text: Three linkage isomers are common for nitrite ligands, O-bonded, N-bonded, and bidentate O,O-bonded. The former two isomers have been characterized for the pentamminecobalt(III) system, i.e.  and , referred to as N-nitrito and O-nitrito, respectively. These two forms are sometimes called nitro and nitrito. These isomers can be interconverted in some complexes.
  An example of chelating nitrite is  – "bipy" is the bidentate ligand 2,2′-bipyridyl. This bonding mode is sometimes described as κ-.
  Focusing on electron-counting in monometallic complexes, O-bonded, N-bonded are viewed as 1-electron pseudohalides ("X-ligand"). The bidentate O,O-bonded is an "L-X ligand", akin to bidentate carboxylate.
  With respect to HSAB theory, the N bonding mode is more common for softer metal centers. The O and O,O-bidentate modes are hard ligands, being found on Lewis-acidic metal centers.
  The kinetically-favored O-bonded isomer  converts to . In its reaction with ferric porphyrin complexes, nitrite gives the O-bonded isomer, . Addition of donor ligands to this complex induces the conversion to the octahedral low-spin isomer, which now is a soft Lewis acid. The nitrite isomerizes to the N-bonded isomer, .
  The isomerization of  to  proceeds in an intramolecular manner.