text: Dioxygen complexes are the precursors to other families of oxygenic ligands.  Metal oxo compounds arise from the cleavage of the O–O bond after complexation. Hydroperoxo complexes are generated in the course of the reduction of dioxygen by metals. The reduction of O by metal catalysts is a key half-reaction in fuel cells.
  Metal-catalyzed oxidations with O proceed via the intermediacy of dioxygen complexes, although the actual oxidants are often oxo derivatives. The reversible binding of O to metal complexes has been used as a means to purify oxygen from air, but cryogenic distillation of liquid air remains the dominant technology.