Iron(III)- and copper(II) complexes of an asymmetric, pentadentate salen-like ligand bearing a pendant carboxylate group.
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, H(3)bhbdpa) 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(H(2)bhbdpa)(+), Cu(Hbhbdpa) and Cu(bhbdpa)(-). The {2NH, 2PhO(-)+COO(-)/H(2)O} 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 mu-carboxylato-mu-hydroxo-bridged dinuclear complex (Fe(2)(bhbdpa)(OH)(3)) is formed from Fe(H(2)bhbdpa)(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 Cu(2)(bhbdpa)(+) detected in the presence of copper(II) is a paramagnetic (S=1) species with relatively weakly coupled metal ions.
Jancsó
Attila
A
Department of Chemistry, University of Turku, Finland.
Paksi
Zoltán
Z
Mikkola
Satu
S
Rockenbauer
Antal
A
Gajda
Tamás
T
D002264:Carboxylic Acids / Q000737:chemistry*; D003300:Copper / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry*; D008024:Ligands; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D011522:Protons
D002264:Carboxylic Acids; D008024:Ligands; D009942:Organometallic Compounds; D011522:Protons; D003300:Copper; D007501:Iron