Six- and seven-coordinate Fe() and Zn() compounds ligated by unsymmetric xanthene-based ligands: characterization and magnetic properties

The synthesis of a set of novel unsymmetric ligands, iXa and iXa-2 , and of their corresponding Fe II and Zn II complexes are described. The ligands incorporate a redox-active α-diimine moiety alongside (2-pyridylmethyl)amino groups. Electrochemical data highlight ligand-centered reduction processes available in these systems. The molecular structures of the series of six- and seven-coordinate metal complexes reveal a pentagonal bipyramidal geometry for all compounds. The ligands and complexes were further characterized in the solution state by NMR spectroscopy, with assignments supported by DFT calculations. The ferrous- iXa and - iXa-2 complexes have a high spin, S = 2 configuration. Magnetic susceptibility studies reveal the unusual low-temperature ferromagnetism of these complexes. Intermolecular interactions between the iron centers are mediated by the PF 6 − counterions, as evidenced by 31 P-NMR studies. We present new ligand platforms for pentagonal bipyramidal metal complexes, and the characterization of the corresponding Zn( ii )- and Fe( ii )-containing compounds.