Molybdenum complexes clusters

V. Solvent Exchange and Ligand Substitution on Some Molybdenum and Tungsten Cluster Complexes... 

Fig. 15. The structures of some molybdenum and tungsten cluster complexes.

Many carbonyl and carbonyl metallate complexes of the second and third row, in low oxidation states, are basic in nature and, for this reason, adequate intermediates for the formation of metal— metal bonds of a donor-acceptor nature. Furthermore, the structural similarity and isolobal relationship between the proton and group 11 cations has lead to the synthesis of a high number of cluster complexes with silver—metal bonds.1534"1535 Thus, silver(I) binds to ruthenium,15 1556 osmium,1557-1560 rhodium,1561,1562 iron,1563-1572 cobalt,1573 chromium, molybdenum, or tungsten,1574-1576 rhe-nium, niobium or tantalum, or nickel. Some examples are shown in Figure 17. 

A few cluster complexes with fused triangles of molybdenum or tungsten have been reported. They are tetranuclear and hexanuclear cluster complexes, which may be viewed also as having fused incomplete cu-banes of M3E4. 

We were quite optimistic in the beginning as the second reduction process corresponds to the formation of a black deposit which was potentially the first electrochemical route to make thick tantalum layers. After having washed off all ionic liquid from the sample we were already a bit sceptical as the deposit was quite brittle and did not look metallic. The SEM pictures and the EDX analysis supported our scepticism and the elemental analysis showed an elemental Ta/Cl ratio of about 1/2. Thus, overall we have deposited a low oxidation state tantalum choride. Despite the initial disappointment we were still eager to obtain the metal and found some old literature from Cotton [122], in which he described subvalent clusters of molybdenum, tungsten and tantalum halides. In the case of tantalum the well-defined Ta6Cli22+ complex was described with an average oxidation number of 2.33 and thus with a Ta/Cl molar ratio very close to 1/2. Such clusters are depicted in Figure 4.15. 

Molybdenum coordination has recently been comprehensively reviewed in Comprehensive Coordination Chemistry, particularly in the areas of mononuclear complexes, polyoxometaUate synthesis, structure, and reactivity see also Polyoxometalates), and in chalcogen-containing cluster complexes. ... 

As used here cluster refers to molecules that contain at least 3 metal atoms and electron configurations suitable for the formation of metal-metal bonds. Molybdenum readily forms strong homoleptic metal-metal bonds (see Homoleptic Compound) and so it is not surprising that molybdenum is readily incorporated into cluster stractures (see Polynuclear Organometallic Cluster Complexes). 

Reviews have appeared of the photophysics of molybdenum complexes, primary and secondary processes in organometallic chemistry, flash photolysis of Pe(CO)5 and Cr(CO)g, dinuclear manganese carbonyl compounds, the photochemistry of metal complexes isolated in low temperature matrices, cluster complexes, diene complexes, photoproduction of coordinativeiy unsaturated species containing rhodium or iridium, and redox chemiluminescence of organometallic compounds.Synthetic and metal organic photochemistry in industry has also been reviewed. 

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