Protactinium tetravalent, compounds

Protactinium exists naturally in the pentavalent state and although it is possible, by employing strongly reducing conditions, to obtain the tetravalent state in solution and in solid compounds this state is, in general, unstable in the presence of oxygen, exceptions being the tetra-fluoride and dioxide, which are stable in the atmosphere. The potential... 

During the past few years numerous new penta- and tetravalent protactinium halides and oxyhalides have been characterized, but of the. possible trivalent compounds only Pals been reported. The presently... 

Complex fluorides containing tetravalent protactinium and the alkali fluorides (Li, Na, K, Rb, and NH4) were prepared from MF -j- PaF4 starting mixtures and by reducing MF-PaF compounds at 400°—500°C. using pure hydrogen, obtained from UH3. The x-ray results on compounds obtained by these methods are presented in Table I. 

Protactinium oxides can be stabilized in the tetravalent and pentavalent state. The most stable oxide phase obtained by the burning of metal or protactinium compounds is the white pentoxide, Pa205. The stmcture of the pentoxide is related to fluorite and has cubic symmetry. Pa02 is a black solid that crystallizes in the cubic fluorite stmcture. 

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