- Nickel(II) chloride, also known as nickel chloride, is an inorganic compound with the chemical formula NiCl₂. It typically exists as a green crystalline solid in its anhydrous form or as bright green to yellow-green crystals when hydrated, most commonly as the hexahydrate (NiCl₂·6H₂O). This compound is a prominent member of the transition metal halides and is widely used in both laboratory and industrial applications due to its solubility in water and its role as a source of nickel ions.
- In its anhydrous form, nickel(II) chloride is hygroscopic, meaning it readily absorbs moisture from the air. The hexahydrate form is the more commonly encountered species and is readily soluble in water, forming an aqua complex in which nickel exists in the +2 oxidation state. The compound forms green solutions with octahedral geometry around the nickel ion, where water molecules coordinate with the metal center.
- Nickel(II) chloride is synthesized by dissolving nickel metal, nickel oxide, or nickel carbonate in hydrochloric acid. In industrial settings, it is often produced as a byproduct in processes involving nickel refining. It serves as an intermediate in the preparation of nickel catalysts, electroplating baths, and pigments, and is widely used in organic synthesis as a Lewis acid or to facilitate cross-coupling reactions like the Kumada and Negishi reactions.
- From a biological and environmental perspective, nickel(II) chloride is a toxic and potentially carcinogenic compound. Exposure can occur through inhalation, ingestion, or dermal contact, with adverse effects including respiratory irritation, skin sensitization, and allergic dermatitis. Prolonged exposure has been linked to nasal and lung cancers, especially in occupational settings. As a result, stringent handling procedures and safety measures are recommended when working with nickel compounds.
- In coordination chemistry, nickel(II) chloride is valued for its ability to form a wide variety of complexes with ligands such as amines, phosphines, and thiols. These complexes are often studied for their magnetic and electronic properties, as well as their catalytic activity. Nickel(II) chloride is also used in battery technologies, particularly in nickel-cadmium and emerging nickel-based energy storage systems.
