| Abstract
| - Density functional theory (DFT) at the hybrid B3LYP level has been applied to the polyhedral boranes BnHnz (n = 8 and 11, z = −2, −4, and −6). The lowest energy structures for all of these borane structures conform to the Wade−Mingos rules, in contrast to some of the isoelectronic Genz clusters.
- Density functional theory (DFT) at the hybrid B3LYP level has been applied to the polyhedral boranes BnHnz (n =8 and 11, z = −2, −4, and −6) for comparison with isoelectronic germanium clusters Genz. The energy differencesbetween the global minima and other higher energy borane structures are much larger relative to the case of thecorresponding bare germanium clusters. Furthermore, for both B8H82- and B11H112-, the lowest energy computedstructures are the corresponding experimentally observed most spherical deltahedra predicted by the Wade−Mingos rules, namely the D2d bisdisphenoid and the C2v edge-coalesced icosahedron, respectively. Only in thecase of B8H82- is there a second structure close (+2.6 kcal/mol) to the D2d bisdisphenoid global minimum, namelythe C2v bicapped trigonal prism corresponding to the “square” intermediate in a single diamond−square−diamondprocess that can lead to the experimentally observed room temperature fluxionality of B8H82-. Stable borane structureswith 3-fold symmetry (e.g., D3h, C3v, etc.) are not found for boranes with 8- and 11-vertices, in contrast to thecorresponding germanium clusters where stable structures derived from the D3d bicapped octahedron and D3hpentacapped trigonal prism are found for the 8- and 11-vertex systems, respectively. The lowest energy structuresfound for the electron-rich boranes B8H84- and B11H114- are nido polyhedra derived from a closo deltahedron byremoval of a relatively high degree vertex, as predicted by the Wade−Mingos rules. They relate to isoelectronicspecies found experimentally, e.g., B8H12 and R4C4B4H4 for B8H84- and C2B9H112- for B11H114-. Three structureswere found for B11H116- with arachno type geometry having two open faces in accord with the Wade−Mingosrules.
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