Mo6S8 cluster, structure

A perspective view of this structure and a projection of the unit cell are shown in Fig. 4.36. Notice the chain structure resulting from the condensation of Ti6Te8 clusters. Similar groups (such as Mo6S8) are found, as building units, in several compounds. 

The binary phase (Mo6S8) contains quite distorted Mo6 octahedra, elongated on a three-fold axis to become trigonal antiprisms. This can be attributed to the fact that there are only 20 cluster electrons. This number is insufficient to form a full set of Mo—Mo bonds, that is, to populate all the 12 bonding orbitals with the result that there is a distorted octahedron with somewhat longer Mo—Mo bonds compared to the 24-electron clusters. In the Chevrel phases the additional metal atoms add electrons to the Mo6 core and it becomes more regular in structure with shorter Mo—Mo bonds. 

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