neptunium

properties
[ Rn ] 5 f 4 6 d 1 7 s 2 93 Np Periodic table
General
Name , symbol , atomic number	Neptunium, Np, 93
Element category	Actinoids
Group , period , block	Ac , 7 , f
Appearance	silvery
CAS number	7439-99-8
EC number	231-108-8
ECHA InfoCard	100.028.280
Mass fraction of the earth's envelope	4 · 10 −14  ppm
Atomic
Atomic mass	237.0482 u
Atomic radius	(α-Np) 130 pm
Electron configuration	[ Rn ] 5 f 4 6 d 1 7 s 2
1. Ionization energy	6th.26554 (25) eV ≈ 604.53 kJ / mol
2. Ionization energy	11.5 (4) eV ≈ 1 110 kJ / mol
3. Ionization energy	19th.7 (4) eV ≈ 1 900 kJ / mol
4. Ionization energy	33.8 (4) eV ≈ 3 260 kJ / mol
5. Ionization energy	48.0 (1.9) eV ≈ 4 630 kJ / mol
Physically
Physical state	firmly
Modifications	3
Crystal structure	orthorhombic
density	20.45 g / cm 3
Melting point	912 K (639 ° C)
boiling point	4175 K (3902 ° C)
Molar volume	11.59 · 10 −6 m 3 · mol −1
Heat of evaporation	1420 kJ / mol
Heat of fusion	39.91 kJ mol −1
Electric conductivity	0.82 A V −1 m −1 at 293 K
Thermal conductivity	6.30 W m −1 K −1 at 300 K
Chemically
Oxidation states	+3, +4, +5 , +6, +7
Normal potential	−1.79  V (Np 3+ + 3 e - → Np)
Electronegativity	1.36 ( Pauling scale )
Isotopes
isotope NH t 1/2 ZA ZE (M eV ) ZP 235 Np {syn.} 396.1 d α 5.192 231 Pa ε 0.124 235 U 236 Np {syn.} 1.54 · 10 5 a ε 0.940 236 U β - 0.490 236 Pu α 5.020 232 Pa 237 Np {syn.} 2.144 x 10 6 a α 4,959 233 Pa 238 Np {syn.} 2.117 d β - 238 Pu 239 Np {syn.} 2,355 d β - 239 Pu
For other isotopes see list of isotopes
Hazard and safety information
Radioactive
GHS hazard labeling no classification available
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Neptunium is a chemical element with the element symbol Np and the atomic number 93. In the periodic table it is in the group of actinides ( 7th period , f-block ). Neptunium is the first of the so-called transuranic elements , which, apart from traces of neptunium and plutonium , no longer occur naturally on earth . Neptunium is a toxic and radioactive heavy metal . It was named after the planet Neptune , which succeeds the planet Uranus . Neptunium follows uranium in the periodic table , followed by plutonium, the naturally occurring element on earth with the highest atomic number.

history

Neptunium is the first of the so-called transuranic elements , the existence and properties of which have long been controversial among physicists.

Possibility of transurans

Mendeleev's periodic table from 1871 with a gap for Neptunium at the bottom, behind uranium ( U = 240 )

Already in Mendeleev's periodic table of elements from 1871 there was a gap behind uranium, the heaviest known element at the time.

More than sixty years later, Ida Noddack commented in May 1934 on the gaps in Mendeleev's periodic table that existed at the time and, at the end of her work, considered the possibility of transuranics. A few weeks later, Enrico Fermi published three papers on this topic. In September 1934, Noddack took a critical look at the supposed discovery of element 93 by Fermi. In her remarks she took u. a. the discovery of neutron-induced nuclear fission in advance: “It is conceivable that when heavy nuclei are bombarded with neutrons, these nuclei disintegrate into several larger fragments, which are isotopes of known elements, but not neighbors of the irradiated elements. “Regardless of Noddack's objections, at that time all working groups followed the hypothesis that irradiating uranium with neutrons always produced elements heavier than uranium.

At the Kaiser Wilhelm Institute for Chemistry in Berlin , Otto Hahn , Fritz Straßmann and Lise Meitner also went in search of transuranium elements during this time. Over many years they tried to elucidate the processes observed in Fermi's experiments. While searching for heavier elements, they found some substances that they described as evidence of transuranium elements.

