In chemistry, a (redox) non-innocent ligand is a ligand in a metal complex where the oxidation state is not 
clear. Typically, complexes containing non-innocent ligands are redox active at mild potentials.  The concept assumes that redox reactions in metal complexes are either metal or ligand localized, which is a simplification, albeit a useful one.
C.K. Jørgensen first described ligands as "innocent" and "suspect": "Ligands are innocent when they allow oxidation states of the central atoms to be defined. The simplest case of a suspect ligand is NO..."