Note 38 — Chapter XXII · IRON, COBALT, AND NICKEL

This compound is known as nickel tetra-carbonyl. It appears to me yet premature to judge of the structure of such an extraordinary compound as Ni(CO)4. It has long been known that potassium combines with CO forming Kn(CO)n (Chapter IX., Note 31), but this substance is apparently saline and non-volatile, and has as little in common with Ni(CO)4 as Na2H has with SbH3. However, Berthelot observed that when NiC4O4 is kept in air, it oxidises and gives a colourless compound, Ni3C2O3,10H2O, having apparently saline properties. We may add that Schützenberger, on reducing NiCl2 by heating it in a current of hydrogen, observed that a nickel compound partially volatilises with the HCl and gives metallic nickel when heated again. The platinum compound, PtCl2(CO)3 (Chapter XXIII., Note 11), offers the greatest analogy to Ni(CO)4. This compound was obtained as a volatile substance by Schützenberger by moderately heating (to 235°) metallic platinum in a mixture of chlorine and carbonic oxide. If we designate CO by Y, and an atom of chlorine by X, then taking into account that, according to the periodic system, Ni is an analogue of Pt, a certain degree of correspondence is seen in the composition NiY4 and PtX2Y2. It would be interesting to compare the reactions of the two compounds.