Cytochrome Oxidase Models. 3. Spin Coupling across Imidazolate Bridges in Binuclear Metalloporphyrin Complexes of Iron and Copper

Article abstract of DOI:10.1021/ja00380a008

Four new μ-imidazolato binuclear metalloporphyrin compounds of Fe^III and Cu^II or Zn^II have been synthesized, isolated, and characterized in the solid state as a model systems for the active of cytochrome c oxidase.The compounds have been derived from III(TPP)X> (X = Cl^- or OSO2CF3^-) and II(imidH)2DAP>²⁺ (M = Zn or Cu) to yield species containing the following μ-imidazolato cationic cores: III(imid)Zn^II>⁺ (1), III(imid)Cu^II>⁺ (2), <(OSO2CF3)Fe^III(imid)Zn^II>⁺ (3), and <(OSO2CF3)Fe^III(imid)Cu^II>⁺ (4).Comparative magnetochemical (15 300 K), Moessbauer (100 K), and EPR (10 K) studies of 1 and 2 are consistent with essentially identical electronic environments about Fe^III (S = 1/2) with -J_FeIII_-CuII -1 in 2.Similar comparative studies of 3 and 4 are somewhat complicated by the presence of what appears to be two distinct molecular species of S = 5/2 and 1/2 coexisting in the same crystalline sample.The magnetic properties and silent EPr behavior of 4 have been rationalized in terms of a (S = 0, 2) mixture arising from strong antiferromagnetic coupling between Fe^III (S = 1/2, 5/2) and Cu^II (S = 1/2), where -J_FeIII_-CuII >/ca. 200 cm^-1.The implication of this result to the possible active-site structure of oxidase has been briefly considered.