Tetrairon

Prussian Blue. Reaction of [Fe(CN)3] with an excess of aqueous h on(Ill) produces the finely divided, intensely blue precipitate Pmssian Blue [1403843-8] (tetrairon(Ill) tris(hexakiscyanoferrate)), Fe4[Fe(CN)3]. Pmssian Blue is identical to Turnbull s Blue, the name which originally was given to the material produced by reaction of [Fe(CN)3] with excess aqueous h on(Il). The soHd contains or has absorbed on its surface a large and variable number of water molecules, potassium ions (if present in the reaction), and h on(Ill) oxide. The h on(Il) centers are low spin and diamagnetic h on(Ill) centers are high spin. Variations of composition and properties result from variations in reaction conditions. Rapid precipitation in the presence of potassium ion affords a colloidal suspension of Pmssian Blue [25869-98-1] which has the approximate composition KFe[Fe(CN)3]. Pmssian Blue compounds are used as pigments in inks and paints and its formation on sensitized paper is utilized in the production of blueprints. 

Examples of O-alkylation have also been demonstrated for triruthenium and triosmium anionic clusters, as well as the tetrairon cluster Fe CO)] - (31-33). This reaction has considerable promise as an entry into many different methylidyne complexes through the replacement of the OR" group, eq. 20 (38). 

Ferric ferrocyanide [tetrairon(III) tris(hexakiscyanoferrate)(Prussian blue) Fe "4[Fe(CN)6]3 [14038-43-8]... 

Iron-sulfur-nitrosyl complexes (continued) from tetranuclear precursors, 32 343 tellurium analogs, 32 350 tetrairon complexes, N NMR spectroscopy, 32 365 x-ray crystallography [Fe(NO)(S2CNR2)2 and related clusters, 32 359-361... 

A. CYCLO OCTAKIS(2,2 -BIPYRIDINE)TETRA( i-CYANO) TETRAIRON(II) TETRAKIS(HEXAFLUOROPHOSPHATE), [Fe4(bpy)8( t-CN)4][PF6]4... 

Poly(propylene amine) dendrimers carrying at their periphery 9, 16, and 27 (compound 8 in Fig. 6.8) tetrairon [ CpFe(p3-CO) 4] clusters have been recently prepared... 

The electrochemical properties of the two types of iron-cluster-derivatized AuNPs resemble that of the monomeric tetrairon cluster, except that they additionally show adsorption due to their large size, and evidence that all the Fe4 clusters are active at about the same potential, thereby indicating that they are sufficiently remote from one another to behave independently. The changes in the cyclic voltammetric pattern caused by the addition of H2P04 and ATP2- oxoanions evidence recognition features that are very different from those obtained with dendritic ferrocene exoreceptors. In particular, the results show that with these iron-cluster-derivatized AuNPs... 

B. Conversion of Di- and Tetrairon Complexes into Paramagnetic Monoiron Complexes... 

The recent upsurge of interest in iron-sulfur-nitrosyl complexes has been stimulated in part by the reported isolation of [Fe2(SMe)2(NO)4] from natural sources (12), by the obvious resemblances between these complexes and the naturally occurring [2Fe-2S] and [4Fe-4S] clusters of iron sulfur proteins (23, 14), and by the connections between tetrairon-sulfur-nitrosyls and cubane-type clusters (15). Most of the work in this area has been published in the past 5 years or so, and no review has previously been made. However, a number of excellent reviews of the wider aspects of metal-nitrosyl chemistry have appeared (16 19). 

Neutral [Fe2(SR)2(NO)4] complexes, 3a and 3b, having a wide range of substituents R, are now known. When R is alkyl or aryl, the complexes can be synthesized from mono-, di-, or tetrairon precursors, and this forms a convenient basis for the classification of synthetic routes to [Fe2(SR)2(NO)4]. 

The tetrathiomolybdate anion [MoS4]2 acts as a chelating ligand toward iron in both diiron complexes [Fe2(SR)2(NO)4] and tetrairon complexes [Fe4S3(NO)7] and [Fe4S4(NO)4] to yield two paramagnetic iron-nitrosyls which have been assigned (55) the constitutions 15 and 16 ... 

All of the tetrairon complexes have 15N chemical shifts characteristic of linear Fe-N-0 groups. 

The diamagnetic behavior of the diiron and tetrairon complexes, despite the presence of formally d1 and/or d9 iron centers, indicates very strong coupling between the individual paramagnetic centers all theoretical treatments of polynuclear iron-sulfur-nitrosyl complexes to date have been based on the assumption of diamagnetism in even-electron species and have employed molecular orbital methods at various levels of approximation. 

The mononuclear dinitrosyl complexes [Fe(NO)2(SR)2] are readily formed in DMF solution from both diiron and tetrairon precursors when a DMF solution of such a complex is made less polar by addition of a large volume of benzene or toluene, the green [Fe(NO)2(SR)2] is rapidly and smoothly converted to red [Fe2(SR)2(NO)4] [Eq. (20)]. 

Another class of tetrairon complexes containing Fe2(CO)8 fragments has also been described. Stone (66,67) reported a low-yield synthesis of the spiro-cyclic tin complex [Sn Fe2(CO)8 2], 54, the structure of which was determined by X-ray crystallography (68). As shown in Fig. 18, 54 contains a tetragonally distorted tetrahedral tin atom bonded by Sn—Fe bonds to two Fe2(CO)8 fragments. The original report by Stone (67) briefly mentioned the... 

Another class of tetrairon tin compounds, described by Stone (67) and Fritchie (73), are derived from reactions between alkylchlorostannanes and iron carbonyl species. The latter report describes the structure of [Sn Fe2-(CO)8( t-SnMe2) 2], 61, which contains a central tetrahedral tin atom bonded to two Fe2(CO)8(/i-SnMe2) fragments. 

Finally, we note a number of higher nuclearity iron-containing clusters. Hieber (74) reported a complex formulated as [Sn2Fe5(CO)2o], 62, although no structural details were presented. Hieber also described a complex formulated as [PbFe3(CO)12], but later work by Whitmire (71) indicates that this compound is probably the tetrairon species, 56. Mackay and Nicholson (75) have described the synthesis and structures of three polynuclear species [Fe2(CO)7 //-E(Fe2(CO)8) 2] (63, E = Ge 64, E = Sn) and [Fe3(CO)10- //-Ge(Fe2(CO)8) 2], 65, from reactions involving germanium or tin... 

Further examples of Bi2 clusters in this class are the anionic and dianionic complexes [Bi2Fe3(CO)9], 2 (130 and 131), reported by Whitmire (128) as resulting from sequential one-electron reduction of 126 with sodium amalgam, and the dibismuth-tetrairon dianion [Bi2Fe4(CO)I3]2 (132) obtained from... 

Some striking demonstrations of metal-metal bond lability are provided by cluster rearrangements due to protonation. This is the case for some anionic osmium clusters (cf. Section VI). It involves ligand activation for some tetrairon clusters (51-53). Thus, the clusters 9 and 11 open up upon protonation, and compensation for the lost iron - iron bonds in the products 10 and 12 comes from the bonding between one iron atom and a carbonyl oxygen. The relation of these unusual nucleophile-electrophile interactions to cluster-induced CO transformations is obvious. 

Dicarboxypyridine, with trinuclear Os clusters, 6, 747 Dichalcogenides, addition to alkynes, 10, 752 Di(/i4-chalcogenido)tetrairon complexes, preparation, 6, 277... 

---