Irène Joliot-Curie and Paul Savitch also devoted themselves to the search for transurans in Paris from 1937 onwards . In 1937/1938 her working group carried out experiments in which an element similar to lanthanum was released, the chemical identification of which turned out to be extremely difficult and which they interpreted as a possible evidence of element 93 based on the assumptions about chemical relationships at the time. They considered it possible that the substance discovered “ has an atomic number of 93 and that the transuranic elements found by Hahn, Meitner and Straßmann to date are elements 94 to 97. "

In fact, the observations made by Hahn, Straßmann, Meitner, Joliot-Curie and Savitch were not evidence of the transuranic elements they were looking for, but rather the nuclear fission of uranium, which was still unrecognized at the time . Their research therefore contributed comparatively little to the knowledge about the chemical element later called "neptunium", since they considered the numerous fission products formed during the nuclear fission of uranium to be evidence of the sought-after transuranic elements and described them as such in their publications.

Exploration of Neptunium

Edwin M. McMillan and Philip H. Abelson synthesized the radioactive element neptunium for the first time in 1940 by bombarding uranium with neutrons.

${\displaystyle \mathrm {^{238}_{\ 92}U\ +\ _{0}^{1}n\ \longrightarrow \ _{\ 92}^{239}U\ {\xrightarrow[{23\ min}]{\beta ^{-}}}\ _{\ 93}^{239}Np\ {\xrightarrow[{2,355\ d}]{\beta ^{-}}}\ _{\ 94}^{239}Pu} }$

The times given are half-lives .

Arthur C. Wahl and Glenn T. Seaborg discovered the neptunium isotope ²³⁷ Np in 1942 . It arises from ²³⁷ U, which is a β-emitter with a half-life of around 7 days, or through an (n, 2n) process from ²³⁸ U. ²³⁷ Np is an α-emitter with a half-life of 2.144 · 10 ⁶ years.

${\displaystyle \mathrm {^{238}_{\ 92}U\ {\xrightarrow[{}]{(n,\ 2n)}}\ _{\ 92}^{237}U\ {\xrightarrow[{7\ d}]{\beta ^{-}}}\ _{\ 93}^{237}Np\ {\xrightarrow[{2,144\ x\ 10^{6}\ a}]{\alpha }}\ _{\ 91}^{233}Pa} }$

In 1950 the Neptunium isotopes ²³¹ Np, ²³² Np and ²³³ Np were generated from ²³³ U, ²³⁵ U and ²³⁸ U by bombardment with deuterons . In 1958, the Neptunium isotopes ²³⁴ Np, ²³⁵ Np and ²³⁶ Np were generated from highly enriched ²³⁵ U by bombardment with deuterons . The 1-hour Neptunium activity, which was previously assigned to the ²⁴¹ Np, on the other hand, belongs to the isotope ²⁴⁰ Np.

Extraction and presentation

Extraction of Neptunium isotopes

Neptunium is a by-product of energy generation in nuclear reactors . One tonne of spent nuclear fuel can contain around 500 grams of neptunium. The resulting neptunium consists almost exclusively of the isotope ²³⁷ Np. It arises from the uranium isotope ²³⁵ U through double neutron capture and subsequent β-decay .

${\displaystyle \mathrm {^{235}_{\ 92}U\ +\ _{0}^{1}n\ \longrightarrow \ _{\ 92}^{236}U_{m}\ {\xrightarrow[{120\ ns}]{}}\ _{\ 92}^{236}U\ +\ \gamma } }$

${\displaystyle \mathrm {^{236}_{\ 92}U\ +\ _{0}^{1}n\ \longrightarrow \ _{\ 92}^{237}U\ {\xrightarrow[{6,75\ d}]{\beta ^{-}}}\ _{\ 93}^{237}Np} }$

Depiction of elemental Neptunium

Metallic neptunium can be obtained from its compounds by reduction . First, neptunium (III) fluoride was reacted with elemental barium or lithium at 1200 ° C.

