Spectroscopic and pH-metric studies of the complexation of 3-[2-(4-methylquinolin-2-yl)hydrazono]butan-2-one oxime compound

The electronic absorption spectra of the oximic quinolinyl hydrazone (MHQ; H₂L) and its Co(II) and Cu(II)-complexes have been studied in Britton–Rhobinson buffer solutions of varying pH's in 75% dioxane-water. The dissociation constant of the hydrazone (pK^H) as well as the stability constants (log K) of its chelates were determined spectrophotometrically and pH-metrically. The obtained data are in good agreement. Beer's law is valid in the ranges (0.64–6.99) and (2.36–6.48) μg/mL for Cu(II) and Co(II)-ions, respectively. On the other hand, the pK^H and log K were determined pH-metrically in 75% solvent-water; (solvent = dioxane, ethanol, methanol and isopropanol). The variation of pK^H or log K as a function of solvent parameters viz. 1/D, E_T, AN and π* was used to evaluate the dissociation and stability constants in the aqueous medium. Furthermore, the reaction of the oximic hydrazone (H₂L) with copper(II)-nitrate and chloride in addition to copper(I)-iodide afforded square planar mononuclear and binuclear complexes in which the oximic hydrazone showed three different modes of bonding. The obtained complexes reflect the strong bridging ability of the oximato group as well as its ambidentate and flexidentate characters.