Molybdenum complexes cyanides

Seven and eight coordinate molybdenum complexes and related molybaenum(IV) oxo complexes with cyanide and isocyanide ligands. S. J. Lippard, Prog. Inorg. Chem., 1976, 21, 91-103 (44). 

Lippard, Stephen J., Seven and Eight Coordinate Molybdenum Complexes and Related Molybdenum (IV) Oxo Complexes, with Cyanide and Isocyanide... 

Fig. 9 Photocurrent quantum efficiency of tungsten ( ) and molybdenum (S) cyanide-complexed Ti02 electrodes compared with that of untreated Ti02( a)...

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. 

Thiocyanates of Molybdenum.—Thiocyanates containing molybdenum as a cation are not known, but compounds similar to the complex cyanides, in which the metal figures as the central atom of a complex anion, have been prepared. 

This can be explained by the fact that these syntheses all consist of two separate steps. In the first step the molybdenum is reduced in acid medium from the +6 to the +5 oxidation state. In the second step potassium cyanide is introduced, and formation of the molybdenum (IV) cyanide complex takes place in alkaline medium as a result of disproportionation of the molybdenum (V) into the +4 and -1-6 oxidation states. As a result of the disproportionation, the conversion cannot possibly exceed 50%. One method described in the literature is not subject to this limitation however, the procedure is rather lengthy and complex. ... 

Cyanides.—A concise review of the seven- and eight-co-ordinate molybdenum complexes and related molybdenum(vi) 0x0 complexes, with cyanide and isocyanide ligands has appeared and Group Via cyanide complexes have been reviewed within the broader scope of transition metal cyanides. ... 

Molybdenum(II) complexes mandelic acid, 474 Molybdenum(IV) complexes cyanides synthesis, 9 histidine, 747... 

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. 

In perchloric acid solution, oxidation of [Mo(CN)g] by VO2 is biphasic, consisting of parallel cyanide-bridged inner-sphere and outer-sphere pathways. Both pathways are catalyzed by [H ] which is presumed to coordinate to the molybdenum complex and ionic-strength dependencies indicate that [HNa2Mo(CN)g] and [HNaMo(CN)g] are the reactive species. Photoexcitation of the intervalence transfer band in the [Mo(CN)g] , CUaq ion pair leads to electron transfer and allows determination of the dark reaction rate. The oxidation of Mn04 by [Mo(CN)g] has also been examined, in alkaline media. The reaction is outer sphere as are the corresponding reactions of [W(CN)g] and... 

Another type of demasking involves formation of new complexes or other compounds that are more stable than the masked species. For example, boric acid is used to demask fluoride complexes of tin(IV) and molybdenum(VI). Formaldehyde is often used to remove the masking action of cyanide ions by converting the masking agent to a nonreacting species through the reaction ... 

This is by far the most stable and best-known oxidation state for chromium and is characterized by thousands of compounds, most of them prepared from aqueous solutions. By contrast, unless stabilized by M-M bonding, molybdenum(III) compounds are sparse and hardly any are known for tungsten(III). Thus Mo, but not W, has an aquo ion [Mo(H20)g] +, which gives rise to complexes [MoXg] " (X = F, Cl, Br, NCS). Direct action of acetylacetone on the hexachloromolybdate(III) ion produces the sublimable (Mo(acac)3] which, however, unlike its chromium analogue, is oxidized by air to Mo products. A black cyanide,... 

Cyanide complexes of molybdenum(II) generally appear elsewhere under other classifications, where CN- is an andlliary ligand. The homoleptic anions [Mo(CN)6]4- and [Mo(CN)7]5- (pentagonal bipyramid) have been reviewed elsewhere.10... 

---