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

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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