Structure of 2-(((1-(3-bromophenyl)ethylidene)hydrazono)methyl)phenol and its application in the spectrophotometric determination of iron(iii)

A new reagent based on salicylaldehyde was synthesized, its crystalline structure determined, and the complex formation of this reagent with iron(III) was studied by the spectrophotometric method. The crystalline structure of the reagent was established using X-ray structural analysis. The dissociation constant of the reagent in a water-ethanol medium was determined potentiometrically: pK = 9.66 ± 0.02. The interaction of iron(III) with 2-(((1-(3-bromophenyl)ethylidene)hydrazono)methyl)phenol was studied in the presence and absence of diantipyrylmethane (DAM), diantipyrylphenylmethane (DAFPM), and diantipyrylpropylmethane (DAPM). Optimal conditions for complex formation (λопт, pНопт) were found. It was established that iron(III) forms colored mixed-ligand complexes with the reagent in the presence of the third components – DAM, DAFPM, and DAPM, with a hypsochromic shift observed in the absorption spectrum. The maximum yield of complexes was achieved in a more acidic medium compared to the binary complex. The molar absorption coefficients of the complexes and their compliance with Beer's law were determined. The component ratios in the homogeneous and mixed-ligand complexes were established by the isomolar series method, the relative yield method of Starik-Barbanel, and the equilibrium shift method. All methods showed that the Fe(III)–R component ratio in the binary complex is 1:2, while in the mixed-ligand complexes Fe(III)–R–DAM, Fe(III)–R–DAFPM, and Fe(III)–R–DAPM, the ratios are 1:2:1, 1:1:1, and 1:1:2, respectively. The mixed-ligand complexes of iron(III) with 2-(((1-(3-bromophenyl)ethylidene)hydrazono)methyl)phenol are characterized by good chemical-analytical properties. The developed method was applied for determining trace amounts of iron(III) in oil sludge.