Synthesis, structure and effect on cotton seed germination and seedling vigor of bis(2-hydroxybenzoate) bis(pyridine-3-carboxamide) copper(II)

Abstract A novel copper(II) coordination complex, bis(2-hydroxybenzoate) bis(pyridine-3-carboxamide) copper(II) [Cu(HB) 2 (P3CA) 2 ], was synthesized and structurally characterized using single-crystal X-ray diffraction, spectroscopic techniques (FT-IR, UV–Vis), SEM–EDS, and XRF analyses. The complex exhibits a distorted octahedral geometry with N 2 O 4 coordination involving nitrogen from pyridine-3-carboxamide and oxygen from salicylate ligands. Hirshfeld surface analysis confirmed that strong hydrogen bonding and π–π stacking interactions stabilize the supramolecular structure. Computational studies using DFT revealed significant electron delocalization and donor-acceptor behaviour, suggesting high electronic mobility. Molar conductivity data highlighted efficient ionic dissociation in solution. The biological relevance was explored through phytotesting on cotton ( Gossypium hirsutum ) seeds, revealing that low concentrations of the complex significantly improved germination and seedling vigour. A concentration of 0.04 % showed 100 % germination and enhanced seedling biomass. These findings demonstrate the multifunctional nature of the complex, combining structural stability, electronic activity, and plant growth-promoting effects. The synthesized [Cu(HB) 2 (P3CA) 2 ] complex demonstrated significantly enhanced antimicrobial activity, 15–25 % against Bacillus subtilis and Pseudomonas aeruginosa , and 55 % against Candida albicans compared to salicylic acid, as evaluated by the agar well diffusion method.