Isoelectronic cluster metal complex

The structures of [Mo(CO)4(AuPPh3)5]+ " and [Mo(CO)3(AuPPh3)7]+ are shown in Fig. 5. The structure of [Mo(CO)5(AuPPh3)3]+ was not determined. It can, however, be assumed that it has the same structure as the isoelectronic cluster V(CO)5(AuPPh3)3.f Flomonuclear gold cluster compounds are always formed as by-products, but the amount can be reduced by using an excess of the metal carbonyl complex. 

Exclusive of metal-metal bonding, the six metal atoms in the octahedral cluster metal carbonyls Mg(CO)10 (M = Co, Rh, and Ir) as well as their iso-electronic analogs Me(CO)i52 and Mg (CO) have (6)(9) + (2)(16) = 86 outer valence electrons. The hydride H2Rug(CO)i0 and the carbide Rug(C0)i7C are two types of octahedral cluster ruthenium carbonyl complexes that likewise have 86 outer valence electrons exclusive of metal-metal bonding and thus may be regarded as isoelectronic with Mg(CO) g (M = Co, Rh, and Ir). 

There are a sufficiently large number of complexes, mainly of germanium, containing more than one type of transition metal, to warrant a separate discussion some examples have already been mentioned (viz. 38 and 57). Mackay and Nicholson (89,91) have described the reaction between [Fe2-(CO)8(//-GeH2)2] and [Co2(CO)8], which affords the mixed cobalt-iron clusters [Fe2(CO)8 /i-Ge(Co2(CO)7) 2], 82, and [Fe2(CO)7 /i-Ge(Co2-(CO)7) 2], 83, the latter having been characterized by X-ray diffraction. This is isoelectronic with the iron-germanium cluster, 63, and both adopt very similar structures. 

Mixed metal clusters have also become very numerous and well known. These range from simple cases, where obvious isoelectronic replacements are made, as exemplified by Co4(CO)i2 and RhCo3(CO)i2, to very large and complex species such as [Ni9Pt3(CO)2iH]. There is no end in sight to the possibilities for more mixed metal clusters. 

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