Actinide complexes oxyhalides

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. 

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. 

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