Tetraamminecopper(II) sulfate is the salt with the formula u(NH₃)₄O₄·H₂O. This dark blue to purple solid is a

salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quant ...

of the

metal complex A coordination complex consists of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of bound molecules or ions, that are in turn known as ''ligands'' or complexing agents. Many ...

u(NH₃)₄(H₂O)sup>2+. It is closely related to

Schweizer's reagent Schweizer's reagent is the metal ammine complex with the formula u(NH3)4(H2O)2OH)2. This deep-blue compound is used in purifying cellulose. It is prepared by precipitating copper(II) hydroxide from an aqueous solution of copper sulfate using so ...

, which is used for the production of

cellulose Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units. Cellulose is an important structural component of the primary cell w ...

fibers in the production of rayon.

Synthesis

This compound can be prepared by adding concentrated solution of

ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous wa ...

to a saturated aqueous solution of copper sulfate pentahydrate followed by precipitation of the product with ethanol or isopropanol.Editor G.Brauer "Tetraamminecopper (II) Sulfate" Handbook of Preparative Inorganic Chemistry, 2nd Ed., Academic Press, 1965, New York. Vol. 2. p. 1021. : 4 NH₃ + CuSO₄·5H₂O → u(NH₃)₄O₄·H₂O+ 4 H₂O

Chemical reaction and solubility

The deep blue crystalline solid tends to hydrolyse and evolve (release) ammonia upon standing in air. It is fairly soluble in water. The brilliant dark blue-violet color of tetraamminecopper(II) sulfate solution is due to presence of u(NH₃)₄sup>2+. Often, the dark blue-violet color is used as a positive test to verify the presence of Cu²⁺ in a solution.

Structure and properties

The solid state structure of tetraamminecopper(II) sulfate monohydrate confirms that the compound is a salt. The complex cation is u(NH₃)₄(H₂O)sup>2+, which has a square pyramidal geometry. The Cu-N and Cu-O bond length are about 210 and 233 pm, respectively, as determined by

X-ray crystallography X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angles ...

.{{cite journal, author=B. Morosin, title=The Crystal Structures of Copper Tetraammine Complexes. A. Cu(NH₃)₄SO₄^.H₂O and Cu(NH₃)₄SeO₄, journal=Acta Crystallographica, year=1969, volume=B25, page=19–30, doi=10.1107/S0567740869001725 The correct concentrations of ammonia and copper sulfate solution needed to synthesize the complex can be determined by colorimetry. The combination of the correct concentrations will produce the highest absorbance read out on the colorimeter and as a result the formula of the complex can be verified.

Corrosion

The characteristic deep blue colour of the tetraammine complex is found in

brass Brass is an alloy of copper (Cu) and zinc (Zn), in proportions which can be varied to achieve different mechanical, electrical, and chemical properties. It is a substitutional alloy: atoms of the two constituents may replace each other wit ...

and

copper alloys Copper alloys are metal alloys that have copper as their principal component. They have high resistance against corrosion. The best known traditional types are bronze, where tin is a significant addition, and brass, using zinc instead. Both of ...

where attack from ammonia has occurred, leading to cracking. The problem was first found in ammunition cartridge cases when they were stored near animal waste, which produced trace amounts of ammonia. This type of corrosion is known as

season cracking Season cracking is a form of stress-corrosion cracking of brass cartridge cases originally reported from British forces in India. During the monsoon season, military activity was temporarily reduced, and ammunition was stored in stables until the ...

Uses

The closely related

is used for the production of

cuprammonium rayon Cuprammonium rayon is a rayon fiber made from cellulose dissolved in a cuprammonium solution, Schweizer's reagent. It is produced by making cellulose a soluble compound by combining it with copper and ammonia with caustic soda. The solution is ...

References

Copper complexes Sulfates Ammine complexes