Transition metal clusters face bridging

Although the above mentioned face- and edge-halide-bridged clusters are characterised by 84 and 76 valence electrons respectively, it was apparent by the early 1970 s that the great majority of octahedral transition metal clusters possess 86 electrons. Braterman rationalised the 86 cluster valence electron count for octahedral metal carbonyl clusters, such as [Co6(CO)i6]75), [Ru6C(CO)17]76) and [Co6(CO)i4]4- 77) in terms of localised M-CO... 

The simultaneous function of a transition metal atom as a lone-pair acceptor and as a cluster vertex atom is realized in [(77 -Ge9)Cu(ry -Geg)] (Fig. 5j), in which the two [Geg]" units are connected in an r/ - and an r/" -fashion to the same Cu ion. Transition metal bridges between Geg clusters are also found in various other coordination modes in [Ge9(/i -Au)3Geg] (Fig. 5k), three bridging Au atoms each are coordinated by two Ge atoms of two different Geg units in an almost linear way and entertain aurophUic interactions within the resulting triangle of Au" " ions two [GegR3] anions are coordinated via their triangular face to ( M = Zn, Cd,... 

Fig. 1. Edge-bridging (a) and face-capping (b) bonding modes adopted by M(PR3) (M = Cu, Ag, or Au R = alkyl or aryl) units in mixed-metal clusters. M is a transition metal other than a Group IB metal.

Although compounds with edge and face-bridging ligands may be formally considered as main group-transition metal mixed clusters (s. Chap. 3), in these section they will be referred to only as ligands. 

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