oxohydroxo

Oxohydroxo is a term used in inorganic chemistry to describe a ligand motif or a structural unit that contains both oxide (O2−) and hydroxide (OH−) groups coordinated to a metal center. The oxohydroxo designation emphasizes the coexistence of these two oxygen-containing groups within a single coordination sphere or as a bridging feature between metal centers.

In many coordination compounds, oxohydroxo units arise from deprotonation of aquo or hydroxo ligands, or from partial oxidation processes that convert a hydroxido fragment into an oxo fragment. Structurally, oxohydroxo motifs can appear as μ-oxohydroxo bridges that link two metal centers, as terminal oxo and hydroxo ligands on the same metal, or as parts of larger metal-oxide/hydroxide clusters. The exact geometry and connectivity depend on the metal, oxidation state, and supporting ligands.

Oxohydroxo species can participate in a range of chemical behaviors, including proton-coupled electron transfer, base and nucleophile activity, and redox processes. The presence of both oxo and hydroxo groups can influence redox potentials, magnetic interactions, and catalytic properties, particularly in reactions involving oxygen transfer, water oxidation, or O–O bond formation. The motif also serves as a model for understanding hydrogen-bond networks and proton relays in catalytic cycles.

Occurrences of oxohydroxo motifs are widespread in transition-metal chemistry, including iron, manganese, copper, and ruthenium systems, as well as in some metal-oxide clusters and enzymes that operate under redox and proton-transfer conditions. The term remains descriptive, with specific structures varying according to the metal center and ligands involved.