Molybdenum oxyfluorides

Molybdenum hexafluoride [7783-77-9] MoF, is a volatile liquid at room temperature. It is very moisture sensitive, hydrolysing immediately upon contact with water to produce HF and molybdenum oxyfluorides. MoF should therefore be handled in a closed system or in a vacuum line located in a chemical hood. The crystals possess a body-centered cubic stmcture that changes to orthorhombic below —96° C (1,2). The known physical properties are Hsted in Table 1. 

Three other binary compounds of molybdenum and fluorine are known to exist molybdenum trifluoride [20193-58-2] MoF, molybdenum tetrafluoride [23412-45-5] MoF, and molybdenum pentafluoride [13819-84-6] MoF. Also known are the two oxyfluorides, molybdenum dioxydifluoride [13824-57-2] M0O2F2, and molybdenum oxytetrafluoride [14459-59-7] MoOF. The use of these other compounds is limited to research appHcations. 

A rich variety of complex oxyfluoride compounds containing tungsten, molybdenum, and titanium and displaying spontaneous polarization was discovered and described in [396 - 399]. 

Powdered niobium metal, 20.0 g. (—200 mesh), and tin(II) fluoride, 52.0 g. (40 mesh),t are mixed in a molybdenum crucible in an Inconel- or nickel-pipe reactor approximately 3 in. in diameter and 10 in. long and heated to 400-500°C. in a stream of dry nitrogen. The niobium(V) fluoride volatilizes from the reaction mixture and condenses on the water-cooled lid of the reactor, which leaves metallic tin in the crucible. The yield of niobium(V) fluoride is 21.1 g., or 95% of theoretical. A very small amount of blue niobium oxyfluoride (composition of variable oxygen and fluorine content) often forms as an impurity because of the presence of minute amounts of oxygen. Anal. Calcd. for NbFs Nb, 49.44 F, 50.56. Found Nb, 49.43 F, 50.2. 

Zmbov et al. (1 ) Investigated the stabilities of some molybdenum and tungsten oxyfluorides by means of mass spectrometry. These studies led to enthalpies of formation for MoO F Cg), WO F (g), and WOF (g) which were used by the authors to develop a correlation among the enthalpies of formation of the oxides, oxyfluorides, and fluorides of Mo and W. a H (298.15 K) varies almost linearly with the number of oxygen atoms (1 ) for the series WF, WOF and VO o Assuming a similar variation for MoFg, MoOF and... 

As usually prepared, uranium hexafluoride may he contaminated with other volatile fluorides, and hydrogen fluoride, molybdenum hexafluoride, vanadium oxyfluoride are among the common and objectionable impurities that may be present. Purification is usually achieved by distillation procedures and a considerable amount of useful and practical information on purification procedures has recently become available (24, 62, 81). A procedure for the purification of UFe that has been recently introduced by Gathers el al. (16) involves the formation of a complex compound between uranium hexafluoride and an alkali metal fluoride. Ruff and Heinzelmann (68) first observed complex formation between uranium hexafluoride and sodium or potassium fluoride, and this was confirmed by Martin et al. (69). These reports were received with a certain reserve, because efforts made during World War II to prepare addition compounds of uranium hexafluoride were singularly unsuccessful (41). Nevertheless, complex compounds are indeed formed, according to the reaction... 

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