Closo-Boranes comparison

Arachno Clusters 2n + 6 Systems). In comparison to the number of known closo and nido boranes and heteroboranes, there are relatively fewer arachno species. Partly because of the lack of a large number of stmctures on which to base empirical rules, arachno stmctures appear to be less predictable than their closo and nido counterparts. For example, there are two isomeric forms of one with the arachno [19465-30-6] framework shown... 

In comparison with the enormous number of carboranes the family of the heavier group 14 heteroborane clusters is yet very small. Most of the heteropoly-borane skeletons with Si, Ge, Sn or Pb atoms belong to the group of larger sized closo- and nido-clusters and the chemistry of these heteroboranes is essentially concentrated on the heteroatoms. 

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