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Different rules (4''n'', 5''n'', or 6''n'') are invoked depending on the number of electrons per vertex.
The 4''n'' rules are reasonably accurate in predicting the structures of clusters having about 4 electrons per vertex, as is the case for many [[
However, hypho clusters are relatively uncommon due to the fact that the electron count is high enough to start to fill antibonding orbitals and destabilize the 4''n'' structure. If the electron count is close to 5 electrons per vertex, the structure often changes to one governed by the 5n rules, which are based on 3-connected polyhedra.
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# For clusters consisting mostly of transition metals, any main group elements present are often best counted as ligands or interstitial atoms, rather than vertices.
# Larger and more electropositive atoms tend to occupy vertices of high connectivity and smaller more electronegative atoms tend to occupy vertices of low connectivity.
# In the special case of [[Boranes|boron hydride]] clusters, each boron atom connected to 3 or more vertices has one terminal hydride, while a boron atom connected to two other vertices has two terminal hydrogen atoms. If more hydrogen atoms are present, they are placed in open face positions to even out the coordination number of the vertices.
# For the special case of transition metal clusters, [[ligands]] are added to the metal centers to give the metals reasonable coordination numbers, and if any [[hydrogen]] [[atoms]] are present they are placed in bridging positions to even out the coordination numbers of the vertices.
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