs of Coordination Polymers Based on 2,2′-((5-(Methoxycarbonyl)-1,3-phenylene)bis(oxy))dipropanoic Acid

Hydrothermal reactions of rare earth (Nd, Sm, Eu, and Tb) and l- or d-lactic acid are used to construct four pairs of homochiral metal–organic frameworks (HMOFs) with polymetallic building blocks, namely, {[Nd₂(L)₂(H₂O)₃]·4H₂O}_n (1-r)/(1-s) and {[Ln₂(L)₂(H₂O)₂]·4H₂O}_n {Ln = Sm (2), Eu (3), Tb (4)} (n-r)/(n-s). The eight complexes were characterized by single-crystal X-ray diffraction, infrared spectra, elemental analysis, thermogravimetric analysis, electronic circular dichroism (ECD) spectra, and powder X-ray diffraction measurements. The complexes 1–4 featuring a 3D porous metal–organic framework crystallize in chiral space groups, and their chirality is proven by the solid-state ECD spectra. Moreover, the second-harmonic generation (SHG) investigation reveals that the complexes 1-r, 2-r, 3-r, and 4-r have medium SHG eficiencies. The complexes 2, 3, and 4 exhibit relatively high luminescence properties, which could be ascribed to ligand-centered emission. The luminescence of complex 4-r could be quenched by nitrobenzaldehyde, which may be used for molecular sensing and recognition.