SOLUTION CHEMISTRY OF N,N'-ETHYLENEBIS(SALICYLIDENEIMINE) AND ITS COPPER(II), NICKEL(II) AND IRON(III) COMPLEXES

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-degrees-C and 0.1 mol dm-3 KClO4 ionic strength): en + Hsal if-an-only-if Hsalen; en + 2Hsal if-an-only-if H2sal2en; en + sal- if-an-only-if salen-; en + 2sal- if-an-only-if sal2en2-; sal- + en + M(N+) if-an-only-if [M(salen)](n-1)+; 2sal- + en + M(n+) if-an-only-if [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-beta configuration (iron(III) complex) in the presence of a bidentate ligand such as catecholate (cat2-) in order to accommodate the chelating bidentate ligand. This non-planar configuration is not observed in the sal2en2- containing copper(II) and nickel(II) complexes. All these features are analyzed and discussed.