Dissociation constants of some Schiff bases and stability constants of their copper, cobalt, nickel and zinc complexes

Abstract

The stoichiometry and stability constant of metal complexes with 4-(3-methoxy-salicylideneamino)-5-hydroxynaphthalene-2,7-disulfonic acid monosodium salt (H 2 L) and 4-(3-methoxysalicylideneamino)-5-hydroxy-6-(2,5-dichlorophenylazo)-2,7-naphthalene disulfonic acid monosodium salt (H 2 L 1 ) were studied by potentiometric titration. The stability constants of H 2 L and H 2 L 1 Schiff bases have been investigated by potentiometric titration and u.v.-vis spectroscopy in aqueous media. The dissociation constants of the ligand and the stability constants of the metal complexes were calculated pH-metrically at 25°C and 0.1 M KCl ionic strength. The dissociation constants for H 2 L were obtained as 3.007, 7.620 and 9.564 and for H 2 L 1 , 4.000, 6.525, 9.473 and 10.423, respectively. The complexes were found to have the formulae [M(L) 2 ] for M = Co(II), Ni(II), Zn(II) and Cu(II). The stability of the complexes follows the sequence: Zn(II) < Co(II) < Cu(II) < Ni(II). The high stability of H 2 L 1 towards Cu(II) and Ni(II) over the other ions is remarkable, in particular over Cu(II), and may be of technological interest. Concentration distribution diagram of various species formed in solution was evaluated for ligands and complexes. The formation of the hydrogen bonds may cause this increased stability of ligands. The pH-metric data were used to find the stoichiometry, deprotonation and stability constants via the SUPERQUAD computer program.

The Green Route from Carbon Monoxide Fixation to Functional Polyamines: A Class of High-Performing Metal Ion Scavengers

“…The fact that the Co­(II) uptake is higher than the Cu­(II) one is probably related to its specific interactions with imines (see FT-IR data). This is in agreement with other studies , and indirectly confirms the restively strong character of such affinity when taking into account the fact that Co does not display any relevant affinity for carbonyl groups (which should result indeed in the reverse order, that is, Cu > Co). This observation is probably valid also for Ni, which shows an affinity toward imine groups (Table ) only in X-PKPip and X-PKLys.…”

(E)-N′-(5-Bromo-2-methoxybenzylidene)-4-chlorobenzohydrazide

“…Schiff bases are very important ligands as they can readily form stable complexes with most metal ions (Tuncel & Sari, 2007;Sallam, 2007;Salmon et al, 2005;Ali et al, 2005;Arıcı et al, 2005;Hebbachi & Benali-Cherif, 2005;Sarı et al, 2006). Furthermore, Schiff bases and their metal complexes have excellent biological properties (Kurtoglu & Ispir, 2007;Qi et al, 2007).…”