Ligands enclosing marks

Neutral and Cationic Ligands. Neutral and cationic ligands are used without change in name and are set off with enclosing marks. Water and ammonia, as neutral ligands, are called aqua and ammine, respectively. The groups NO and CO, when linked directly to a metal atom, are called nitrosyl and carbonyl, respectively. 

Organic ligands are cited under C, and NO and CO are regarded as neutral. Because square brackets are always of highest seniority (or priority), a hierarchical sequence of enclosing marks is adopted to ensure that this seniority is preserved [ ], [()], [ () ], [ [()] ], [ [()] ], etc. 

Coordination compounds. [In the formula of a coordination entity.] the symbol of the central atom(s) is placed first, followed by the ionic and then the neutru] ligands. Square brackets are used to enclose the whole coordination entity whether charged or not. This practice need not be used for simple species such us the common oxoanions (NO, NOT, SO -, OH-, etc.). Enclosing marks are nested within the square brackets as follows [()]. U<) , [()]>]. [( [()] ]]. etc. 

The formula for the entire coordination entity, whether charged or not, is enclosed in square brackets. When ligands are polyatomic, their formulae are enclosed in parentheses. Ligand abbreviations are also usually enclosed in parentheses. The nesting order of enclosing marks is as given in Sections IR-2.2 and IR-4.2.3. Square brackets are used only to enclose coordination entities, and parentheses and braces are nested alternately. 

Note that in some cases it may be useful to introduce additional enclosing marks to ensure clarity for example, to avoid possible confusion between chloromethylamine, CICH2NH2, and (chloro)methylamine, which implies two separate ligands, Cl and CH3NH2. It is for the writer to decide whether such a strategy is useful, depending on the particular case under... 

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