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 synthesi zed. Each ligand contains a carboxylate moiety designed to bridge two metal atoms. These central carboxylate moieties are derived from substituted ben zoic acids that in turn are linked to terminal nitrogen or oxygen donors by spacers so that framework-type polydentate ligands similar to the polypept ide frames in diiron metallobiosites are formed. Reaction of these ligands with Fe(ClO4)(3) . 9H(2)O leads to ferric mu-oxo-mu-carboxylato iron comple xes of the general formulas [Fe2O(L)(2)(H2O)(2)] (ClO4)(2) and [Fe2O(L)(B2O )] (CIO4)(2) (L = ligand), containing one or two immobilized bridging carbo xyIates, 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, Mo ssbauer) indicate that they dissociate to monomeric Fe2O units in dilute CH 3CN solutions. (C) 2000 Elsevier Science Inc. All rights reserved.