Electride
An electride is an ionic compound in which an electron is 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.
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[edit] Solid salts
Addition of 2,2,2-cryptand to a solution of [Na(NH3)6]+e− affords [Na(2,2,2-crypt)]+e−. Evaporation of these solutions yields a blue-black paramagnetic salt with the formula [Na(2,2,2-crypt)]+e−.
The solid salts decompose above 240 K, although [Ca24Al28O68]4+(e-)4 is stable at room temperature.[3] In these salts, the electron is delocalized between the cations. Electrides are paramagnetic and Mott insulators.
[edit] 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. Such solutions slowly lose their colour as the electrons reduce ammonia:
- [Na(NH3)6]+e− + NH3 → NaNH2 + H2
[edit] 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.
[edit] References
- ^ Dye, J. L. (2003). "Electrons as Anions". Science 301 (5633): 607–608. doi:10.1126/science.1088103. PMID 12893933.
- ^ Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5
- ^ Buchammagari, H. et al. (2007). "Room Temperature-Stable Electride as a Synthetic Organic Reagent: Application to Pinacol Coupling Reaction in Aqueous Media". Org. Lett. (ACS Publications) 9 (21): 4287–4289. doi:10.1021/ol701885p. PMID 17854199. http://pubs.acs.org/doi/abs/10.1021/ol701885p.
- ^ Marques M. et al. (2009). "Potassium under Pressure: A Pseudobinary Ionic Compound". Physical Review Letters 103 (11): 115501.
- ^ Gatti M. et al. (2010). "Sodium: A Charge-Transfer Insulator at High Pressures". Physical Review Letters 104 (11): 216404.
- ^ Marques M. et al. (2011). "Crystal Structures of Dense Lithium: A Metal-Semiconductor-Metal Transition". Physical Review Letters 106 (9): 095502.
[edit] Further reading
- J. L. Dye, M. J. Wagner, G. Overney, R. H. Huang, T. F. Nagy, and D. Tománek (1996). "Cavities and Channels in Electrides" (reprint). J. Am. Chem. Soc. 118 (31): 7329. doi:10.1021/ja960548z. http://www.pa.msu.edu/cmp/csc/eprint/DT088.pdf.
