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 [Ca24Al28O644+(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,
CeI 2, LaI 2, GdI 2, and PrI 2 are
all electride salts with a tricationic metal ion.[6][7]
Organic electrides
Organic electrides may be made by active-metal reduction of organic or organometallic species. Magnesium addition to a nickel(II)-bipyridyl (bipy) complex in
tetrahydrofuran (THF) gives the room-temperature stable [(THF)4Mg4(μ2-bipy)4–, in which the electride ion is centered within a square formed by four Mg2+ centers within the larger complex.[8]
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:
This conversion is catalyzed by various metals.[9] 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,[10][11][12] usually with a complex optical response.[13] A sodium compound called
disodium helide has been created under 113 gigapascals (1.12×10^6 atm) of pressure.[14]
Layered electrides (Electrenes)
Layered electrides or electrenes are
single-layer materials consisting of alternating atomically thin two-dimensional layers of electrons and ionized atoms.[15][16] 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.[15]
^Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001.
ISBN0-12-352651-5
^Buchammagari, H.; et al. (2007). "Room Temperature-Stable Electride as a Synthetic Organic Reagent: Application to Pinacol Coupling Reaction in Aqueous Media". Org. Lett. 9 (21): 4287–4289.
doi:
10.1021/ol701885p.
PMID17854199.
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.
PMID26652208.