Chapter 5 - The Halides of Molybdenum

Abstract: The article contains sections titled: 1. Introduction 2. Properties 3. Occurrence 3.1. Minerals 3.2. Deposits 4. Production 4.1. Concentration 4.2. Processing of Concentrate 4.3. Recovery from Spent Petroleum Catalysts 4.4. Recovery during Production of Tungsten Ores 4.5. Production of Molybdenum Metal Powder 4.6. Production of Compact Molybdenum Metal 4.7. Processing of Molybdenum 4.8. Molybdenum-Base Alloys 5. Uses 6. Production of Ferromolybdenum 6.1. Ferromolybdenum Grades 6.2. Raw Materials 6.3. Submerged Arc Furnace Carbothermic Reduction 6.4. Metallothermic Reduction 7. Molybdenum Compounds 7.1. Overview of Molybdenum Chemistry 7.2. Molybdenum Oxides 7.3. Molybdenum Chalcogenides 7.4. Molybdenum Halides 7.5. Molybdates, Isopolymolybdates, and Heteropolymolybdates 7.6. Other Molybdenum Compounds 8. Uses of Molybdenum Compounds 8.1. Catalysis 8.2. Lubrication 8.3. Corrosion Inhibition 8.4. Flame Retardancy and Smoke Suppression 8.5. Pigments 8.6. Agriculture 9. Analysis 10. Economic Aspects 11. Environmental Aspects 12. Toxicology and Occupational Health

Abstract: The basic properties of molybdenum and subsequently the methods of producing metallic molybdenum are described. Selected classes of important inorganic compounds (molybdenum halides, molybdenum oxides, iso- and hetero-polyoxomolybdates) as well as molybdenum hexacarbonyl and hybrid inorganic–organic materials are presented. Thereafter the focus is directed to various applications of metallic molybdenum, its alloys and compounds such as catalysts, lubricants and refractory ceramics. In conclusion, molybdenum’s medicinal role and the antimicrobial activity of MoO3 and solid solutions Mo n W1-n O3 are discussed.

Abstract: The structures of the STAM/sub 6/X/sub 8/!/sup 4+/, M=Mo, W(?), STAM/sub 6/Cl/sub 12//sup 2+/, M = Nb, Ta, and STAM/sub 3/X/sub 12/!/sup 3-/, M= Re, species, which contain clusters of heavy transition metal atoms are compared; and the occurrence of approximately square MX/sub4/ units is noted as a common feature. The metal-metal bonding within the clusters is treated by a simple molecular orbital method, and it is shown that in this way all the general aspects of the electronic structures can be straightforwardly accounted for. Clues provided as to other possible metal ion cluster compounds are discussed. (auth)

Abstract: Die Molybdanchloride wurden einer erneuten chemischen und physikalischen Untersuchung unterworfen. Die Synthese im Temperaturgefalle lieferte die Verbindungen MoCl4, α-MoCl3 und MoCl2 (≙Mo6Cl12) in reiner, kristallisierter Form. Auf gleichem Wege wurde die neue Verbindung MoCl3,08 („β-MoCl3”) gefunden. Das im festen Zustande dimere MoCl5 verdampft monomolekular (Massenspektrometer). Der thermische Zerfall (Thermogravimetrie, Massenspektrometer) von MoCl3 erfolgt nach wahrend MoCl2 nach . Kristallstrukturuntersuchungen lieferten folgende Informationen: MoCl4 kristallisiert trigonal in einem Schichtengitter mit hexagonal dichter Cl-Packung. Die Mo-Atome besetzen 75% der Metallplatze einer Trichloridstruktur, wobei im Mikrobereich Ordnungszustande auftreten. α-MoCl3 und β-MoCl3 kristallisieren monoklin in Schichtengittern mit kubisch (α) bzw. hexagonal (β) dichter Cl-Packung. Die Mo-Atome sind paarweise als Mo2-Gruppen aneinander gebunden (MoMo = 2,76 A). Mo6Cl12(MoCl2) kristallisiert orthorhombisch. Die Struktur enthalt [Mo6Cl8]-Gruppen, die 2-dimensional unendlich miteinander verknupft sind: {[Mo6Cl8]Cl2}Cl4/2. Die Bindungsabstande MoMo innerhalb der regularen Mo6-Oktaeder betragen 2,61 A. Der Vergleich der Vergleich der Raumbeanspruchung („pro Cl”) zeigt, das diese beim Ubergang von den hoheren Molybdanchloriden zum Mo6Cl12 wegen dessen sperrigen Aufbaus sprunghaft groser wird. Magnetische Messungen liefern fur MoCl5 und MoCl4 nahezu den reinen Spinwert, wahrend die fur α-MoCl3, β-MoCl3 und Mo6Cl12 gemessenen Werte wegen der MoMo-Wechselwirkungen sehr viel kleiner sing. Mo6Br12, Mo6J12, W6Cl12, W6Br12 und W6J12 sind mit Mo6Cl12 isotyp. Chemical and physical properties of the molybdenum chlorides have been reinvestigated. By synthesis in a temperature gradient crystalline samples of MoCl4, α-MoCl3 and MoCl2 (≙Mo6Cl12) were prepared. The new compound MoCl3,08 (“β-MoCl3”) was found in the same way. MoCl5, being dimeric in the solid state, is monomeric in the vapour (mass spectrum). Thermal dissociation (TGA, mass spectrum) of MoCl3 proceeds according to 2 MoCl3 MoCl2 + MoCl4,g; P(MoCl4, 800°C) = 12 atm, whereas MoCl2 decomposes according to 2 MoCl2 Mo + MoCl4,g; P(MoCl4, 860°C) = 0,4 atm. Crystal structure analyses submitted the following informations: MoCl4 (trigonal) forms a layer structure with a hexagonal closepacked Cl sequence. Three quarters of the metal positions of a corresponding trichloride structure are randomly occupied by Mo atoms. α-MoCl3 and β-MoCl3 (both monoclinic) have layer structures with cubic (α) and hexagonal (β) close Cl arrangements and with certain adjacent octahedral holes occupied by molybdenum forming Mo2 pairs (MoMo = 2,76 A). Mo6Cl12 (MoCl2) (orthorhombic) is built up by [Mo6Cl8] clusters, linked to a 2-dimensional arrangement: {[Mo6Cl8]Cl2}Cl4/2. The MoMo distance in the regular octahedral Me6 group is 2,61 A. Comparing the volumes per one Cl atom, it can be seen, that these are abruptly increased on going from the molybdenum chlorides of higher oxidation state to Mo6Cl12 with its cumbersome structure. The magnetic moments of MoCl5 and MoCl4 nearly correspond to the spin-only values, whereas the moments of α-MoCl3, β-MoCl3, and Mo6Cl12 are much smaller, caused by MoMo interaction. Mo6Br12, Mo6I12, W6Cl12, W6Br12, and W6J12 are isotypic with Mo6Cl12.