Mixed-metal complexes in solution. A potentiometric and spectrophotometric study of copper(II)–nickel(II)–δ-hydroxylysine complexes in aqueous solution

Abstract

Binary and ternary complexes (homo- and hetero-polynuclear) formed in the system copper(II)–nickel(II)–δ-DL- hydroxylysine have been studied by potentiometry at different temperatures and by visible spectrophotometry. In the presence of both copper(II) and nickel(II) a quite complicated complexation scheme has been observed, with the participation of the acid and aminoethanol moieties of the ligand molecule and the consequent formation of mono- and poly-nuclear species: [ML]⁺, [M(HL)]²⁺, [M(HL)₂]²⁺, [ML₂H]⁺, [NiLH₂]³⁺, [NiL₂], [NiL₃]^–, and [M₂L₂H_–2], [M₂L₂H_–2]²⁺,[Cu₂L₂H_–1]⁺, [Ni₂L₂]²⁺(with M = Cu²⁺ or Ni²⁺ and L^–= anion of δ-hydroxylysine). In addition to the above binary complexes, the mixed-metal species [CuNiL₂H_–2] and [Cu₂NiL₂H_–2]²⁺ have been found in solution. Structures in solution of relevant species have been proposed, both on the basis of visible spectra calculated for each copper(II) complex and upon thermodynamic parameters obtained by potentiometric measurements at different temperatures.