Iron clusters nitrogen

The similarity of the reactivity patterns for niobium and cobalt and the non-reacti vi ty of iron with nitrogen suggests that dissociative chemisorption is taking place. Dissociation of molecularly chemisorbed nitrogen is an activated process on all metals(35) and is most exothermic for the early metals in the periodic tab e(36). The limited observations on clusters seems to be consistent with these trends. 

Parks EK, Kerns MP, Riley SJ (2000) The structure of nickel-iron clusters probed by adsorption of molecular nitrogen. Chem Phys 262 151... 

Niobium and cobalt clusters exhibit size-sensitive reactions with nitrogen with a reactivity pattern similar to that observed for hydrogen. The reactivity of rhodium clusters (n = 1-12) toward N2 has also been studied. In this case the atoms through the tetramer appear to be inert, with reactivity turning on at Rhj. Maximum reactivity occurs at Rh7, and subsequently drops off by roughly a factor of 2 in going from Rh, to Rh,. Iron clusters appear to be nearly unreactive toward N2. Attempts to induce low-pressure ammonia synthesis on gas-phase iron clusters indicate that hydrogenated iron clusters Fe H are also unreactive toward N2. ... 

Fig. 1. Diferric iron clusters form hemer3fthrin, ribonucleotide reductase R2 subunit, and methane monooxygenase hydroxylase. The figure was made with the RasMol 2.0 program, and the protein coordinates as PDB files were obtained from Brookhaven Protein Data Bank. Only the amino acids (histidines, green carboxylates, black oxygen, red nitrogen, yellow acetate, blue iron, violet) coordinated to the iron cluster are shown, coordinated waters are not indicated. The first subunit containing the cluster is shown. Diferric Hr is from sipunculid worm Themiste dyscritra). The RNR-R2 is from E. coli. The MMOH is from Methvlococcus caosulatus (Bath).

Fig. 5 Representation of the active site of the nitrogenase. The central part corresponds to the MoFe7 9 cluster. The carbon, molybdenum, oxygen, iron, sulfur, nitrogen, and hydrogen atoms are represented by spheres of dijferent shades of gray, from dark to bright, respectively...

There are hundreds of iron-containing enzymes. In general, the iron can exist as (a) a mononuclear site, in which it is coordinated by a tetrapyrrole structure (hemes) or strictly by amino acid residues that donate oxo, nitrogen, or sulfur ligands (b) a dinuclear site in which the irons are bridged by oxo, nitrogen, or sulfur coordination (c) a trinuclear site as in the 3Fe-4S clusters or (d) a tetranuclear site as in the [4Fe-4S] clusters. 

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