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Copper cyanide forms a complex coordination compound, when dissolved in a solution containing excess ($\ce{CN^-}$) ions.

My question is whether it forms $\ce{[Cu(CN)_4]^{3-}}$ only or both $\ce{[Cu(CN)_3]^{2-}}$ and $\ce{[Cu(CN)_4]^{3-}}$ complexes?

Wikipedia says that both complexes are formed, but I am not sure if its a reliable source.

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  • $\begingroup$ Wikipedia is always a reliable source. $\endgroup$ – Nilay Ghosh Aug 22 '17 at 3:44
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No, both $\ce{[Cu(CN)3]^2-}$  and $\ce{[Cu(CN)4]^3-}$ species are formed. According to Wikipedia article of copper cyanide:

... but rapidly dissolves in solutions containing $\ce{CN−}$ to form $\ce{[Cu(CN)3]^2-}$ and $\ce{[Cu(CN)4]^3-}$, which exhibit trigonal planar and tetrahedral coordination geometry, respectively. These complexes contrast with those of silver and gold cyanides, which form $\ce{[M(CN)2]−}$ ions in solution.The coordination polymer $\ce{KCu(CN)2}$ contains $\ce{[Cu(CN)2]−}$ units, which link together forming helical anionic chains.

See this paper for more details.

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