Borane chemistry structural ideas

In the last 50 years, there has been a wealth of fascinating chemistry published on the boranes and heteroboranes Their unique structures have forced us to rethink our ideas on bonding and they have proven to be invaluable reagents in other areas of chemistry. ... 

As a result of the systematic application of coordination-chemistry principles, dozens of previously unsuspected structure types have been synthesized in which polyhedral boranes or their anions can be considered to act as ligands which donate electron density to metal centres, thereby forming novel metallaborane clusters, - Some 40 metals have been found to act as acceptors in this way (see also p. 178). The ideas have been particularly helplul m emphasizing the close interconnection between several previously separated branches of chemistry, notably boron hydride cluster chemistry, metallaborane and metallacarbaborane chemistry (pp. 189-95), organometallic chemistry and metal-metal cluster chemistry. All are now seen to be parts of a coherent whole. 

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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