The phrase "transition metal dioxygen complex" refers to a chemical compound that consists of a transition metal atom bonded to two oxygen atoms. This type of complex is commonly found in many biological and industrial applications, including in enzymes, dyes, and catalysts. Synonyms for transition metal dioxygen complexes include metal-oxo complexes, metal-peroxo complexes, and metal-superoxo complexes, depending on the specific oxidation state and coordination geometry of the metal center. These complexes play an important role in various chemical reactions and biological processes, and their properties and reactivity can be finely tuned by controlling the metal center and ligand environment.