Tetrakis(acetonitrile)copper(I) hexafluorophosphate
Tetrakis(acetonitrile)copper(I) hexafluorophosphate is a salt with the formula [Cu(CHCN)]PF. It is a colourless solid that is used in the synthesis of other copper complexes. The cation [Cu(CHCN)] is a well-known example of a transition metal nitrile complex. Structure. As confirmed by X-ray crystallographic studies, 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, and nitrate. With the weakly coordinating anion B(CF), salts of [Cu(CHCN)] are obtained. The acetonitrile ligands protect the Cu ion from oxidation to Cu. Acetonitrile  is not bound very strongly to the copper ion, thus the complex is a useful source of Cu(I). With other counteranions, complexes of [Cu(MeCN)] are observed. 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(CHCN)]PF is generally produced by the addition of HPF to a suspension of copper(I) 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 Cu impurities. Reactions and applications. As the coordinated acetonitrile ligands may be displaced in other solvents, the [Cu(CHCN)]PF 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 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: