Nickelionen

Nickel ions are positively charged nickel species, with the most common oxidation state being Ni2+. In aqueous solutions Ni2+ forms the hexaaquanickel(II) complex [Ni(H2O)6]2+, which is typically pale blue and paramagnetic due to two unpaired electrons. Ni3+ can exist under strongly oxidizing conditions, but it is much less common in ordinary chemistry and biology.

In solution and coordination chemistry, Ni2+ readily forms octahedral complexes with a wide range of ligands. The hexaaqua complex is a typical starting point, and substitution by ammine, cyanide, and various organic ligands yields colored coordination compounds. Nickel(II) also hydrolyzes and can form Ni(OH)2 in basic media; Ni2+ can further participate in the formation of more complex oxides and cyanide-containing species such as [Ni(CN)4]2− under suitable conditions. The d8 configuration of Ni2+ gives rise to characteristic bonding and spectroscopic properties in many ligands.

Occurrence, production, and applications: Nickel occurs in minerals such as pentlandite and garnierite and is extracted from sulfide ores and laterites. It is refined for industrial use and is a key element in stainless steel and nickel-based alloys, as well as in catalysts (including Raney nickel) and energy storage technologies such as nickel–metal hydride batteries and certain electroplating processes.

Biological role and safety: Nickel is an essential trace element for some microorganisms and plants, involved in enzymes such as urease and hydrogenase. In humans, exposure to nickel compounds can cause allergic reactions and has been linked to carcinogenic risks in some contexts. Safe handling emphasizes minimizing inhalation and dermal contact, and many nickel compounds are subject to regulatory controls.