Copper(II) complexes of 3,3'-[Ethane-1,2-diylbis(imino)]bis(propanamide) in solution

Abstract

The interaction of copper(II) ions with 3,3'-[ethane-1,2-diylbis(imino)]bis(propanamide) (H₂eip) in 0.1 mol l^-l KNO₃ at 25ºC has been studied by means of spectrophotometry and potentiometry. The acid dissociation constants of the ligand have also been determined under the same conditions. Equilibria (1) and (2) apply to the free ligand:

(H₂eip)H₂²+KA↔(H₂eip)H⁺+H⁺

(1) (H₂eip)H₂²+KA↔(H₂eip)H⁺ (2)

For the copper complexes, equilibria (3)-(5) were found to hold:

Cu²⁺H₂eip↔Cu(H₂eip)²⁺ (3)

Cu⁽H₂eip)²⁺↔Cu(H₂eip)⁺+H⁺ (4) Cu(Heip)⁺↔Cu(eip)+H⁺ (5)

The values of the equilibrium constants are: pK_A 5.79, pK_B 8.88, log K 11.89, pK'₁ 8.06, pK'₂ 9.48. The absorption maxima and the extinction coefficients of Cu(H₂eip²⁺ and Cu(eip) are, respectively, γ_max654 nm, ε_max138 cm^-1 mol^-1 1 and γ_max 543 nm, ε_max 98.6 cm^-1 mol^-1 l.