Octahedral clusters boranes

Many further examples could be added to those already cited to support the close relationship between carbonyl clusters and borane clusters, particularly for species based on an octahedron. These other clo80 octahedral clusters include anions such as Co0(CO)i6 (34), [Fe6(CO)ieC] - (35, 40), [Rhe(CO)i5l]- (6), [Nie(CO)i2] - (31), [Co4Ni2(CO)i4] (5), and [Rhi2(CO)8o], in which two Rhg octahedra are linked by a metal-metal bond and two bridging carbonyl groups (2). 

Recent treatments have described the skeletal bonding64,68,71) contributions for ligated transition metal moieties in metalloboranes and in transition-metal clusters. Wade indicated the important similarity between boranes and transition-metal clusters, in particular the species [B6H6]2" and several octahedral transition-metal clusters and Mingo82,83), on the basis of detailed molecular orbital calculations for [Co6(CO)14]4, has confirmed the validity of these comparisons. 

Alternatively, one might explore close-packed structures of boranes. Consider, for example, the difference between deltahedral and tetra-capped octahedral BioHio structures (Fig. 4). The former is stable as the dianion (11 cluster pairs) while, based on Extended Htickel calculations (60), the latter is slightly more stable for the +6 cation (7 cluster pairs). The capping principle predicts 7 cluster pairs for capped octahedra (61). A structurally characterized transition metal analogue of the tetra-... 

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