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.^[1]

Tetrakis(acetonitrile)copper(I) hexafluorophosphate

Names
IUPAC name Tetrakis(acetonitrile)copper(I) hexafluorophosphate
Identifiers
CAS Number	64443-05-6 Y
ECHA InfoCard	100.198.153
PubChem CID	11068737
CompTox Dashboard (EPA)	DTXSID70983013
Properties
Chemical formula	[Cu(CH3CN)4]PF6
Molar mass	372.7198 g/mol
Appearance	White powder
Melting point	160 °C (320 °F; 433 K)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

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.^[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:

2 [Cu(CH₃CN)₄]⁺ + 6 H₂O → [Cu(H₂O)₆]²⁺ + Cu + 8 CH₃CN

See also

• Tetrakis(acetonitrile)copper(I) tetrafluoroborate

References

1. 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 Crystallogr. B. 31 (1): 314–317. Bibcode:1975AcCrB..31..314C. doi:10.1107/S0567740875002634.
3. 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.
4. 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.
5. Kubas, G.J. (1990). Tetrakis(acetonitirile)copper(I) Hexaflurorophosphate. Inorganic Syntheses. Vol. 28. pp. 68–69. doi:10.1002/9780470132593.ch15.
6. Elsayed Moussa, Mehdi; Piesch, Martin; Fleischmann, Martin; Schreiner, Andrea; Seidl, Michael; Scheer, Manfred (2018). "Highly soluble Cu(i)-acetonitrile salts as building blocks for novel phosphorus-rich organometallic-inorganic compounds" (PDF). Dalton Transactions. 47 (45): 16031–16035. doi:10.1039/C8DT03723J. PMID 30321246.
7. 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.