Niobium, hexanuclear cluster

The second class of hexanuclear clusters also contains an octahedron of metal atoms, but they are coordinated by twelve halide ligands along the edges (Fig. 16.64b). Niobium and tantalum form clusters of this type. Here the bonding situation is somewhat more complicated The metal atoms are surrounded by a very distorted square prism of (bur metal and four halogen atoms. Furthermore, these compounds are electron deficient in the same sense as the boranes—there are fewer pairs of electrons than orbitals to receive them and so fractional bond orders of are obtained. 

Hexanuclear Clusters of six molybdenum, niobium, or tantalum atoms have been known for many... 

Formation of Heavy Transition Metal Group V Metal-Metal Bonds 9.2.8.2. In Niobium and Tantalum Halides Without Hexanuclear Cluster Units... 

In Niobium and Tantalum Halides Without Hexanuclear Cluster Units... 

Hexanuclear Clusters Clusters of six molybdenum, niobium, or tantalum atoms have been known for many years, predating the work with rhenium. There two types In the first, an octahedron of six metal atoms is coordinated by eight chloride ligands, one on each face of the octahedron. This is found in molybdenum dichloride, Mo6C112, better formulated as [Mo6C18]C14. Each Mo (II) atom can use its four electrons to form four bonds with adjacent molybdenum atoms and can receive dative bonds from the four chloride ligands. 

The alkali alkoxide method has been extended to the preparation of alkoxides of the hexanuclear niobium and tantalum cluster units, e.g., [M6Xi2](OMe)2.4MeOH (where M = Nb or Ta and X = Cl or Br), and M2[Ta2Cli2](OMe)6.6MeOH. 

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