New dimeric Schiff base quinoline complexes: Synthesis,spectral characterization,electrochemistry and cytotoxicity

A novel Schiff base ligand (H‐DPPMHQ) derived from 2‐hydrazineylquinoline and 1,3‐diphenyl‐1H‐pyrazole‐5‐carbaldehyde and its dimeric complexes with compositions [Cr(DPPMHQ)Cl]₂?2Cl and [M(DPPMHQ)Cl]₂ (where M = Cu(II), Co(II), Ni(II) and Zn(II)) have been synthesized and characterized using physicochemical methods like elemental analysis, magnetic susceptibility and molar conductivity measurements, multispectral techniques and electrochemical studies. The molar conductance data reveal that all metal chelates are non‐electrolytes, except the Cr(III) complex which shows a Λ_M value of 146.82 Ω^?1 cm² mol^?1, indicating that it is a 1:2 electrolyte. Infrared spectral results show that the metal is organized through four nitrogen atoms (azomethine and deprotonated imine groups, pyrazole and quinoline rings) besides chlorine atoms. The NH proton is also displaced during complexation, as indicated by ¹H NMR spectral data. Based on the electron spin resonance and ligand field parameter data, the bonding parameters of these complexes have been calculated. Using Coats–Redfern and Horowitz–Metzger equations, thermodynamic parameters were determined. The spectral data indicate that the dimeric complexes have octahedral geometry around the central metal ions. The cytotoxic activities of all compounds were evaluated towards human breast cancer (MCF‐7) and lung cancer (A549) cell lines.