Olation
At low pH, many metal ions exist in aqueous solution as aqua coordination complexes, often with the formula [M(HO)]. As the pH increases, one O-H bond ionizes to give the hydroxide complex, the conjugate base of the parent hexaaqua complex:
The hydroxo complex is poised to undergo olation, which is initiated by displacement of one water by a neighboring complex:
In this product, the hydroxide ligand bridges between the two metals, this bridge is denoted with the symbol μ.
In the resulting 5+ ion, the remaining water and hydroxo ligands are highly acidic and the ionization and condensation processes can continue at still higher pHs. The formation of the oxo-dimer is a process called "oxolation," although sometimes olation and oxolation are not distinguished:
Ultimately one observes the formation of the metal oxide:
Aluminium hydroxide
Gibbsite is also known as hydrargillite, named after the Greek words for water (') and clay ('). The first compound named "hydrargillite" was thought to be aluminium hydroxide, but was later found to be aluminium phosphate; despite this, both "gibbsite" and "hydrargillite" are used to refer to the same polymorphism of aluminium hydroxide, with "gibbsite" used most commonly in the United States and "hydrargillite" used more often in Europe. In 1930, it was referred to as "α-alumina trihydrate" to contrast it with bayerite, which was called "β-alumina trihydrate" (the alpha and beta designations were used to differentiate the more- and less-common forms respectively). In 1957, a symposium on alumina nomenclature attempted to develop a universal standard, resulting in gibbsite being designated γ-Al(OH), bayerite becoming α-Al(OH), and nordstrandite being designated Al(OH). Based on their crystallographic properties, a suggested nomenclature and designation is for gibbsite to be α-Al(OH), bayerite to be designated β-Al(OH), and both nordstrandite and doyleite are designated Al(OH). Under this designation, the α and β prefixes refer to hexagonal, close-packed structures and altered or dehydrated polymorphisms respectively, with no differentiation between nordstrandite and doyleite.