Cupric cyanide, Cu(CN)₂

The Cupric cyanide, Cu(CN)₂, is obtained as a brownish-yellow precipitate by the interaction of solutions of potassium cyanide and cupric sulphate, but it is very unstable, decomposing at ordinary temperatures into cupric cuprous cyanide, Cu[Cu(CN)₂]₂,5H₂O, with evolution of cyanogen. On heating, it is converted into cuprous cyanide. With hydrazine cyanide it unites to form a monohydrazinate, Cu(CN)₂,N₂H₄, yellow needles insoluble in water, m.p. 160° to 162° C.