Iron complexes nitrosyl bonding studies

A number of transition metal nuclei can be studied by Mossbauer techniques (e.g., Fe, Ni, Ru, W, Os, Ir, and Pt). Of these, only Ir, Ru, and Fe have been used to study nitrosyl bonding. The most detailed studies have been on the well-known iron complexes [Fe(CN)5(NO)] - (87. 89) and [Fe(NO)(dtc)z] (88-90) (dtc is N,N-dialkyldithiocarbamato). In the latter, high-spin/low-spin equilibria can be followed by Fe Mossbauer spectroscopy, and the Mossbauer parameters agree well with data from electron spin resonance (ESR) spectroscopy in determining the ground states of these complexes. 

As part of the work on model heme FeNO complexes, mechanistic studies on the reversible binding of nitric oxide to metmyoglobin and water soluble Fe, Co and Fe porphyrin complexes in aqueous solution, ligand-promoted rapid NO or NO2 dissociation from Fe porphyrins, reductive nitrosylation of water-soluble iron porphyrins, activation of nitrite ions to carry out O-atom transfer by Fe porphyrins, demonstration of the role of scission of the proximal histidine-iron bond in the activation of soluble guanylyl cyclase through metalloporphyrin substitution studies, reactions of peroxynitrite with iron porphyrins, and the first observation of photoinduced nitrosyl linkage isomers of FeNO heme complexes have been reported. 

Once again, the trans cr-bonding alkyl or aryl ligand exerts a powerful influence on the M-N-O bond angle. Studies on transient intermediates during photolysis of Ru-NO nitrosyls have revealed different modes of binding (and dissociation) of coordinated NO at the ruthenium centers. Metastable NO linkage isomers have been observed for MNO (M = Fe, Ru, Os) and for MNO ° complexes of Ni, as well as for FeNO iron nitrosyl porphyrins [208-212]. 

---