Cobalt(II) complexes derived from two Pyrazine-2-carboxamide-based ligands: Synthesis, crystal structures, visual and reusable Fe³⁺ sensing via test strips in aqueous and real water samples, with antibacterial and antioxidant studies

چکیده مقاله

The novel Co(II) complexes [Co(L^2I)₂(CH₃CN)₂(Cl)₂] (1) and [Co(L^2Br)₂(CH₃OH)₂(Cl)₂] (2) were synthesized and their structures elucidated by single crystal X-ray diffraction methods. Both complexes are mononuclear; complex 1 crystallizes in the monoclinic crystal system with space group C2/c, while complex 2 crystallizes in the triclinic system with space group Pī. In each complex, the Co(II) ion is six-coordinated, exhibiting a distorted octahedral geometry in 1 and a regular octahedral geometry in 2. Coordination involves two nitrogen atoms from the N-(2-halophenyl)pyrazine-2-carboxamide ligands (L^2I in 1 and L^2Br in 2) occupying axial positions, along with two chloride ions and two solvent molecules (acetonitrile in 1 and methanol in 2) coordinating in the equatorial plane. The two ligands, L^2I (N-(2-iodophenyl)pyrazine-2-carboxamide) and L^2Br (N-(2-bromophenyl)pyrazine-2-carboxamide), also function as sensitive and selective chemosensors for the detection of Fe³⁺ ions in the presence of various metal ions in DMSO. They exhibit significant fluorescence quenching and enhanced absorption intensity upon interaction with Fe³⁺ ions. The limit of detection for L^2I and L^2Br towards Fe³⁺ was determined to be 11.7 and 11.6 μM, respectively, while the association constants were calculated as 4.90 × 10⁴ for L^2I and 1.75 × 10³ M⁻¹ for L^2Br. Additionally, receptor L^2I demonstrated high sensitivity to Fe³⁺ in real water samples, resulting in a color change from colorless to bright yellow on test paper strips. Antibacterial culture experiments were conducted with compounds 1, 2, and the complex L^2I + Fe³⁺ against Staphylococcus aureus, Escherichia coli, and Candida albicans. The antioxidant activity of L^2I, L^2Br, 1, and 2 has also been investigated. © 2025 Elsevier B.V.