Copper(II) complexes of N-(2-methoxyphenyl)pyrazine-2-carboxamide: Synthesis, crystal structure, colorimetric and fluorescent sensing, application in rapid naked-eye detection and reversible test strips in aqueous media, antimicrobial evaluation, ...

چکیده مقاله

This study explores the synthesis and characterization of three novel copper(II) complexes based on N-(2-methoxyphenyl)pyrazine-2-carboxamide (L^Pz-2-OMe) and assesses the ligand's potential as a dual-mode chemosensor for Cu²⁺ detection. The complexes were synthesized and characterized using CHN elemental analysis, IR spectroscopy, and single-crystal X-ray diffraction. Complex 1 exhibits a distorted square pyramidal geometry around the Cu²⁺ center, while complexes 2 and 3 adopt distorted octahedral geometries. Notably, solvent variation had a pronounced impact on the coordination environment in complexes 2 and 3, highlighting the solvent's role in influencing crystal packing and coordination behavior. Supramolecular architectures are stabilized through hydrogen bonding and π–π stacking interactions. The L^Pz-2-OMe ligand demonstrated effective colorimetric and fluorescent sensing abilities toward Cu²⁺, showing a rapid, stable, and reversible response with detection limits of 1.74 × 10⁻⁴ M (UV–Vis) and 1.88 × 10⁻⁴ M (fluorescence), and a Stern–Volmer constant (K_sv) of 1.67 × 10⁴ M⁻¹. Hirshfeld surface and void analyses revealed key intermolecular interactions and efficient molecular packing. DFT calculations provided further insight into the molecular electrostatic potential distribution and frontier molecular orbitals. Antimicrobial assays indicated that while the free ligand showed negligible activity, the copper complexes exhibited significantly enhanced antibacterial effects, likely due to increased lipophilicity and stronger interactions with bacterial membranes. MIC and MBC evaluations confirmed bacteriostatic behavior at lower concentrations and bactericidal effects at higher doses. Overall, L^Pz-2-OMe represents a promising multifunctional platform for the design of Cu²⁺ sensors with potential applications in environmental and biomedical monitoring. © 2025 Elsevier B.V.