Synthesis, isolation and characterization of dinuclear oxidodiiron(III) complexes modified by monodentate pyridines

• Iron(III) complexes with different pyridine ligands were synthesized.
• Bimetallic complexes were obtained.
• Different geometries (octahedral vs tetrahedral) for the iron centres were observed.
• The two iron(III) centres are bridged by an oxo ligand.

In the present study, iron complexes modified by differently substituted monodentate pyridine ligands containing a [Fe–O–Fe] unit have been synthesized, isolated and characterized. Noteworthy, the complexes are easily accessible by the reaction of pyridines with iron(II) chloride in the presence of molecular oxygen, which is the source for the oxido bridge as proven by labelling experiments. Interestingly, in dependency of the electronic and steric properties of the applied ligand different geometries have been observed by X-ray diffraction analysis. On one hand with pyridine or 4-dimethylaminopyridine as ligand (L) a L4ClFe–O–FeCl3 motif was accessible, while with 4-tert-butylpyridine a L2Cl2Fe–O–FeCl2L2 motif was realized. With the aid of Mößbauer spectroscopy an oxidation state + III was assigned for all iron centres. Moreover, the complexes were easily converted by addition of silver benzoate to trinuclear complexes with a [Fe3O] core.

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