Enhancement of Electrical Conductivity due to Structural Distortion from Linear to Nonlinear Dicarboxylato-Bridged Zn(II) 1D-Coordination Polymers

Abstract

Coordination polymers are useful materials in different fields of applications, including the development of supramolecular electrical devices for the use of renewable energy sources. In this work, we have designed two new classes of mixed-ligand one-dimensional coordination polymers (1D CPs) [Zn(ADC)(PBT)2(H2O)2]n (1) and [Zn(Succ)(PBT)2(H2O)2]n (2) (ADC2–, acetylenedicarboxylato; Succ2–, succinato; PBT, 2-pyridin-4-ylbenzothiazole) and characterized them by elemental analysis, infrared spectra (IR), single-crystal X-ray diffraction data, powder X-ray diffraction (PXRD), and thermogravimetric analysis (TGA) data. In the structural motif Zn(II) is bridged by an aliphatic dicarboxylato ligand (ADC/Succ) and two axial positions are occupied by pyridyl-N of PBT along with water coordination. ADC acts as a monodentate carboxylato-O ligand in compound 1, whereas in 2 Succ serves as a carboxylato-O,O chelator. Compounds 1 and 2 are both isostructural and construct 3D supramolecular networks by hydrogen bonds (bonding) and π···π interactions along with weak C–H···π interactions. Fascinatingly, compound 1 exhibits an ∼700 times higher Schottky barrier diode (SBD) electrical conductivity (1.31 × 10–2 S m–1) in comparison to compound 2 (1.80 × 10–5 S m–1). The impedance electrical conductivities of 1 (1.22 × 10–4 S m–1) and 2 (3.24 × 10–6 S m–1) differ significantly; in addition, the direct current conductivities are 1.08 × 10–4 S m–1 (1) and 5.55 × 10–6 S m–1 (2). To shed light on the charge transport mechanism of the compounds, the mobility, transit time, and density of states at a quasi-Fermi level have been evaluated. Linear dicarboxylato bridging with an sp-hybrid acetylene motif may be the reason for faster charge flow in 1 in comparison to the sp3 hybrid nonlinear succinato bridging compound 2.