Iron mixed cluster compounds

The interactions of NO with the iron-sulfur cluster moieties of several enzymes generate iron-sulfur-nitrosyl cluster compounds [156]. However, synthetic nitrosyl clusters such as Roussins black salt (RBS), Roussins red salt (RRS), Roussins red ester (RRE) and [FeNOS]4 (Fig. 5.3) are well known [129, 157] and can be synthesized easily [158-164]. For example, the RBS can be prepared by mixing FeS04 with NaN03 and (NH4)2S in aqueous solution [158]. RRE salts are generally insoluble in water, but recently the water soluble sulfonated derivative, Na2[Fe2(SCH2CH2S03)2(N0)4], has been prepared [165]. 

Electric fleld gradient, 22 214-218 Electroabsorption spectroscopy, 41 279 class II mixed-valence complexes, 41 289, 291, 294-297 [j(jl-pyz)]=+, 41 294, 296 Electrocatalytic reduction, nickel(n) macro-cyclic complexes, 44 119-121 Electrochemical interconversions, heteronuclear gold cluster compounds, 39 338-339 Electrochemical oxidation, of iron triazenide complexes, 30 21 Electrochemical properties fullerene adducts, 44 19-21, 33-34 nickeljll) macrocyclic complexes, 44 112-113... 

Recent work by Ford et al. demonstrates that a variety of metal carbonyl clusters are active catalysts for the water-gas shift under the same reaction conditions used with the ruthenium cluster (104a). In particular, the mixed metal compound H2FeRu3(CO)13 forms a catalyst system much more active than would be expected from the activities of the iron or ruthenium systems alone. The source of the synergetic behavior of the iron/ruthenium mixtures is under investigation. The ruthenium and ruthenium/iron systems are also active when piperidine is used as the base, and in solutions made acidic with H2S04 as well. Whether there are strong mechanistic similarities between the acidic and basic systems remains to be determined. 

Ketenyl complexes, in Ru-Os mixed-metal clusters, 6, 1080 Ketenylidenes, in iron cluster compounds, 6, 301 Ketenylidenetriphenylphosphoranes, with platinum, 8, 632 Ketimines... 

Other Papers.—Various iron species prepared by the vacuum pyrrolysis of acetyl-ferrocene-furfural resins at 400°C have been studied by Mossbauer spectroscopy. These consist of an amorphous glass-like carbon matrix containing free iron atoms, Fe+ ions, iron clusters, superparamagnetic iron, and ferromagnetic iron.333 The effect of pressure of up to 50kbar on the absorption spectra of five iron(m), two iron(n) and one mixed valence compound has been studied. In six of the compounds, but not in basic ferric acetate or soluble Prussian Blue, the observed pressure-induced bands were assigned to d-d transitions of converted iron(n) for the ferric compounds and to spin-forbidden d-d bands for the ferrous compounds. The charge-transfer band from iron(n) to iron(m) in soluble Prussian Blue showed a blue shift at pressures up to 7.2 kbar.334... 

Current concepts in modem chemistry/Transition metal cluster chemistry/Main group-transition metal mixed clusters/Cluster compounds of main group elements/ Synthetic analogues of the active sites of iron-sulfur proteins... 

Heteronuclear compounds with an Fe-M bond have received much attention in the past decade. Significant progress has been made both in their synthetic methodologies and in the study of their chemical reactivity. There are more than 300 papers that have reported on the chemistry of this class of compounds, and more than 700 structurally characterized mixed-metal compounds that contain iron have appeared since this area was reviewed in COMC (1995). Clearly, this volume of data and information should be best presented in a systematic way, for which a tabulated form is preferable. All of the heterodinuclear species and mixed-metal clusters with known structures are therefore presented in Tables 1-3 respectively. 

Mixed-metal clusters of Fe-Ru and Fe-Os will be surveyed in Ghapter 6.10, which is dedicated to iron organo-metallic compounds. Table 13 lists the Ru-Os mixed-metal clusters with known structures. 

A number of iron-cobalt mixed metal cluster compounds have been obtained by sequential addition of [Co2(CO)g] and [Fe2(CO)g] to [Cp Fe (C0)2-C = C-C=C-H] (77) (Scheme 24). Their formation involves addition of a metal fragment to the C = C bonds, reorganisation of the cluster framework, transfer of metal fragments, valence isomerisation of the C4(H) linkage and 1,2-H shift of the C4H ligand. 

This cluster formally contains three iron(III) and one iron(E). It is present in a class of proteins called high potential iron-sulfur proteins (HiPIP). It has also been prepared through oxidation of [(RS)4Fe4S4]2 model compounds [57]. Both in the model compound at low temperatures and in proteins there is electron delocalization on one mixed valence pair [58-62]. Therefore, the polymetallic center is constituted by two iron ions at the oxidation state +2.5 and two iron ions at the oxidation state +3. Hamiltonian (6.20), or a more complicated one [40, 41,43], can be used to describe the electronic structure. Indeed, a delocalization operator is sometimes needed in the Hamiltonian [40,41,43]. Consistently with magnetic Mossbauer data the S M subspin involving the mixed valence pair is 9/2, whereas the S n subspin involving the iron(IH) ions is 4. Mossbauer and EPR data do not exclude % and 3, respectively, for the two pairs [57] in any case, the... 

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