Editing Protactinium (section)

===Organometallic compounds===
[[File:Uranocene-3D-balls.png|thumb|upright|The proposed structure of the protactinocene (Pa(C<sub>8</sub>H<sub>8</sub>)<sub>2</sub>) molecule]]
Protactinium(IV) forms a tetrahedral complex tetrakis(cyclopentadienyl)protactinium(IV) (or Pa(C<sub>5</sub>H<sub>5</sub>)<sub>4</sub>) with four [[Cyclopentadienyl complex|cyclopentadienyl]] rings, which can be synthesized by reacting protactinium(IV) chloride with molten Be(C<sub>5</sub>H<sub>5</sub>)<sub>2</sub>. One ring can be substituted with a halide atom.<ref name="g1278">[[#Greenwood|Greenwood]], pp. 1278–1279</ref> Another organometallic complex is the golden-yellow bis(π-cyclooctatetraene) protactinium, or [[protactinocene]] (Pa(C<sub>8</sub>H<sub>8</sub>)<sub>2</sub>), which is analogous in structure to [[uranocene]]. There, the metal atom is sandwiched between two [[cyclooctatetraene]] ligands. Similar to uranocene, it can be prepared by reacting protactinium tetrachloride with dipotassium [[cyclooctatetraene|cyclooctatetraenide]] (K<sub>2</sub>C<sub>8</sub>H<sub>8</sub>) in [[tetrahydrofuran]].<ref name="cene" />