Triangulated dodecahedron structure

The solid state structure of [c/oio-B8H8]2 is very similar to that of an idealized triangulated dodecahedron and is shov/n in Fig. 19118). Bond distances not related by molecular symmetry are given in Table 6. 

There are three especially important idealized structures the cube (Oh), the square antiprism (D ), and the triangulated dodecahedron (DM). All three are depicted in Fig. 1-4, which also shows how each of the latter two can be obtained by distortions of the cube. The cube rarely occurs in discrete complexes, although it is found in various solid arrays (e.g., the CsCl structure). Since each of the other two structures, which can be so easily obtained from it, allow the same close metal-ligand contacts while alleviating the ligand-ligand repulsions, their energetic superiority over the cube is understandable. 

The adherence to close-packed structural arrangements lends support to the idea that these compounds can be used as models for metal surface chemistry—with respect to chemisorbed species and their mobility and reactions of substrates on these surfaces. It also indicates a marked deviation from the behavior of boranes and their derivatives. Structures based upon some polyhedra favored by boron, such as the pentagonal bipyramid, triangulated dodecahedron, and especially the icosahedron, are absent so far in metal-carbonyl cluster chemistry. In this connection, it has been mentioned that [M(CO)3],g compounds should be the closest analogs to On skeletal electron counting... 

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