Syntheses and Electronic Structure of Bimetallic Complexes Containing a Flexible Redox-Active Bridging Ligand

The new ligand L1, 1-N,1-N-bis­(pyridine-2-ylmethyl)-3-N-(pyridine-2-ylmethylidene)­benzene-1,3-diamine, was synthesized as a platform for the study of bimetallic complexes containing redox-active ligands. The asymmetric L1 contains a redox-active α-iminopyridine unit bridged to redox-inert bis­(2-pyridylmethyl)­amino counterpart and offers two distinct coordination sites. The coordination chemistry of L1 with Fe, Cu, and Zn was examined. Reaction with zinc afforded the asymmetric binuclear complex [(L1)­Zn2Cl4] (1), whereas the symmetric [(L1)2Fe2(OTf)2]­(OTf)2 (2) and [(L1)2Cu2]­(OTf)4 (3) were isolated in reactions with iron and copper. Both metal- and ligand-centered redox processes are available to the series of metal compounds. EPR and Mössbauer spectroscopy and magnetic susceptibility studies establish that both 2 and 3 are paramagnetic; the vanishingly small ferromagnetic interaction produces decoupled high-spin FeII (S = 2) ions in 2. DFT calculations provide further insight into the nature of the exchange interactions in the dimeric systems.