Organoneptunium chemistry is the chemical science exploring the properties, structure, and reactivity of organoneptunium compounds, which are organometallic compounds containing a carbon to neptunium chemical bond. [1] Several such compounds exist even though the element itself, neptunium, is man-made and highly radioactive: tricyclopentadienylneptunium-chloride, [2] [3] tetrakis(cyclopentadienyl)neptunium(IV) [4] and neptunocene Np(C8H8)2.