SYNTHESIS AND CHARACTERIZATION OF THE ASYMMETRICALLY COORDINATED DINUCLEAR COMPLEX (PH(2)ACAC)FE-III)(MU-O)(FE-III(CL-4-CAT)L)](CLO4) AND ITS ONE-ELECTRON REDUCED AND OXIDIZED FORMS - MODELS FOR DINUCLEAR NONHEME ACTIVE-SITES

The asymmetrically coordinated complex Ph(2)acac)Fe-III}(mu-O){Fe-III( Cl-4-cat)L}](BPh4). 1.5toluene has been synthesized and structurally c haracterized (Ph(2)acac(-) = 1,3-diphenylpropane-1,3-dionate, Cl-4-cat (2-) = tetrachlorocalecholate). L=1,4,7-trimethyl-1,4,7-triazacyclonon ane). This species can be electrochemically oxidized and reduced by on e electron, respectively, yielding two species which both have an S = 1/2 ground state. It is shown that the oxidation is ligand-centered, a ffording a coordinated semiquinonate(1-) ligand with S = 1/2 which is antiferromagnetically coupled to a high-spin Fe-III ion (S = 5/2) yiel ding an S = 2 state which, in turn, is antiferromagnetically coupled ( through the oxo bridge) to the second high-spin Fe-III ion (S = 5/2) y ielding the observed S = 1/2 ground state. In contrast, the reduction is metal-centered generating a mixed-valent species with an [Fe-III-O- Fe-II](3+) core, intramolecular antiferromagnetic coupling again produ ces an S = 1/2 ground state. The symmetrical complex [{LFeIII(Ph(2)aca c>}(2)(mu-O)](ClO4)(2) has also been synthesized, as have the mononucl ear species [LFeII(Ph(2)acac)Cl] and [LFeIII(aacac)Cl](ClO4). 1 mesity lene [aacac(-) = 3-(9-anthryl)acetylacetonate(1-)], all of which have been characterized by X-ray crystallography. The magnetism, the Mossba uer-, EPR-, and UV-VIS-spectra and the electrochemistry of complexes a re reported.