Two zinc(II)-based coordination polymers with flexible dicarboxylate and pyridine mixed ligands: effect of π•••π interactions on electrical activity

Two novel coordination polymers (CPs) [Zn(cis-1,4-chdc)(4-phpy)]n, (1) and [Zn(cis-1,4-chdc)(py)]n, (2) (1,4-H2chdc = 1,4-cyclohexanedicarboxylic acid, 4-phpy = 4-phenylpyridine and py = pyridine) have been synthesized and characterized by elemental analysis, infrared spectra, single crystal X-ray diffraction (SCXRD) technique, powder X-ray diffraction (PXRD) patterns and thermogravimetric analysis (TGA). Both the compounds form one-dimensional (1D) chain-like structure constructed by Zn2(CO2)4 paddle-wheel dimers interconnected via double strands of cis-1,4-chdc-bridge, where pyridine based ligands are decorated as arms on both sides of Zn2 dimers. In compound 1, polymeric 1D chains undergo self-assembly via π•••π stacking interactions among 4-phpy ligands to form a 2D network, whereas this kind of interaction is absent in 2. Interestingly, both the compounds exhibit electrical conductivity and reveal Schottky barrier diode behavior. However, compound 1 shows better electrical conductivity (1.09 × 10-3 Sm-1) with respect to compound 2 (6.01 × 10-5 Sm-1) because of the presence of π•••π interactions.