Copper(I) Cyanide

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Copper(I) cyanide is an inorganic salt with the formula CuCN. It is a pale yellow-white colour; however, it is commonly found as a green solid, but this is due to copper(II) cyanide impurities. Copper(I) cyanide is used as a catalyst in electroplating of copper.

Synthesis
Copper(I) cyanide can be made by reacting copper(II) sulfate with sodium bisulfite and sodium cyanide at 60 °C in aqueous solution. Upon addition of sodium bisulfite to the copper(II) sulfate the solution will turn from a blue to a green colour. Once the solution has turned green sodium cyanide can be added to complete the reaction.

Another way in which copper(I) cyanide can be produced is the direct reaction between copper(II) sulfate with sodium cyanide. This method precipitates both dicyanide as well as copper(II) cyanide, which makes it a impure sample.

Structure
Copper cyanide is a coordination polymer. It exists in two polymorphs both of which contain -[Cu-CN]- chains made from linear copper(I) centres linked by cyanide bridges. The chains link into a hexagonal pattern in solid copper(I) cyanide. At lower temperatures the chains bend and into a rippled pattern and are no longer linear.