Nickel carbonyl
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Nickel carbonyl, or tetracarbonyl nickel is a covalent compound of nickel, which is, unusually for a metal compound, a colorless liquid at room temperature. Its formula is Ni(CO)4. It is highly toxic and may be fatal if ingested or absorbed through the skin. Nickel carbonyl is extremely volatile. It evaporates at room temperature. The vapours can autoignite.
Nickel metal at room temperature is able to react with carbon monoxide (CO) to form the tetracarbonyl. On moderate heating nickel tetracarbonyl decomposes to carbon monoxide and nickel metal. These two reactions form the basis for the Mond process for making pure nickel.
Toxicology
Nickel carbonyl poisoning is characterized by a two-stage illness. The first consists of headaches and chest pain lasting a few hours, ususally followed by a short remission. The second phase is a chemical pneumonitis which starts after typically 16 hours with symptoms of cough, breathlessness and extreme fatigue. These reach greatest severity after four days, possibly resulting in death from cardiorespiratory or renal failure. Convalescence is often extremely protracted, often complicated by exhaustion, depression and dyspnea on exertion. Permanent respiratory damage is unusual. There is debate about the carcinogenicity of nickel carbonyl gas.