Cobalt carbonyl

Dicobalt octacarbonyl

Names
IUPAC name Octacarbonyldicobalt(Co—Co)
Other names Cobalt carbonyl, di-mu-Carbonylhexacarbonyldicobalt, Cobalt octacarbonyl, Cobalt tetracarbonyl dimer, Dicobalt carbonyl, Octacarbonyldicobalt
Identifiers
CAS Number	10210-68-1 Y
3D model (JSmol)	Interactive image
ChemSpider	2007057 Y
ECHA InfoCard	100.030.454
PubChem CID	25049
RTECS number	GG0300000
UNII	MDH533S43Q N
UN number	3281
InChI InChI=1S/8CO.2Co/c8*1-2;;/q;;;;;;;;2*+2 Y Key: MQIKJSYMMJWAMP-UHFFFAOYSA-N Y InChI=1/8CO.2Co/c8*1-2;;/q;;;;;;;;2*+2 Key: MQIKJSYMMJWAMP-UHFFFAOYAG
SMILES [Co+2].[Co+2].[C-]#[O+].[O+]#[C-].[O+]#[C-].[O+]#[C-].[O+]#[C-].[O+]#[C-].[O+]#[C-].[O+]#[C-]
Properties
Chemical formula	Co2(CO)8
Molar mass	341.95 g/mol
Appearance	red-orange crystals white crystalline solid when pure
Density	1.87 g/cm3
Melting point	51 to 52 °C (124 to 126 °F; 324 to 325 K)
Boiling point	52 °C (126 °F; 325 K) c.a. decomposes
Solubility in water	insoluble
Vapor pressure	0.7 mmHg (20 °C)
Structure
Dipole moment	1.33 D (C2v isomer) 0 D (D3d isomer)
Hazards
Main hazards	Toxic, evolves CO gas on decomposition
Safety data sheet	External MSDS
Flash point	nonflammable
US health exposure limits (NIOSH):
PEL (Permissible)	none
REL (Recommended)	TWA 0.1 mg/m3
IDLH (Immediate danger)	N.D.
Related compounds
Related metal carbonyls	Iron pentacarbonyl Diiron nonacarbonyl Nickel tetracarbonyl
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N  (what is YN ?)
Infobox references

Dicobalt octacarbonyl is the inorganic compound Co₂(CO)₈. This metal carbonyl is a reagent and catalyst in organometallic chemistry and organic synthesis. It is used as a catalyst for hydroformylation, the conversion of alkenes into aldehydes. It is highly reactive towards alkynes, and is sometimes used as an alkyne protecting group. As the cobalt-alkyne complex, it plays a role in promoting both the Nicholas reaction and the Pauson–Khand reaction.

It is synthesised by the high pressure carbonylation of cobalt(II) salts, often in the presence of cyanide. It is an orange-colored, pyrophoric solid that is thermally unstable. It exists as two isomers in solution that rapidly interconvert.

The major isomer contains two bridging CO ligands linking the Co atoms and six terminal CO ligands, three on each Co atom. It can be described by the formula (CO)₃Co(μ-CO)₂Co(CO)₃ and has C_2vsymmetry. This structure resembles Fe₂(CO)₉, but with one fewer bridging CO. The Co---Co distance is 2.52 Å, and the Co–CO_terminal and Co–CO_bridge distances are 1.80 and 1.90 Å, respectively. Analysis of the bonding suggests the absence of a direct Co–Co bond.

The minor isomer has no bridging CO ligands, but instead has a direct Co–Co bond and eight terminal CO ligands, four on each Co atom. It can be described by the formula (CO)₄Co-Co(CO)₄ and has D_3d symmetry. It features an unbridged Co-Co bond that is 2.70 Å in length. The minor isomer has been crystallized together with C₆₀.