What is an innocent ligand vs. a non-innocent ligand?
Answers
An innocent ligand is one that binds to a transition metal in such a way that the oxidation state of the metal is able to be determined with clarity, i.e. the method of binding and the contributed charge are both unambiguous.
On the other hand, a non-innocent ligand can bind in multiple ways in which the contributed charge must be stated first before being able to determine the oxidation state of a transition metal with clarity.
Some examples of innocent ligands:
acetylacetonato (a bidentate that bonds via the πsystem established by the two oxygens)
ammine (NH2) (simple monodentate ligand)
ethylenediamine (H2N−(CH2)2−NH2; cis) (bidentate ligand that binds in a similar way to the ammine ligand)
Some examples of non-innocent ligands:
Nitrosyl (NO+ vs. NO−)
Dioxo (O−2 vs. O2−2)
Dithiolene (three different possible bonding modes!!!)