aquatetramminenickelII

Aqua tetrammine nickel(II) is an inorganic coordination compound with the chemical formula [Ni(NH₃)₄(H₂O)₂]²⁺. This complex is often encountered as a salt, such as aqua tetrammine nickel(II) sulfate, [Ni(NH₃)₄(H₂O)₂]SO₄. It is a bright blue solid. The central nickel ion is in the +2 oxidation state and is coordinated to four ammonia molecules and two water molecules. These ligands are arranged in an octahedral geometry around the nickel ion.

The synthesis of aqua tetrammine nickel(II) typically involves the reaction of a nickel(II) salt, such as nickel(II) sulfate or nickel(II) chloride, with an excess of ammonia in an aqueous solution. The ammonia displaces other ligands that might be coordinated to the nickel ion. For example, starting from nickel(II) sulfate hexahydrate, reaction with aqueous ammonia can yield the desired complex.

Aqua tetrammine nickel(II) and its salts are soluble in water. The presence of the ammonia ligands makes the solution alkaline. This compound is a common example used in introductory coordination chemistry to illustrate concepts like ligand exchange and octahedral geometry. It is important to note that the aqua tetrammine nickel(II) complex is in equilibrium with other nickel-amine-aqua complexes depending on the concentration of ammonia and the presence of other ligands. The precise composition can vary.