Molybdenum complexes monometallic

In this paper a study is presented on the preparation of a series of supported catalysts by precipitation of metal cyanide complexes in the presence of suspended supports. As supports alumina, titania, and silica, have been used. The metals studied comprise iron, cobalt, nickel, copper, manganese, palladium, and molybdenum. Both monometallic, bimetallic and even trimetallic cyanides were precipitated. The stoichiometry of the precipitated complexes was controlled by the valency of the metal ions and by using both nitroprusside and cyanide complexes. Electron microscopy was used to evaluate the distribution of the deposited complex cyanides on the supports. 57Fe-M6ssbauer spectra were measured on the dried precipitated complexes to gain information on the chemical composition of the iron containing complexes. 

Very recently Geus and co-workers [44, 45] have applied another method based on chemical complexes. This is the complex cyanide method to prepare both monocomponent (Fe or Co) and multicomponent Fischer-Tropsch catalysts. A large range of insoluble complex cyanides are known in which many metals can be combined, e.g. iron(n) hexacyanide and iron(m) hexacyanide can be combined with iron ions, but also with nickel, cobalt, copper, and zinc ions. Soluble complex ions of molybdenum(iv) which can produce insoluble complexes with metal cations are also known. Deposition precipitation (Section A.2.2.1.5) can be performed by injection of a solution of a soluble cyanide complex of one of the desired metals into a suspension of a suitable support in a solution of a simple salt of the other desired metal. By adjusting the cation composition of the simple salt solution, with a same cyanide, it is possible to adjust the composition of the precursor from a monometallic oxide (the case when the metallic cation is identical to that contained in the complex) to oxides containing one or several foreign elements. 

The ambivalent donor or acceptor role of low-valent metal carbonyl species, such as M(CO)5 [M = chromium, molybdenum, tungsten], in monometallic p-substituted pyridine (or stilbazole) complexes was investigated in detail by Kanis et al. in the early 1990s, and later by Roberto et al. (Figure 1.22). " As already seen before, when the substituent is an... 

In bimetallic complexes, the oxidation state is calculated hy supposing that the metal-metal bond(s), if any, is/are broken homoly tic-ally. This procedure is justified by the fact that the electronegativities of the two metal centres are equal if they are identical, or similar in hetero-nuclear complexes (see Table 1.2(a)). The presence of one or more bonds between the metals therefore has no effect on their oxidation state. For example, the complex [Mo(Cl)2(PR3)2]2 can initially be considered to be decomposed into two monometallic neutral fragments [Mo(Cl)2(PR3)2] in which the oxidation state of molybdenum is +2. 

A1 Obaidi, N., Chaudhury, M., Clague, D., Jones, C.J., Pearson, J.C., McCleverty, J.A., and Salam S.S. (1987) Monometallic, homo- and hetero-bimetallic complexes based on redox-active tris(3,5-dimethylpyrazolyl)borato molybdenum and tungsten nitrosyls, part 4. The effects of ligating atom type on reduction potentials of monometallic complexes, J.ChemSoc., Dalton Trans., 1733-6. 

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