A Hexanuclear Iron(II) Layer with Two Square-Planar FeO Units Spanned by Tetrasiloxide Ligands: Mimicking of Minerals and Catalysts.

A hexanuclear iron(II) siloxide complex has been prepared by reacting an incompletely condensed silsesquioxane first with NaOMe and then with Fe(OTf). In the process of product formation, the siloxane framework undergoes a transformation and it was shown that this happens already upon addition of base: Treatment of the ligand precursor with NaOMe leads to a completely condensed silsesquioxane cage with 12 Si atoms that is composed of 2 equiv of the tetrasiloxide ligands found in the product complex. Its iron centers form a two-dimensional array reminiscent of the situations found in minerals and two-dimensional oxide films caused by segregation of FeO and silica. As the hexairon(II) assembly contains two high-spin square-planar FeO units-suggested to represent the active sites in Fe-zeolites, which react with NO to generate strongly oxidizing sites-it was treated with MeNO. This led to the oxidation of two of the iron centers to the oxidation state +III and elimination of one iron ion, so that a pentanuclear, mixed valent iron siloxide was formed. All complexes were fully characterized.