Application of [(2-hydroxybenzaldehyde)-3-isatin]-bis-hydrazone for photometric determination of palladium(ii) in nickel anode material

A new complexing analytical reagent was synthesized via the condensation of salicylaldehyde with isatin hydrazone. The dissociation constant of the reagent was determined to be pK = 9.48 ± 0.03. The structure of the reagent was characterized using X-ray diffraction and NMR spectroscopy. Spectrophotometric studies were conducted to investigate the complexation of palladium(II) with [(2-hydroxybenzaldehyde)-3-isatin]-bis-hydrazone (R), both in the presence and absence of third components: diantipyrylmethane (DAM), 8-hydroxyquinoline (8-Ox), and diphenylguanidine (DPG). Optimal complexation conditions (optimal wavelength and pH) were established. It was found that Pd(II) forms colored mixed-ligand complexes with the reagent and these third components. The Pd(II)–R complex showed maximum absorbance at 440 nm, while Pd(II)–R–DAM, Pd(II)–R–8-Ox, and Pd(II)–R–DPG had absorption maxima at 465, 490, and 450 nm, respectively. Molar absorption coefficients were: Pd(II)–R: 6000 L/(mol·cm), Pd(II)–R–DAM: 10,000 L/(mol·cm), Pd(II)–R–8-Ox: 8000 L/(mol·cm), Pd(II)–R–DPG: 7500 L/(mol·cm). The optimal pH values were: Pd(II)–R: pH 4, Pd(II)–R–DAM and Pd(II)–R–DPG: pH 2, Pd(II)–R–8-Ox: pH 3. Stability constants of the complexes were determined. The applicability of Beer's law was established, and calibration equations were obtained via the least squares method. The component ratios in both binary and mixed-ligand complexes were determined using molar ratio, continuous variation (Job’s method), and equilibrium shift methods. All methods showed the following stoichiometries: Pd(II)–R (binary complex): 1 : 2, Pd(II)–R–8-Ox and Pd(II)–R–DPG: 1 : 1 : 1, Pd(II)–R–DAM: 1 : 2 : 1. The effect of various interfering ions and masking agents on complex formation was studied. It was found that Na(I), K(I), Ca(II), Ba(II), Cd(II), Ni(II), Cr(III), Co(II), Pd(IV), platinum group metals, and many anions do not interfere with the determination of Pd(II). The developed method was successfully applied for the determination of trace amounts of palladium(II) in nickel anode material.

palladium, nickel anode, structure of coordination compounds, salicylaldehyde, diantipyrylmethane, 8-hydroxyquinoline, diphenylguanidine, spectrophotometric method