Tétracarbonyle de nickel

Nickel carbonyl (IUPAC name: tetracarbonylnickel) is a nickel(0) organometallic compound with the formula Ni(CO)4. This colorless liquid is the principal carbonyl of nickel. It is an intermediate in the Mond process for producing very high-purity nickel and a reagent in organometallic chemistry, although the Mond Process has fallen out of common usage due to the health hazards in working with the compound. Nickel carbonyl is one of the most dangerous substances yet encountered in nickel chemistry due to its very high toxicity, compounded with high volatility and rapid skin absorption. In nickel tetracarbonyl, the oxidation state for nickel is assigned as zero, because the Ni-C bonding electrons come from the C atom and are still assigned to C in the hypothetical ionic bond which determines the oxidation states. The formula conforms to the 18-electron rule. The molecule is tetrahedral, with four carbonyl (carbon monoxide) ligands. Electron diffraction studies have been performed on this molecule, and the Ni–C and C–O distances have been calculated to be 1.838(2) and 1.141(2) angstroms respectively. Ni(CO)4 was first synthesised in 1890 by Ludwig Mond by the direct reaction of nickel metal with carbon monoxide. This pioneering work foreshadowed the existence of many other metal carbonyl compounds, including those of vanadium, chromium, manganese, iron, and cobalt. It was also applied industrially to the purification of nickel by the end of the 19th century. At , carbon monoxide is passed over impure nickel. The optimal rate occurs at 130 °C. Ni(CO)4 is not readily available commercially. It is conveniently generated in the laboratory by carbonylation of commercially available bis(cyclooctadiene)nickel(0). It can also be prepared by reduction of ammoniacal solutions of nickel sulfate with sodium dithionite under an atmosphere of CO. On moderate heating, Ni(CO)4 decomposes to carbon monoxide and nickel metal. Combined with the easy formation from CO and even very impure nickel, this decomposition is the basis for the Mond process for the purification of nickel or plating onto surfaces.