Uranyl hydroxide
Uranyl hydroxide is a hydroxide of uranium with the chemical formula UO(OH) in the monomeric form and (UO)(OH) in the dimeric; both forms may exist in normal aqueous media. Uranyl hydroxide hydrate is precipitated as a colloidal yellowcake from oxidized uranium liquors near neutral pH.
Hydroxide
The hydroxide ion appears to rotate freely in crystals of the heavier alkali metal hydroxides at higher temperatures so as to present itself as a spherical ion, with an effective ionic radius of about 153 pm. Thus, the high-temperature forms of KOH and NaOH have the sodium chloride structure, which gradually freezes in a monocinically distorted sodium chloride structure at temperatures below about 300 °C. The OH groups still rotate even at room temperature around their symmetry axes and, therefore, cannot be detected by X-ray diffraction. The room-temperature form of NaOH has the thallium iodide structure. LiOH, however, has a layered structure, made up of tetrahedral Li(OH) and (OH)Li units. This is consistent with the weakly basic character of LiOH in solution, indicating that the Li–OH bond has much covalent character.