NickelII

Nickel(II), also written nickel II, denotes the nickel ion in the +2 oxidation state, written Ni2+. It is the most common oxidation state of nickel in compounds and dominates nickel chemistry. In water, Ni2+ forms the hexaaqua complex [Ni(H2O)6]2+, which appears blue and is a common starting point for many reactions.

Electronic configuration of Ni2+ is [Ar]3d8. In octahedral coordination, Ni2+ commonly exhibits two unpaired electrons, giving paramagnetic behavior with a magnetic moment near 3 Bohr magnetons. In very strong-field environments, four-coordinate square-planar Ni(II) complexes such as [Ni(CN)4]2− can be diamagnetic.

Common Ni(II) compounds include nickel(II) sulfate NiSO4, nickel(II) chloride NiCl2, nickel(II) nitrate Ni(NO3)2, nickel(II) carbonate NiCO3 (insoluble), nickel(II) hydroxide Ni(OH)2, and nickel oxide NiO. Ni2+ forms many coordination complexes with ligands such as ammonia, ethylenediamine, and cyanide; the cyanide complex [Ni(CN)4]2− is a classic example.

Natural occurrence: nickel occurs in sulfide and oxide minerals; major ore is pentlandite (Ni,Fe)9S8 with associated sulfides; laterite deposits supply lateritic nickel ore. Industrially, Ni2+ salts are produced by dissolution of nickel-containing materials or by precipitation from nickel solutions.

Biological and industrial roles: nickel is an essential trace element for some enzymes (e.g., urease, hydrogenases) and is widely used in electroplating, catalysts, and rechargeable batteries. Safety: many nickel salts are toxic and can cause skin sensitization; inhalation of nickel compounds is associated with cancer risk; proper handling is required.