Anionic carbonyl clusters with interstitial main-group atoms

4 Anionic carbonyl clusters with interstitial main-group atoms 

There is much interest in transition-metal carbonyl clusters containing interstitial (or semi-interstitial) atoms in view of the fact that insertion of the encapsulated atom inside the metallic cage increases the number of valence electrons but leaves the molecular geometry essentially unperturbed. The clusters are generally anionic, and the most common interstitial heteroatoms are carbon, nitrogen, and phosphorus. Some representative examples are displayed in Fig. 19.4.3. 

The [Osi8Hg3(C)2(CO)42]2 clusteris composed of two tricapped octahedral Os9(C)(CO)2iunits sandwiching a Hg3 triangle (Fig. 19.4.3(b)). Each corner Os atom in the top and bottom faces has three terminal carbonyl groups, and the remaining Os atoms each have two. 

The core of the [Fe6Ni6(N)2(CO)24]2- cluster comprises a central Ni6 octahedron that shares a pair of opposite faces with two Ni3Fe3 octahedra, as shown in Fig. 19.4.3(c). The interstitial N atoms occupy the centers of the Ni3Fe3 octahedra. Each Fe atom has two terminal carbonyl groups, and each Ni atom has one. 

The metallic core of the [Rh28(N)4(CO)4iH ]4- cluster is composed of three layers of Rh atoms in a close-packed ABC sequence, as shown in Fig. 19.4.3(d). Four N and an unknown number of H atoms occupy the octahedral holes. 

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