Cage compounds closoboranes and carboranes

The structure of the decaclosoborane(-2) BioH q maybe described in terms of a tetragonal antiprism, i.e. a cube where the top face has been rotated through 45° relative to the bottom face. The two square faces of the antiprism are capped by BH fragments number 

1 and 10. See Fig. 12.8. In B9H9 one of the capping BH groups has been removed. The structure of Bi2H 2 is again very symmetric, the twelve B atoms lie at the comer of an icosahedron, one of the Platonic solids where all faces are equilateral triangles. 

---