Oxoanion ligands

Another rather unusual case of rapid aquation is provided by those oxoanion ligands MO in which the M-0 bond is sufficiently weak for it to break rather than the Co-0 bond. This time we have an intramolecular reaction of a coordinated ligand. A recent example is provided by aquation of the [Co(NH3)5(OMo03)]+ cation (57). This aquation pathway is actually more commonly encountered for chromium(III) complexes. 

Aqueous carbonate complexes of An ions, An(C03) ", =1—5, form stepwise with increasing solution pH and carbonate concentration." As with other oxoanionic ligand systems, the stability of the carbonate complexes decreases across the series, such that the pentacarbonato complex is well studied for Th and U. The tetracarbonato complex is more important for Np and Pu in solution, although salts of the pentacarbonato anion are known across the series. Most studies of Th, U, Np, and Pu do indicate that mixed hydroxyocarbonate complexes, An(0H) t(C03) " " e.g, Th(0H)3(C03) for Th, are important in describing the aqueous solution behavior. For the lower order carbonates the actinide is presumably nine or ten-coordinate with waters and bidentate carbonate in the inner coordination sphere. For the penta-and hexacarbonato complexes there is no evidence that any water molecules remain bound to the actinide center. 

Two examples of cw-ligand labilization by oxoanion ligands have already... 

The oxoanions of these elements represent an extensive set of potential ligands, characterized by a dominant, but not exclusive, tendency towards O bonding. Practically every known oxoanion has been introduced into the Co coordination sphere during the last century. 

This system is additive and was developed originally to name coordination compounds, although it can be used in other circumstances when appropriate. For a discussion, see the Nomenclature of Inorganic Chemistry, Chapter 10. The compound to be named is considered as a central atom together with its ligands, and the name is developed by assembling the individual names of the constituents. This system has also been applied to name oxoacids and the related anions. Coordination names for oxoanions are cited in the examples throughout the text, and they are presented in detail in Section 4.4.5 (p. 69). 

---