Coordination chemistry actinides

Because of the technical importance of solvent extraction, ion-exchange and precipitation processes for the actinides, a major part of their coordination chemistry has been concerned with aqueous solutions, particularly that involving uranium. It is, however, evident that the actinides as a whole have a much stronger tendency to form complexes than the lanthanides and, as a result of the wider range of available oxidation states, their coordination chemistry is more varied. 

Thirdly, some obvious applications of coordination chemistry are omitted from this volume if they are better treated elsewhere. This is the case when a specific application is heavily associated with one particular element or group of elements, to the extent that the application is more appropriately discussed in the section on that element. Essentially all of the coordination chemistry of technetium, for example, relates to its use in radioimmunoimaging inclusion of this in Chapter 20 of this volume would have left the chapter on technetium in Volume 5 almost empty. For the same reason, the applications of actinide coordination complexes to purification, recovery,... 

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 importance of hydroxypyridinones in connection with the decorporation of plutonium (Section IV.C.7) and the similarities between the coordination chemistries of early actinides and lanthanides... 

Although coordination number 8 cannot be regurded as common, the number of known compounds has Increased rapidly in recent years, so thai it is now exceeded only by four- and six-coordiration. The factors important in this increase can be traced largely to improved three-dimensional X-ray lechniques and to increased interest in ihe coordination chemistry oflanthanide and actinide elements (see Chapter 14). 

A new field of coordination chemistry is that of polymetallic cage and cluster complexes [Mm(p-X)xLJz with molecular (i.e. discrete) structure. They contain at least three metal atoms, frequently with bridging ligands X and terminal ligands L. These compounds link the classical complexes (m = 1) and the non-molecular (m - oo) binary and ternary compounds of the metals.1 Molecular polymetallic clusters (with finite radius) also provide a link with the surfaces (infinite radius) of metals and their binary compounds.2"5 Polymetallic complexes are known for almost all metals except the actinides. 

Viewed in the context of the actinide lifespan, the nuclear fuel cycle involves the diversion of actinides from their natural decay sequence into an accelerated fission decay sequence. The radioactive by-products of this energy producing process will themselves ultimately decay but along quite different pathways. Coordination chemistry plays a role at various stages in this diversionary process, the most prominent being in the extraction of actinides from ore concentrate and the reprocessing of irradiated fuel. However, before considering these topics in detail it is appropriate to consider briefly the vital role played by coordination chemistry in the formation of uranium ore deposits. 

Jensen, M.P., Bond, A.H., Rickert, P.G., Nash, K.L. 2002. Solution phase coordination chemistry of trivalent lanthanide and actinide cations with bis(2,4,4-trimeth-ylpentyl)dithiophosphinic acid. Journal of Nuclear Science and Technology (S3) 255-258. 

Recently, the first U(V) heteroleptic cyclo-octatetraene-dithiolene complex 992 was synthesized by AgBPh4 oxidation in THF of the [(COT)UIV(dddt)2][Na(18-crown-6)]2 precursor, which was synthesized by reacting [(COT)UX2(THF)J (X = BH4, n = 0 X = I, n = 2) with Na2dddt [490]. In general, despite the relatively small number of reported actinide S-containing complexes, they have a potentially rich coordination chemistry of such compounds of hard /-elements with soft S-ligands [489] and possible applications [491]. 

Soloveichik, G.L. Actinides Inorganic Coordination Chemistry. In Encyclopedia of Inorganic Chemistry. (Edit. King, R.B.). John Wiley Chichester, 1994, vol. 1, p. 2. 

Scientific Committee of International Conferences First International Transplutonium Element Symposium, Argonne, IL, USA, 1963 Third International Transplutonium Element Symposium, Argonne, IL, USA, 1971 Fifteenth International Conference on Coordination Chemistry, Moscow, USSR, 1973 First International Symposium on the Electronic Structure of the Actinides, Argonne, IL, USA, 1974... 

Low-Temperature Absorption Spectra of Actinide Cyclopentadienides, W.T. Camall, P.R. Fields, and R.G. Pappalardo. In Progress in Coordination Chemistry. Proceedings of the 11th International Conference on Coordination Chemistry, Haifa and Jerusalem, September 1968. M. Cais (Ed.), Elsevier, Amsterdam, 1969, p. 411. 

Recent Developments in the Interpretation of Trivalent Lanthanide and Actinide Absorption Spectra, W.T. Camall. In Novel in Coordination Chemistry, Section Lectures of the 13th International Conference of Coordination Chemistry, Cracow-Zakopane, Poland, September 14-22, 1970. B.J. Trzebiatowska and M. Rudolf (Eds.), Panstwowe Wydawnictwo Naukowe, Wroclaw, 1974, pp. 89-100. 

It is to be hoped that with improved three-dimensional x-ray techniques and with ever increasing interest in the coordination chemistry of actinides, more attention from a coordination chemist will be drawn to these fascinating complexes. 

One of the most recent developments in phospholyl coordination chemistry is that of the lanthanide and actinides. Here the greater CNs possible for these metals means that the full potential of the various binding modes of phospholyl anions (t] rf, and r] rf) may be exploited to the full. Once again, variation in the steric demands of the phospholyl ring may be used to tune their coordination chemistry. A number of comprehensive reviews of these areas have appeared <1998CCR13, 2001EJI891>. 

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. 

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