Tetracobalt dodecacarbonyl is the chemical compound with the formula Co<sub>4</sub>(CO)<sub>12</sub>. It is a black crystalline compound that is insoluble in water and easily oxidized by air. It is an example of a metal carbonyl cluster.
This compound is synthesized by decarbonylation of Co<sub>2</sub>(CO)<sub>8</sub>.
The molecule consists of a tetrahedral Co<sub>4</sub> core, but the molecular symmetry is C<sub>3v</sub>. Three carbonyl ligands are bridging ligands and nine are terminal. The average Co-Co distance is 2.499 à, the average C-O bond length is 1.133 à, and the average Co-C-O angle is 177.5ð.
Rh<sub>4</sub>(CO)<sub>12</sub> adopts the same C<sub>3v</sub> structure but Ir<sub>4</sub>(CO)<sub>12</sub> has perfect T<sub>d</sub> symmetry with no bridging CO ligands groups. The Rh<sub>4</sub> and Ir<sub>4</sub> clusters are more thermally robust than that of the Co<sub>4</sub> compound, reflecting the usual trend in the strengths of metal-metal bond for second and third row metals vs those for the first row metals. There has been disagreement between the theoretically predicted and experimental structure of tetracobalt dodecacarbonyl.