Bis(mu-alkoxo)-bridged dinuclear iron(III) complexes of pyrazole-based ligands as models for iron-oxo proteins.
S. Tanase, E. Bouwman, G.J. Long, A.M. Shanin, R. de Gelder, A.M. Mills, A.L. Spek, J. Reedijk
POLYHEDRON 2005, 24, 1, 41-48

Abstract:
The synthesis and characterization of two new bis(mu-alkoxo)-bridged dinuclear iron(III) complexes with the ligands 1-(2-hydroxyethyl)-pyrazole (Hnhep) and 1-(2-hydroxyethyl)-3,5-dimethylpyrazole (Hnhed), [Fe(nhep)Cl-2(EtOH)](2) (1) and [Fe(nhed)Cl-2](2) (2) are reported. The crystal structures of both complexes reveal the presence of centrosymmetric dinuclear units. In compound 1, the iron(III) center has a coordination number of six with a slightly distorted octahedral geometry. In compound 2, the bulkier nhed ligand, with methyl groups at the 3- and 5-positions of the pyrazole ring, leads to a coordination number of five at the iron(III) center in a distorted square pyramidal geometry. The magnetic properties of both complexes have been investigated in the range 2-300 K and indicate the presence of fairly weak antiferromagnetic exchange interactions between iron(III) ions (J(1) = -10.04 cm(-1) for 1 and J(2) = - 12.5 cm(-1) for 2). The inactivity of both complexes in the cyclohexane hydroxylation appears to be partly due to the presence of the strong iron(III)-chloride bond that does not allow exchange with the reactant molecules.