Halogeno-, oxohalogeno-, and ethoxyhalogeno-complexes of quinquevalent protactinium, uranium, niobium, and tantalum

Metal penta-chlorides and -bromides react with tetraethylammonium chloride or triphenylphosphine oxide (tppo) in anhydrous ethanol to yield ethoxyhalogeno-complexes of the types NEt₄[M(OEt)₂X₄] and M(OEt)₂X₃,(tppo), respectively (M = Pa, Nb, or Ta; X = Cl or Br). In the presence of an excess of tetraethylammonium chloride reactions involving niobium(V), but not those involving protactinium(V) or tantalum(V), result directly in the formation of oxopentahalogeno-complexes, [NEt₄]₂[NbOX₅]. Analogous protactinium(V) complexes and [PaOCl₃-(tppo)₂] and [PaOBr₃(tppo)₂] crystallise when the appropriate ethoxy-complex and either tetraethylammonium chloride or triphenylphosphine oxide are heated with methyl cyanide containing ca. 0·5% water. These are the first examples of complexes containing the PaO group. Pentahalide complexes of the type [MX₅(tppo)₂](M = Pa and U) are obtained from reactions in anhydrous methyl cyanide or methylene dichloride. Some chemical properties, conductivity studies, and i.r. spectral and X-ray diffraction results are reported.