6533b834fe1ef96bd129deed

RESEARCH PRODUCT

Solution chemistry of N,N'-ethylenebis(salicylideneimine) and its copper(II), nickel(II) and iron(III) complexes

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Abstract Potentiometric determination of protonation-deprotonation equilibria of the N,N'-ethylenebis(salicylideneimine) (H2sal2en), the related N-(2-aminoethyl)salicylideneimine, (Hsalen), and their organic fragments, salicylaldehyde (Hsal) and ethylenediamine (en), has been used to study the equilibria involved in the formation of Schiff bases from Hsal, sal− and en and in their complex formation with copper(II), nickel(II) and iron(III) ions in dimethyl sulfoxide (dmso)-water (80:20 wt./wt.) mixture (25 °C and 0.1 mol dm−3 KClO4 ionic strength): en+Hsal⇔Hsalen; en+2Hsal⇔H2sal2en; en+ sal−⇔salen−; en+2sal−⇔sal2en2−; sal−+en+MN+⇔[M(salen)](n−1)+; 2sal−+en+Mn+⇔ [M(sal2en)](n−2)+. In these three cases, the ligand sal2en2− exhibits a planar configuration. However, it is forced to adopt the non-planar cis-β configuration (iron(III) complex) in the presence of a bidentate ligand such as catecholate (cat2−) in order to accommodate the chelating bidentate ligand. This nonplanar configuration is not observed in the sal2en2− containing copper(II) and nickel(II) complexes. All these features are analyzed and discussed.