Page 27 - Nomenclature of Inorganic Chemistry (IUPAC Recommendations 2005)

G R A M M A R I R-2.2

IR-2.2.2 Square brackets
IR-2.2.2.1 Use in formulae

Square brackets are used in formulae in the following ways.
(a) To enclose the whole coordination entity of a n eutral (formal) coordination compound.

Examples:
5
1. [Fe(Z -C 5 H 5 ) 2 ] ( for use of the symbol Z see Sections IR-9.2.4.3 and IR-10.2.5.1)
2
2. [Pt(Z -C 2 H 4 )Cl 2 (NH 3 )]
3. [PH(O)(OH) 2 ]

No numerical subscript should follow the square b racket used in this context. For example,
where the molecular formula is double the empirical formula, this s hould b e i ndicated inside
the square bracket.

Example:

4. CH 2
Cl Cl
H C Pt Pt CH 2
2
Cl Cl
H C
2
2
2
[{Pt(Z -C 2 H 4 )Cl(m-Cl)} 2 ] i s m ore i nformative than [Pt 2 (Z -C 2 H 4 ) 2 Cl 4 ]; the representation
2
[Pt(Z -C 2 H 4 )Cl 2 ] 2 is incorrect.
(b) To enclose a c harged (formal) coordination entity. In this case, t he superscript showing
the charge appears outside the square bracket as do any subscripts indicating the number of
ions in the salt.

Examples:

5. [BH 4 ]
6. [Al(OH)(OH 2 ) 5 ] 2þ
2
7. [Pt(Z -C 2 H 4 )Cl 3 ]
8. Ca[AgF 4 ] 2
9. [Co(NH 3 ) 5 (N 3 )]SO 4
10. [S 2 O 5 ] 2
11. [PW 12 O 40 ] 3

(c) In a s alt c omprising b oth cationic and anionic coordination entities, each ion is separately
enclosed in square brackets. (The cation is placed before the anion a nd no individual charges
are shown.) Any subscripts indicating the number of complex ions in the salt are shown
outside the square b rackets.

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