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Neptunocene
Names
	IUPAC name Bis(η8-cyclooctatetraenyl)neptunium(IV)
	Other names Neptunium cyclooctatetraenide; Np(COT)2
Identifiers
CAS Number	154974-81-9 ;
3D model (JSmol)	Interactive image;
	InChI InChI=1S/2C5H5.Np/c21-2-4-5-3-1;/h21-5H;/q2*-1;+2 Key: FXDJOXAJBKYPFW-UHFFFAOYSA-N;
	SMILES c1=c[cH-]c=c[cH-]c=c1.[Np+4].c1=c[cH-]c=c[cH-]c=c1;
Properties
Chemical formula	C16H16Np
Molar mass	445 g·mol−1
Appearance	dark brown crystals as a solid, yellow in dilute solution
Solubility in water	insoluble, does not react with water
Solubility in chlorocarbons	sparingly soluble (ca. 0.5 g/L)
Hazards
	Occupational safety and health (OHS/OSH):
Main hazards	radiation hazard, pyrophoric
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Neptunocene, Np(C₈H₈)₂, is an organoneptunium compound composed of a neptunium atom sandwiched between two cyclooctatetraenide (COT^2-) rings. As a solid it has a dark brown/red colour but it appears yellow when dissolved in chlorocarbons, in which it is sparingly soluble.^[1]^[2]^[3]^[4]^[5] The compound is quite air-sensitive.^[1]^[2]^[5]

It was one of the first organoneptunium compounds to be synthesised, and is a member of the actinocene family of actinide-based metallocenes.^[2]

Structure

The sandwich structure of neptunocene has been determined by single crystal XRD.^[4] The COT^2- rings are found to be planar with 8 equivalent C–C bonds of 1.385 Å length, and sit parallel in an eclipsed conformation. The Np–COT distance (to the ring centroid) is 1.909 Å and the individual Np–C distances are 2.630 Å.^[4]

Neptunocene assumes a monoclinic crystal structure (P2₁/n space group) which is isomorphous to uranocene and thorocene but not to plutonocene.^[4]

Synthesis and properties

Neptunocene was first synthesised in 1970 by reacting neptunium(IV) chloride (NpCl₄) with dipotassium cyclooctatetraenide (K₂(C₈H₈)) in diethyl ether or THF:^[1]

NpCl₄ + 2 K₂(C₈H₈) → Np(C₈H₈)₂ + 4 KCl

The same reaction conditions have been routinely reproduced since then for the synthesis of the compound.^[3]^[4]

The three actinocenes uranocene, neptunocene, and plutonocene share virtually identical chemistry: they do not react in the presence of water or dilute base, but are very air-sensitive, quickly forming oxides.^[1]^[2]^[3] All three are only slightly soluble (up to about 10⁻³ M concentrations) in aromatic or chlorinated solvents such as benzene, toluene, carbon tetrachloride or chloroform.^[1]^[2]^[4]^[5]

References

^ ^a ^b ^c ^d ^e Karraker, David G.; Stone, John Austin.; Jones, Erwin Rudolph.; Edelstein, Norman. (1970). "Bis(cyclooctatetraenyl)neptunium(IV) and bis(cyclooctatetraenyl)plutonium(IV)". Journal of the American Chemical Society. 92 (16): 4841–4845. doi:10.1021/ja00719a014. ISSN 0002-7863. Archived from the original on 2024-05-03. Retrieved 2021-03-22.
^ ^a ^b ^c ^d ^e Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. pp. 1278–1280. ISBN 9780750633659.
^ ^a ^b ^c Eisenberg, David C.; Streitwieser, Andrew; Kot, Wing K. (1990). "Electron transfer in organouranium and transuranium systems". Inorganic Chemistry. 29 (1): 10–14. doi:10.1021/ic00326a004. ISSN 0020-1669. Archived from the original on 2024-05-03. Retrieved 2021-03-22.
^ ^a ^b ^c ^d ^e ^f Ridder, D. J. A. De; Rebizant, J.; Apostolidis, C.; Kanellakopulos, B.; Dornberger, E. (1996). "Bis(cyclooctatetraenyl)neptunium(IV)". Acta Crystallographica Section C. 52 (3): 597–600. doi:10.1107/S0108270195013047. ISSN 1600-5759. Archived from the original on 2021-06-12. Retrieved 2021-03-22.
^ ^a ^b ^c Yoshida, Zenko; Johnson, Stephen G.; Kimura, Takaumi; Krsul, John R. (2006). "Neptunium". In Morss, Lester R.; Edelstein, Norman M.; Fuger, Jean (eds.). The Chemistry of the Actinide and Transactinide Elements (PDF). Vol. 3 (3rd ed.). Dordrecht, the Netherlands: Springer. pp. 699–812. doi:10.1007/1-4020-3598-5_6. Archived from the original (PDF) on 2018-01-17. Retrieved 2016-08-07.