page_title: Neptunium
section_title: Organometallic
hierarchical_section_title: Neptunium / Chemistry and compounds / Organometallic
caption_attribution_description: Ball-and-stick model of the neptunocene molecule, Np(C8H8)2], as found in the solid state. X-ray crystallographic data from D. J. A. De Ridder, J. Rebizant, C. Apostolidis, B. Kanellakopulos and E. Dornberger (March 1996). "Bis(cyclooctatetraenyl)neptunium(IV)". Acta Cryst. C52 (3): 597-600. DOI:10.1107/S0108270195013047.. Model constructed in CrystalMaker 8.1. Image generated in Accelrys DS Visualizer.
context_page_description: Neptunium is a chemical element with the symbol Np and atomic number 93. A radioactive actinide metal, neptunium is the first transuranic element. Its position in the periodic table just after uranium, named after the planet Uranus, led to it being named after Neptune, the next planet beyond Uranus. A neptunium atom has 93 protons and 93 electrons, of which seven are valence electrons. Neptunium metal is silvery and tarnishes when exposed to air. The element occurs in three allotropic forms and it normally exhibits five oxidation states, ranging from +3 to +7. It is radioactive, poisonous, pyrophoric, and capable of accumulating in bones, which makes the handling of neptunium dangerous.
  Although many false claims of its discovery were made over the years, the element was first synthesized by Edwin McMillan and Philip H. Abelson at the Berkeley Radiation Laboratory in 1940. Since then, most neptunium has been and still is produced by neutron irradiation of uranium in nuclear reactors. The vast majority is generated as a by-product in conventional nuclear power reactors.
context_section_description: A few organoneptunium compounds are known and chemically characterized, although not as many as for uranium due to neptunium's scarcity and radioactivity. The most well known organoneptunium compounds are the cyclopentadienyl and cyclooctatetraenyl compounds and their derivatives. The trivalent cyclopentadienyl compound Np(C₅H₅)₃·THF was obtained in 1972 from reacting Np(C₅H₅)₃Cl with sodium, although the simpler Np(C₅H₅) could not be obtained. Tetravalent neptunium cyclopentadienyl, a reddish-brown complex, was synthesized in 1968 by reacting neptunium(IV) chloride with potassium cyclopentadienide:
  NpCl₄ + 4 KC₅H₅ → Np(C₅H₅)₄ + 4 KCl
  It is soluble in benzene and THF, and is less sensitive to oxygen and water than Pu(C₅H₅)₃ and Am(C₅H₅)₃. Other Np(IV) cyclopentadienyl compounds are known for many ligands: they have the general formula (C₅H₅)₃NpL, where L represents a ligand.Neptunocene, Np(C₈H₈)₂, was synthesized in 1970 by reacting neptunium(IV) chloride with K₂(C₈H₈). It is isomorphous to uranocene and plutonocene, and they behave chemically identically: all three compounds are insensitive to water or dilute bases but are sensitive to air, reacting quickly to form oxides, and are only slightly soluble in benzene and toluene. Other known neptunium cyclooctatetraenyl derivatives include Np(RC₈H₇)₂ (R = ethanol, butanol) and KNp(C₈H₈)·2THF, which is isostructural to the corresponding plutonium compound. In addition, neptunium hydrocarbyls have been prepared, and solvated triiodide complexes of neptunium are a precursor to many organoneptunium and inorganic neptunium compounds.
caption: Structure of neptunocene
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