Synthesis, Chemical−Physical Characterization, and Redox Properties of a New Mixed-Ligand Heterobimetallic N-Bridged Dimer: (μ-Nitrido)[((tetraphenylporphyrinato)manganese)((phthalocyaninato)iron)]

A new mixed-ligand heterobimetallic μ-nitrido bridged complex of the formula (TPP)Mn−N−Fe(Pc) (I) has been prepared from (TPP)MnN3 and (Pc)Fe (TPP = tetraphenylporphyrinato anion, Pc = phthalocyaninato anion) and its molecular and electronic structure were investigated by EPR, IR, Raman, UV−visible and Mössbauer spectroscopy as well as by electrochemistry and magnetic susceptibility measurements. The complex, formally a mixed-valence Mn−Fe d8 system, is low-spin (diamagnetic). Mössbauer data indicate an unbalanced positive charge distribution for the two metal centers and an approach to the formally mixed-valence species (TPP)MnIV=N−FeIII(Pc). This assignment differs from findings for the related complex (TPP)FeIII1/2−N−FeIII1/2(Pc) (II) and other similar N-bridged analogues, including (TPP)FeIVN−RuIII(Pc). A metal centered one-electron oxidation occurs by reaction of I with dilute HClO4 and leads to formation of a Mn(IV)N−Fe(IV) species, I-ClO4. Pyridine can coordinate with I to give a mono(pyridine) adduct and the formation constant for this reaction has been determined spectrophotometrically in CH2Cl2 solutions. The singly oxidized complex, I-ClO4, also reacts with pyridine and is converted to a bis-pyridine derivative containing the fragment [(py)(TPP)Mn−N−Fe(Pc)(py)]+. Complex I can undergo five reversible one-electron oxidations in CH2Cl2 and up to six electrons can be extracted from the neutral complex in pyridine. Both sets of reactions were characterized by cyclic voltammetry which was used to determine the half-wave potentials for each electrode reaction and also to evaluate formation constants for pyridine binding to the neutral and singly oxidized forms of the complex.