Studies on the Preparation of Dinuclear Transition Metal Complexes, and the Activation-states of Small Molecules and the Magnetic Interactions involved therein

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(1) Dinuclear Iron Complexes: dinuclear mixed-valence iron(II,III) centers have been known to be involved in the iron proteins such as semi-methemerythrin and pink uteroferrin. We designed two new dinucleating ligands, 2,6- bis[bis(2-pyridylmethyl and 2-benzimidazolylmethyl)aminomethyl]-4-methylphenol, which have bilaterally bisymmetric structures. The dinuclear iron(II,II), (II,III) and (III,III) complexes containing the above ligands and carboxylate ions were newly prepared. From the results of electronic, ESR and Mossbauer spectra, and mignbtic susceptibilities, it was found that (1) the iron(II,III) complex is much more stabilized than the iron(II,II) and (III,III) complexes; (2) the iron(II,III) complex belongs to the so-called Class II mixed-valence complex; and (3) a weak antiferromagnetic interaction it exerted between the two iron ions.(2) Dinuclear and Tetranuclear Manganese Complexes: the dinuclear and tetranuclear manganese centers in photosystem II (PS II) in green plants have been shown to play a-n essential role for the catalytic oxidation of water to molecular oxygen (2H_2O -> O_2 + 4H^+ + 4e ). We newly prepared the dinuclear manganese(II,II), (II,III), (III,IV), and (IV,IV) complexes with 2,6 bis[bis(2-pyridylmethyl)aminomethyl]-4-methylphenol. and the tetranuclear manganese(II,III,III,II) complexes with tris(2-pyridylmethyl)amine (N_4-py).The structures of the complexes were clarified by means of X-ray crystallography. Among these complexes, the N_4-py complex showed the sign of possibility of the catalytic oxidation of water, but we have not yet obtained good enough evidences. The study in this category has great potentialities for future level opment.(3) We succeeded in isolating the dinuclear cobalt(II,II) complexes which bind reversibly molecular oxygen. A weak antiferromagnetic interaction was recognized in the dinuclear chromium(III,III) complexes which contain a linear cyanide ion as the bridging ligand.