Speciation of the nickel(II) complexes with oxalic and malonic acids studied in 1.0 mol dm⁻³ NaCl at 25°C

Abstract

In this article, we present the results of the speciation of the binary nickel(II)-oxalic acid (H₂L) and nickel(II)-malonic acid (H₂L) systems studied by electromotive forces measurements emf (H) using 1.0 mol dm⁻³ NaCl as the ionic medium at 25°C. The experimental data were analyzed by a computational least-squares program LETAGROP/FONDO, a version of the LETAGROP program, written to analyze regular formation function and reduced formation functions, taking into account the hydrolysis of the nickel(II) cation and the acid base reactions of the ligands which were kept fixed during the analysis. In the nickel(II)-oxalic acid system the complexes [NiHL]⁺, [NiL], [Ni(OH)L]⁻, and [NiL₂]²⁻ were observed and for the nickel(II)-malonic acid system the complexes [NiHL]⁺, [NiL], [Ni(OH)L]⁻, and [Ni(OH)₂L]²⁻ were detected. The stability constants were determined and the species distribution diagrams as a function of pH are briefly discussed.

Keywords:

• Nickel(II) complexes
• Oxalic acid
• Malonic acid
• Potentiometric studies
• Speciation

Acknowledgments

We acknowledge the Decanato de Investigación y Desarrollo (DID) from Simón Bolívar University for the financial support. We also acknowledge Professors Antonio Barriola, Antonio Zapata, and Simón López from the Simón Bolívar University for their help during the work.