Page 63 - Nomenclature of Inorganic Chemistry (IUPAC Recommendations 2005)

S O L I D S IR-11.4

subscripts such as a, b, . . . , w hich are not s elf-explanatory, is not approved. In some c ases,
such as oxides and sulfides, the number of subscripts can be reduced by defining specific
symbols to indicate site symmetries, e.g. ( ) for tetrahedral sites, [ ] for octahedral sites,
{ } for dodecahedral sites. To avoid c onfusion, such enclosing marks should b e r estricted to
cases where they are not being used to express multiplication. The m eaning o f t he symbols
should be clearly stated in the text.

Examples:

1. Mg tet Al oct,2 O 4 or (Mg)[Al 2 ]O 4 denotes a n ormal spinel.
2. Fe tet Fe oct Ni oct O 4 or (Fe)[FeNi]O 4 denotes NiFe 2 O 4 (inverse spinel type).

IR-11.4.4 Indication of charges

Charges a re indicated by a r ight upper index. When formal charges are given, t he usual
convention holds: o ne unit of positive charge is indicated by a s uperscript þ, n units of positive
charge by a s uperscript nþ, o ne unit of negative c harge by a s uperscript , n units of negative
charge by a s uperscript n . T hus A nþ denotes n units of formal positive charge on an atom of
symbol A. In defect chemistry, charges are defined preferably with respect to the ideal
unperturbed crystal. In this case, they are called effective charges. One unit of positive
*
effective charge is shown by a s uperscript dot, , ( not to be confused with the radical dot
0
described in Section IR-4.6.2) and one unit of negative effective c harge by a p rime, ; n units of
effective charge are indicated by superscript n * or . n0 T he use of double d ots * * or double
2 *
00
primes in the case of two effective charges is also allowed. Thus A and A * * indicate that an
atom of symbol A h as two units of effective positive c harge. Sites that have no effective charge
relative to the unperturbed lattice may be indicated explicitly by a s uperscript cross, i.e. ‘x’ .

Examples:
V
V
0
0
1. Li Li;1 2x Mg * Li;x Li;x Cl Cl and Li x Li;1 2x Mg * Li; x Li; x Cl x Cl are equivalent expressions for
a s ubstitutional solid solution of MgCl 2 in LiCl.
x
00
00
2. Y Y;1 2x Zr * Y;2x O O 3 and Y x Y;1 2x Zr * Y;2x O O are equivalent expressions for an
i;x
i;x
3
interstitial solid solution of ZrO 2 in Y 2 O 3 .
*
3. Ag Ag;1 x Ag;x Ag Cl Cl indicates that a f raction x of the Ag ions is removed from
þ
V
0
i;x
the Ag sites to interstitial sites, leaving the silver site vacant.
Formal charges may be preferred in cases where the unperturbed crystal contains an element
in more than one oxidation state.
Examples:
2
4. La 2þ La 3þ V ðS Þ ð05x51=3Þ
La;1 3x La;2þ2x La;x 4
5. Cu þ Fe 3þ Tl Se 2 Se ð05x51=2Þ shows that Fe 3þ partly replaces
þ
Se;1þ2x
Cu;x
Se;1 2x
Cu;2 x
Tl
Cu in Cu 2 Tl Se Se .
þ
2
þ
þ

0
Free electrons are denoted by e , f ree h oles b y h * . A s c rystals are macroscopically neutral
bodies, the sums of the formal charges and of the effective charges must be zero.
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