Pentahalides, actinide

S). Similar compounds with bis(diphenylphoBphino)methane disulfide and the corresponding diselenide have also been prepared (Table X). These are the first examples of coordination of sulfur and selenium donors to actinide pentahalides and it will be interesting to see whether uranium pentahalides behave in a similar fashion since the analogous niobium(V) and tantalum(V) compounds are also known (43). 

Even fewer complexes with nitrogen donor ligands have been reported and all are methyl cyanide adducts (Tables X and XI). Protactinium pentabromide forms a soluble 1 3 complex in contrast to the 1 1 complexes formed by niobium and tantalum pentahalides (46). Other actinide pentahalide-methyl cyanide complexes are still unknown. Protactinium tetrachloride, tetrabromide, and tetraiodide react with anhydrous, oxygen-free methyl cyanide to form slightly soluble 1 4 complexes (44, 48) which are isostructural with their actinide tetrahalide analogs. 

The main types of actinide(V) oxohalide are given in Table 52. The oxohalides can be prepared by heating the parent pentahalide with the appropriate quantity of oxygen for example, Pa2OCl8 is obtained by this method at 400 °C. NpOF3 has been prepared by heating the hydrate in dry HF at 100-150 °C. 

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. 

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. 

The pentahalides of Pa and U generally add another ligand to form octahedral complexes of the form AnXg . The fluorides of Np and Pu have been isolated as AnFg , AnFy and AnFs . The predominate anionic complexes for the hexavalent actinides are based on UFg. Uranium hexafluoride will add up to two additional fluoride ions to form UFy andUFs using standard techniques. The unique UFg ion is formed from the thermal decomposition of Na2UFs. 

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