Metal ions molybdenum complexes

The ability of metal ions to form complexes with formazans is utilized to determine these ions either directly (for low valent reducing ions) or indirectly in the presence of a reducing agent. Among others, molybdenum(VI) and vanadium(V) have been determined using this method.442,443 Indirect methods have been reported for the analyses of substances that do not reduce tetrazolium salts. Examples include arsenic in nickel ores436 and traces of selenium.437 A method for the extraction and analysis of a number of metal ternary ion association complexes has been described.444 - 448... 

Chromium(IV) and chromium(V), previously encountered as the oxides and halides and as unstable intermediates in solution, are now represented by complexes of ligands stabilized by heavy substitution against oxidation by the metal ion, and oxo and nitrido derivatives. These remain unimportant oxidation states compared with molybdenum and tungsten. 

Krylov (62) studied the adsorption of oxygen and propylene on vanadium oxide/MgO and molybdenum oxide/MgO catalysts by ESR and IR at 25°C. He observed the formation of Qr radicals and ir-allyl complexes during the simultaneous adsorption of 02 and C3H . The data indicated that an electron transfer took place from the olefin to the oxygen through the transition metal ion forming the following complex ... 

For both complexes, reversible metal-centered one-electron oxidations and reductions have been observed. The products of such redox processes have been examined by monitoring the EPR and electronic spectra obtained by controlled-potential electrolysis and, in the case of the molybdenum complex, have been identified as [Mo(IV)0(TMTEC)]+ and [Mo(VI)0(TMTEC)] ions. 

In contrast to the molybdenum complex, [CpCr(CO)3]2 gives ions only up to m/e 202 and 201, corresponding to [CpCr(CO)3H]+ and [CpCr(CO)3]+, respectively (151). The ions CpCr(CO)+ ( = 0-2) were also produced, but no bimetallic ions have been observed, suggesting that the compound may be monomeric in the vapor phase and implying a very weak metal-metal bond. 

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. 

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