02-UTILIZATION & PROCESSING
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LO39 SYNTHESIS AND PROPERTIES OF DINUCLEAR
IRON-OX0 COMPLEXES WITH A BRIDGING DICARBOXYLATE LIGAND. Robert H. Beer and Stephen J. Lippard, Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139 USA. Synthesis of complexes with the (Fe2(0)(02CR)2J2+ core has bean achieved with m phenylenedipropionic acid, a ligand in which the bridging carboxylates are linked. This bridging dicarboxylate ligand facilitates the assembly of complexes not readily isolated using simple carboxylate salts, including a dinuclear complex with terminal bidentate nitrogen donors and labile ligands. Despite the significant structural change between complexes containing terminal tridentate and bidentate nitrogen donors, little or no difference is observed in their spectroscopic and magnetic properties. Complexes with a terminal labile ligand are comparable to the dinuclear iron cores in the proteins hemerythrin and ribonucleotide reductase, and undergo facile exchange reactions useful for preparing new compounds
LO4()
SPECTROSCOPIC STUDIES OF IRON(II1) COMPLEXES OF TPA (TRIS (2-PYRIDYLMETHYL)AMINE). MODELS FOR NONHEME IRON PROTEINS. Richard E. Norman, Shiping Yan, and Lawrence Que, Jr. Department of Chemistry, University of Minnesota, Minneapolis, MN 55455, USA TPA is a tetradentate ligand which, when bound to iron(III), generates a highly Lewis acidic metal site. This acidity promotes the formation of 0x0 bridges: ~e#‘PA)20(Y)]n+(C104)n where Y is a bridging ligand such as various carboxylates or phosphates. Through appropriate choice of Y the 0x0 bridge angle may be varied allowing the assessment of its impact upon the spectral properties of the resulting complexes. Surprisingly, these complexes contain inherently distinct iron sites with different TPA orientations. While the amine N is trans to the 0x0 bridge for one iron site, it is cis for the other. These complexes may well serve as models for dinuclear iron 0x0 proteins, such as ribonucleotide reductase, which may contain distinctly dissimilar iron sites.
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CHARACTERIZATION OF A MIXED VALENCE IRON-OX0 DIMER WITH TPA = TRIS(2 PYRIDYLMETHYL)AMINE. Linda L.Pearce, &ghme Merrege Lawrence Que, Jr., Dept.of Chemistry, University of Minnesota, Minneapolis MN55455. Several iron 0x0 proteins(hemerythrin, uteroferrin and methane monooxygenase) exhibit an EPR signal with gav < 2 arising from antiferromagnetic coupling in the mixed valence oxidation state. The reduction of [Fe2(TPA)2O(C@5~)](C104)3 by addition of one equivalentof cobaltocene (or by bulk electrolysis at -68 mv ) gives rise to a mixedvalence complex with an EPR signal (linewidth = 5OOG) at g=1.94. Power saturation studies show a coupling constant decrease ( J=-31 cm-l, H = J StS2) for the mixedvalence complex compared to its diferric form (J=238 cm-l). The Miissbauer spectrum indicates a valence-trapped species; in addition, its UV -visible spectrum shows new features. The characterization of this complex and other Fe(II)Fe(III) complexes will be discussed.
