text: Some metal carbynes dimerize to give dimetallacyclobutadienes. In these complexes, the carbyne ligand serves as a bridging ligand.
  Several cluster-bound carbyne complexes are known, typically with CO ligands. These compounds do not feature MC triple bonds; instead the carbyne carbon is tetrahedral. Tricobalt derivatives are prepared by treating cobalt carbonyl with haloforms:
  :2 HCBr +  Co(CO) → 2 HCCo(CO) + 18 CO + 3 CoBr