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 Fe^II (S = 2) ions in 2. DFT calculations provide further insight into the nature of the exchange interactions in the dimeric systems.