Trigonal bipyramidal clusters boranes

Closo, nido, and arachno boranes form series with formulae B H2 +4, and B H2 +6 coirfirming their status as formally subvalent componnds. Boranes and carboranes (in which one or more boron atoms in the cluster have been replaced by a carbon atom) have been extensively researched and described, and will not be discussed further here. In an example of the application of Wade s rules to a heavier main group cluster, 805 nses 10 of the total 22 valence electrons in 5 lone pairs. This allows 12 electrons, or 2n 4- 2 for n = 5 for cluster bonding and specifies a closo structure, matching the observed Z>3h trigonal bipyramidal structure. 

Cluster Shapes and Ion Packing The structures of tetrahedral trigonal bipyramidal [Es] , and bicapped quadratic-antiprismatic [Eio] clusters strictly follow Wade s rules and form 12 = 4x2 + 4) skeletal electron (ske) nido-, 12 = 5x2 + 2) ske closo-, and 22 = 10 x 2 + 2) ske doso-dusters, respectively [34]. Each Group 14 atom has four valence electrons, two of which remain as a lone pair at each vertex equivalent to the covalent exo-BH bonds in boranes and are not involved in the framework bonding. 

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