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 α-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))Zn(2)Cl(4)] (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 Mössbauer 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.