Nomenclature of boranes
The nomenclature of boranes, and of related species such as carboranes, is a specialized subset of inorganic nomenclature, due to the unique variety of structures adopted by boranes.
Even in simple compositional nomenclature, it is necessary to specify both the number of boron atoms and the number of hydrogen atoms. It is also common to specify the structural type by means of a prefix which relates the structure of the boron cluster to a closed deltahedron with missing vertices. Finally, a full structural description must specify which boron–boron "edges" are bridged by hydrogen atoms, which requires a systematic numbering system for the cluster atoms.[1]
Stoichiometric names
A neutral boron hydride is called a borane, and is a parent hydride for nomenclature purposes. The number of boron atoms in the borane is indicated by the normal multiplicative prefixes, while the number of hydrogen atoms is given in Arabic numberals in parentheses immediately after the name.[1] For example:
- diborane(6), B2H6
- tetraborane(10), B4H10
- pentaborane(9), B5H9
Structural descriptors
The structural descriptor in borane nomenclature is closely related to the electronic structure of the compound, as was first proposed by Ken Wade. The structure of the boron cluster is seen as being related to a regular deltahedron (polyhedron with only triangular faces). The parameter n is the number of vertices of the deltahedron (e.g., n = 4 for a tetrahedron), which is often greater than the number of boron atoms: that is the structure of the cluster is often a deltahedron with missing vertices. The structural descriptor gives the number of missing vertices:
| Structural descriptor |
Number of missing vertices |
Number of skeletal electron pairs |
Parent borane |
|---|---|---|---|
| closo | 0 | n+1 | BnHn+2 |
| nido | 1 | n+2 | BnHn+4 |
| arachno | 2 | n+3 | BnHn+6 |
| hypho | 3 | n+4 | BnHn+8 |
| klado | 4 | n+5 | BnHn+10 |
References
- ↑ 1.0 1.1 Nomenclature of Inorganic Chemistry; IUPAC Recommendations 2005; Royal Society of Chemistry: Cambridge, 2005; pp 89–94. ISBN 0-85404-438-8, <http://www.iupac.org/publications/books/rbook/Red_Book_2005.pdf>.
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