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

The new ligand L-1, 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 L-1 contains a redox-active alpha-iminopyridine unit bridged to redox-inert bis(2-pyridylmethyl)amino counterpart and offers two distinct coordination sites. The coordination chemistry of L-1 with Fe, Cu, and Zn was examined Reaction with zinc afforded the asymmetric binuclear complex [(L-1)Zn2Cl4] (1), whereas the symmetric [(L-1)(2)Fe-2(OTf)(2)](OTf)(2) (2) and [(L-1)(2)Cu-2](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 Mossbauer spectroscopy and magnetic susceptibility studies establish that both 2 and 3 are paramagnetic; the vanishingly small ferromagnetic interaction produces decoupled high-spin Fe-II (S = 2) ions in 2. DFT calculations provide further insight into the nature of the exchange interactions in the dimeric systems.