Iron compounds coordination chemistry

Dr. Erickson For those interested in coordination chemistry, certain other transition metal atoms are suitable for Mossbauer spectroscopy. One in particular is ruthenium which is just below iron in the Periodic Table. It is a difficult isotope to work with since it requires helium temperatures almost exclusively. I don t know whether it is possible to work at nitrogen temperatures or not, but Kistner at Brookhaven has examined various ruthenium compounds from the 2-j- to the 8+ oxidation states with interesting results. These are not published yet, but at least his work offers the possibility of going down one element below the other in the Periodic Table to study chemical effects. Osmium, which is below ruthenium, can also be Mossbauered. Some sort of systematic study like this involving elements in the various transition series would be extremely interesting. 

Carrano CJ, Raymond KN (1978) Coordination Chemistry of Microbial Iron Transport Compounds. 10. Characterization of the Complexes of Rhodotorulic Acid, a Dihydroxa-mate Siderophore. J Am Chem Soc 100 5371... 

A brief historical note on the structure of the iron-sulfur clusters in ferredoxins is relevant. After the first analytical results revealed the presence of (nearly) equimolar iron and acid-labile sulfur, it was clear that the metal center in ferredoxins did not resemble any previously characterized cofactor type. The early proposals for the Fe S center structure were based on a linear chain of iron atoms coordinated by bridging cysteines and inorganic sulfur (Blomstrom et al., 1964 Rabino-witz, 1971). While the later crystallographic analyses of HiPIP, PaFd, and model compounds (Herskovitz et al., 1972) demonstrated the cubane-type structure of the 4Fe 4S cluster, the original proposals have turned out to be somewhat prophetic. Linear chains of sulfide-linked irons are observed in 2Fe 2S ferredoxins and in the high-pH form of aconitase. Cysteines linked to several metal atoms are present in metallothionein. The chemistry of iron-sulfur clusters is rich and varied, and undoubtedly many other surprises await in the future. 

The coordination chemistry of these ligands was studied at an early date161,164 and many interesting properties have been revealed, such as isomerism164 and high-spin to low-spin transitions for the iron compounds.62,127,164... 

Much work has been undertaken to modify electrode surfaces with films which are themselves conducting. The most promising approaches involve organic charge transfer and radical ion polymers. Coordination chemistry has, to date, played little part in this work (a good recent review is available),67 but one example relating to ferrocene chemistry can be quoted. In this example a well known electron acceptor, 7,7, 8,8 -tetracyanoquinodimethane (TCNQ 27), is modified and incorporated into polymer (28) in which the iron(II) of the ferrocene unit is the electron donor. The electrical conductivity of such a film will depend on partial electron transfer between ion and TCNQ centres as well as on the stacking of the polymer chains. The chemistry of other materials, based on coordination compounds, which have enhanced electrical conductivity is covered in Chapter 61. 

Other complexes containing the coordination units FeN2S2 [842] and FeN2S4 [843— 845] are also known. These compounds have due importance in coordination chemistry since they provide a possibility to study the changes of iron spin states in accessible temperature intervals [845]. Moreover, they are permanently used as models of active centers in some iron-containing nonporphyrine metalloenzymes, in particular, nitrylhydrataze [804,846-850]. 

The coordination chemistry of oxalate (ox, C2042-) compounds provides a series of very interesting compounds from the stereochemical and magnetic points of view [197]. Most frequently the compounds form honeycomb layers in the presence of transition metal ions, in which the stereochemistry of the metal ion coordination sphere alternates between A and A. However, a three-dimensional homochiral structure is also possible. On the other hand, the negative charge of the oxalates necessitates the incorporation of cations between them, which provides the opportunity to introduce chirality and additional functionality in materials. The compound formed between homochiral manganese II oxalate and iron II tris bipyridinc (bpy) with formula [Mn oxls]2 " [Fcn(bpy)3]2+ crystallises in the space group fJ4 32. 

HPhe preceding and following chapters amply illustrate the reasons why microbial iron transport compounds are worthy of our attention—both from the biochemical and medical points of view. However, one might wonder what this has to do with coordination chemistry. The obvious answer is that these are, after all, coordination compounds. But more than that, when viewed from the perspective of a coordination chemistry, new experiments or new approaches suggest themselves. This is always the exciting potential of interdisciplinary research. This chapter is the result of a research project which has involved extensive collaboration between J. B. Neilands laboratories and my own. Many of the details of the transport studies of kinetically inert, metal-substituted siderophores in... 

Nearly all iron complexes of synthetic macrocyclic ligands contain nitrogen either as the only ligand atom or as the major donor present. Moreover, most macrocyclic ligands are tetradentate usually presenting a roughly planar N4 donor set to the centrally complexed metal ion. The comprehensive review by Melson390 of the coordination chemistry of macrocyclic compounds should be consulted for work published up until 1978. 

The iron porphyrins and related compounds constitute an extremely important class of coordination complex due to their chemical behaviour and involvement in a number of vital biological systems. Over recent years a vast amount of work on them has been published. Chapter 21.1 deals with the general coordination chemistry of metal porphyrins, hydroporphyrins, azaporphyrins, phthalocyanines, corroles, and corrins. Low oxidation state iron porphyrin complexes are discussed in Section 44.1.4.5 and those containing nitric oxide in Section 44.1.4.7, while a later section in this chapter (44.2.9.2) is mainly concerned with iron(III) and higher oxidation state porphyrin complexes. Inevitably however, a considerable amount of information on iron(II) complexes is contained in that section as well as in Chapter 21.1. Therefore in order to prevent excessive duplication, the present section is restricted to highlighting some of the more important aspects of the coordination chemistry of the iron(II) porphyrins while the related unusually stable phthalocyanine complexes are discussed in the previous section. 

Research of A. N. Nesmeyanov on organo-iron compounds The role of organometallic compounds in the development of coordination chemistry Chemistry of heteroorganic compounds... 

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