Transition metal tetrahedral cluster

The predictions of structures of transition-metal carbonyl clusters using Wade s rules are not infallible. For example, the clusters M4(CO)i2 (M = Co, Rh, Ir) have 60 valence electrons and are predicted to be nido complexes (14 + 4 valence electrons). A nido structure would correspond to a trigonal bipyramid parent structure with one position vacant. X-ray crystallographic studies, however, have shown these complexes to have tetrahedral metal cores. 

Slovokhotov, Yu.L. and Struchkov, Yu.T (1984) X-ray crystal structure of a distorted tetrahedral cluster in the salt [(Ph P)4Au4N] BF4 . Geometrical indication of stable electronic configurations in post-transition metal complexes and the magic number 18-e in centred gold clusters. Journal of Organometallic Chemistry, 177, 143-146. 

Neutron Diffraction Studies of Tetrahedral Cluster Transition Metal Hydride Complexes HFeCo3(CO)9-(P(OCH3)3)3 and H3Ni4(C5H5)4... 

Of the linear clusters, the organogermanium-substituted transition metal carbonyl compounds are the simplest. In every case, the coordination at germanium is tetrahedral, while the transition element retains the geometry of the parent carbonyl compound (50,108,119,155, 157, 181). The Ge—M bond is almost without exception shorter than the sum of the Ge—M covalent radii (Table VI), which is cited as evidence for (d — d)-n multiple bonding. 

Mixed-Metal Clusters Containing a Tetrahedral Au3M (M = Transition Metal) Unit... 

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