NiCl2

Nickel(II) chloride, NiCl2, is an inorganic salt of nickel in the +2 oxidation state. It exists mainly as two forms: the anhydrous salt NiCl2 and the hexahydrate NiCl2·6H2O. The anhydrous form is a hygroscopic, pale green solid that absorbs moisture from air, while the hexahydrate forms green crystals that dissolve readily in water.

Preparation and properties: NiCl2 can be prepared by direct reaction of nickel metal with chlorine gas (Ni + Cl2 → NiCl2) or by treating nickel oxide or nickel carbonate with hydrochloric acid, followed by dehydration. The hexahydrate forms when NiCl2 is crystallized from aqueous solution. In solution, NiCl2 behaves as a typical Ni(II) salt and forms a variety of coordination complexes with ligands such as phosphines, bipyridine, and other donors. The anhydrous salt is more prone to forming polymeric or ionic networks in the solid state, while the hydrated form features octahedral coordination around nickel.

Applications and use: NiCl2 serves as a common precursor for nickel complexes and catalysts used in organometallic and organic synthesis, including nickel-catalyzed cross-coupling reactions. It is also employed in electroplating and as a starting material for various nickel salts. In solution, NiCl2 provides Ni(II) sources for a wide range of laboratory syntheses and catalytic processes.

Safety: Nickel(II) chloride is corrosive and can irritate skin, eyes, and the respiratory tract. Nickel salts are considered potential occupational carcinogens; exposure to dust or fumes should be minimized, and contact with skin should be avoided. It should be stored in a dry, tightly closed container.