Synthesis and properties of binuclear nitride-bridged iron octaphenyltetraazaporphyrin. E.p.r. studies of dioxygen adduct formation

Summary The synthesis and characterization are reported for (-nitrido)bis[(octaphenyltetraazaporphyrinato)iron] ([OPTAP)Fe]₂N). The [(OPTAP)Fe]₂N dimer is paramagnetic with one unpaired electron per dimer unit and shows a typical axially symmetric e.p.r. spectrum in non-polar solvents at liquid N₂ temperature (g=2.126, g=2.001), with well-resolved superhyper-fine splitting resulting from the -nitrido bridge (A^N=2.48mT, A^N=2.60mT).A pyridine monoadduct of [(OPTAP)Fe]₂N, formed in frozen glasses has been characterised by changes in e.p.r. spectra. Electronic spectra show no pyridine adduct formation at 298 K. Mössbauer parameters (IS=–0.042 mm/s, QS=1.769mm/s at 298K) are indicative of the predominant iron(IV) character in [(OPTAP)Fe]₂N.The pyridine monoadduct binds O₂ reversibly. The O₂ adduct was characterized by e.p.r. spectroscopy (g₁=2.062, g₂=2.007, g₃=2.000). O₂ titration as monitored by e.p.r. shows that the adduct stoichiometry is one O₂ per dimer. A spin-pairing model for O₂ binding accounts for the observed O₂-[(OPTAP)Fe]₂N interaction.