Electride

An electride is an ionic compound in which an electron serves the role of the anion.[1]

## Contents

* 1 Solutions
* 2 Solid salts
* 2.1 Organometallic electrides
* 3 Reactions
* 4 High-pressure elements
* 5 Layered electrides (Electrenes)
* 6 See also
* 7 References
* 8 Further reading
* 9 External links

## Solutions

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. Despite the name, the electron does not leave the sodium-ammonia complex, but it is transferred from Na to the vacant orbitals of the coordinated ammonia molecules.[3]

Similar solutions exist in hexamethylphosphoramide.[4]

## Solid salts

Many "inorganic electrides" have been described.[5]

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−.

Many early crystalline organic electrides decompose above 240 K, whereas the mayenite-derived calcium aluminate electride C12A7:e− is stable at room temperature.[5] The parent oxide 12CaO·7Al2O3 has a cage framework that can be represented as [Ca24Al28O64]4+; in the electride, extra-framework oxide ions are replaced by electrons in the cages, giving [Ca24Al28O64]4+(4e−).[6] C12A7:e− has been used as a low-work-function electron donor and as a catalyst support, for example in ruthenium-catalyzed ammonia synthesis.[7] In electride salts, the electron is delocalized between the cations. Properties of these salts have been analyzed.[8]

ThI2 and ThI3 have also been proposed to be electride compounds.[9] Similarly, CeI2, LaI2, GdI2, and PrI2 are all electride salts with a tricationic metal ion.[10][11]

### Organometallic electrides

Magnesium reduced nickel(II)-bipyridyl (bipy) complex have been labeled organic electrides. An example is [(THF)4Mg4(μ2-bipy)4]–, in which the electride is the singly occupied molecular orbital (SOMO) formed by the Mg-square cluster within the larger complex.[12]

## Reactions

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.[13] An electride, [Na(NH3)6]+e−, is formed as a reaction intermediate.

## High-pressure elements

In quantum chemistry, an electride is identified by a maximum of the electron density, characterized by a non-nuclear attractor, a large and negative Laplacian at the critical point, and an electron localization function isosurface close to 1.[14] Electride phases are typically semiconducting or have very low conductivity,[15]Cite error: Closing `</ref>` missing for `<ref>` tag the universal but robust gapless surface state in insulating electride that forming a de facto real space topological distribution of charge carriers,[16] and the colossal charge state of some impurities in them.[17]

## Layered electrides (Electrenes)

Layered electrides or electrenes are single-layer materials consisting of alternating atomically thin two-dimensional layers of electrons and ionized atoms.[18][19] 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.[18]

