Valency of molybdenum

Fig. 1.—Values of the metallic radius for ligancy 12, represented by circles, for the elements yttrium to silver. The straight line represents the expected values for valence of other metals equal to the valence of molybdenum that is, it shows the effect of increasing nuclear charge only.

The approximate correctness of the relative values of fav given in the table is supported by the observed values of the metallic radii. Values of R for ligancy 12 are shown in Figure 1, with a straight line with slope that represents the change in radius with atomic number for constant valence and type of orbital, as given in Figure 3 of an earlier paper.17 The points lie above the line by amounts that indicate a monotonic decrease in valence to both sides of molybdenum. 

Complexes of molybdenum in the lower valence-states of -t 2 and + 3 have been produced only in the past two years. For the Mo(II) species, the usual starting-material is Mo2(acetate>4. Reaction of this with KS2COEt in THF gives two products, a green complex tentatively assigned as [Mo2(Etxant>4], which solvates to form the red complex [Mo2(Etxant)4(THF)2]. The structure of the latter complex was elucidated by X-ray analysis 169). Steele and Stephenson 170) were also able to synthesize a red, crystalline solid (methanol solution), which they formulated as [Mo(Etxant)2]2 (XI), and reacted this with Lewis bases, e.g., pyridine, to form [Mo(Etxant)2L]2- Thus, there appears to be a difference between the two compounds formulated as [Mo2(Et-xant)2]2 that... 

A favorable combination of valence forces of both components seems to be the basic principle of the nickel-molybdenum ammonia catalyst. It has been found (50) that an effective catalyst of this type requires the presence of two solid phases consisting of molybdenum and nickel on the one hand and an excess of metallic molybdenum on the other. Similar conditions prevail for molybdenum-cobalt and for molybdenum-iron catalysts their effectiveness depends on an excess of free metal, molybdenum for the molybdenum-cobalt combination and iron for the molybdenum-iron combination, beyond the amounts of the two components which combine with each other. A simple explanation for the working mechanism of such catalysts is that at the boundary lines between the two phases, an activation takes place. In the case of the nickel-molybdenum catalyst, the nickel-molybdenum phase will probably act preferentially on the hydrogen and the molybdenum phase on the nitrogen. 

Camara, B., Lutze, W. Lux, J. 1980. An investigation of the valency state of molybdenum in glasses with and without fission products. In Northrup Jr, C. J. M. (ed) Scientific Basis for Nuclear Waste Management, Plenum Press, New York, 2, 93-102. 

Solid-state sulfide compounds MMo2S4 (M = V, Cr, Fe, Co) contain infinite chains of Mo4S6 clusters with intracluster Mo-Mo distances (2.756-2.989 A) and intercluster distance (2.960 A) for the cobalt derivative (112). As the valence of M is +2, judging from magnetic measurements, and the average oxidation state of molybdenum +3, the CVE for M2Mo4S8 is 12. This agrees with five intracluster and one intercluster... 

Mom+ and Mow+ are written to indicate forms of molybdenum present during the reaction without specifying an exact oxidation level of structure. The number of molybdenum compounds of various valences (Table I) which catalyze this reaction suggest that the initial molybdenum compound may be converted to the same active forms (Step 1). These active forms then complex with the hydroperoxide rapidly (Step 2). 

Haber (59, 113) has reported data supporting the concept that the low-valence cation is responsible for propylene activation. He studied the kinetics of catalyst reduction for a-, /)-, and y-bismuth molybdates using both hydrogen and propylene as reductants. Because the coordination of molybdenum varies among the three phases (tetrahedral in a phase, tetrahedral and octahedral in /3 phase, and octahedral in y phase), the... 

In the sixth group, chromium, molybdenum, tungsten, and uranium constitute Family A. In their trioxides they show the characteristic valence of the sixth group and resemble in properties the non-metals of Family B, of which sulphur is the type. In their lower oxides they possess none of the characteristics of Group VI but show the general base-f orming properties of the heavy metals. 

Hu et al. (1995) reported extensive Raman experiments characterizing supported molybdenum oxide catalysts during methanol oxidation. In contrast to the stable oxidation state of vanadia, the valence of surface molybdenum species decreased during catalysis. The original band... 

FIGURE 9 Relative position of Mo K-edge feature (as defined by arrow in inset) as a function of the Mo valence for a series of Molybdenum oxides (Ressler et al., 2002). Reprinted from (Ressler et al., 2002), Copyright 2002, with permission from Elsevier. 

Based on the studies of the XANES (X-ray absorption near edge structure) spectra of LiVMoOe and the standard samples (such as V2O5, VO2, M0O3, M0O2, etc) at the V and Mo K-edges, we can determine the valence of the vanadium ion is about 4.5 while that of molybdenum ion is 6. 

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