Nickel complexes extended ligand structures

The above study has been extended to the synthesis of 4 which was prepared in a similar fashion to 1 and 3 starting from tris(l,4,7-triazacyclonon-l-ylmethyl)benzene [12], The X-ray structure of the [Ni2(4)(H20)3]4+ cation shows that both nickel ions adopt distorted octahedral coordination geometries, with one nickel being sandwiched between two tacn residues while the other is coordinated to the third tacn residue with the coordination sphere being completed by three water ligands. Electrochemical studies indicate that the sandwiched Ni(II) centres in this and the related nickel complexes mentioned above may the be reversibly oxidised to the Ni(III) state. In the case of the dinuclear bis-sandwich complex, [Ni2(4)](C104)4, the electrochemical results indicate that the two nickel centres behave in an essentially independent manner. 

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