Mononuclear Fe(II) and Fe(III) complexes with the tetradentate ligand N,N '-bisbenzyl-N,N '-bis(2-pyridylmethyl)-ethane-1,2-diamine. Synthesis and characterisation

Two new mononuclear iron complexes, [(LBzl(2))Fe(II)Cl-2]. H2O and [(LBzl(2 )) Fe(III)Cl-2]. Pf(6) (LBzl(2) = N,N'-bisbenzyl-N,N'-bis(2-pyridylmethyl)- ethane- 1,2-diamine) have been synthesised in view of generating complexes to mimic the active site of methane monooxygenase. Their structures have be en determined by X-ray analysis. In both species, the iron atom shows a pse udo-octahedral coordination with two pyridine nitrogen atoms in axial posit ions and two amine nitrogen atoms in the equatorial plane. Two other equato rial positions are occupied by chloride ions. The coordination bond lengths clearly indicate the sensitivity of the ligand to the oxidation state of t he iron. Thus, the Fe-N and Fe-Cl bond distances in Fe(II) complex are more elongated than corresponding distances in Fe(III). A statistical examinati on of the bond distances of hexacoordinated Fe(II) and Fe(III) complexes us ing the Cambridge Structural Database provides evidence to relate both comp lexes to their spin state. The redox potential of the Fe(III)/Fe(II) couple was determined by cyclic voltammetry. The UV-Vis spectra are dominated by charge transfer transitions. The X-band EPR spectrum of [(LBzl(2)) FeCl2]. PF6 is characteristic of an S = 5/2 species with an unusual zero-field spli tting. (C) 2000 Elsevier Science S.A. All rights reserved.