Molybdenum divalent

Divalent molybdenum compounds occur in mononuclear, dinuclear, and hexanuclear forms. Selected examples are shown in Figure 6. The mononuclear compounds are mostiy in the realm of organometaUic chemistry (30—32). Seven-coordinate complexes are common and include MoX2(CO)2(PR3)2, where X = Cl, Br, and I, and R = alkyl MoCl2(P(CH3)3)4, heptakis(isonitrile) complexes of the form Mo(CNR) 2 (Fig. 6d), and their chloro-substituted derivatives, eg, Mo(CNR)3CR. The latter undergo reductive coupling to form C—C bonds in the molybdenum coordination sphere (33). 

The electrolyte is made by in situ chlorination of vanadium to vanadium dichloride in a molten salt bath. Higher valent chlorides are difficult to retain in the bath and thus are not preferred. The molten bath, which is formed by sodium chloride or an equimolar mixture of potassium chloride-sodium chloride or of potassium chloride-lithium chloride or of sodium chloride-calcium chloride, is contained in a graphite crucible. The crucible also serves as an anode. Electrolysis is conducted at a temperature about 50 °C above the melting point of the salt bath, using an iron or a molybdenum cathode and a cathode current density of 25 to 75 A dnT2. The overall electrochemical deposition reaction involves the formation and the discharge of the divalent ionic species, V2+ ... 

Kuroda and Tarui [498] developed a spectrophotometric method for molybdenum based on the fact that MoVI catalyses the reduction of ferric iron by divalent tin ions. The plot of initial reaction rate constant versus molybdenum concentration is rectilinear in the range 0.01-0.3 mg/1 molybdenum. Several elements interfere, namely, titanium, rhenium, palladium, platinum, gold, arsenic, selenium, and tellurium. 

There are a few features relative to POMs that are necessary for obtaining the best performance. In all cases. Vanadium is present in the structure of the P/Mo Keggin anion, while the cations include different components, that is, protons, divalent transition metal ions (preferably either Fe " " or Cu " "), and alkali metal ions (preferably Cs" "). The role of Cu ions is to catalyze the reduction of molybdenum, thus increasing the activity of the catalyst it also affects the surface acidity. 

Surface analyses were investigated mainly by using XPS (Fig. 7). It was clearly indicated that many composite oxides found by XRD are located un-homogeneously in the catalyst particle. Molybdenum and bismuth are undoubtedly concentrated in the surface layer of the catalyst particle and divalent and trivalent metal cations are found in the bulk of the catalyst. As a result, it is clear that bismuth molybdates, especially its a-phase, is located on the surface of each particle, and metal molybdates of divalent and trivalent cations are situated in the bulk of the catalyst. 

In keeping with its 4d%5s electron configuration, molybdenum forms many compounds in which its oxidation state is 6+. to an even greater extent than chromium. Also, like chromium, it forms compounds in which II is divalent and those in which it is trivalenl unlike chromium, il forms a number of pentavalenl compounds, and a few more tetravalent compounds, especially complexes. 

Among the divalent compounds of molybdenum are the dihromidc. MoBr-, and the dichloride. MoCI . There is also a complex ion of divalent molybdenum MosClJ. (flat is of particular interest because it does not yield Mo21 ions. The chloride sail of the ion. Mo CLi- has been shown, by precipitation with Ag+, to have two-thirds of its chlorine content present in a complex, so ils structure is established as [Mt CIsJCU, It is obtained by higher temperature disntutation of MoClj, while the corresponding dibromide ean be produced by direct reaction of the elements,... 

In keeping witii its 5d 6s2 electron configuration, tungsten forms many compounds in which its oxidation state is 6+, just as molybdenum does. It forms divalent and tetravalent compounds to about the same extent as molybdenum but its bivalent and pentavalent compounds are somewhat fewer. Its anion chemistry is closely akin to that of molybdenum. 

Additionally, Aykan et al. (98) reported the results for scheelite-type systems in which A sites are occupied by divalent elements and bismuth, and M sites contain vanadium and molybdenum. The tolerance for vacancies in this system was reported to be 15% of the A cation sites. Good yields of acrolein were obained when bismuth and defects were present in the scheelite-structured catalysts. 

Molybdenum trioxide, intercalation into, 12, 823 Molybdocenes, as anticancer agents, 1, 892 MOMNs, see Metal-organometallic coordination networks Monisocyanides, with silver(I) complexes, 2, 223 Monitoring methods, kinetic studies, 1, 513 Mono(acetylacetonate) complexes, with Ru and Os halfsandwich rf-arenes, 6, 523 tj2-Monoalkene monodentate ligands, with platinum divalent derivatives, 8, 617 tetravalent derivatives, 8, 625 theoretical studies, 8, 625 zerovalent derivatives, 8, 612... 

One oil contained a soluble molybdenum friction modifier additive while the other did not. The IR bands in the 1200 to 1100 cm 1 and 650 to 600 cm 1 regions have been assigned to the symmetric PO 2 stretching and symmetric bending modes, respectively, observed in divalent cations in metaphosphate glasses. 

The thiomolybdites are a class of molybdenum-sulfur compounds which contain molybdenum in a low oxidation state, usually +3. Two main types of such materials exist. The first type has the formula MMoS2 where M is a monovalent cation, usually an alkali metal. The second type has the formula MMo2S4 where M is a divalent cation, usually a transition metal. There are other thiomolybdite species, of composition other than that described above, which have been identified in ternary phase studies involving the M-Mo-S system (M = a transition element), but these have not been well characterized. 

Firsova et al. (122) reported that the room temperature Mossbauer spectrum of supported tin molybdate, which had been aged in vacuo at 723 K, showed the presence of tetravalent tin. Only after exposure to oxygen at 473 K did the sample act as an adsorbent for propylene. It then gave a Mossbauer spectrum that showed the reduction of the tetravalent tin to the divalent state. Reduction without exposure to oxygen was achieved at 673 K but supported tin in the absence of molybdenum was not reduced. The results were interpreted in terms of the proposals (123) for the synergistic oxidation-reduction during catalysis. 

In the fused state, the straightforward method is to allow either the lanthanide metal or the alkaline earth metal to react with a melt of the alkaline earth halide and the lanthanide trihalide. This approach yields the desired divalent ions if inert containers are used. Satisfactory reduction has been obtained in molybdenum, tungsten, and tantalum. The... 

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