Coordination chemistry, molybdenum

Iron-Sulfur Proteins Molybdenum Inorganic Coordination Chemistry Molybdenum MPT-containing Enzymes Tungsten Inorganic Coordination Chemistry. 

Biochemical aspects of molybdenum coordination chemistry. J. T. Spence, Coord. Chem. Rev., 1969, 4, 475-498 (74). 

Seven coordination in molybdenum chemistry analysis of oligonuclear structures. M. Melnik and P. Sharrock, Coord. Chem. Rev., 1985, 65, 49 (91). 

Because of factors beyond the editors control, the submission of manuscripts for this chapter was delayed. In order to minimize any delay in publishing Comprehensive Coordination Chemistry as a whole, the coverage of molybdenum appears at the end of this volume, commencing on page 1229. 

The preparation and properties of compounds containing metal-metal bonds, in which molybdenum features prominently or exclusively, have been the subject of several recent and authoritative reviews/-10 The following sections will, therefore, concentrate on the salient aspects of the coordination chemistry of these systems and the reader is referred to these reviews for further information. 

Mononuclear examples are dominant in the simple coordination chemistry of molybdenum(VI). This is due in part to the absence of d electrons in Movl complexes, which precludes the formation of MoVI—Mo 1 metal-metal bonds. However, note must be taken of the very large class of homo- and hetero-polymolybdates which contain polynuclear Mo. These... 

The biological importance of molybdenum, and the challenge to reproduce the spectroscopic properties and the reactions of the molybdenum centres of the oxomolybdoenzymes, have been considerable stimuli for the development of the coordination chemistry of this element (see Chapters 36.4 and 36.5). 

Complexes of molybdenum form the largest set of any of the transition metals. Many of these compounds display spectroscopic properties, isomerism and structural features that illustrate the coordination chemistry of polypyrazolylborate complexes. In addition, this system illustrates that trispyrazolylborate ligands are more bulky than their formal analogue C5H5. 

There are two principal synthetic routes to dicarboxylate complexes. One of these uses an aqueous solution of the alkali metal dicarboxylate and the corresponding metal halide,93 while the other depends upon the dicarboxylic acid reduction of higher oxidation state metals. This reductive property of oxalic acid results in its ready dissolution of iron oxides and hence a cleaning utility in nuclear power plants.94 Mention must also be made of the successful ligand exchange synthesis of molybdenum dicarboxylates, Mo(dicarboxylate)2 H2 O, from the corresponding acetate complex. Unfortunately the polymeric, amorphous and insoluble nature of these complexes has restricted the study of these systems, which may well provide examples of multiple M—M bonding in dicarboxylate coordination chemistry.95... 

The flotation process is applied on a large scale in the concentration of a wide variety of the ores of copper, lead, zinc, cobalt, nickel, tin, molybdenum, antimony, etc., which can be in the form of oxides, silicates, sulfides, or carbonates. It is also used to concentrate the so-called non-metallic minerals that are required in the chemical industry, such as CaF2, BaS04, sulfur, Ca3(P03)2, coal, etc. Flotation relies upon the selective conversion of water-wetted (hydrophilic) solids to non-wetted (hydrophobic) ones. This enables the latter to be separated if they are allowed to contact air bubbles in a flotation froth. If the surface of the solids to be floated does not possess the requisite hydrophobic characteristic, it must be made to acquire the required hydrophobicity by the interaction with, and adsorption of, specific chemical compounds known as collectors. In separations from complex mineral mixtures, additions of various modifying agents may be required, such as depressants, which help to keep selected minerals hydrophilic, or activators, which are used to reinforce the action of the collector. Each of these functions will be discussed in relation to the coordination chemistry involved in the interactions between the mineral surface and the chemical compound. 

It is over eight years since the last comprehensive review appeared on metal isocyanide chemistry. In the interim, reviews have appeared on specific aspects of isocyanide chemistry. Lippard reviewed seven and eight coordination in molybdenum isocyanide compounds (7), Yamamoto reviewed metal(O)- isocyanide complexes (2), and in related reviews on car-bene complexes by Cotton and Lukehart (5), Lappert et al. (4), and Casey (5), mention was made of carbenes synthesized from metal isocyanides. 

Mechanistic speculations about the molybdoenzymes must be considered to be in their infancy with the possible exception of those for xanthine oxidase. Although the detailed structural nature of the molybdenum site is unknown, there is sufficient information from biochemical and coordination chemistry studies to allow informed arguments to be drawn. Here we first discuss evidence for the nuclearity of the molybdenum site and then discuss both oxo-transfer and proton-electron transfer mechanisms for molybdenum enzymes. A final discussion considers the unique aspects of nitrogenase and the possible reasons for the use of molybdenum in enzymes. 

During the last decade of the twentieth century, the inorganic and coordination chemistry of molybdenum has expanded substantially. Among the major developments in this period have been (1) the introduction of a versatile range of polydentate Ugands, including the tripodal tris(amido), triamidoamtne, and tris(pyrazolyl)borato species which have enabled the stabiUzation of novel species and chemistry ... 

Molybdenum coordination has recently been comprehensively reviewed in Comprehensive Coordination Chemistry, particularly in the areas of mononuclear complexes, polyoxometaUate synthesis, structure, and reactivity see also Polyoxometalates), and in chalcogen-containing cluster complexes. ... 

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