Tetrakis(acetonitrile)copper(I) hexafluorophosphate


Tetrakiscopper hexafluorophosphate is a salt with the formula PF6. It is a colourless solid that is used in the synthesis of other copper complexes. The cation + is a well-known example of a transition metal nitrile complex.

Structure

As confirmed by X-ray crystallographic studies, copper 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, and nitrate. With the weakly coordinating anion B4−, salts of + 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.

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. PF6 is generally produced by the addition of HPF6 to a suspension of copper oxide in acetonitrile:
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 PF6 compound may serve as a precursor in the non-aqueous syntheses of other Cu compounds.
Water-immiscible organic nitriles have been shown to selectively extract Cu 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: