text: Conventionally, redox reactions of coordination complexes are assumed to be metal-centered.  The reduction of MnO to MnO is described by the change in oxidation state of manganese from 7+ to 6+.  The oxide ligands do not change in oxidation state, remaining 2-.  Oxide is an innocent ligand.  Another example of conventional metal-centered redox couple is
  [[Cobalt(III) hexammine chloride|Co(NH)]]/[Co(NH)].  Ammonia is innocent in this transformation.
  Redox non-innocent behavior of ligands is illustrated by nickel bis(stilbenedithiolate) ([Ni(SCPh)]). As all bis(1,2-dithiolene) complexes of nd metal ions, three oxidation states can be identified: z = 2-, 1-, and 0.  If the ligands are always considered to be dianionic (as is done in formal oxidation state counting), then z = 0 requires that that nickel has a formal oxidation state of +IV. The formal oxidation state of the central nickel atom therefore ranges from +II to +IV in the above transformations (see Figure). However, the formal oxidation state is different from the real (spectroscopic) oxidation state based on the (spectroscopic) metal d-electron configuration. The stilbene-1,2-dithiolate behaves as a redox non-innocent ligand, and the oxidation processes actually take place at the ligands rather than the metal. This leads to the formation of ligand radical complexes. The charge-neutral complex (z =0), showing a partial singlet diradical character, is therefore better described as a Ni derivative of the radical anion SCPh. The diamagnetism of this complex arises from anti-ferromagnetic coupling between the unpaired electrons of the two ligand radicals.
  Another example is higher oxidation states of copper complexes of diamido phenyl ligands that are stabilized by intramolecular multi center hydrogen bonding