Protactinium halide complexes

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. 

DMSO) complexes (18) are relatively unstable toward oxidative decomposition. The known complexes are listed in Table X, together with infrared data, and are compared with the complexes formed by other actinide halides in Table XI. The protactinium(IV) complexes have been prepared by reacting the anhydrous halide with the appropriate ligand in nonaqueous, oxygen-free solvents such as methylene dichloride, chloroform, or methyl cyanide. 

The protactinium(IV) fluoro complexes have been prepared either by hydrogen reduction of a pentavalent complex at 400°C or by heating together appropriate amounts of MF and PaF4 in sealed vessels. The reaction between ammonium fluoride and protactinium tetrafluoride to yield (NH4)4PaFg, the only octafluoro complex known, takes place when the component halides are ground together at room temperature (4,114). 

It is convenient to discuss protactinium(IV) and (V) bromo and iodo complexes together since they have only been prepared by reacting together the component halides in anhydrous methyl cyanide (40, 46, 48). Thus NMe4PaBrg, NEtiPaBrg, and PhgMeAsPala are isolated (40,46) by removal of solvent in vacuo at room temperature. Hexabromo-niobates(V) and tantalates(V) have been prepared in a similar manner (46). Attempts to obtain octabromo complexes for these three elements have been unsuccessful. The orange hexabromoprotactinates(V) are... 

Tn reviewing the chemistry of the actinides as a group, the simplest approach is to consider each valence state separately. In the tervalent state, and such examples of the divalent state as are known, the actinides show similar chemical behavior to the lanthanides. Experimental diflB-culties with the terpositive actinides up to plutonium are considerable because of the ready oxidation of this state. Some correlation exists with the actinides in studies of the lanthanide tetrafluorides and fluoro complexes. For other compounds of the 4-valent actinides, protactinium shows almost as many similarities as dijSerences between thorium and the uranium-americium set thus investigating the complex forming properties of their halides has attracted attention. In the 5- and 6-valent states, the elements from uranium to americium show a considerable degree of chemical similarity. Protactinium (V) behaves in much the same way as these elements in the 5-valent state except for water, where its hydrolytic behavior is more reminiscent of niobium and tantalum. 

Tetrachloride and tetrabromide complexes are known for thorium, protactinium, uranium, neptunium, and plutonium. These are similarly produced by halide-based oxidation of metals or hydrides, or by halogenation of oxides. A common structural type is reported for most compounds. The reported structure of thorium tetrachloride reveals that the coordination geometry about the metal is dodecahedral.The compounds are generally volatile and can be sublimed. The gas-phase electron diffraction structure of suggests that the molecule is... 

Binary halides. A number of homoleptic halides of pentavalent protactinium, uranium, and neptunium have been reported. In particular, the fluoride complexes AnFs are prepared by high... 

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