text: This ligand is the main one found in a Chini cluster. Four of these ligands are found in Collman's reagent.
full_question: This ligand is the main one found in a Chini cluster. Four of these ligands are found in Collman's reagent. Walter Hieber synthesized many coordination complexes containing this ligand. This is the main ligand found in the cobalt catalyst which was originally used in the oxo process for hydroformylation. Along with cyanide and nitric oxide, this ligand lies at the top of the strong-field end of the spectrochemical series. This ligand has a vibrational frequency of 2143 cm-1 in the free state, but when bound to a metal this frequency decreases to 1700-2100 cm-1 due to pi backbonding. Four of these ligands are removed from a nickel center due to heating in the Mond process. This ligand has around 200 times the affinity of oxygen when binding to hemoglobin, making this compound a potentially fatal respiratory toxin. For 10 points, name this compound that forms carbonyl ligands.
first_sentence: This ligand is the main one found in a Chini cluster. Four of these ligands are found in Collman's reagent.
raw_answer: carbon monoxide [or carbonyl ligand until it is read]