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

Abstract

The interactions of 3,3'-[ethane-1,2-diylbis(imino)]bis(propanamide) (H₂eip) with cobalt(II), nickel(II) and zinc(II) ions in 0.1 mol 1^-1 KNO₃ at 25ºC have been studied by means of potentiometry. In addition, the nickel system has also been studied by means of spectrophotometry, infrared and ¹³C n.m.r. spectroscopy. Equilibria (1) and (2) were found to hold:

Ni²⁺+H₂eip↔Ni(H₂eip)²⁺ (1) Ni²⁺+H₂eip↔Ni(H₂eip)2H⁺ For the other metal ions only equilibrium (1) was observed experimentally. The values of the equilibrium constants for cobalt, nickel and zinc are log K₁ 5.39, 7.59 and 5.05 respectively, and pK₁'' 19.24 for nickel. For Ni(H₂eip)²⁺, three absorption maxima were found at γ_max 746, 595 and 367 nm with ε_max values 6.5, 6.9 and 11.5 cm^-1 mol^-1l. respectively; for Ni(eip), only one absorption maximum at γ_max 446 nm with ε_max 91.9 cm^-1 mol^-1 l. was observed.