(4) From complex cyanides:
Although of no preparative importance, the formation of Ni(CO)4 by the disproportionation of a Ni(I)
complex is of scientific interest. Reduction of a solution of the well-known potassium tetracyanonickelate
complex with potassium amalgam gives a red solution containing tetracyano dinickelate ion. This ion
absorbs carbon monoxide and disproportionates in water to Ni(CO)4.