Olation

General information

The olation is one of the two reactions, with the Oxolation, leading to the formation of polyoxométallates (POM), at the base of the solid metallic oxide syntheses (oxyhydr) starting from metal ions in aqueous solution, in particular in soft Chimie.

It is about a reaction of condensation between two coordinate metal complexes by ligands aquo (H₂0):

^z + ^z --> ^2z + H₂0

M represents metal. L represents indifferently a ligand aquo or hydroxo. Z represents the load of the complex.

When the formed complex is of zero load (Z = 0), it can be the " precursor of load nulle" necessary to the solid metallic oxide formation (oxyhydr) by Polycondensation. If not, it is possible to obtain polyanions.

Mechanism

The olation is done by dissociative mechanism:

Stage 1 : A water molecule, whose pKa is lowered by the electric attraction of metal, releases a proton (hydroxylation).

ML_n (H₂O) --> L_nM-OH + H⁺

Stage 2 : Then, a water molecule related to another metal center is detached from this one (limiting stage). The reaction speed depends on the lability of the water molecule.

ML_n (H₂O) --> ML_n + H₂O

Stage 3 : Lastly, the free doublet of the hydroxide formed in stage 1 comes to supplement the gap created in stage 2:

L_nM-OH-ML_n

When the complex created has a zero load, the mechanism can continue and tend to the formation of a gel. In the contrary case, one obtains a polycation.

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