page_title: Nickel
section_title: Nickel(II)
hierarchical_section_title: Nickel / Compounds / Nickel(II)
caption_attribution_description: English: Color of various Ni(II) complexes in aqueous solution. From left to right, hexaamminenickel(II), tris(ethylenediamine)nickel(II), tetrachloronickelate(II) and hexaaquanickel(II)
context_page_description: Nickel is a chemical element with the symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile. Pure nickel, powdered to maximize the reactive surface area, shows a significant chemical activity, but larger pieces are slow to react with air under standard conditions because an oxide layer forms on the surface and prevents further corrosion. Even so, pure native nickel is found in Earth's crust only in tiny amounts, usually in ultramafic rocks, and in the interiors of larger nickel–iron meteorites that were not exposed to oxygen when outside Earth's atmosphere.
  Meteoric nickel is found in combination with iron, a reflection of the origin of those elements as major end products of supernova nucleosynthesis. An iron–nickel mixture is thought to compose Earth's outer and inner cores.
  Use of nickel has been traced as far back as 3500 BCE. Nickel was first isolated and classified as a chemical element in 1751 by Axel Fredrik Cronstedt, who initially mistook the ore for a copper mineral, in the cobalt mines of Los, Hälsingland, Sweden.
context_section_description: Nickel(II) forms compounds with all common anions, including sulfide, sulfate, carbonate, hydroxide, carboxylates, and halides. Nickel(II) sulfate is produced in large quantities by dissolving nickel metal or oxides in sulfuric acid, forming both a hexa- and heptahydrates useful for electroplating nickel. Common salts of nickel, such as chloride, nitrate, and sulfate, dissolve in water to give green solutions of the metal aquo complex [Ni(H
  ₂O)
  ₆]²⁺
  .
  The four halides form nickel compounds, which are solids with molecules that feature octahedral Ni centres. Nickel(II) chloride is most common, and its behavior is illustrative of the other halides. Nickel(II) chloride is produced by dissolving nickel or its oxide in hydrochloric acid. It is usually encountered as the green hexahydrate, the formula of which is usually written NiCl₂•6H₂O. When dissolved in water, this salt forms the metal aquo complex [Ni(H
  ₂O)
  ₆]²⁺
  . Dehydration of NiCl₂•6H₂O gives the yellow anhydrous NiCl
  ₂.
  Some tetracoordinate nickel(II) complexes, e.g. bis(triphenylphosphine)nickel chloride, exist both in tetrahedral and square planar geometries. The tetrahedral complexes are paramagnetic, whereas the square planar complexes are diamagnetic. In having properties of magnetic equilibrium and formation of octahedral complexes, they contrast with the divalent complexes of the heavier group 10 metals, palladium(II) and platinum(II), which form only square-planar geometry.
  Nickelocene is known; it has an electron count of 20, making it relatively unstable.
caption: Color of various Ni(II) complexes in aqueous solution. From left to right, [Ni(NH
  3)
  6]2+
  , [Ni(C2H4(NH2)2)]2+, [NiCl
  4]2−
  , [Ni(H
  2O)
  6]2+
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