Metal cluster compounds table

As is the case for transition metal cluster compounds in general, singlecrystal X-ray diffraction is normally the only technique available for the unambiguous structural characterization of heteronuclear Group IB metal clusters. Tables I, II, and IV-XIV indicate the mixed-metal clusters containing one or more ML (M = Cu, Ag, or Au L = two-electron donor ligand) units which have been studied by X-ray crystallography. Other... 

Table 2. Structural data for H3O2 bridging ligands in trinuclear metal cluster compounds... 

Ever since Parkyns (60) prepared nickel particles on oxide (A1203, Si02) surfaces by decomposition of nickel carbonyl, metal cluster compounds (alkoxides, carbonyls, organometallics, etc.) have been used increasingly for the production of laboratory metal catalysts (Table I), and several reviews have appeared on this subject (6l-65a,b). 

The preceding paragraphs have introduced the various preparation methods leading eventually to supported metal particles. These methods fall obviously into two categories depending on whether the metal is basically in its zerovalent state (decomposition of metal cluster compound, chemical deposition, ion implantation, and vapor-phase deposition) or in an oxidized state (coprecipitation, impregnation, and ion ex-change)(Table I). 

It must be pointed out that the exact nature of the catalytic species has not been established in the case of the metal cluster compounds listed in Table I. Rearrangement of the added cluster compounds to some other cluster species under the reaction conditions is readily conceivable, and in several cases, very probable. 

Owing to their structures and reactivities, clusters containing M4C, M3CR, and M3CR2 skeletons are of particular interest. In addition to the previously described four metal atom compounds (Table 3.14, footnote references b and c), they comprise trinuclear M3 complexes having /X3-CCO, and //2-CH2 bridges ... 

The known halides of vanadium, niobium and tantalum, are listed in Table 22.6. These are illustrative of the trends within this group which have already been alluded to. Vanadium(V) is only represented at present by the fluoride, and even vanadium(IV) does not form the iodide, though all the halides of vanadium(III) and vanadium(II) are known. Niobium and tantalum, on the other hand, form all the halides in the high oxidation state, and are in fact unique (apart only from protactinium) in forming pentaiodides. However in the -t-4 state, tantalum fails to form a fluoride and neither metal produces a trifluoride. In still lower oxidation states, niobium and tantalum give a number of (frequently nonstoichiometric) cluster compounds which can be considered to involve fragments of the metal lattice. 

Metal Preferences. LVC s are formed mainly by transition metals to the right in the periodic table (especially elements in Group 8). This is in part due to the availability of d electrons that can be used in back-donation to the 7r-accepting ligands. Moreover, the formation of LVC s is not particularly "row-sensitive" by which I mean that the first-transition-series metals, Fe, Co and Ni, tend to form most of the same cluster compounds as their congeners, Ru, Rh, Pd and Os, Ir, Pt. 

The topic of molecular transition metal-gold bond-containing compounds, especially of cluster compounds, has developed considerably in recent years (Table 4.6). 

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