Iron(III)- and copper(II) complexes of an asymmetric, pentadentate salen-like ligand bearing a pendant carboxylate group

Attila Jancsó, Zoltán Paksi, Satu Mikkola, Antal Rockenbauer, Tamás Gajda

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Abstract

The equilibrium and solution structural properties of the iron(III) and copper(II) complexes of an asymmetric salen-like ligand (N,N′-bis(2- hydroxybenzyl)-2,3-diamino-propionic acid, H3bhbdpa) bearing a pendant carboxylate group were characterized in aqueous solution by potentiometric, pH-dependent electron paramagnetic resonance (EPR) and UV-Vis (UV-Visible) measurements. In the equimolar systems the pentadentate ligand forms very stable, differently protonated mononuclear complexes with both metal ions. In the presence of iron(III) {NH, PhO-, COO-}, {2NH, 2PhO-, COO-} and {2NH, 2PhO-, COO-, OH-} coordinated complexes are dominant. The EPR titrations reflected the presence of microscopic complex formation pathways, leading to the formation of binding isomers in case of Cu(H2bhbdpa)+, Cu(Hbhbdpa) and Cu(bhbdpa)-. The {2NH, 2PhO- + COO -/H2O} coordinated Cu(bhbdpa) is the only species between pH 6-11. At twofold excess of metal ion dinuclear complexes were detected with both iron(III) and copper(II). In presence of iron(III) a μ-carboxylato-μ- hydroxo-bridged dinuclear complex (Fe2(bhbdpa)(OH)3) is formed from Fe(H2bhbdpa)2+ through overlapping proton release processes, providing one of the rare examples for the stabilization of an endogenous carboxylate bridged diiron core in aqueous solution. The complex Cu2(bhbdpa)+ detected in the presence of copper(II) is a paramagnetic (S = 1) species with relatively weakly coupled metal ions.

Original languageEnglish
Pages (from-to)1480-1489
Number of pages10
JournalJournal of Inorganic Biochemistry
Volume99
Issue number7
DOIs
Publication statusPublished - Jul 1 2005

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Keywords

  • Copper(II) complexes
  • Equilibrium and solution structural studies
  • Iron(III) complexes
  • Salen-like ligands

ASJC Scopus subject areas

  • Biochemistry
  • Inorganic Chemistry

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