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Tetraamminecopper(II) sulfate monohydrate, or more precisely tetraammineaquacopper(II) sulfate, is the
salt In common usage, salt is a mineral composed primarily of sodium chloride (NaCl). When used in food, especially in granulated form, it is more formally called table salt. In the form of a natural crystalline mineral, salt is also known as r ...
with the formula , or more precisely This dark blue to purple solid is a sulfuric acid salt of the Complex (chemistry)">metal complex A coordination complex is a chemical compound consisting 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 ...
(tetraammineaquacopper(II)
cation An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...
). It is closely related to Schweizer's reagent, which is used for the production of cellulose fibers in the production of rayon.


Synthesis

This compound can be prepared by adding concentrated
aqueous solution An aqueous solution is a solution in which the solvent is water. It is mostly shown in chemical equations by appending (aq) to the relevant chemical formula. For example, a solution of table salt, also known as sodium chloride (NaCl), in water ...
of
ammonia Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pu ...
to a saturated aqueous solution of copper(II) sulfate pentahydrate followed by precipitation of the product with
ethanol Ethanol (also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound with the chemical formula . It is an Alcohol (chemistry), alcohol, with its formula also written as , or EtOH, where Et is the ps ...
or
isopropanol Isopropyl alcohol (IUPAC name propan-2-ol and also called isopropanol or 2-propanol) is a colorless, flammable, organic compound with a pungent alcoholic odor. Isopropyl alcohol, an organic polar molecule, is miscible in water, ethanol, an ...
.Editor G.Brauer "Tetraamminecopper (II) Sulfate" Handbook of Preparative Inorganic Chemistry, 2nd Ed., Academic Press, 1965, New York. Vol. 2. p. 1021. :


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 (tetraamminecopper(II) cation). Often, the dark blue-violet color is used as a positive test to verify the presence of in a solution.


Structure and properties

The solid state structure of tetraamminecopper(II) sulfate monohydrate confirms that the compound is a
salt In common usage, salt is a mineral composed primarily of sodium chloride (NaCl). When used in food, especially in granulated form, it is more formally called table salt. In the form of a natural crystalline mineral, salt is also known as r ...
. The
complex Complex commonly refers to: * Complexity, the behaviour of a system whose components interact in multiple ways so possible interactions are difficult to describe ** Complex system, a system composed of many components which may interact with each ...
cation An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...
is (tetraammineaquacopper(II) cation), which has a square pyramidal molecular 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 of determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to Diffraction, diffract in specific directions. By measuring th ...
.{{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, issue=1 , pages=19–30, doi=10.1107/S0567740869001725, bibcode=1969AcCrB..25...19M The correct concentrations of
ammonia Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pu ...
and copper(II) sulfate solution needed to synthesize the complex can be determined by colorimetry. The combination of the correct concentrations will produce the highest
absorbance Absorbance is defined as "the logarithm of the ratio of incident to transmitted radiant power through a sample (excluding the effects on cell walls)". Alternatively, for samples which scatter light, absorbance may be defined as "the negative log ...
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 and zinc, in proportions which can be varied to achieve different colours and mechanical, electrical, acoustic and chemical properties, but copper typically has the larger proportion, generally copper and zinc. I ...
and
copper alloys Copper alloys are metal Alloy, alloys that have copper as their principal component. They have high resistance against corrosion. Of the large number of different types, the best known traditional types are bronze, where tin is a significant addi ...
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.


Uses

The closely related Schweizer's reagent is used for the production of cuprammonium rayon.


References

Copper complexes Sulfates Ammine complexes Tetraamminecopper(II) compounds