${\displaystyle {\ce {2 NpF3 + 3 Ba -> 2 Np + 3 BaF2}}}$

properties

Physical Properties

Neptunium metal has a silver appearance, is chemically reactive and exists in at least three different modifications:

Modifications at atmospheric pressure

Phase designation	stable temperature range	Density (temperature)	Crystal system
α-Np		20.25 g / cm 3 (20 ° C)	orthorhombic
β-Np	above 280 ° C	19.36 g / cm 3 (313 ° C)	tetragonal
γ-Np	above 577 ° C	18.0 g / cm 3 (600 ° C)	cubic

Neptunium has one of the highest densities of all elements. Along with rhenium , osmium , iridium and platinum , it is one of the few elements that have a density higher than 20 g / cm ³ .

Chemical properties

Neptunium forms a number of compounds in which it can exist in the oxidation states +3 to +7. Thus, together with plutonium, neptunium has the highest possible oxidation level of all actinides. In aqueous solution, the neptunium ions have characteristic colors, the Np ³⁺ ion is purple-violet, Np ⁴⁺ yellow-green, Np ^V O ₂ ⁺ green, Np ^VI O ₂ ²⁺ pink-red and Np ^VII O ₂ ³⁺ deep green.

Biological aspects

A biological function of the neptunium is not known. Anaerobic microorganisms can reduce Np (V) to Np (IV) using Mn (II / III) and Fe (II) species. The factors that influence the biosorption and bioaccumulation of neptunium by bacteria were also examined .

Isotopes

A total of 20 isotopes and 5 nuclear isomers are known of neptunium . The longest-lived isotopes are ²³⁷ Np with 2.144 million years, ²³⁶ Np with 154,000 years and ²³⁵ Np with 396.1 days half-life. The remaining isotopes and core isomers have half-lives between 45 nanoseconds ( ^{237 m 1} Np) and 4.4 days ( ²³⁴ Np).

• ²³⁵ Np decays with a half-life of 396.1 days in 99.99740% of cases by electron capture to uranium ²³⁵ U and in 0.00260% of cases by alpha decay to protactinium ²³¹ Pa, which is one step behind ²³⁵ U on the uranium actinium Row is located.

• With a half-life of 154,000 years, ²³⁶ Np decays in 87.3% of cases by electron capture to uranium ²³⁶ U, in 12.5% ​​of cases by beta decay to plutonium ²³⁶ Pu and in 0.16% of cases by alpha decay to protactinium ²³² Pa. The uranium ²³⁶ U is part of the thorium series and decays at 23.42 million years to its official initial nuclide thorium ²³² Th. The ²³⁶ Pu decays with a half-life of 2.858 years through α-decay to the intermediate ²³² U, which with a Half-life of 68.9 yearsdecaysto ²²⁸ Th, which is on the main strand of the series.

• ²³⁷ Np decays with a half-life of 2.144 million years through alpha decay to protactinium ²³³ Pa. ²³⁷ Np is the official starting point of the Neptunium series , a decay chain thatendsat the isotope thallium ²⁰⁵ Tl.

See also : List of Neptunium Isotopes

Cleavage

A sample of neptunium metal ( ²³⁷ Np), encased by a thick layer of tungsten and nickel (shiny) in shells made of enriched uranium (tarnished black).

As with all transurane nuclides, neutron-induced nuclear fission is also possible with the Np isotopes. The isotopes with an odd number of neutrons in the nucleus - ²³⁶ Np of the long-lived ones - have large effective cross- sections for fission by thermal neutrons ; at ²³⁶ Np it is 2600  barns , so it is "easy to split".

With the ²³⁷ Np occurring in the nuclear reactor fuel, this cross section is only 20 millibarns. However, due to other nuclear physical properties, this isotope is suitable for maintaining a chain reaction with the fission by fast neutrons in the pure material . At the Los Alamos National Laboratory , its critical mass was experimentally determined to be around 60 kg. Therefore, ²³⁷ Np is a possible material for nuclear weapons.

use

The ²³⁷ Np produced in nuclear reactors from ²³⁵ U can be used to obtain ²³⁸ Pu for use in radionuclide batteries . To do this, it is separated from the spent reactor fuel (along with insignificant amounts of other neptunium isotopes) and put into fuel rods that contain only neptunium. These are put back into the nuclear reactor, where they are again irradiated with neutrons; ²³⁸ Pu is incubated from the ²³⁷ Np .

