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.[1]
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.[2][3] Similar complexes with other anions including the perchlorate, tetrafluoroborate, and nitrate are known.[1]
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.[4] [Cu(CH3CN)4]PF6 is generally produced by the addition of HPF6 to a suspension of copper(I) oxide in acetonitrile:[5]
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.[5]
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-[1] and tri-acetonitrilo[6] complexes and is also a useful source of unbound Cu(I).[5]
Water-immiscible organic nitriles have been shown to selectively extract Cu(I) from aqueous chloride solutions.[7] Through this method, copper can be separated from a mixture of other metals. Dilution of acetonitrile solutions with water induces disproportionation:
1 2 3 Silvana F. Rach, Fritz E. Kühn "Nitrile Ligated Transition Metal Complexes with Weakly Coordinating Counteranions and Their Catalytic Applications" Chem. Rev., 2009, volume 109, pp 2061–2080. doi:10.1021/cr800270h
↑ Black, J. R.; Levason, W.; Webster, M. (1995). "Tetrakis(acetonitrile-N)copper(I) Hexafluorophosphate(V) Acetonitrile Solvate". Acta Crystallographica Section C Crystal Structure Communications. 51 (4): 623–625. Bibcode:1995AcCrC..51..623B. doi:10.1107/S0108270194012527.
↑ Morgan, H.H.; Sand, Henry Julics Salomon (1923). "Preparation and Stability of Cuprous Nitrate and Other Cuprous Salts in the Presence of Nitriles". J. Chem. Soc.19: 2901. doi:10.1039/CT9232302901.
↑ Preston, J. S.; Muhr D. M; Parker A. J. (1980). "Cuprous hydrometallurgy: Part VIII. Solvent extraction and recovery of copper(I) chloride with organic nitriles from an iron(III), copper(II) chloride, two-step oxidative leach of chalcopyrite concentrate". Hydrometallurgy. 5 (2): 227. Bibcode:1980HydMe...5..227P. doi:10.1016/0304-386X(80)90041-9.
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