Oxyhalides, actinide

Although not binary compounds, a discussion of actinide oxyhalides is not out of place here. A number of these are formed by the earlier actinides, another difference between the 4f and 5f metals. 

Thorium forms one series of halides, another one of oxyhalides, and also a series of double or complex halides. In general, stability of these compounds toward heat decreases as die atomic weight of die halogen increases. These compounds are often isostructural with the corresponding compounds of other actinide elements in the (IV) oxidation state. 

Thousands of compounds of the actinide elements have been prepared, and the properties of some of the important binary compounds are summarized in Table 8 (13,17,18,22). The binary compounds with carbon, boron, nitrogen, silicon, and sulfur are not included these are of interest, however, because of their stability at high temperatures. A large number of ternary compounds, including numerous oxyhalides, and more complicated compounds have been synthesized and characterized. These include many intermediate (nonstoicliiometric) oxides, and besides the nitrates, sulfates, peroxides, and carbonates, compounds such as phosphates, arsenates, cyanides, cyanates, thiocyanates, selenocyanates, sulfites, selenates, selenites, teflurates, tellurites, selenides, and tellurides. 

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 absorption spectra of these complexes can be obtained in the visible and near infrared region using solutions of the triphenylphos-phonium salts, but if the ultraviolet spectrum is desired, the complex must be formed in solution using an aliphatic quaternary ammonium halide and the actinide trihalide or oxyhalide. 

During the past few years numerous new penta- and tetravalent protactinium halides and oxyhalides have been characterized, but of the. possible trivalent compounds only Pal3 has been reported. The presently known halides and oxyhalides are compared with those of the other actinide elements in Tables I and II, respectively. It is immediately... 

Oxyhalides of the actinides are known mainly for the TABLE XIII Other Early Actinide Compounds ... 

Estimates of enthalpies of formation of a large group of higher actinide halides and oxyhalides have also been made by the Orsay thermochromatography group [119]. We have not accepted their values because they represent tracer-level phenomena that hypothesize a number of compounds not seen on the macroscopic level or that decompose at temperatures alleged for their thermo-chromatographic deposition temperatures. 

There are many oxyhalides of actinide oxidation states 34- through 6-t-. In general these are more stable than a mixture of oxide and halide, e.g. 

A comprehensive review of actinide halides and oxyhalides is found in a book... 

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