${\displaystyle \mathrm {^{237}_{\ 93}Np\ +\ _{0}^{1}n\ \longrightarrow \ _{\ 93}^{238}Np\ {\xrightarrow[{2,117\ d}]{\beta ^{-}}}\ _{\ 94}^{238}Pu} }$

The times given are half-lives .

links

Neptunium in the oxidation states +3 to +7 in aqueous solution.

→ Category: Neptunium compound

Oxides

Oxides are known in the stages +4 to +6: Neptunium (IV) oxide (NpO ₂ ), Neptunium (V) oxide (Np ₂ O ₅ ) and Neptunium (VI) oxide (NpO ₃  · H ₂ O) . Neptunium dioxide (NpO ₂ ) is the most chemically stable oxide of neptunium and is used in nuclear fuel rods .

Halides

For neptunium, halides in the oxidation states +3 to +6 are known.

For level +3 all compounds of the four halogens fluorine , chlorine , bromine and iodine are known. In addition, it forms halides in the levels +4 to +6.

In the +6 oxidation state, neptunium hexafluoride (NpF ₆ ) is of particular importance. It is an orange-colored solid with very high volatility that changes to a gaseous state at 56 ° C. In this property it is very similar to uranium hexafluoride and plutonium hexafluoride , so it can also be used in enrichment and isotope separation .

Oxidation number	F.	Cl	Br	I.
+6	Neptunium (VI) fluoride NpF 6 orange
+5	Neptunium (V) fluoride NpF 5 light blue
+4	Neptunium (IV) fluoride NpF 4 green	Neptunium (IV) chloride NpCl 4 red-brown	Neptunium (IV) bromide NpBr 4 dark red
+3	Neptunium (III) fluoride NpF 3 violet	Neptunium (III) chloride NpCl 3 green	Neptunium (III) bromide NpBr 3 green	Neptunium (III) iodide NpI 3 violet

Organometallic compounds

Analogous to uranocene , an organometallic compound in which uranium is complexed by two cyclooctatetraene ligands, the corresponding complexes of thorium , protactinium , plutonium, americium and also of neptunium, (η ⁸ -C ₈ H ₈ ) ₂ Np, were prepared.

safety instructions

Classifications according to the CLP regulation are not available because they only include chemical hazard and play a completely subordinate role compared to the hazards based on radioactivity.

literature

• Gmelin's Handbook of Inorganic Chemistry , System No. 71, Transuranium Elements:
  • Part A 1 II, pp. 14-17
  • Part A 2, pp. 100-118, 180-181, 250-253, 258
  • Part B 1, pp. 1-9
  • Part C, pp. 2-3, 7-10, 82-83, 92-114, 157-159, 174-175, 189-194, 200-201, 228, 245, 248-249, 251, 272
  • Part D 1, pp. 27-30, 37-58, 100-105
• Cornelius Keller : The chemistry of Neptunium , in: Fortschr. chem. Forsch. , 1969/70 , 13/1 , pp. 1–124 ( doi: 10.1007 / BFb0051170 ).
• Zenko Yoshida, Stephen G. Johnson, Takaumi Kimura, John R. Krsul: Neptunium , in: Lester R. Morss, Norman M. Edelstein, Jean Fuger (eds.): The Chemistry of the Actinide and Transactinide Elements , Springer, Dordrecht 2006 ; ISBN 1-4020-3555-1 , pp. 699-812 ( doi: 10.1007 / 1-4020-3598-5_6 ).
• S. Fried, NR Davidson: The Basic Dry Chemistry of Neptunium , (1947) Report MDDC-1332, United States Atomic Energy Commission - Argonne National Laboratory, Declassified: July 18, 1947.
• AF: Neptunium on the Moon , Die Zeit , March 3, 1972, No. 9.
• GA Burney, RM Harbor: Radiochemistry of Neptunium , Report NAS-NS-3060, United States Atomic Energy Commission, 1974 ( PDF ; 6.7 MB).
• Kurt Starke : Zur Frühgeschichte des Neptunium , in: Isotopes in Environmental and Health Studies , 1990 , 26  (8), pp. 349-351 ( doi: 10.1080 / 10256019008624331 ).

