Spontaneous reduction of mononuclear high-spin iron(III) complexes to mononuclear low-spin iron(II) complexes in aqueous media and nuclease activity via self-activation.

Mononuclear high-spin [Fe(III) (Pyimpy)Cl3 ]⋅2 CH2 Cl2 (1⋅2 CH2 Cl2 ) and [Fe(III) (Me-Pyimpy)Cl3 ] (2), as well as low-spin Fe(II) (Pyimpy)2 ](ClO4 )2 (3) and [Fe(II) (Me-Pyimpy)2 ](ClO4 )2 (4) complexes of tridentate ligands Pyimpy and Me-Pyimpy have been synthesized and characterized by analytical techniques, spectral, and X-ray structural analyses. We observed an important type of conversion and associated spontaneous reduction of mono-chelated high-spin Fe(III) (1⋅2 CH2 Cl2 and 2) complexes to low-spin bis-chelated Fe(II) complexes 3 and 4, respectively. This process has been explored in detail by UV/Vis, fluorescence, and (1) H NMR spectroscopic measurements. The high positive potentials observed in electrochemical studies suggested a better stabilization of Fe(II) centers in 3 and 4. Theoretical studies by density functional theory (DFT) calculations supported an increased stabilization for 3 in polar solvents. Self-activated nuclease activity of complexes 1⋅2CH2 Cl2 and 2 during their spontaneous reduction was examined for the first time and the mechanism of nuclease activity was investigated.