Structural and Spectroscopic Studies of Fluoroprotactinates

Seven protactinium­(V) fluoride compounds have been synthesized, and their crystal structures and Raman spectra are reported. (NH4)2PaF7, K2PaF7, Rb2PaF7, and Cs2PaF7 were found to crystallize in the monoclinic space group P21/c for the ammonium compound and C2/c for the K+-, Rb+-, and Cs+-containing compounds, with nine-coordinate Pa forming infinite chains through fluorine bridges. Na3PaF8 crystallizes in the tetragonal space group I4/mmm with eight-coordinate Pa in tetragonal geometry, while tetramethylammonium fluoroprotactinate shows two different structures: (Me4N)2(H3O)­PaF8, an eight-coordinate molecular compound crystallizing in the monoclinic space group C2/c, and (Me4N)­PaF6, an eight-coordinate Pa compound forming infinite chains and crystallizing in the orthorhombic space group Pnnm. A comparison of solid- and solution-state Raman data indicates that the PaF8– anion could be the predominant Pa­(V) complex in concentrated solutions of aqueous HF.