Web links

Commons : Neptunium  - collection of images, videos and audio files

Wiktionary: Neptunium  - explanations of meanings, word origins, synonyms, translations

• Entry to Neptunium. In: Römpp Online . Georg Thieme Verlag, accessed on January 3, 2015.
• Robin Giroux: Neptunium , Chemical & Engineering News, 2003.
• Science online lexicons: Neptunium compounds in the lexicon of chemistry.

Individual evidence

1. ↑ ^{a b c d e f} Harry H. Binder: Lexicon of the chemical elements , S. Hirzel Verlag, Stuttgart 1999, ISBN 3-7776-0736-3 , pp. 413-419.
2. ↑ The values ​​of the atomic and physical properties (info box) are taken from www.webelements.com (Neptunium) , unless otherwise stated .
3. ↑ ^{a b c d e} Entry on neptunium in Kramida, A., Ralchenko, Yu., Reader, J. and NIST ASD Team (2019): NIST Atomic Spectra Database (ver. 5.7.1) . Ed .: NIST , Gaithersburg, MD. doi : 10.18434 / T4W30F ( https://physics.nist.gov/asd ). Retrieved June 13, 2020.
4. ↑ ^{a b c d e} Entry on neptunium at WebElements, https://www.webelements.com , accessed on June 13, 2020.
5. ^ ^{A b} A. F. Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 102nd edition. Walter de Gruyter, Berlin 2007, ISBN 978-3-11-017770-1 , p. 2149.
6. ↑ The hazards emanating from radioactivity do not belong to the properties to be classified according to the GHS labeling. With regard to other hazards, this element has either not yet been classified or a reliable and citable source has not yet been found.
7. ↑ Ida Noddack: The Periodic System of the Elements and its gaps , in: Angewandte Chemie , 1934 , 47  (20), pp. 301-305 ( doi: 10.1002 / ange.19340472002 ).
8. ^ E. Fermi: Radioactivity Induced by Neutron Bombardment , in: Nature , 1934 , 133 , pp. 757-757 ( doi: 10.1038 / 133757a0 ).
9. ↑ E. Fermi: Element No. 93 , in: Nature , 1934 , 133 , pp. 863-864 ( doi: 10.1038 / 133863e0 ).
10. ^ E. Fermi: Possible Production of Elements of Atomic Number Higher than 92 , in: Nature , 1934 , 133 , pp. 898-899 ( doi: 10.1038 / 133898a0 ).
11. ↑ Ida Noddack: About the element 93 , in: Angewandte Chemie , 1934 , 47  (37), pp. 653-655 ( doi: 10.1002 / anie.19340473707 ).
12. ^ I. Curie, P. Savitch: Sur les radioéléments formés dans l'uranium irradié par les neutrons II . Le Journal de Physique et le Radium 9 (1938) pp. 355-359.
13. ^ E. McMillan, PH Abelson: Radioactive Element 93 , in: Physical Review , 1940 , 57 , pp. 1185-1186 ( doi: 10.1103 / PhysRev.57.1185.2 ).
14. ^ New elements , in: Angewandte Chemie , 1947 , 59  (2), pp. 61–61.
15. ^ AB Garrett: The Chemistry of Elements 93, 94, 95 and 96 (Neptunium, Plutonium, Americium and Curium) , in: The Ohio Journal of Science , 1947 , XLVII  (3), pp. 103-106 ( PDF ).
16. ↑ K. Wirtz: The new elements Neptunium, Plutonium, Americium and Curium. In: Journal for Nature Research . 1, 1946, pp. 543-544 ( online ).
17. ↑ LB Magnusson, SG Thompson, GT Seaborg: New Isotopes of Neptunium , in: Physical Review , 1950 , 78  (4), pp. 363-372 ( doi: 10.1103 / PhysRev.78.363 ).
18. ↑ JE Gindler, JR Huizenga, DW Engelkemeir: Neptunium Isotopes: 234, 235, 236 , in: Physical Review , 1958 , 109  (4), pp. 1263-1267 ( doi: 10.1103 / PhysRev.109.1263 ).
19. ↑ Richard M. Lessler, Maynard C. Michel: Isotopes Np ²⁴⁰ and Np ²⁴¹ , in: Physical Review , 1960 , 118  (1), pp. 263-264 ( doi: 10.1103 / PhysRev.118.263 ).
