Halides actinide

The Actinide and Transactinide Elements (Z=90-112) Table 31.6 Properties of actinide halides ... 

Metallothermic reduction of an actinide halide was the first method applied to the preparation of an actinide metal. Initially, actinide chlorides were reduced by alkali metals, but then actinide fluorides, which are much less hygroscopic than the chlorides, were more... 

Table 2 Free energies offormation of some lanthanide and actinide halides...

The latest developments in the preparation of anhydrous actinide halides and their reduction to metals at the microscale have been reviewed by Haire ... 

Values in boldface type are from Durwent and represent his estimates of ihc "best value" and uncertainties for the energies required to break the bonds at 0 K. Where values are not available from Darwent. they arc taken from Brewer and coworkers for metal halides and dihaiidcs (boldface italics) or from Feber for transition metal, lanthanide, and actinide halides (italics). These values represent enthalpies of atomization at 298 K. The remaining values are from Cottrell (Arabic numerals) and other sources (Arabic numerals with superscripts keyed to references at end of table). 

Fuger, J., Parker, V.B., Hubbard, W.N., Oetting, F.L., 1983. The chemical thermodynamics of actinide elements and compounds. Part 8. The Actinide Halides. IAEA. 

The Absorption Spectra and Excited State Relaxation Properties of Lanthanide and Actinide Halide Vapor Complexes. I. ErCl3(AlCl3L, W.T. Camall, J.P. Hessler, H.R. Hoekstra, and C.W. Williams, J. Chem. Phys. 68, 4304-4309 (1978). 

Analysis of the Absorption Spectra of Complex Pentavalent Actinide Halides. LiUF6, o -NaUF6 and CsUFg. H.G. Hecht, J.G. Malm, J. Foropoulus, and W.T. Camall, J. Chem. Phys. 84, 3653-3662 (1986). 

The compounds known are summarized in Table 10.1. The only compound of an early actinide in the -1-2 state is Thl2, a metallic conductor which is probably Th + (e )2 (D)2-Certain heavier actinides form MX2 (Am, Cf, Es), which usually have the structure of the corresponding EuX2 and are thus genuine M + compounds. All four trihalides exist for all the actinides as far as Es, except for thorium and protactinium. Tetrafluorides exist for Th-Cm and the other tetrahalides as far as NpX4 (and in the gas phase in the case of PuCE). Pentahalides are only known for Pa, U, and Np whilst there are a few MFe (M = U-Pu), uranium is the only actinide to form a hexachloride. The known actinide halides are generally stable compounds most are soluble in (and hydrolysed by) water. 

The best-studied aqueous actinide halide systems are the fluorides and the chlorides. Fluoride and chloride ions are added to the actinyl centers in a stepwise fashion (Scheme 4). The end member in the actinyl fluoride system is the pentafluoride, An02F5 . For the uranyl analog, the U = O and U-F bond distances were found to be 1.79 and 2.18A respectively. The uranium tetrafluoride ion, U02F4 , has been isolated as a dimer with two bridging fluoride ligands. The U = O, U-Fterminai, uud U-Fbridging distauces for this complex were found to be 1.79, 2.15 to 2.20 A, and 2.30 A, respectively. 

Alkoxide and aryloxide ligands are excellent ligands for the actinides. As a result, these ligands have been studied extensively in the coordination chemistry and reactivity of tri-, tetra-, penta-, and hexavalent actinides. The alkoxides and aryloxides can be synthesized by a variety of routes the two most popular routes include direct reaction of actinide halides with alkali metal salts of the alkoxide or aryloxide of interest and protonolysis of actinide amides by alcohols. 

Some of the general trends among the actinide halides are as follows ... 

A wide variety of anionic actinide halide complexes are well known and typically are isolated with alkah or aUcahne-earth metal ions. The tendency and stability ofthe anionic complexes follow the trend F > Cl > Br I. The bivalent fluorides and... 

Actinide halides and oxyhalides are known to form numerous complexes with oxygen and nitrogen donor ligands and the preparation and properties of such compounds have recently been reviewed (12, 13). Relatively few protactinium halide complexes are known, but this situation reflects the lack of research rather than a tendency not to form complexes. However, there is sufficient information available for certain ligands to permit a comparison with the behavior of other actinide halides, and to illustrate the similarities and differences observed with the tetrahalides of thorium to plutonium inclusive and, to a lesser extent, with the protactinium and uranium pentahalides. 

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