Tetrakis(acetonitrile)copper(I) hexafluorophosphate

Tetrakis(acetonitrile)copper(I) hexafluorophosphate is a salt with the formula [Cu(CH₃CN)₄]PF₆. It is a colourless solid that is used in the synthesis of other copper complexes. The cation [Cu(CH₃CN)₄]⁺ is a well-known example of a transition metal nitrile complex.

Structure

As confirmed by X-ray crystallographic studies, the copper(I) ion is coordinated to four almost linear acetonitrile ligands in a nearly ideal tetrahedral geometry. Similar complexes with other anions including the perchlorate, tetrafluoroborate, and nitrate are known.

Synthesis

The cation was first reported in 1923 with a nitrate anion as a byproduct of the reduction of silver nitrate 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 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 Cu²⁺ impurities.

Reactions and applications

The acetonitrile ligands protect the Cu⁺ ion from oxidation to Cu²⁺, but are rather poorly bound: with other counterions, the complex forms di- and tri-acetonitrilo complexes and is also a useful source of unbound Cu(I).

Water-immiscible organic nitriles have been shown to selectively extract Cu(I) 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

References