Alkalide
Chemical compound
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Through Alkali metal, Electric charge and Oxidation state
"Normal" alkali metal compounds
Alkali metals form many well-known stable salts. Sodium chloride (common table salt), Na+Cl−, illustrates the usual role of an alkali metal such as sodium. In the empirical formula for this ionic compound, the positively charged sodium ion is balanced by a negatively charged chloride ion. The traditional explanation for stable Na+ is that the loss of one electron from elemental sodium to produce a cation with charge of +1 produces a stable closed-shell electron configuration.
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Nomenclature and known cases
There are known alkalides for some of the alkali metals:
Alkalides of the other alkali metals have not yet been discovered:
Examples
Normally, alkalides are thermally labile due to the high reactivity of the alkalide anion, which is theoretically able to break most covalent bonds including the carbon–oxygen bonds in a typical cryptand. The introduction of a special cryptand ligand containing amines instead of ether linkages has allowed the isolation of kalides and natrides that are stable at room temperature.
Several alkalides have been synthesized:
- A compound in which hydrogen ions are encapsulated by adamanzane, known as hydrogen natride or "inverse sodium hydride" (hydrogen sodide or hydrogen natride H+Na−), has been observed.
- Sodium-crypt natride, [Na(cryptand[2.2.2])]+Na−, has been observed. This salt contains both Na+ and Na−. The cryptand isolates and stabilizes the Na+, preventing it from being reduced by the Na−.
- Barium azacryptand-sodide, Ba2+[H5Azacryptand[2.2.2]]−Na−⋅2CH3NH2, has been synthesized.
- Anionic sodium dimers (Na2)2− have been observed.