Page 101 - Nomenclature of Inorganic Chemistry (IUPAC Recommendations 2005)

S U B S T I T U T I V E N O M E N C L A T U R E IR-6.2

catena-triborane(5)
4. H 2 BBHBH 2
catena-triborene(3)
5. HB¼BBH 2
For cyclic systems, the prefix ‘cyclo’ in connection with the name of the corresponding
chain compound, or the Hantzsch–Widman (H–W) nomenclature system (see Section
IR-6.2.4.3), may be used.

Example:
6. H H
B B

B B
H H
cyclotetraborane
H–W name: tetraboretane

IR-6.2.3.3 Systematic numbering of polyhedral c lusters

It is necessary to number the boron skeleton for each cluster systematically, so as to permit
the unambiguous naming of the substituted derivatives. For this purpose, the boron atoms of
closo structures are considered to occupy planes disposed sequentially, perpendicular to the
axis of highest order symmetry. (If there are two such axes, the ‘longer’, in terms of the
greater number of perpendicular p lanes crossed, is chosen.)
Numbering begins at the nearest boron atom when t he cluster is viewed along t his axis
and proceeds either clockwise or anti-clockwise, dealing with all skeletal atoms of the first
plane. Numbering then continues i n t he same sense in the next plane, beginning w ith the
boron atom nearest to the lowest numbered boron atom in the preceding plane when g oing
forward in the direction of numbering.
Example:

1. 4 4
1 1
8 5 5

7 7 3
9 2 2
10
6 6

2
closo-B 10 H 10 (hydrogen atoms omitted for clarity)
The numbering in nido clusters is derived from that of the related closo cluster. In the case of
arachno and more open clusters, the opened side is presented towards the observer and the
boron atoms considered as projected onto a p lane a t t he rear. They are then numbered
sequentially in zones, commencing at the central boron atom of highest connectivity and
proceeding clockwise or anti-clockwise until the innermost zone is completed. The next
zone is then numbered i n t he same sense starting from the 12 o’clock position, and so on

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