Stability of Co(III), Ni(II), and Cu(II) Complexes with 2-Furan- and 2-Thiophenecarboxyhydrazones of Pyridoxal 5-Phosphate in Neutral Aqueous Solutions

Abstract

The complexation of nickel(II), cobalt(III), copper(II) ions with 2-furan- and 2-thiophenecarbohydrazones of pyridoxal 5-phosphate in aqueous solutions was studied spectrophotometrically. The stoichiometries and conditional stability constants of the complexes at pH 7.4, T = 298.2 K, and I = 0.25 M were determined. In aqueous solutions, the coordination complexes under study contain one metal ion and two ligand molecules. For doubly charged metal cations, the conditional stability constants $$\log \beta _{2}^{'}$$ lie in the range of 10.4–11, while those for Co(III) complexes lie in the range of 14.7–15.2. The influence of the nature of hydrazide residue on the stability of complexes of d-metal ions with hydrazones is found to be small. A preliminary analysis of the potential usefulness of the studied hydrazones as indicators of the presence of Co(III), Ni(II), Cu(II) ions in solutions is performed.