Metaloxohydroxo

Metaloxohydroxo, or metal-oxo-hydroxo, refers to inorganic species in which a metal center or centers are coordinated by oxide (O2−) and hydroxo (OH−) ligands. The term covers isolated metal–oxo and metal–hydroxo units as well as polynuclear clusters in which oxo and hydroxo groups bridge two or more metal centers. These motifs are common in coordination chemistry, bioinorganic chemistry, and catalytic materials.

Structural motifs often include terminal M=O units, μ-oxo bridges that connect two metals, and μ-hydroxo bridges that link metals through OH groups. Mixed oxo/hydroxo cores can form cubane-like clusters or larger assemblies, with oxidation states varying with the metal and synthesis. The combination of oxo and hydroxo ligands influences reactivity, acidity, and redox properties, enabling diverse catalytic transformations.

Examples and relevance span multiple metals, including manganese, iron, ruthenium, and vanadium. In biology, the oxygen-evolving complex of photosystem II contains a Mn4CaO5 cluster with oxo and hydroxo bridges as part of water oxidation. Synthetic models of metal-oxo-hydroxo species serve as platforms to study proton-coupled electron transfer, O–O bond formation, and other catalytic processes. Materials containing metaloxohydroxo motifs also appear in heterogeneous catalysis and energy-related applications.

Characterization typically involves X-ray crystallography to determine structure, complemented by Mössbauer spectroscopy or EPR for electronic structure, and EXAFS, UV-Vis, and resonance Raman for bonding and oxidation-state information. The term describes a broad class of compounds rather than a single well-defined species, reflecting the diverse chemistry of oxo and hydroxo ligands around metal centers.