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

A newly designed mixed-ligand coordination polymer [Zn₄(bdc)₄(ppmh)₂(H₂O)]_n (1) (H₂bdc = 1,4-benzene dicarboxylic acid, ppmh = N-pyridin-2-yl-N′-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 ppmh, 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 (bdc) 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 1 is higher by 1 order (1.37 × 10^–6 S/cm) than that of the free ligand, ppmh (6.2 × 10^–7 S/cm). Especially, the responsivity of the compound 1 was 56.21 mA/W, which is 11 times higher than that of the ligand ppmh (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 1 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 1 accounts the generation of intracellular reactive oxygen species.