| Oxidation State | Substances |
| Ni-I | [Ni (CO)6 ]2- |
| Ni0 | Ni (CO)4 , K4[Ni (CN)4 ] |
| NiI | K2[NI (CN)4 ] |
| NiII | NiO, Ni (OH)2 , [Ni (H2O)6 ]2+ (aq), NiF2 , |
| NiCl2 , etc., salts, NiAs, [NiCl4 ]2- , | |
| complexes, [NI (C5H5)2 ] | |
| NiIII | NiO (OH), NiF3 ?, NiF63- |
| NiIV | NiO2 ?, NiF62- |
| NiVI | K2NiO4 ? |
