The NO2 ligand, which represents the nitrite ion (NO2-), can coordinate to a central metal atom in two different ways, giving rise to distinct names based on the atom through which it binds.
Understanding the NO2 Ligand (Nitrite Ion)
The nitrite ion (NO2-) is an ambidentate ligand, meaning it has two different potential donor atoms through which it can bind to a metal center. In the case of NO2-, these donor atoms are nitrogen (N) and oxygen (O). The specific binding mode is indicated in its nomenclature.
Nomenclature Based on Binding Site
When the nitrite ion acts as a ligand, its name depends on which atom forms the bond with the metal:
-
Binding through Nitrogen (N-bound):
When the nitrite ligand binds to the metal via its nitrogen atom, it is systematically named nitrito-N-. A common alternative name for this binding mode is nitro.- Example: In a complex like [Co(NH3)5(NO2)]Cl2, the NO2 ligand is bound through nitrogen, and the complex is named pentaamminenitrito-N-cobalt(III) chloride, or pentaamminenitrocobalt(III) chloride.
-
Binding through Oxygen (O-bound):
When the nitrite ligand binds to the metal via one of its oxygen atoms, it is systematically named nitrito-O-. It can also simply be called nitrito. The formula for this binding mode is often represented as ONO-.- Example: In a complex like [Co(NH3)5(ONO)]Cl2, the ONO ligand is bound through oxygen, and the complex is named pentaamminenitrito-O-cobalt(III) chloride, or pentaamminenitritocobalt(III) chloride.
Summary of Ligand Names
The following table summarizes the names for the nitrite ligand based on its coordination mode:
| Molecular Formula | Binding Atom | Ligand Name | Common Alternative Name |
|---|---|---|---|
| NO2- | Nitrogen | Nitrito-N- | Nitro |
| ONO- | Oxygen | Nitrito-O- | Nitrito |
This distinction is crucial in coordination chemistry for accurately describing the structure and properties of complexes containing the nitrite ligand.
