Tungsten structural data

The compounds WL2(NCS)4 (L = py or bipy) have been characterized (130), and a series of tungsten(V) (750) and tungsten(VI) (306, 751) compounds prepared without structural data. 

Crystal structure data Model the surface structure to determine the preferred arrangement of the tungsten diphenoxide species on the hydroxyl-ated support 135... 

Although Mo (II) and W(II) exhibit the most extensive seven-coordinate chemistry yet known (consistent with the application of the effective atomic number rule to these systems), a survey of the substituted metal carbonyl complexes of molybdenum and tungsten reveals no structural data for compounds of the type M(00)3(6-6)2 where 6-6 is a bidentate monoanionic ligand. No tungsten tricarbonyls of this type have been reported to date, but McDonald and co-workers have synthesized and studied the closely related W(CO)2(PPh3) (6-6)2 compounds where 6-6 is a chelating dithiocarbamate (7), xanthate, or dithiophos-phate (8). For molybdenum, the compounds Mo(CO)3(dtc)2(dtc = R2NCS2") (9) are examples of the M(CO)3(6-6)2 type as is Mo(CO)3-[S2P(i-Pr)2]2 (10), which has been well characterized in solution. 

In order to obtain valid structural data on the novel triphosphabenzvalenes, the bridgehead phosphorus atom P(l) of 96 was subjected to complexation with pentacarbonyl(terahydrofuran)tungsten to afford the -tungsten complex 97 [54]. Coordination of the metal complex to P(2) or P(5) does not occur for steric reasons this also confirms that P(l) is the most reactive of the three phosphorus atoms. 

Figure 9.2. Variation in the heat of adsorption of hydrogen on tungsten with coverage and surface structure. Data from Ref. 166.

This review is structured as follows. In the next section we present the theory for adsorbates that remain in quasi-equilibrium throughout the desorption process, in which case a few macroscopic variables, namely the partial coverages 0, and their rate equations are needed. We introduce the lattice gas model and discuss results ranging from non-interacting adsorbates to systems with multiple interactions, treated essentially exactly with the transfer matrix method, in Sec. II. Examples of the accuracy possible in the modehng of experimental data using this theory, from our own work, are presented for such diverse systems as multilayers of alkali metals on metals, competitive desorption of tellurium from tungsten, and dissociative... 

Essentially six resonance structures (G-L in Eig. 11) have to be taken into account for complexes 72, their spectroscopic data, as well as the X-ray structural analysis performed on the tungsten derivative, suggesting that strongly dipolar ylidic structures J-L are the most important contributions to the overall bonding situation. 

Mixed Metal Complexes. In contrast to the reaction producing [Fe5C(CO)j4 ] discussed above, treatment of Fe2(CO)g with [(jr-Cp)Mo(CO)3] at room temperature in THF yields [(7r-Cp)2Mo2Fe2(CO),Q] , for which structure (17) is suggested on the basis of i.r. data. The analogous tungsten compound has also been isolated, but no hydrides were isolated upon acidification. ... 

A heptacovalent structure cannot be devised to fit the NMR data because directed bonds from tungsten to both the donor ligand and the sixth fluorine... 

The fundamental vibrations have been assigned for the M-H-M backbone of HM COho, M = Cr, Mo, and W. When it is observable, the asymmetric M-H-M stretch occurs around 1700 cm-1 in low temperature ir spectra. One or possibly two deformation modes occur around 850 cm l in conjunction with overtones that are enhanced in intensity by Fermi resonance. The symmetric stretch, which involves predominantly metal motion, is expected below 150 cm l. For the molybdenum and tungsten compounds, this band is obscured by other low frequency features. Vibrational spectroscopic evidence is presented for a bent Cr-H-Cr array in [PPN][(OC)5Cr-H-Cr(CO)5], This structural inference is a good example of the way in which vibrational data can supplement diffraction data in the structural analysis of disordered systems. Implications of the bent Cr-H-Cr array are discussed in terms of a simple bonding model which involves a balance between nuclear repulsion, M-M overlap, and M-H overlap. The literature on M-H -M frequencies is summarized. 

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