Molybdenum halides

CVD Reactions. MoSi2 is usually deposited by the reaction of a molybdenum halide with silane. The simplified reactions are as... 

Both homogeneous and heterogeneous catalysts can be used in olefin metathesis.6 26 28 29 31 In general, tungsten or molybdenum halides or carbonyl complexes... 

The conclusion that variations in the coupling of vibrational modes in these dimers is not responsible for the entire frequency shift is an important point in that it justifies the search for a chemical rationale of the bonding differences in Mo2Xf and Mo2(02CR)4. The authors suggest that 6 bonds may make an important bonding contribution in rhenium dimers and molybdenum carboxylates to account for Fmm near 4.5 mdyne A-1. Furthermore, it is proposed that such a 6 component would probably not contribute significantly in the molybdenum halides where is near 3.5 mdyne A"1, possibly... 

Thus far, dimensional reduction has not been applied in this way to any of the other parent solids listed in Table I. Of particular interest are systems that straddle the divide between the edge-bridged and face-centered octahedral geometries. Will reduced niobium-molybdenum halide mixtures simply disproportionate or will they lead to new mixed-metal clusters If the latter, then where does the crossover in cluster geometries occur An important factor in applying dimensional reduction is recognizing the variability in the stable electron counts within a particular cluster system. An extreme case occurs... 

ANHYDROUS MOLYBDENUM HALIDES AND OXIDE HALIDES—A SUMMARY... 

The lower molybdenum halides are prepared by the reduction or thermal decomposition of the appropriate higher halide. A variety of reducing agents (examples H2, SnCl2, PF3) have proved useful. 

Infrared spectral analysis9 is employed as a check for other impurities which might be present in the molybdenum(IV) chloride. Molybdenum oxychlorides can be easily identified by their characteristic absorptions in the 900-1000-em.-1 region, which is typical of Mo—O groups. In addition, an examination of the far infrared spectrum should show only the characteristic bands of molybdenum(IV) chloride at 404, 350, and 268 cm.-1. These can be distinguished from those of other molybdenum halide species. A test for the presence of molybdenum (III) chloride, which often occurs as a side product in other preparations of molybdenum(IV) chloride, is treatment with 6 N hydrochloric acid. Complete solubility indicates the absence of this chloride. 

Reduction of [Mo CIg] and [Mo ClgX ] anions (X = Cl, Br, or I) by certain tertiary phosphines gave complexes of stoicheiometry MOgClgX3(PR3)3, which are formulated to have an ionic structure [MOgCl8(PR3)g] [Mo Clg]X in which the cation is a derivative of the previously unknown [Mo Clg] cluster. The use of photoelectron spectroscopy to determine structures of metal halide clusters has been reviewed. " A detailed study of the force fields for MojXg anions (X = Cr or Br) has indicated that 6 bonds do not play a significant part in the M—M bond strength of molybdenum halides. ... 

Near quantitative yields are achieved for the molybdenum halides, but substantially lower yields (50%) are obtained in the synthesis of the tungsten clusters, which require higher temperatures and the use of Vycor reaction vessels. A higher yield low-temperature synthesis was devised by McCarley and co-workers for W6C112 using iron as the reducing agent (14). 

The hexanuclear molybdenum halide clusters (Mo6Xs)X4, i.e. (Mo6X 8)CP2CF 4/2, are known to react with some transition metal halide compounds forming two different types of cluster polymeric clusters with bridging outer halide ligands (X ) and discrete clusters with terminal halide ligands (X ). 

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