Metalhydroxo

Metalhydroxo refers to chemical species in which a metal center is bonded to a hydroxide ligand (OH−). In coordination chemistry, hydroxo ligands arise from hydrolysis of metal aquo complexes and can appear as mononuclear M–OH units or as μ‑hydroxo bridges linking two or more metal centers. The term covers discrete complexes as well as extended networks found in solid metal hydroxides.

In solution, hydroxo formation is often pH-dependent; deprotonation of coordinated water or aqua ligands yields M–OH species and release of protons. In the solid state, hydroxo groups form part of metal hydroxide lattices. Coordination modes vary: terminal M–OH bonds and μ‑OH bridges between two metals, with higher nuclearity structures common in bioinorganic and inorganic chemistry.

Metalhydroxo species are common intermediates in catalysis and redox chemistry, including water-splitting and hydrolysis reactions. They also appear in biological systems as transient intermediates in metal-oxo/hydroxo cycles within enzymes and metal-transport proteins. Stability is often enhanced by suitable ligands that support dinuclear or polynuclear assemblies, or by bridging motifs.

Characterization relies on spectroscopy and crystallography. Infrared or Raman spectroscopy can reveal M–OH and O–H vibrations, UV–visible spectroscopy informs on electronic structure, and X-ray diffraction provides solid-state structures. Related terms include metal hydroxide (M(OH)n) solids and metal-oxo/hydroxo species, with hydroxo ligands capable of hydrogen bonding and participating in proton-coupled electron transfer.