Complexes and clusters

One of the motivations for studying Van der Waals complexes and clusters is that they are floppy systems with similarities to the transition states of chemical reactions. This can be taken one stage further by studying clusters that actually are precursors for chemical reactions, and can be broken up to make more than one set of products. A good example of this is H2-OH, which can in principle dissociate to fonn either H2 + OH or H2O + H. Indeed, dissociation to H2 O -t H is energetically favoured the reaction H2 + OH—> H2 O -t H is exothennic by about 5000... 

The red tetrathiomolybdate ion appears to be a principal participant in the biological Cu—Mo antagonism and is reactive toward other transition-metal ions to produce a wide variety of heteronuclear transition-metal sulfide complexes and clusters (13,14). For example, tetrathiomolybdate serves as a bidentate ligand for Co, forming Co(MoSTetrathiomolybdates and their mixed metal complexes are of interest as catalyst precursors for the hydrotreating of petroleum (qv) (15) and the hydroHquefaction of coal (see Coal conversion processes) (16). The intermediate forms MoOS Mo02S 2> MoO S have also been prepared (17). 

Table 1. Metal—Metal Bonding in Molybdenum Complexes and Clusters...

More recendy, molecular molybdenum-sulfur complexes and clusters have been used as soluble precursors for M0S2 in the formulation of lubricating oils for a variety of appHcations (70). Presumably, the oil-soluble molybdenum—sulfur-containing precursors decompose under shear, pressure, or temperature stress at the wear surface to give beneficial coatings. In several cases it has been shown that the soluble precursors are trifunctional in that they not only display antifriction properties, but have antiwear and antioxidant characteristics as weU. In most cases, the ligands for the Mo are of the 1,1-dithiolate type, including dithiocarbamates, dithiophosphates, and xanthates (55,71). 

Fierro-Gonzalez, J.C., Kuba, S., Hao, Y. et al. (2006) Oxide- and zeolite-supported molecular metal complexes and clusters physical characterization and determination of structure, bonding, and metal oxidation state, J. Phys. Chem. B, 110, 13326. 

A review23 with 1,160 references describes the chemistry of Pd and Pt complexes and cluster compounds, catalysis by Pd and Pt complexes, and nonstoichiometric binary and ternary compounds. 

The single-bond compounds between Si, Ge, and Sn and chalcogens (S, Se, Te) are reactive and used as synthetic intermediates in the synthesis of organic compounds, organochalcogen compounds, organo-silicon, -germanium and -tin compounds, and transition metal-chalcogen complexes and clusters. 

However, a detailed model for the defect structure is probably considerably more complex than that predicted by the ideal, dilute solution model. For higher-defect concentration (e.g., more than 1%) the defect structure would involve association of defects with formation of defect complexes and clusters and formation of shear structures or microdomains with ordered defect. The thermodynamics, defect structure, and charge transfer in doped LaCo03 have been reviewed recently [84],... 

R M. Felker, P. M. Maxton, and M. W. Schaeffer, Nonlinear Raman studies of weakly bound complexes and clusters in molecular beams. Chem. Rev. 94, 1787 1805 (1994). 

In general, correlation corrections are larger for a holes than for ir holes. It is not unusual for these differential correlation effects to change the predicted order of final states. Heterocyclic organic molecules with nitrogen-centered, nonbonding electrons are not alone in this respect. Organometallics, transition metal complexes, and clusters of metal oxides and metal halides also require this kind of theoretical interpretation. 

J. Guzman and B. C. Gates, Supported molecular catalysts metal complexes and clusters on oxides and zeolites, Dalton Trans. 17, 3303—3318 (2003). 

Sulfide minerals were formed mostly hydrothermally from post-magnetic fluids it appears remarkable that the formation of many ore deposits cannot be conclusively explained because of the very low solubility of the corresponding sulfide. Though it was postulated earlier (28, 29, 95) that polysulfido complexes might have been responsible for the transport of metals and sulfur together (80), it was later proved that many discrete polysulfido complexes and clusters of metals exist in polysulfide solutions (see, e.g., 136,138). 

Table 16.1 Synthesis of some Re, Fe and Ru carbonyl complexes and clusters on the surface of Si02, MgO or...

As a general trend, uncharged carbonyl complexes and clusters are obtained on the surface of rather neutral supports such as silica [4—6] whereas the synthesis of... 

Table 16.4 Traditional synthesis of Ru metal carbonyl complexes and clusters in solution."...

I 76 Surface-Mediated Organometallic Syntheses Table 16.5 Traditional synthesis of Os metal carbonyl complexes and clusters in solution". 

Reactions carried out on the surface of inorganic oxides allow convenient high-yield and selective syntheses of various metal carbonyl complexes and clusters, starting from easily available materials (Tables 16.1-16.3). The synthetic procedures are straightforward and the recovery of products is easy. Since the use of a solid as reaction medium is not Umited in the manner in solution by boiling points and by the thermal instabiUty of some solvents, it is possible to work at atmospheric pressure even at rather high temperatures. Therefore, in many cases, yields and pressure are better and lower, respectively, than those of the traditional syntheses in solution (Tables 16.4—16.6). 

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