20. ↑ Klaus Hoffmann: Can you make gold? Crooks, jugglers and scholars. From the history of the chemical elements . Urania-Verlag, Leipzig, Jena, Berlin 1979, p. 233 .
21. ^ AF Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 102nd edition. Walter de Gruyter, Berlin 2007, ISBN 978-3-11-017770-1 , p. 1956.
22. ^ The Biochemical Periodic Tables - Neptunium .
23. ↑ JE Banaszak, SM Webb, BE Rittmann, J.-F. Gaillard, DT Reed: Fate of Neptunium in an anaerobic, methanogenic microcosm , in: Mat Res Soc Symp Proc. , 1999 , 556 , pp. 1141-1149 ( abstract ; PDF ).
24. ↑ T. Sasaki, T. Kauri, A. Kudo: Effect of pH and Temperature on the Sorption of Np and Pa to mixed anaerobic bacteria , in: Appl. Radiate. Isot. , 2001 , 55  (4), pp. 427-431 ( PMID 11545492 ).
25. ↑ W. Songkasiri, DT Reed, BE Rittmann: bio-sorption of neptunium (V) by Pseudomonas Fluroescens in: Radiochimica Acta , 2002 , 90 , pp 785-789.
26. ^ AJ Francis, JB Fillow, CJ Dodge, M. Dunn, K. Mantione, BA Strietelmeier, ME Pansoy-Hjelvik, HW Papenguth: Role of Bacteria as Biocolloids in the Transport of Actinides from a Deep Underground Radioactive Waste Repository , in: Radiochimica Acta , 1998 , 82 , pp. 347-354 ( abstract ; PDF ).
27. ↑ G. Audi, O. Bersillon, J. Blachot, AH Wapstra: The NUBASE evaluation of nuclear and decay properties. In: Nuclear Physics. Volume A 729, 2003, pp. 3-128. doi : 10.1016 / j.nuclphysa.2003.11.001 . ( PDF ; 1.0 MB).
28. ↑ http://www.iaea.org/inis/collection/NCLCollectionStore/_Public/36/116/36116453.pdf
29. ↑ ^{a b} G. Pfennig, H. Klewe-Nebenius, W. Seelmann-Eggebert (Eds.): Karlsruher Nuklidkarte , 6th edition, corrected. Edition 1998.
30. ↑ P. Weiss: Little-studied metal goes critical - Neptunium Nukes? , in: Science News , October 26, 2002 ( full text ), accessed December 5, 2008.
31. ↑ Russell D. Mosteller, David J. Loaiza, Rene G. Sanchez: Creation of a Simplified Benchmark Model for the Neptunium Sphere Experiment , PHYSOR 2004 - The Physics of Fuel Cycles and Advanced Nuclear Systems: Global Developments Chicago, Illinois, April 25- 29, 2004, on CD-ROM, American Nuclear Society, Lagrange Park, IL. (2004) ( PDF ( Memento of the original from June 7, 2013 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this note. ). 
32. ^ Rene G. Sanchez, David J. Loaiza, Robert H. Kimpland, David K. Hayes, Charlene C. Cappiello, William L. Myers, Peter J. Jaegers, Steven D. Clement, Kenneth B. Butterfield: Criticality of a ²³⁷ Np Sphere , in: Nuclear Science and Engineering , 2008 , 158 , pp. 1-14 ( online ).
33. Jump up ↑ David Albright, Kimberly Kramer: Neptunium 237 and Americium: World Inventories and Proliferation Concerns , August 2005 ( PDF ).
34. ↑ Walter Seifritz: Nuclear explosive devices - threat or energy supply for mankind? , Thiemig-Verlag, Munich 1984.
35. ^ Robert G. Lange, Wade P. Carroll: Review of recent advances of radioisotope power systems , Energy Conversion and Management , 2008 , 49  (3), pp. 393–401 ( doi: 10.1016 / j.enconman.2007.10.028 ) .
36. ^ AF Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 102nd edition. Walter de Gruyter, Berlin 2007, ISBN 978-3-11-017770-1 , p. 1972.
37. ^ AF Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 102nd edition. Walter de Gruyter, Berlin 2007, ISBN 978-3-11-017770-1 , p. 1969.
38. ↑ Christoph Elschenbroich : Organometallchemie , 6th edition, Wiesbaden 2008, ISBN 978-3-8351-0167-8 , p. 589.