## 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. ↑ Zurek, Eva; Edwards, Peter P.; Hoffmann, Roald (2009-10-19). "A Molecular Perspective on Lithium–Ammonia Solutions" (in en). Angewandte Chemie International Edition 48 (44): 8198–8232. doi:10.1002/anie.200900373. ISSN 1433-7851. https://onlinelibrary.wiley.com/doi/10.1002/anie.200900373.
4. ↑ Ellis, John E. (2006-04-17). "Adventures with Substances Containing Metals in Negative Oxidation States" (in en). Inorganic Chemistry 45 (8): 3174-3175. doi:10.1021/ic052110i. ISSN 0020-1669. https://pubs.acs.org/doi/10.1021/ic052110i.
5. ↑ 5.0 5.1 Hosono, Hideo; Kitano, Masaaki (2021). "Advances in Materials and Applications of Inorganic Electrides". Chemical Reviews 121 (5): 3121–3185. doi:10.1021/acs.chemrev.0c01071. PMID 33606511.
6. ↑ Matsuishi, Satoru; Toda, Yoshitake; Miyakawa, Masashi; Hayashi, Katsuro; Kamiya, Toshio; Hirano, Masahiro; Tanaka, Shigeki; Hosono, Hideo (2003). "High-Density Electron Anions in a Nanoporous Single Crystal: [Ca24Al28O64]4+(4e−)". Science 301 (5633): 626–629. doi:10.1126/science.1083842.
7. ↑ Kitano, Masaaki; Kanbara, Shunsuke; Inoue, Yasunori; Kuganathan, Navaratnarajah; Sushko, Peter V.; Yokoyama, Tomohiro; Hara, Michikazu; Hosono, Hideo (2015). "Electride support boosts nitrogen dissociation over ruthenium catalyst and shifts the bottleneck in ammonia synthesis". Nature Communications 6 (1). doi:10.1038/ncomms7731.
8. ↑ 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. .
9. ↑ 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. ISBN 978-1-4020-3555-5. http://radchem.nevada.edu/classes/rdch710/files/thorium.pdf.
10. ↑ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. pp. 1240-2. ISBN 978-0-08-037941-8.
11. ↑ Nief, F. (2010). "Non-classical divalent lanthanide complexes". Dalton Trans. 39 (29): 6589–6598. doi:10.1039/c001280g. PMID 20631944.
12. ↑ Day, Craig S.; Do, Cuong Dat; Odena, Carlota; Benet-Buchholz, Jordi; Xu, Liang; Foroutan-Nejad, Cina; Hopmann, Kathrin H.; Martin, Ruben (13 July 2022). "Room-Temperature-Stable Magnesium Electride via Ni(II) Reduction". J. Am. Chem. Soc. 144 (29): 13109–13117. doi:10.1021/jacs.2c01807. PMID 35830190.
13. ↑ Greenlee, K. W.; Henne, A. L. (1946). "Sodium Amide". Inorganic Syntheses. 2. pp. 128–135. doi:10.1002/9780470132333.ch38. ISBN 978-0-470-13233-3.
14. ↑ Postils, Verònica; Garcia-Borràs, Marc; Solà, Miquel; Luis, Josep M.; Matito, Eduard (2015-03-05). "On the existence and characterization of molecular electrides" (in en). Chemical Communications 51 (23): 4865–4868. doi:10.1039/C5CC00215J. ISSN 1364-548X. https://pubs.rsc.org/en/content/articlelanding/2015/cc/c5cc00215j.
15. ↑ Marques M. (2009). "Potassium under Pressure: A Pseudobinary Ionic Compound". Physical Review Letters 103 (11). doi:10.1103/PhysRevLett.103.115501. PMID 19792381. Bibcode: 2009PhRvL.103k5501M.
16. ↑ Wang, Dan; Song, Hongxing; Zhang, Leilei; Wang, Hao; Sun, Yi; Wu, Fengchao; Chen, Ying; Chen, Xiangrong et al. (2024-02-01). "Universal Metallic Surface States in Electrides" (in en). The Journal of Physical Chemistry C 128 (4): 1845–1854. doi:10.1021/acs.jpcc.3c07496. ISSN 1932-7447. https://pubs.acs.org/doi/10.1021/acs.jpcc.3c07496.
17. ↑ Zhang, Leilei; Wu, Qiang; Li, Shourui; Sun, Yi; Yan, Xiaozhen; Chen, Ying; Geng, Hua Y. (2021-02-10). "Interplay of Anionic Quasi-Atoms and Interstitial Point Defects in Electrides: Abnormal Interstice Occupation and Colossal Charge State of Point Defects in Dense fcc-Lithium" (in en). ACS Applied Materials & Interfaces 13 (5): 6130–6139. doi:10.1021/acsami.0c17095. ISSN 1944-8244. https://pubs.acs.org/doi/10.1021/acsami.0c17095.
18. ↑ 18.0 18.1 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.
19. ↑ 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.
* Janesko, Benjamin G.; Scalmani, Giovanni; Frisch, Michael J. (2016). "Quantifying Electron Delocalization in Electrides". Journal of Chemical Theory and Computation 12 (1): 79–91. doi:10.1021/acs.jctc.5b00993. PMID 26652208.
* Brazil, Rachel (2026-01-26). "Meet the mysterious electrides". Knowable Magazine (Annual Reviews). doi:10.1146/knowable-012626-2. ISSN 2575-4459.

## External links

* Brazil, Rachel (2026-01-27). "Meet the mysterious electrides". https://arstechnica.com/science/2026/01/meet-the-mysterious-electrides/.

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