Coordination Chemistry of the Actinides

Studies of the coordination chemistry of the actinides have been limited by a number of factors - the care needed in handling radioactive materials and the possibility of damage to human tissue from the radiation toxicity (especially Pu) the very small quantities available and very short half-lives of the later actinides radiation and heating damage to solutions and radiation damage (defects and dislocations) to crystals. 

The vast majority of the studies reported have concerned the metals thorium and uranium, particularly the latter, due to accessibility of raw materials, ease of handling, and the long lifetimes of the relatively weakly a-emitting elements Th and U. In many cases, compounds of neptunium and plutonium with similar formulae to U and Th analogues have been made and found to be isomorphous and thus presumably isostructural. This chapter will therefore commence with, and concentrate largely on, the chemistry of complexes of these elements, followed by sections on the other actinides. 

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As a consequence of the considerable radiotoxicity of these elements there have been very few investigations into the coordination chemistry of the actinides in comparison to other transition elements. The greatest expansion in the coordination chemistry of the actinides might come in the development of new complexing agents which can be used to remove the small quantities of these elements which become contaminants of the human body during the reprocessing of nuclear fuel. 

The coordination chemistry of the actinides in aqueous environments can be segregated along two lines, low valency (di-, tri- and tetravalent) and high valency (penta- and hexavalent). For actinide ions with a low valency, the coordination chemistry is dominated by ionic bonding. As a result, the coordination number and geometry of these aqueous complexes is dictated by the steric bulk and electronic... 

The coordination chemistry of the actinides, especially thorium and uranium, continues to be of great interest. Considered hard metal ions, An(III to VI) have the... 

The small steric size and propensity of cyanide groups to bridge metal centers have limited their use as ligands in molecular coordination chemistry of the actinides, where they are prone to form amorphous polymeric products. Limited metathesis studies have been conducted. Reaction of tetravalent halides with alkali metal cyanides in liquid ammonia is reported to give rise to a product of the formula UX3(CN)-4NH3, whereas use of the larger thorium ion yields unidentified products. 

This section is not intended to be an inclusive list of the uses of the actinides. The uses highlighted were selected on the basis of how widespread the use is or where inorganic and/or coordination chemistry of the actinides play a central role. 

In summary, the pubhcation of this volume is a strong indicator of the substantial activity currently taking place in the organometalHc and coordination chemistries of the actinides. The future promises to hold many more surprises. 

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