PUB - Publikationen an der Universität Bielefeld

Four dinuclear Co-II complexes have been synthesized and structurally characterized with the dinucleating ligand susan (susan - 4,7-di methyl-1,1,10,10-tetra(2-pyridyl methyl)-1,4,7,1 0tetraazadecane) varying in the exogeneous ligands: [(susan)- {Co-II(CH3CN)(2)}(2)](PF6)(4), [(susan){Co-II Cl)(2)](ClO4)(2), [(susan)- {(CoBr)-Br-II}(2)](ClO4)(2), and [(susan){Co-II(mu-OH)COII}](ClO4)(3). The Co-II ions are six-coordinate with CH,CN ligands and five-coordinate with anionic ligands. The electronic absorption spectra reflect the differences in the electronic structures, not only between the six- and five-coordinate complexes, but also between the fivecoordinate complexes. These variations are also reflected in the magnetic properties with the highest orbital angular momen tum contribution in six-coordinate [(susan){Co-II(CH3CN)(2)}(2)](PF6)(4). The lower symmetry in the five-coordinate complexes reduces the orbital angular momentum contribution. The hydroxobridged complex [(susan){Co-II(mu-OH)COII}](ClO4)(3) exhibits an additional antiferromagnetic interaction. The electrochemical characterization reveals that the pi-acceptor ligand CH3CN facilitates not only reduction from Co-II to COI but also oxidation to Co-III while the pi-donor ligands Br-, Cl-, and mu-OH impede both reduction to COI and oxidation to Co-III. [(susan){Co-II- (CH3CN)(2)}(2)](PF6)(4) and [(susan){(CoCl)-Cl-II}(2)](ClO4)(2) show electrocata- lytic proton reduction at a potential of approximate to - 1.9 V vs Fc(+)/Fc that is associated with a ligand-centered reduction.