Molybdenum chemical properties

Chemical Properties. Molybdenum has good resistance to chemical attack by mineral acids, provided that oxidizing agents ate not present. The metal also offers excellent resistance to attack by several liquid metals. The approximate temperature limits for molybdenum to be considered for long-time service while in contact with various metals in the hquid state ate as follows ... 

The discovery of the elements 43 and 75 was reported by Noddack et al. in 1925, just seventy years ago. Although the presence of the element 75, rhenium, was confirmed later, the element 43, masurium, as they named it, could not be extracted from naturally occurring minerals. However, in the cyclotron-irradiated molybdenum deflector, Perrier and Segre found radioactivity ascribed to the element 43. This discovery in 1937 was established firmly on the basis of its chemical properties which were expected from the position between manganese and rhenium in the periodic table. However, ten years later in 1937, the new element was named technetium as the first artificially made element. 

Brewer, L. (ed.). 1980. Molybdenum Physico-Chemical Properties of Its Compounds and Alloys. Atom. Ener. Rev. Spec, issue No. 7. 714 pp. Avail, from UNIPUB, 345 Park Ave. S., New York. 10010. 

Because of the enormous synthetic potential of molybdenum- [22] and ruthenium-based [57,806] single-component catalysts, a closer look at the scope and limitations of the most promising compounds known to date is appropriate. The systematic exploration of the synthetic possibilities offered by these new catalysts has just begun, and many new developments are to be expected in the near future [744,746,747,807]. As quick reference for the organic chemist, the most relevant chemical properties of two types of frequently used catalyst (Figure 3.46) are listed below. These carbene complexes are quite robust and well-suited to the metathesis of elaborate organic intermediates. 

Molybdenum was first identified as a distinct element by Swedish chemist Karl Wilhelm Scheele in 1778. The metal was isolated by Hjelm in 1782 by reduction of its oxide with carbon. Moissan in 1895 isolated the metal in highly purified form by electrolytic reduction of its oxide and studied many of its physical and chemical properties. The element derived its name in 1816 from the word molybdos, meaning a soft mineral that appeared like lead. 

Elemental composition Mo 66.66%, 0 33.34%. Molybdenum(Vl) oxide may be identified from its physical and chemical properties and by x-ray analysis. Molybdenum content in the oxide can be measured by various instrumental techniques (see Molybdenum). 

There are undoubtedly more elements on the way, as little by little the Periodic Table is extended into uncharted waters. And as this happens, we will learn about how these new elements behave. In 1997 an international team that included scientists from GSI, Berkeley, and Dubna was able to deduce that element 106 (seaborgium) has chemical properties similar to molybdenum and tungsten. In a sense this might have been expected, since seaborgium sits below these elements in the Periodic Table. But in fact the result was a surprise, because the chemical behaviour of the preceeding superheavy elements 104 and 105 is distorted by the effects of relativity on the electrons surrounding the immense nuclei. 

Jhe distribution of beryllium, boron, titanium, vanadium, chromium, cobalt, nickel, copper, zinc, gallium, germanium, tin, molybdenum, yttrium, and lanthanum in the principal coal-producing beds of the Interior Province has been studied by the U. S. Geological Survey. Data, methods of sampling, and analyses are discussed by Zubovic and others (II, 12). This chapter discusses the occurrence of 13 of these elements with respect to geological and geochemical environments of coal deposition and chemical properties of the elements. Zinc and tin are not included in this study because they were detected in only a few samples. 

Although the hypothesis of Egumi may be an oversimplification, it is certainly true that Fe /Feu is widely used in redox systems. Zn " in hydrolysis, esterification, and similar reactions, and molybdenum in nitrogenase. xanthine oxkkise. nitnite reductase, etc Putting abundance aside, discuss the specific chemical properties of these metals this make them well suited for their tasks. 

