Syntheses, Structures, and Second-Order Nonlinear Optical Properties of Chiral Zinc(II) Coordination Polymers Based on (R)‑4-(4-(1-Carboxyethoxy)­phenoxy)-3-fluorobenzoic Acid and Effect of the Second Ligand with Imidazole Group

To investigate the construction of novel chiral coordination polymers and the effect of N-donor ligands with different lengths as the second ligand, five new chiral zinc­(II) coordination polymers based on (R)-4-(4-(1-carboxyethoxy)­phenoxy)-3-fluorobenzoic acid (H2cpfa), namely, [Zn­(cpfa)] (1), [Zn2(cpfa)2­(biim-4)2]­·2H2O (2), [Zn2(cpfa)2­(bix)2]­·2H2O (3), [Zn2(cpfa)2­(bix)2]­·CH3OH­·H2O (4), and [Zn2(cpfa)2­(bimb)2]­·CH3OH­·H2O (5) (where biim-4 = 1,1′-(1,4-butanediyl)­bis­(imidazole), bix = 1,4-bis­(imidazole-1-ylmethyl) benzene, bimb = 4,4′-bis­((1H-imidazol-1-yl)­methyl)­biphenyl), have been synthesized under hydro­(solvo)­thermal conditions. Their structures are determined by single crystal X-ray diffraction and further characterized by infrared spectra (IR), elemental analyses, powder X-ray diffraction (PXRD), circular dichroism spectra (CD), and thermogravimetric (TG) analyses. Complex 1 features a three-dimensional (3D) rhombic right-handed structure with a rare topology of 5,5T2. Complexes 2–5 involving N-donor ligands with different lengths display similar two-dimensional (2D) sq1 networks. Complex 2 is a 2D 4-connected undulated layer with (H2O)2 dimers filling in the cavities. Similar 2D undulated layers in complex 3 are connected via O–H···O hydrogen-bonds between cpfa2– anions and lattice water molecules to generate a 3D supramolecular structure. In complex 4, 2D (4,4)-sq1 sheets with large cavities form a 2-fold interpenetrated sq1 network, with the two adjacent layers stacking in an ABAB fashion. Complex 5 exhibits a structure very similar to 4, except with double right-handed helical chains available. The structures of above chiral complexes based on H2cpfa could be affected by the combined N-donor ligands’ tuning ability to the coordination number of the Zn­(II) center and the coordination configuration of the H2cpfa ligand. Furthermore, the second-order nonlinear optical properties of complexes 1–5 are also studied, and the second-harmonic generation efficiencies of the complexes could be tuned by the introduction of second N-donor ligands.