Biologically Relevant
Heterodinuclear Iron–Manganese
Complexes
Michaël Carboni
Martin Clémancey
Florian Molton
Jacques Pécaut
Colette Lebrun
Lionel Dubois
Geneviève Blondin
J.-M. Latour
10.1021/ic301725z.s001
https://acs.figshare.com/articles/journal_contribution/Biologically_Relevant_Heterodinuclear_Iron_Manganese_Complexes/2482504
The heterodinuclear complexes [Fe<sup>III</sup>Mn<sup>II</sup>(L-Bn)(μ-OAc)<sub>2</sub>](ClO<sub>4</sub>)<sub>2</sub> (<b>1</b>) and [Fe<sup>II</sup>Mn<sup>II</sup>(L-Bn)(μ-OAc)<sub>2</sub>](ClO<sub>4</sub>) (<b>2</b>) with the unsymmetrical
dinucleating ligand HL-Bn
{[2-bis[(2-pyridylmethyl)aminomethyl]]-6-[benzyl-2-(pyridylmethyl)aminomethyl]-4-methylphenol}
were synthesized and characterized as biologically relevant models
of the new Fe/Mn class of nonheme enzymes. Crystallographic studies
have been completed on compound <b>1</b> and reveal an Fe<sup>III</sup>Mn<sup>II</sup>μ-phenoxobis(μ-carboxylato) core.
A single location of the Fe<sup>III</sup> ion in <b>1</b> and
of the Fe<sup>II</sup> ion in <b>2</b> was demonstrated by Mössbauer
and <sup>1</sup>H NMR spectroscopies, respectively. An investigation
of the temperature dependence of the magnetic susceptibility of <b>1</b> revealed a moderate antiferromagnetic interaction (<i>J</i> = 20 cm<sup>–1</sup>) between the high-spin Fe<sup>III</sup> and Mn<sup>II</sup> ions in <b>1</b>, which was confirmed
by Mössbauer and electron paramagnetic resonance (EPR) studies.
The electrochemical properties of complex <b>1</b> are described.
A quasireversible electron transfer at −40 mV versus Ag/AgCl
corresponding to the Fe<sup>III</sup>Mn<sup>II</sup>/Fe<sup>II</sup>Mn<sup>II</sup> couple appears in the cyclic voltammogram. Thorough
investigations of the Mössbauer and EPR signatures of complex <b>2</b> were performed. The analysis allowed evidencing of a weak
antiferromagnetic interaction (<i>J</i> = 5.72 cm<sup>–1</sup>) within the Fe<sup>II</sup>Mn<sup>II</sup> pair consistent with
that deduced from magnetic susceptibility measurements (<i>J</i> = 6.8 cm<sup>–1</sup>). Owing to the similar value of the
Fe<sup>II</sup> zero-field splitting (<i>D</i><sub>Fe</sub> = 3.55 cm<sup>–1</sup>), the usual treatment within the strong
exchange limit was precluded and a full analysis of the electronic
structure of the ground state of complex <b>2</b> was developed.
This situation is reminiscent of that found in many diiron and iron–manganese
enzyme active sites.
2012-10-01 00:00:00
FeIIMnII
enzyme
EPR
susceptibility
FeIIIMnII
1 H NMR spectroscopies
antiferromagnetic interaction
investigation
FeII
Mo
quasireversible electron transfer
cm
FeIII
analysis