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 <i>P</i>2₁/<i>c</i> for the ammonium compound and <i>C</i>2/<i>c</i> 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 <i>I</i>4/<i>mmm</i> 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 <i>C</i>2<i>/c</i>, and (Me₄N)­PaF₆, an eight-coordinate Pa compound forming infinite chains and crystallizing in the orthorhombic space group <i>Pnnm</i>. 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