Synthesis, characterization and NLO properties of a new 3D coordination polymer assembled from p-aminobenzoic acid

摘要

Reaction of Zn(NO_3)_2·6H_2O with p-aminobenzoic acid in a 1:2 molar ratio under ethanol medium at room temperature affords a new three dimensional (3D) coordination polymer [Zn(PABA)_2] ·H_2O (1) (PABA = p-aminobenzoic acid). Single-crystal X-ray diffraction reveals that 1 crystallizes in the ortho-rhombic system, space group p2_12_12_1, a = 7.614(2), b = 11.133(3), c= 16.869(4). 1 adopts a 3D open framework with H_2O molecules in the cavities. PABA, acting as bridging ligand as well as coordinating ligand, adopts a different coordination mode to bridge Zn atoms and form the 3D supramolecular structure which is further stabilized by N-H...O, O-H...O hydrogen bonding and π-π stacking interactions. Powder second-harmonic generation (SHG) efficiency measurement with Nd: YAG laser (1064 nm) radiation shows that the SHG efficiency of 1 is equivalent to KDP crystal. The present work also demonstrates that the framework of 1 is retained after removal of the guest H_2O molecules, and the H_2O molecules can be reintroduced into the framework, indicating that this complex may also be used to generate porous materials.