Chemistry:Tetrakis(acetonitrile)copper(I) hexafluorophosphate

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Tetrakis(acetonitrile)copper(I) hexafluorophosphate
Structural formulas of the tetrakis(acetonitrile)copper(I) cation and the hexafluorophosphate anion
Space-filling models of the component ions of tetrakis(acetonitrile)copper(I) hexafluorophosphate
Names
IUPAC name
Tetrakis(acetonitrile)copper(I) hexafluorophosphate
Identifiers
Properties
[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).
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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]

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

References

  1. 1.0 1.1 1.2 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: 314–317. 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. 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. 5.0 5.1 5.2 Kubas, G.J. (1990). "Tetrakis(acetonitirile)copper(I) Hexaflurorophosphate". Inorganic Syntheses 28: 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". Dalton Transactions 47 (45): 16031–16035. doi:10.1039/C8DT03723J. PMID 30321246. https://epub.uni-regensburg.de/38440/1/Scheer%2C%20RSC%2C%20Dalton%20Transactions.pdf. 
  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: 227. doi:10.1016/0304-386X(80)90041-9.