Three-Dimensional-Coordination Polymer of Zn(II)-Carboxylate: Structural Elucidation, Photoelectrical Conductivity, and Biological Activity

Abstract

A newly designed mixed-ligand coordination polymer [Zn₄(bdc)₄(ppmh)₂(H₂O)] <i>_n</i> (<b>1</b>) (H₂ <b>bdc</b> = 1,4-benzene dicarboxylic acid, <b>ppmh</b> = <i>N</i>-pyridin-2-yl-<i>N</i>'-pyridin-4-ylmethylene-hydrazine) has been characterized using different physicochemical techniques. The structure has been confirmed by single crystal X-ray diffraction measurements. There are two pyridyl-N and one hydrazino-imine-N donor centers in <b>ppmh</b>, where two pyridyl-Ns bind simultaneously to two Zn(II) to serve as a bridging agent to form a coordination polymer. The 1,4-benzene dicarboxylato (<b>bdc</b>) is ligated via the aromatic dicarboxylato-O to form a one-dimensional (1D) chain. These two 1D chains about Zn(II) constitute a two-dimensional structure, which undergoes noncovalent interactions (C-H···π and π···π) to generate a three-dimensional supramolecular assembly. Electrical conductivity of <b>1</b> is higher by 1 order (1.37 × 10^-6 S/cm) than that of the free ligand, <b>ppmh</b> (6.2 × 10^-7 S/cm). Especially, the responsivity of the compound <b>1</b> was 56.21 mA/W, which is 11 times higher than that of the ligand <b>ppmh</b> (5.12 mA/W). The specific detectivity of the compound was 2.17 × 10¹⁰ Jones, which is also almost 10 times higher with respect to the specific detectivity of the ligand-based device (4.53 × 10⁹ Jones). The results show that the compound can be valuable for optoelectronic fields. The biological studies suggest that compound <b>1</b> is antibacterial as well as a promising anticancer agent (LD₅₀, 42.2 μg/mL against HepG2 cells), while ligands remain silent. Investigation of the mechanism of the cell killing activity of compound <b>1</b> accounts the generation of intracellular reactive oxygen species.