Physics:Electride

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Short description: Ionic compound with electrons as the anion
Cavities and channels in an electride

An electride is an ionic compound in which an electron serves the role of the anion.[1] Solutions of alkali metals in ammonia are electride salts.[2] In the case of sodium, these blue solutions consist of [Na(NH3)6]+ and solvated electrons:

Na + 6 NH3 → [Na(NH3)6]+ + e−

The cation [Na(NH3)6]+ is an octahedral coordination complex.

Solid salts

Addition of a complexant like crown ether or [2.2.2]-cryptand to a solution of [Na(NH3)6]+e− affords [Na (crown ether)]+e− or [Na(2,2,2-crypt)]+e−. Evaporation of these solutions yields a blue-black paramagnetic solid with the formula [Na(2,2,2-crypt)]+e−.

Most solid electride salts decompose above 240 K, although [Ca24Al28O64]4+(e−)4 is stable at room temperature.[3] In these salts, the electron is delocalized between the cations. Electrides are paramagnetic, and are Mott insulators. Properties of these salts have been analyzed.[4]

ThI2 and ThI3 have also been reported to be electride compounds.[5] Similarly, CeI2, LaI2, GdI2, and PrI2 are all electride salts with a tricationic metal ion.[6][7]

Reactions

Solutions of electride salts are powerful reducing agents, as demonstrated by their use in the Birch reduction. Evaporation of these blue solutions affords a mirror of Na metal. If not evaporated, such solutions slowly lose their colour as the electrons reduce ammonia:

2[Na(NH3)6]+e− → 2NaNH2 + 10NH3 + H2

This conversion is catalyzed by various metals.[8] An electride, [Na(NH3)6]+e−, is formed as a reaction intermediate.

High-pressure elements

Theoretical evidence supports electride behaviour in insulating high-pressure forms of potassium, sodium, and lithium. Here the isolated electron is stabilized by efficient packing, which reduces enthalpy under external pressure. The electride is identified by a maximum in the electron localization function, which distinguishes the electride from pressure-induced metallization. Electride phases are typically semiconducting or have very low conductivity,[9][10][11] usually with a complex optical response.[12] A sodium compound called disodium helide has been created under 113 gigapascals (1.12×10^6 atm) of pressure.[13]

Layered electrides (Electrenes)

Layered electrides or electrenes are single-layer materials consisting of alternating atomically thin two-dimensional layers of electrons and ionized atoms.[14][15] The first example was Ca2N, in which the charge (+4) of two calcium ions is balanced by the charge of a nitride ion (-3) in the ion layer plus a charge (-1) in the electron layer.[14]

See also

  • F-center

References

  1. ↑ Dye, J. L. (2003). "Electrons as Anions". Science 301 (5633): 607–608. doi:10.1126/science.1088103. PMID 12893933. 
  2. ↑ Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN:0-12-352651-5
  3. ↑ Buchammagari, H. (2007). "Room Temperature-Stable Electride as a Synthetic Organic Reagent: Application to Pinacol Coupling Reaction in Aqueous Media". Org. Lett. 9 (21): 4287–4289. doi:10.1021/ol701885p. PMID 17854199. 
  4. ↑ Wagner, M. J.; Huang, R. H.; Eglin, J. L.; Dye, J. L. (1994). "An electride with a large six-electron ring". Nature 368 (6473): 726–729. doi:10.1038/368726a0. Bibcode: 1994Natur.368..726W. .
  5. ↑ Wickleder, Mathias S.; Fourest, Blandine; Dorhout, Peter K. (2006). "Thorium". in Morss, Lester R.; Edelstein, Norman M.; Fuger, Jean. The Chemistry of the Actinide and Transactinide Elements. 3 (3rd ed.). Dordrecht, the Netherlands: Springer. pp. 78–94. doi:10.1007/1-4020-3598-5_3. http://radchem.nevada.edu/classes/rdch710/files/thorium.pdf. 
  6. ↑ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. pp. 1240-2. ISBN 978-0-08-037941-8. 
  7. ↑ Nief, F. (2010). "Non-classical divalent lanthanide complexes". Dalton Trans. 39 (29): 6589–6598. doi:10.1039/c001280g. PMID 20631944. 
  8. ↑ Greenlee, K. W.; Henne, A. L. (1946). Sodium Amide. Inorganic Syntheses. 2. pp. 128–135. doi:10.1002/9780470132333.ch38. ISBN 9780470132333. 
  9. ↑ Marques M. (2009). "Potassium under Pressure: A Pseudobinary Ionic Compound". Physical Review Letters 103 (11): 115501. doi:10.1103/PhysRevLett.103.115501. PMID 19792381. Bibcode: 2009PhRvL.103k5501M. 
  10. ↑ Gatti M. (2010). "Sodium: A Charge-Transfer Insulator at High Pressures". Physical Review Letters 104 (11): 216404. doi:10.1103/PhysRevLett.104.216404. PMID 20867123. Bibcode: 2010PhRvL.104u6404G. 
  11. ↑ Marques M. (2011). "Crystal Structures of Dense Lithium: A Metal-Semiconductor-Metal Transition". Physical Review Letters 106 (9): 095502. doi:10.1103/PhysRevLett.106.095502. PMID 21405633. Bibcode: 2011PhRvL.106i5502M. http://discovery.ucl.ac.uk/1301752/1/1301752.pdf. 
  12. ↑ Yu, Zheng; Geng, Hua Y.; Sun, Y.; Chen, Y. (2018). "Optical properties of dense lithium in electride phases by first-principles calculations". Scientific Reports 8 (1): 3868. doi:10.1038/s41598-018-22168-1. PMID 29497122. Bibcode: 2018NatSR...8.3868Y. 
  13. ↑ Wang, Hui-Tian; Boldyrev, Alexander I.; Popov, Ivan A.; Konôpková, Zuzana; Prakapenka, Vitali B.; Zhou, Xiang-Feng; Dronskowski, Richard; Deringer, Volker L. et al. (May 2017). "A stable compound of helium and sodium at high pressure". Nature Chemistry 9 (5): 440–445. doi:10.1038/nchem.2716. ISSN 1755-4349. PMID 28430195. Bibcode: 2017NatCh...9..440D. 
  14. ↑ 14.0 14.1 Druffel, Daniel L.; Kuntz, Kaci L.; Woomer, Adam H.; Alcorn, Francis M.; Hu, Jun; Donley, Carrie L.; Warren, Scott C. (2016). "Experimental Demonstration of an Electride as a 2D Material". Journal of the American Chemical Society 138 (49): 16089–16094. doi:10.1021/jacs.6b10114. PMID 27960319. https://pubs.acs.org/doi/10.1021/jacs.6b10114. Retrieved 12 October 2021. 
  15. ↑ Druffel, Daniel L.; Woomer, Adam H.; Kuntz, Kaci L.; Pawlik, Jacob T.; Warren, Scott C. (2017). "Electrons on the surface of 2D materials: from layered electrides to 2D electrenes". Journal of Materials Chemistry C 5 (43): 11196–11213. doi:10.1039/C7TC02488F. https://pubs.rsc.org/en/content/articlelanding/2017/tc/c7tc02488f. Retrieved 11 October 2021. 

Further reading

  • J. L. Dye; M. J. Wagner; G. Overney; R. H. Huang; T. F. Nagy; D. Tománek (1996). "Cavities and Channels in Electrides". J. Am. Chem. Soc. 118 (31): 7329–7336. doi:10.1021/ja960548z. 
  • JCTC



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