Through a co-assembling route, mesostructured lamellar molybdenum sulfides are formed hydrothermally at about 85 °C using cationic surfactant molecules as the templates. The reaction temperature and the pH value of the reaction system are important factors that affect the formation of the mesostructured compounds. The amount of the template and that of the S source are less critical in the synthesis of the compounds. For the three as-synthesized mesostructured materials, the interlayer distance increases linearly with the chain length of the surfactant. Infrared and X-ray photoelectron spectroscopy reveals that the individual inorganic layers for the three compounds are essentially the same both in composition and in structure. The formal oxidation state of the molybdenum in the materials is +4 whereas there exist S2 anions and a small amount of (S-S)2 ligands in the mesostructures. The successful synthesis of MoS-L materials indicates that mesostructured compounds can be extended to transition metal sulfides which may exhibit physico-chemical properties more diverse than non-transition metal sulfides because of the ease of the valence variation for a transition metal. 

It is interesting to speculate on the chemical properties of molybdenum which make it suitable for its biological function. Obvious features in the chemistry of molybdenum are (a) a range of oxidation states which can be stabilized in aqueous solution by the common ligands of biology (b) the formation of oxo compounds and the sulfur analogue (c) the ability to participate in atom-transfer reactions and (d) the possibility of higher coordination numbers. 

Heteropoly compounds may be classified according to the ratio of the number of central atoms to the peripheral molybdenum or other such atoms. Compounds with the same number of atoms in the anion usually are isomoiphous and have similar chemical properties. Usually, the heteropolymolybdates and heteropolytungstates containing nontransition elements as central atoms have more structural analogues than those that contain transition elements as central atoms. Table 1 lists all elements... 

The chemical properties of tungsten are similar to those of molybdenum tungsten is more expensive, however, and its industrial use is therefore limited. Especially when hydrogenation is carried out under severe conditions, such as in hydrocracking, sulfided Ni-W/A Os catalysts have advantages over sulfided Ni-Mo/Al203. 

There is a general tendency for wear to be reduced in molybdenum disulphide greases, but the improvement is not as great nor as consistent as for load-carrying capacity. Friction is also generally lower. The effects on physical and chemical properties of greases are more complicated, and addition of molybdenum disulphide has been shown to affect the stability of the gel structure, the oxidation resistance and the corrosion resistance. 

Subject to this complication, the friction properties of the group are generally similar to those of molybdenum disulphide. The actual coefficients of friction vary with load, speed, temperature and humidity, but some reported figures are shown in Table 14.6. The chemical properties are also similar to those of molybdenum disulphide. They are resistant to attack by water, alkalis and most acids, but are attacked by aqua regia and hot concentrated hydrochloric, nitric or sulphuric acids. The most significant differences are in their electrical conductivity and their oxidation resistance. 

Haltner, A.J. and Oliver, C.S., Effects of Chemical Properties of Molybdenum Disulfide on Frictional Behaviour, Symp. on Chem. of Friction and Wear, Divn. of Petroleum Chem., Am. Chem. Soc., (1958). 

Another effect of lanthanide contraction is that the third row of the d-block elements have only marginally larger atomic radii than the second transition series. For example, zirconium and hafnium, niobium and tantalum, or tungsten and molybdenum have similar ionic radii and chemical properties (Zr + 80 pm, Hf + 81 pm Nb + 70 pm, Ta + 73 pm Mo + 62 pm, W + 65 pm). These elements are also found in the same natural minerals and are difficult to separate. 

Element 106. The chemical properties of element 106 (eka-tungsten) are predicted to be similar to those of tungsten, molybdenum and to some extent chromium, offering an even richer chemistry of complex ions than these elements. The hexafluoride should be quite volatile and the hexachloride, pentachloride and oxychloride should be moderately volatile. Penneman and Mann predict a -)-4 oxidation state in aqueous solution. Jprgensen s selection of k is for the hydrated cation and is not intended to account for the effects of complex ion formation. However, since tungsten is stabilized in the oxidation state of -t-6 by the tungstate ion, an analogous situation may be expected for element 106. 

---