Dioxygen Ligands

Complexes with the ligand O₂ are called dioxygen complexes. Myoglobin, haemoglobin, hemerythrin, and hemocyanin are only a few examples of the proteins that carry oxygen and are studied in this field. Many of the compounds formed by transition metals and O₂ are reversible in nature. With a volume percentage of 20%, dioxygen is a significant part of the earth's atmosphere. With two unpaired electrons in each of the doubly degenerate HOMOs, molecular oxygen is a triplet in its ground state. Since it possesses a double bond in its formal structure, molecular oxygen is a strong oxidant in terms of thermodynamics. O₂ may react with ground-state singlet molecules, but due to spin conservation, this reaction is kinetically unfavourable and necessitates the use of additional ground-state radicals, such as flavins, pterins, or metal ions.