Design and synthesis of new models for diiron biosites.

In order to mimic dinuclear active sites of some non-heme diiron proteins, ten new polydentate and potentially dinucleating ligands have been synthesized. Each ligand contains a carboxylate moiety designed to bridge two metal atoms. These central carboxylate moieties are derived from substituted benzoic acids that in turn are linked to terminal nitrogen or oxygen donors by spacers so that framework-type polydentate ligands similar to the polypeptide frames in diiron metallobiosites are formed. Reaction of these ligands with Fe(ClO4)3 x 9H2O leads to ferric mu-oxo-mu-carboxylato iron complexes of the general formulas [Fe2O(L)2(H2O)2](ClO4)2 and [Fe2O(L)(BzO)](ClO4)2 (L = ligand), containing one or two immobilized bridging carboxylates, respectively. While X-ray crystallography shows that some of these complexes are dimers or network polymers in the solid state, electrospray ionization mass spectrometry (ESMS) and spectroscopic data (UV-Vis, NMR, Móssbauer) indicate that they dissociate to monomeric Fe2O units in dilute CH3CN solutions.