Page 176 - Nomenclature of Inorganic Chemistry (IUPAC Recommendations 2005)

IR-9.2 C O O R D I N A T I O N C O M P O U N D S

The only remaining problem is to number the central atoms in cases w here they are the
same but have different coordination environments. In this case, t he central atom with
the larger coordination number is given t he lower number (locant), if applicable. If the
coordination numbers are equal, the central atom with the greater number of ligands or
ligating atoms represented earlier in the name is given t he lower number (locant). Thus, in
Example 2 t he chromium atom with five of the nine ammine ligands attached is given
priority number 1.

Examples:
1 2
5þ
2. ½ðH NÞ Crðm-OHÞCrðNH MeÞðNH Þ
5
3
3 4
2
4
5
nonaammine-1k N,2k N-m-hydroxido-(methanamine-2kN)dichromium(5þ)
1 2
3þ
3. ½ðH 3 NÞ 3 Coðm-NO 2 Þðm-OHÞ 2 CoðNH 3 Þ 2 ðpyÞ
3
2
pentaammine-1k N,2k N-di-m-hydroxido-m-nitrito-1kN:2kO-
(pyridine-2kN)dicobalt(3þ)
1 2
4. ½ðbpyÞðH 2 OÞCuðm-OHÞ 2 CuðbpyÞðSO 4 Þ
2
2
0
aqua-1kO-(2,2 -bipyridine-1k N,N )(2,2 -bipyridine-2k N,N )-di-m-hydroxido-
0
0
0
(sulfato-2kO)dicopper(II)
In some c ases, it is not necessary to number explicitly the two differently coordinated central
atoms to arrive at a n ame, as shown in Example 5. Note the use of a m ultiplicative prefix to
simplify t he name, as also demonstrated in Section IR-9.2.5.4 for fully symmetrical
structures.
Example:
5. [{Co(NH 3 ) 3 } 2 (m-NO 2 )(m-OH) 2 ] 3þ
di-m-hydroxido-m-nitrito-kN:kO-bis(triamminecobalt)(3þ)
IR-9.2.5.6 Trinuclear and larger structures
The methods described in the preceding sections for naming ligands and designating ligating
atoms are general, a nd applicable irrespective of the nuclearity (the n umber of central atoms
involved). However, in most cases numbering of the central atoms is needed in order to
construct a systematic additive name f or a c oordination entity. Obtaining such a n umbering
is the part of the naming process which becomes increasingly complex in the general case as
the nuclearity increases. This section s uggests general procedures for assigning locant
numbers to central atoms.
If no two c entral atoms are the same e lement, locant numbers for the central atoms and
the order they appear i n t he name can be determined using Table VI. The first central atom
reached on following the arrow in the Table receives the highest locant number, while the
last reached is given the locant 1. This method can also be applied to systems where there is
more than one of a g iven t ype of central atom, provided there is symmetry present in the
structure that makes all of the central atoms of a g iven element equivalent. Indeed, in the
extreme case, i t m ay not be necessary t o a ssign locants at all, provided all the central atoms
are equivalent.

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