Tuning of the para-position of pyridyl ligands impacts the electrical properties of a series of Cd(ii) ladder polymers

Abstract

Herein, we report the synthesis, structural characterization and electrical conductivity of three new one-dimensional coordination polymers (1D CPs), [Cd(nip)(4-Clpy)(CH₃OH)] (1), [Cd(nip)(4-Brpy)(CH₃OH)] (2) and [Cd(nip)(4-Phpy)(H₂O)]·DMF·3H₂O (3) (H₂nip = 5-nitroisophthalic acid, 4-Clpy = 4-chloropyridine, 4-Brpy = 4-bromopyridine, 4-Phpy = 4-phenylpyridine and DMF = N,N-dimethylformamide). The conductivity of the compounds was successfully tuned via the modification of the para-position of the 4-Xpy (X = Cl, Br and Ph) ligands. The electrical analysis indicated that compound 3 has the highest conductivity (22.25 × 10⁻⁴ S m⁻¹) under illumination followed by 2 (19.38 × 10⁻⁴ S m⁻¹) and 1 (12.68 × 10⁻⁴ S m⁻¹). The optical characterization and density functional theory (DFT) computation also support the observed progression of conductivity in the materials. Here, the highest conductivity of compound 3 is attributed to the better π⋯π stacking interactions among the 4-Phpy and nip ligands, and the consequently increased charge transport between adjacent chains.