Tetrakis(acetonitrile)copper(I) hexafluorophosphate

Tetrakis(acetonitrile)copper(I) hexafluorophosphate
IUPAC name Tetrakis(acetonitile)copper(I) hexafluorophosphate
Identifiers
CAS number	64443-05-6
Properties
Molecular formula	[Cu(CH3CN)4]PF6
Molar mass	372.7198 g/mol
Appearance	White powder
Melting point	160 °C, 433 K, 320 °F
Y hexafluorophosphate (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Tetrakis(acetonitrile)copper(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.^[1]

Structure

According to X-ray crystallographic studies, the copper(I) ion is coordinated to four almost linear acetonitrile ligands in a nearly ideal tetrahedral geometry.^[2] Related complexes are known with other anions including the perchlorate, tetrafluoroborate, and nitrate. With the weakly coordinating anion B(C₆F₅)₄^-, salts of [Cu(CH₃CN)₂]⁺ are obtained.^[1]

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 with a suspension of copper powder in acetonitrile.^[3] [Cu(CH₃CN)₄]PF₆ is generally produced by the addition of HPF₆ to a suspension of copper(I) oxide in acetonitrile:^[4]

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.^[4]

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.^[4]

Water-immiscible organic nitriles have been shown to selectively extract Cu²⁺ from aqueous chloride solutions.^[5] 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

1. ^ ^{a b} 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
2. ^ Kierkegaard C.P.; Norrestam R. (1975). "Copper(I) tetraacetonitrile perchlorate". Acta Cryst. B31: 314–317. doi:10.1107/S0567740875002634. 
3. ^ 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/CT9232302891. 
4. ^ ^{a b c} Kubas, G.J. (1979). "Tetrakis(acetonitirile)copper(I) Hexaflurorophosphate". Inorganic Syntheses 19: 90–91. doi:10.1002/9780470132593.ch15. 
5. ^ 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: 227. doi:10.1016/0304-386X(80)90041-9.