What is the coordination entity formed when excess of aqueous KCN is added to an aqueous solution of copper sulphate?

i.e., 

Thus, the coordination entity formed in the process is $\mathrm{K}_{2}\left[\mathrm{Cu}(\mathrm{CN})_{4}\right] . \mathrm{K}_{2}\left[\mathrm{Cu}(\mathrm{CN})_{4}\right]$ is a very stable complex, which does not ionize to give $\mathrm{Cu}^{2+}$ ions when added to water. Hence, $\mathrm{Cu}^{2+}$ ions are not precipitated when $\mathrm{H}_{2} \mathrm{~S}_{(g)}$ is passed through the solution.