title: Selective imidazolidine ring opening during complex formation of iron(III), copper(II), and zinc(II) with a multidentate ligand obtained from 2-pyridinecarboxaldehyde N-oxide and triethylenetetramine.
abstract: The condensation of 2-pyridinecarboxaldehyde N-oxide and triethylenetetramine yields a product with two imidazolidine rings, as proven by a solid-state X-ray structure analysis as well as by NMR solution spectra. This ligand, L1, undergoes a ring-opening reaction on complex formation with Cu(II), yielding [CuL2]2+ where L2 functions as a pentadentate ligand, containing only one imidazolidine ring. On complexation with Zn(II) and Fe(III), both rings are opened and the complexes [ZnL3]2+ and [FeL3]3+ with a hexadentate L3 ligand are formed. The recrystallization of [ZnL3]2+ from DMSO solution results in the complex [ZnL1(DMSO)2]2+ in which L1 behaves as a tetradentate ligand. Thus L1, L2, and L3 are structural isomers with two, one, or no imidazolidine rings, as confirmed by X-ray structure analyses. The intramolecular ring formation is the result of the nucleophilic addition of the N(amino) group to the electrophilic sp2-hybridized -HC delta+=N site. Owing to the absence of the chelate effect on the sp3-hybridized carbon atom belonging to the imidazolidine ring, the ring opening is facilitated and readily observed upon complex formation with Cu(II), Zn(II), and Fe(III).
authors.affiliation: Department of Inorganic Chemistry, Slovak Technical University, SK-812 37 Bratislava, Slovakia.
authors.forename: M
authors.initials: M
authors.lastname: Boca
authors.forename: P
authors.initials: P
authors.lastname: Baran
authors.forename: R
authors.initials: R
authors.lastname: Boca
authors.forename: H
authors.initials: H
authors.lastname: Fuess
authors.forename: G
authors.initials: G
authors.lastname: Kickelbick
authors.forename: W
authors.initials: W
authors.lastname: Linert
authors.forename: F
authors.initials: F
authors.lastname: Renz
authors.forename: I
authors.initials: I
authors.lastname: Svoboda