Tetrakis(acetonitrile)copper(I) hexafluorophosphate
Encyclopedia
Tetrakiscopper(I) hexafluorophosphate is a coordination complex with the formula [Cu(CH3CN)4]PF6. It is a colourless solid that is used in the synthesis of copper complexes.

Structure

According to X-ray crystallographic studies
X-ray crystallography
X-ray crystallography is a method of determining the arrangement of atoms within a crystal, in which a beam of X-rays strikes a crystal and causes the beam of light to spread into many specific directions. From the angles and intensities of these diffracted beams, a crystallographer can produce a...

, the copper(I) ion is coordinated to four almost linear acetonitrile ligands in a nearly ideal tetrahedral geometry. Related complexes are known with other anions including the perchlorate, tetrafluoroborate
Tetrafluoroborate
Tetrafluoroborate is the anion BF4−. This tetrahedral species is isoelectronic with tetrafluoromethane, CF4 and tetrafluoroammonium NF4+, and is valence isoelectronic with many stable and important species including the closely related anion perchlorate, ClO4−...

, and nitrate
Nitrate
The nitrate ion is a polyatomic ion with the molecular formula NO and a molecular mass of 62.0049 g/mol. It is the conjugate base of nitric acid, consisting of one central nitrogen atom surrounded by three identically-bonded oxygen atoms in a trigonal planar arrangement. The nitrate ion carries a...

. With the weakly coordinating anion B(C6F5)4-, salts of [Cu(CH3CN)2]+ are obtained.

The acetonitrile ligands protect the Cu+ ion from oxidation to Cu2+. However, acetonitrile is not bound very strongly to the copper ion, thus the complex is a useful source of Cu(I).

Synthesis

The cation was first reported in 1923 with a nitrate anion as a byproduct of the reduction of silver nitrate
Silver nitrate
Silver nitrate is an inorganic compound with chemical formula . This compound is a versatile precursor to many other silver compounds, such as those used in photography. It is far less sensitive to light than the halides...

 with a suspension of copper powder in acetonitrile. [Cu(CH3CN)4]PF6 is generally produced by the addition of HPF6 to a suspension of copper(I) oxide
Copper(I) oxide
Copper oxide or cuprous oxide is the inorganic compound with the formula Cu2O. It is one of the principal oxides of copper. This red-coloured solid is a component of some antifouling paints. The compound can appear either yellow or red, depending on the size of the particles, but both forms...

in acetonitrile:
Cu2O + 2 HPF6 + 8 CH3CN → 2 [Cu(CH3CN)4]PF6 + H2O

The reaction is highly exothermic, and may bring the solution to a boil. Upon crystallization, the resulting microcrystals should be white, though a blue tinge is common, indicating the presence of a Cu2+ species.

Reactions and applications

As the coordinated acetonitrile ligands may be displaced in other solvents, the [Cu(CH3CN)4]PF6 compound may serve as a precursor in the non-aqueous syntheses of other Cu(I) compounds.

Water-immiscible organic nitriles have been shown to selectively extract Cu2+ from aqueous chloride solutions. Through this method, copper can be separated from a mixture of other metals. Dilution of acetonitrile solutions with water induces disproportionation:
2 [Cu(CH3CN)4]+ + 6 H2O → [Cu(H2O)6]2+ + Cu + 8 CH3CN
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