Octahedral Fe(III) and Ni(II) complexes of a bidentate 3-(3,4-dichlorophenyl)-1-(4-(2-hydroxynaphthalen-1-yl)diazenyl)phenyl)prop-2-en-1-one azo-chalcone: Spectroscopic, electronic, and biological insights

The novel azo-chalcone ligand RD was synthesized via Claisen–Schmidt reaction followed by diazotization/coupling with β-naphthol. Fe(III) and Ni(II) complexes (FeRD, NiRD) were characterized as neutral octahedral species ([Fe(RD)₂(H₂O)Cl] and [Ni(RD)₂(H₂O)₂]) by molar conductivity (FeRD: 10.87 µS cm 2 mol⁻ 1 ; NiRD: 10.12 µS cm 2 mol⁻ 1 ). Fourier transform infrared spectroscopy confirmed bidentate coordination via phenolic O (FeRD: 3437 cm⁻ 1 ; NiRD: 3455 cm⁻ 1 ) and azo N (FeRD: 1511 cm⁻ 1 ; NiRD: 1518 cm⁻ 1 ). Magnetic moments (FeRD: 1.87 B.M.; NiRD: 3.21 B.M.) and UV-Vis transitions (FeRD: 435 nm; NiRD: 550 nm) validated geometries. Mass spectra (FeRD: m/z 998.842; NiRD: m/z 985.423) and elemental analysis (FeRD: Fe 6.14% calc/5.57%; NiRD: Ni 6.42% calc/5.94%) supported 1:2 stoichiometry. Density functional theory revealed FeRD’s optimal electronic profile: smallest ΔE (1.55 eV), highest electrophilicity (ω = 9.05 eV), and softness (σ = 0.65 eV⁻ 1 ). Biological assays showed FeRD’s superior activity ( K. pneumoniae : 95%, E. coli : 22 mm inhibition) versus NiRD (90%, 21 mm) and RD (50%, 10 mm). Molecular docking confirmed strongest TyrRS binding for FeRD (–8.70 kcal mol −1 ).