Molecular and Electronic Structures of a Series of Dinuclear Co ^II Complexes Varied by Exogeneous Ligands: Influence of <i>π</i> ‐Bonding on Redox Potentials

Four dinuclear CoII complexes have been synthesized and structurally characterized with the dinucleating ligand susan (susan=4,7-dimethyl-1,1,10,10-tetra(2-pyridylmethyl)-1,4,7,10-tetraazadecane) varying in exogeneous ligands: [(susan){CoII(CH3CN)2}2](PF6)4, [(susan){CoIICl}2](ClO4)2, [(susan){CoIIBr}2](ClO4)2, [(susan){CoII(μ-OH)CoII}](ClO4)3. The ions are six-coordinate CH3CN ligands five-coordinate anionic ligands. electronic absorption spectra reflect differences structures, not only between six- complexes, but also complexes. These variations reflected magnetic properties highest orbital angular momentum contribution [(susan){CoII(CH3CN)2}2](PF6)4. lower symmetry reduces contribution. hydroxo-bridged complex [(susan){CoII(μ-OH)CoII}](ClO4)3 exhibits an additional antiferromagnetic interaction. electrochemical characterization reveals that π-acceptor facilitates reduction from to CoI oxidation CoIII, while π-donor Br−, Cl−, μ-OH− impede both CoIII. [(susan){CoII(CH3CN)2}2](PF6)4 [(susan){CoIICl}2](ClO4)2 show electrocatalytic proton at a potential of ≈−1.9 V vs Fc+/Fc is associated ligand-centered reduction.