Everything about Nickel Carbonyl totally explained
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Nickel carbonyl (
IUPAC name:
tetracarbonylnickel) is a colorless
organometallic complex that's a versatile reagent, first described in 1890 by
Ludwig Mond. It was the first metal simple carbonyl complex to be reported. Its
volatility at
room temperature and
toxicity have earned the compound the nickname "liquid death."
Structure and bonding
Having the molecular formula Ni(CO)
4, nickel carbonyl is composed of a central
nickel atom surrounded by four
carbonyl (
carbon monoxide)
ligands in a
tetrahedral arrangement. The CO ligands, in which the C and the O are connected by
triple bonds (often depicted as double bonds), are
covalently bonded to the nickel atom via the
carbon ends. The structures of these compounds baffled chemists for many years, and most publications before 1950 depicted chains of CO chelated to the metal.
Nickel carbonyl has 18
valence electrons, like many other metal carbonyls such as
iron pentacarbonyl and
molybdenum hexacarbonyl. These metal carbonyls have symmetrical structures and are charge-neutral, resulting in their high volatility. In Ni(CO)
4, the nickel atom has a formal
oxidation number of zero.
Preparation
Ni(CO)
4 was first synthesised in 1890 by
Ludwig Mond by the direct reaction of nickel metal with CO. This pioneering work foreshadowed the existence of many other metal carbonyl compounds, including those of V, Cr, Mn, Fe, and Co.
Nickel metal reacts at room temperature with
carbon monoxide gas to form the tetracarbonyl. At 323
K, carbon monoxide is passed over impure nickel. On moderate heating, such as contact with a hot glass surface, Ni(CO)
4 decomposes back to carbon monoxide and nickel metal. These two reactions form the basis for the
Mond process for the purification of nickel.
Chemical reactions
Like other low-valent metal carbonyls, Ni(CO)
4 undergoes CO substitution reactions and can be
oxidized. Donor ligands such as
triphenylphosphine react to give Ni(CO)
3(PPh
3) and Ni(CO)
2(PPh
3)
2.
2,2'-Bipyridine and related ligands behave similarly.
Chlorine oxidizes nickel carbonyl into
NiCl2, releasing CO gas. Other halogens behave analogously. This reaction provides a convenient method for destroying unwanted portions of the toxic compound.
Reduction or treatment with
hydroxides brings about clusters such as [Ni
5(CO)
12]
2- and [Ni
6(CO)
12]
2-.
Reactions of Ni(CO)
4 with alkyl and aryl halides often result in cabonylated organic products. Vinyl halides, such as PhCH=CHBr, are converted to the unsaturated
esters upon treatment with Ni(CO)
4 followed by sodium methoxide. Such reactions also probably proceed via Ni(CO)
3, which undergoes
oxidative addition.
Metal carbonyls are also susceptible to attack by nucleophiles. Thus, treatment of Ni(CO)
4 with some nucleophiles (Nu
-) results in acyl derivatives including [Ni(CO)
3C(O)Nu)]
-.
Toxicology and safety considerations
Ni(CO)
4 is highly hazardous, much more so than implied by its CO content, reflecting the effects of the nickel if it was released in the body. Nickel carbonyl may be fatal if absorbed through the skin or more likely, inhaled due to its high volatility. Its
LC50 for a 30-minute exposure has been estimated at 3 ppm, and the concentration that's immediately fatal to humans would be 30 ppm. Some subjects exposed to puffs up to 5 ppm described the odour as musty or sooty, but since the compound is so exceedingly toxic its smell provides no reliable warning against a potentially fatal exposure.
(External Link
) Historically, laboratories that used Ni(CO)
4 would keep a canary in the lab as an indicator of nickel carbonyl toxicity, due to the higher sensitivity of birds to this toxin.
The vapours of Ni(CO)
4 can autoignite.
Nickel carbonyl poisoning is characterized by a two-stage illness. The first consists of headaches and chest pain lasting a few hours, usually 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. The carcinogenicity of Ni(CO)
4 is a matter of debate.
Further Information
Get more info on 'Nickel Carbonyl'.
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