HYDROXOCOMPOUNDS OF FE(III) AS COLLOIDAL AND HETEROGENEOUS CATALYSTS FOR WATER OXIDATION TO DIOXYGEN - EXPERIMENTAL-EVIDENCE FOR A CORRELATION OF CATALYTIC ACTIVITY AND THE STRUCTURE OF THE CATALYSTS

Catalytic activity of a large set of Fe(III)-hydroxocompounds with var ious well-defined structures was studied in reaction of the oxidation of water to dioxygen by Ru(bpy)(3)(3+) as an one-electron oxidizer. Fe (III)-hydroxocompounds which have the smallest distance between Fe(III ) cations and a large amount of the terminal OH groups which should po ssess rather strong acidic properties are found to have the best catal ytic activity. Thus, the catalytic active sites seem to be constructed from two Fe ions inside octahedrons connected by their edges through oxo or hydroxo groups. gamma-FeOOH and a tetrameric complex Fe-4(OH)(1 0)(SO4) appear to be the most suitable materials with the best activit y.