US EPA

AbstractThe asymmetrically coordinated complex [{L(Ph₂acac)Fe^III}(-O){Fe^III(Cl₄-cat)L}](BPh₄)1.5toluene has been synthesized and structurally characterized (Ph₂acac=1,3-diphenylpropane-1,3-dionate, Cl₄-cat²=tetrachlorocatecholate, L=1,4,7-trimethyl-1,4,7-triazacyclononane). This species can be electrochemically oxidized and reduced by one electron, respectively, yielding two species which both have an S=1/2 ground state. It is shown that the oxidation is ligand-centered, affording a coordinated semiquinonate(1) ligand with S=1/2 which is antiferromagnetically coupled to a high-spin Fe^III ion (S=5/2) yielding 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) yielding 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 produces an S=1/2 ground state. The symmetrical complex [{LFe^III(Ph₂acac)}₂(-O)](ClO₄)₂ has also been synthesized, as have the mononuclear species [LFe^II(Ph₂acac)Cl] and [LFe^III(aacac)Cl](ClO₄)1 mesitylene [aacac=3-(9-anthryl)acetylacetonate(1)], all of which have been characterized by X-ray crystallography. The magnetism, the Mssbauer-, EPR-, and UV-VIS-spectra and the electrochemistry of complexes are reported.