Molybdenum interaction with chromium

In the absence of interaction with other hgands or orbitals, the back-bonding interaction in the yz plane for the 6 = 90° orientation would be degenerate with that in the xz plane for the 6 = 0° orientation. Thus, for the chromium and molybdenum derivatives M(CO)5 (ethylene), there would be no preference for either the yz or the xz plane. In fact, at this level of approximation, no barrier would be expected for a rotation from the yz to the xz plane, that is, the interaction with a linear combination of xz and yz would also be equivalent in energy. 

Titration of the products formed by the interactions of chromium(VI) and molybdenum(VI) oxide with KN03 runs in one stage and leads to the formation of neutral chromates and molybdates, respectively. The investigators calculated the constants of oxide ion addition to Cr207 and Mo30 q according to the following reactions ... 

The interaction of norbornene with iron, chromium, molybdenum, and tungsten atoms affords highly unstable and uncharacterized systems of polymeric materials (102, 134). The use of other strained olefins, such as /ran.v-cyclooctene, in metal atom syntheses has yet to be explored. 

The unique ligating behavior of the bridging 2,6-dimethoxyphcnyl ligand with respect to promoting a substantial decrease in the metal atom separation for molybdenum(II) dimers is even more prominent in the case of chromium. The chromium-chromium distance of 1.847(1) A in Cr2(DMP)4 (90) is more than 0.1 A less than the corresponding value in any other chromous dimer yet reported. To compare homonuclear multiple bonds among elements with inherently different atomic radii, Cotton, Koch, and Millar proposed a normalized value for intemuclear distances based on Pauling s atomic radius of the element in question (209). A simple definition of formal shortness as t/(M—M)/2r(M) then follows as a measure of the relative compactness of the attractive interaction (90). The formal shortness ratio of 0.778 for the quadruple bond in... 

We begin with the structure of a noble metal catalyst, where the emphasis is placed on the preparation of rhodium on aluminum oxide and the nature of the metal support interaction. Next, we focus on a promoted surface in a review of potassium on noble metals. This section illustrates how single crystal techniques have been applied to investigate to what extent promoters perturb the surface of a catalyst. The third study deals with the sulfidic cobalt-molybdenum catalysts used in hydrotreating reactions. Here, we are concerned with the composition and structure of the catalytically active surface, and how it evolves as a result of the preparation. In the final study we discuss the structure of chromium oxide catalysts in the polymerization of ethylene, along with the polymer product that builds up on the surface of the catalyst. 

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