|Jmol-3D images||Image 1|
|Molar mass||170.73 g/mol|
|Appearance||colorless or very-pale-yellow liquid
|Odor||musty, like brick dust|
|Melting point||−17.2 °C (1.0 °F; 256.0 K)|
|Boiling point||43 °C (109 °F; 316 K)|
|Solubility in water||.018 g/100 mL (10 °C)|
|Solubility||miscible in most organic solvents
soluble in nitric acid, aqua regia
|Viscosity||3.05 x 10−4 Pa s|
|320 J K−1 mol−1|
Std enthalpy of
Std enthalpy of
|EU classification||Flammable ('F)
Carc. Cat. 3
Repr. Cat. 2
Very Toxic (T+)
Dangerous for the environment (N)
|R-phrases||R61, R11, R26, R40, R50/53|
|S-phrases||S53, S45, S60, S61|
|Flash point||4 °C (39 °F; 277 K)|
|Related metal carbonyls||Iron pentacarbonyl
|Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)|
|(what is: / ?)|
Nickel carbonyl (IUPAC name: tetracarbonylnickel) is the organonickel compound with the formula Ni(CO)4. This pale-yellow liquid is the principal carbonyl of nickel. It is an intermediate in the Mond process for the purification of nickel and a reagent in organometallic chemistry. Nickel carbonyl is one of the most toxic substances encountered in industrial processes.
Structure and bonding
In nickel tetracarbonyl, the oxidation state for nickel is assigned as zero. The formula conforms to 18-electron rule. The molecule is tetrahedral, with four carbonyl (carbon monoxide) ligands attached to nickel. The CO ligands, in which the C and the O are connected by triple bonds, are covalently bonded to the nickel atom via the carbon ends. 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 CO. This pioneering work foreshadowed the existence of many other metal carbonyl compounds, including those of V, Cr, Mn, Fe, and Co. It was also applied industrially to the purification of nickel by the end of the 19th century.
On moderate heating, Ni(CO)4 decomposes to carbon monoxide and nickel metal. Combined with the easy formation from CO and even impure nickel, this decomposition is the basis for the Mond process for the purification of nickel. Thermal decomposition commences near 180 °C and increases at higher temperature
Reactions with nucleophiles and reducing agents
Like other low-valent metal carbonyls, Ni(CO)4 is susceptible to attack by nucleophiles. Attack can occur at nickel center, resulting in displacement of CO ligands, or at CO. Thus, donor ligands such as triphenylphosphine react to give Ni(CO)3(PPh3) and Ni(CO)2(PPh3)2. Bipyridine and related ligands behave similarly. The monosubstitution of nickel tetracarbonyl with other ligands can be used to determine the Tolman electronic parameter, a measure of the electron donating or withdrawing ability of a given ligand.
Treatment with hydroxides gives clusters such as [Ni5(CO)12]2− and [Ni6(CO)12]2−. These compounds can also be obtained by reduction of nickel carbonyl.
Thus, treatment of Ni(CO)4 with carbon nucleophiles (Nu−) results in acyl derivatives such as [Ni(CO)3C(O)Nu)]−.
Reactions with electrophiles and oxidizing agents
Nickel carbonyl can be oxidized. 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.
Reactions of Ni(CO)4 with alkyl and aryl halides often result in carbonylated organic products. Vinylic 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 oxidative addition. Allylic halides give the pi-allyl nickel compounds, such as (allyl)2Ni2Cl2:
- 2 Ni(CO)4 + 2 ClCH2CH=CH2 → Ni2(μ-Cl)2(η3-C3H5)2 + 8 CO
Toxicology and safety considerations
The hazards of Ni(CO)4 are far greater than that implied by its CO content, reflecting the effects of the nickel if 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 is 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 because the compound is so exceedingly toxic, its smell provides no reliable warning against a potentially fatal exposure.
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.
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