We made a solution of Tetrakis Copper(I) hexafluorophosphate and the usual color is yellowish. As it oxidizes to Cu(II), it should turn blue.

However, our current mixture has an off color that is pink. Looking up alternative copper colors, there will be copper rose. What would cause that color?

  • 1
    $\begingroup$ quickly looked into the Wiki if you made a solution in water, disproportionation occured, gigiving $Cu(II)$ and $Cu(0)$. Normal color of $Cu(0)$ is red. This link webexhibits.org/causesofcolor/9.html gives good explanation, why gold is yellow. Copper gets its red color roughly in same way $\endgroup$ – permeakra Feb 6 '13 at 12:37
  • $\begingroup$ @Permeakra, I have a strong inclination you're right. The Cu(I) hasn't been stored correctly so that reaction is likely to happen. $\endgroup$ – bobthejoe Feb 7 '13 at 1:33

I assume you mean tetrakis(acetonitrile)copper(I) hexafluorophosphate. This compound contains a tetrahedral complex of $\ce{Cu+}$ with 4 $\ce{CH3CN}$ ligands which stabilize the copper(I) center. They are, however, easily exchanged in the presence of other potential ligands, and with water, disproportionation to $\ce{Cu^2+}$ and elemental $\ce{Cu}$ will occur.

$$\ce{2[Cu(CH3CN)4]^+ + 6H2O ->~ [Cu(H2O)6]^2+ + Cu\downarrow + 8 CH3CN }$$

The pale blue color of the hexaaquacopper(II) complex might not be visible at low concentrations, and the pink color that you have observed arises from fine particles of the elemental $\ce{Cu}$ precipitate.


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