Actinide compounds and complexes

Examples of the stereochemistry of actinide compounds and complexes are given in Table 28-4. For the +3 oxidation state, where the resemblance... 

This section deals with the structure and chemistry of actinide compounds and complexes, excluding derivatives of uranyl and related systems. 

In the preceding section, the magnetic field was mainly used to determine the saturation magnetization of ferromagnets. However, it is now well established that many actinide compounds have complex magnetic behaviour and the application of an external field may change or suppress antiferromagnetic structures. 

The aim of this chapter is to review the chemistry of chalcogenolates in the last 10 years. The more recent reviews in this field included chalcogenolates of the s-block elements,early transition metal thiolates,metal complexes with selenolate and tellurolate ligands, copper(I), lithium and magnesium thiolates,functionalized thiolate complexes,pentafluorobenzenethiolate platinum group compounds, tellurium derivatives, luminescent gold compounds, and complexes with lanthanide or actinide. ... 

One of the benefits of computational chemistry is the ability to model compounds and complexes that are hard to synthesize or are inherently difficult to study. Schreck-enbach used a relativistic DFT to model 18-crown-6 complexes of the actinide species U02 , Np02, and Pu02 " " and found good agreement with experimentally determined bond lengths for Np(V). Experimental uncertainties were... 

The many possible oxidation states of the actinides up to americium make the chemistry of their compounds rather extensive and complicated. Taking plutonium as an example, it exhibits oxidation states of -E 3, -E 4, +5 and -E 6, four being the most stable oxidation state. These states are all known in solution, for example Pu" as Pu ", and Pu as PuOj. PuOl" is analogous to UO , which is the stable uranium ion in solution. Each oxidation state is characterised by a different colour, for example PuOj is pink, but change of oxidation state and disproportionation can occur very readily between the various states. The chemistry in solution is also complicated by the ease of complex formation. However, plutonium can also form compounds such as oxides, carbides, nitrides and anhydrous halides which do not involve reactions in solution. Hence for example, it forms a violet fluoride, PuFj. and a brown fluoride. Pup4 a monoxide, PuO (probably an interstitial compound), and a stable dioxide, PUO2. The dioxide was the first compound of an artificial element to be separated in a weighable amount and the first to be identified by X-ray diffraction methods. 

The methods used to describe the electronic structure of actinide compounds must, therefore, be relativistic and must also have the capability to describe complex electronic structures. Such methods will be described in the next section. The main characteristic of successful quantum calculations for such systems is the use of multiconfigurational wave functions that include relativistic effects. These methods have been applied for a large number of molecular systems containing transition metals or actinides, and we shall give several examples from recent studies of such systems. 

Many substituted uranocenes have been made and there is a substantial body of organometallic chemistry of uranocene derivatives now known 16, 17). Some of this chemistry will be mentioned in passing but wiU not be covered in a systematic way since other reviews of the organic chemistry are available 18). The only other actinide cyclooctatetraene complex structurally characterized to date is bis[(l,3,5,7-tetramethylcyclooctatetraenyl]uranium(IV) 19), which was of interest because the presence of methyl groups allowed the planarity and relative orientation of the dianion rings to be determined. Crystal and molecular parameters for these three actinide compounds are summarized in Table 1. 

It is interesting to compare these actinide(IV) cyclooctatetraene complexes with similar compounds of the group IVB transition elements Ti, Zr and Hf. Bis (cyclooctatetraene) complexes of aU three are known although structural data is only available for the first two. All would appear to involve both planar and non-planar COT rings and to exhibit a sHpped sandwich structure rather than the true sandwich structure of uranocene. 

Among the natural and artificial radioactive elements (Tc, Pm, Po, Fr, Ra, Ac, and actinides), coordination and organometallic compounds of only technetium and the actinide series (An) are well represented at the present time. The interest in their metal complexes has been motivated by the extended use of Tc, available in kilogram amounts, for medical and technical purposes, meanwhile actinides are important on their own for the nuclear industry. A lot of original papers, reviews, and chapters of some books are dedicated to Tc and An complexes [263-281], In the present section, dedicated to the coordination and organometallic chemistry of the actinides and Tc, we intend to present the synthetic techniques for these compounds according to their ligand nature. 

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]. 

---