Exploring the structural and antimicrobial properties of copper(II) complexes of 2,2′-bipyridine and dicyanamide by X-ray crystallography, DFT calculations and molecular docking studies

The structural consequences of metal-mediated dicyanamide transformation in copper(II)–2,2′-bipyridine systems, and their impact on supramolecular stabilization and antibacterial activity, remain insufficiently explored. Against this backdrop, two mixed-ligand copper(II) complexes were synthesized and structurally elucidated by single-crystal X-ray diffraction, supported by spectroscopic, thermal, computational and biological investigations. Complex 1 , [Cu(bpy)₂(SCN)]CN₃·H₂O, crystallizes in the triclinic P1̅ space group and exhibits a distorted trigonal bipyramidal CuN₅ core with Cu N bond lengths of 1.9887 (Świtlicka, 2024 (14))–2.0785 (Jensen et al., 2002 (15)) Å. In contrast, complex 2, Cu(bpy)₃(OH)·H₂O, adopts a hexagonal P6/mcc lattice featuring a distorted octahedral CuN₆ environment with Cu N distances of 2.119 (Palmer and Piper, 1966 (2)) Å. Copper-mediated in situ transformation of dicyanamide generated cyanoiminoazanide (CN₃ − ) and tricyanomethanide (C(CN)₃ − ) anions. UV–Vis spectra displayed MLCT bands at 398–444 nm and d–d transitions at 669–693 nm. Thermogravimetric analysis revealed multistep decomposition between 300 and 1000 °C (Li et al., 2021 (1)) and 40–950 °C (Palmer and Piper, 1966 (2)). QTAIM and NCI plot analyses confirmed stabilizing O–H···N hydrogen bonds with electron density up to 0.01085 a.u. Both complexes exhibited moderate antimicrobial activity (MIC 125–1000 μg/mL), with complex 2 showing enhanced potency against Klebsiella pneumoniae and Candida auris (MIC = 125 μg/mL). Molecular docking suggested favorable binding to bacterial DNA gyrase and topoisomerase IV, supporting a plausible topoisomerase-mediated mode of action. • Two mixed-ligand copper(II) complexes of 2,2′-bipyridine [Cu(bpy)₂(SCN)]CN₃·H₂O ( 1 ) and [Cu(bpy) 3 ](C 4 N 3 )(OH)‧H 2 O ( 2 ) have been synthesized and characterized. • Metal-mediated in situ transformation of dicyanamide resulting in cyanoiminoazanide (CN₃ − ) anion, for complex 1 , and tricyanomethanide (C(CN)₃ − ), for complex 2 . • QTAIM and NCI plot analyses confirmed stabilizing O–H···N hydrogen bonds with electron density up to 0.01085 a.u. • Both complexes each exhibit a single emission peak at 543 nm upon excitation at 360 nm indicating charge transfer from the ligand to the metal (bpy → M 2+ ) • Moderate but broad-spectrum antimicrobial activity, with minimum inhibitory concentrations as low as 125 μg/mL for complex 2 . • Favorable binding within the catalytic pockets of bacterial DNA gyrase and topoisomerase IV.