Protactinium complexes with triphenylphosphine

Protactinium pentachloride (42) and pentabromide (43) form both 1 1 and 1 2 complexes with phosphine oxides, the former being analogous to those formed by niobium, tantalum, and uranium pentahalides (26, 42, 43). Unlike niobium and tantalum pentachloride (42, 64) however, they do not react with excess triphenylphosphine oxide (TPPO) to form... 

Both protactinium pentachloride and pentabromide react with triphenylphosphine sulfide and selenide to form stable 1 1 complexes... 

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