Clusters molybdenum

Mitchell S A, Llan L, Rayner D M and Hackett P A 1995 Reaction of molybdenum clusters with molecular nitrogen J. Chem. Rhys. 103 5539... 

Molybdenum (Clusters and Metal-Metal Bonds) (see also Table 6)... 

Boulanger C, Lequir JM (1988) Molybdenum cluster chalcogenide electrochemistry-111. 

A cationic molybdenum sulfide cluster [Mo3S4(H20)9] " with incomplete cubane-type structure and a cationic nickel-molybdenum mixed sulfide cluster [Mo3NiS4Cl(H20)9p " with complete cubane-type structure were introduced into zeolites NaY, HUSY and KL by ion exchange. Stoichiometry of the ion exchange was well established by elemental analyses. The UV-visible spectra and EXAFS analysis data exhibited that the structure of the molybdenum cluster remained virtually intact after ion exchange. MoNi/NaY catalyst prepared using the molybdenum-nickel sulfide cluster was found to be active and selective for benzothiophene hydrodesulfurization. 

In the preparation of Mo/KL, the addition of 1 was stopped when pH of the solution was lowered to about 3. The resulting Mo/KL contained only 2.1 wt% (74% of added molybdenum clusters) of molybdenum. Chlorine was absent, which indicates that the cluster 1 acted as a tetravalent cation. The LTL structure is characterized by a monodimensional system of channels, whose diameter (0.70 nm) [14] is close to the size of the cluster 1. It is conceivable that, once the cluster 1 was incorporated into an LTL main channel and present at a site near the external surface, the sites deep in the channel are no more accessible to another cluster. 

Crystallographic data for the material tabulated here has been deposited with the CCDC as supplementary publication CCDC-136762 CSD WISVOJ. For the manganese-molybdenum cluster the checkers also obtained a second crystalline modification with an alternative unit cell, namely, Ri, a = ll. ilS (5) A, c = 44.25 (2) A, V = 11570 (5) A, featuring a different packing arrangement of the cluster units. 

The structures of the Cr6 core are affected by the terminal phosphine ligands. The variation of the chromium octahedra contrasts with molybdenum clusters, which always have almost regular octahedral geometry. In a crystal, the structure of a molecule is influenced by steric... 

The preceding three reduced molybdenum clusters indicate that rhomboidal cluster units are common among this kind of oxide, and the Mo-Mo distances in the cluster units are dependent on CVE assignable to the Mo4 units. MO calculations on Mo4 molecular cluster compounds containing 10 CVE and 8 CVE have shown that the 8-electron clusters distort from a second-order Jahn-Teller effect (116). Such a distortion has been observed in the 8-electron W4(OEt)16 (117). 

Likewise, only one type of molybdenum cluster with organic ligands was reported. The complex [29] could be obtained as a cation from Cp(CO)3MoCl and (Me3Sn)2S 384 or neutral from HMo(CO)2[P(OPh)3]Cp and propylene sulfide (35). 

Despite the proposal239 in 1929 that molybdenum(IV) complexes such as Mo304(C204)3+ contains an Mo304 4+ core, it was some 50 years later that the significance of trimeric molybdenum clusters was clearly appreciated. Three types of Mo3 cluster have been... 

Figure 10-9. The structure of the unique iron-molybdenum cluster found at the active site of nitro-genase. The molybdenum is co-ordinated to an extremely unusual homocitrate ligand. There is another iron-sulfur cluster close to this site.

The proteins involved in the reduction of nitrogen to ammonia and other accessible forms contain several such clusters coupled with molybdenum centres. The structure of the central iron-molybdenum cluster at the centre of nitrogenase is shown in Fig. 10-9. Even with the detailed knowledge of this reaction site, the mode of action of nitrogenase is not understood. 

Molybdenum Clusters of the Type Mo Cl L. The chemistry described here was initiated with the notion that it should be possible to observe addition of molecular species X-Y across multiple metal-metal bonds, for example as in the process... 

A major difference in reactivity of the tungsten cluster as compared to the molybdenum clusters is evidenced by the extreme sensitivity of the former to decomposition in air. Further work on the synthesis and reactions of the tungsten clusters is in progress. 

Table 2 Mo NMR parameters of molybdenum clusters C [(Mo6Yg)X6J"" in CH3CN. TTie reference is MoOj from Na2Mo04 in D2O...

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