Alkalide

"Normal" alkali metal compounds

Alkali metals form many well-known stable salts. Sodium chloride (common table salt), , 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 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.

Nomenclature and known cases

There are known alkalides for some of the alkali metals:

• Sodide or natride,
• Potasside or kalide,
• Rubidide,
• Caeside,

Alkalides of the other alkali metals have not yet been discovered:

• Lithide,
• Francide,

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 ), has been observed.
• Sodium-crypt natride, [Na([cryptand2.2.2])]+Na−, has been observed. This salt contains both and . The cryptand isolates and stabilizes the , preventing it from being reduced by the .
• Barium azacryptand-sodide, Ba2+[H5Azacryptand[2.2.2]]−Na−⋅2CH3NH2, has been synthesized.
• Anionic sodium dimers have been observed.

References

References

1. (1974). "Crystalline salt of the sodium anion (Na⁻)". [[J. Am. Chem. Soc.]].
2. (1974). "Alkali anions. Preparation and crystal structure of a compound which contains the cryptated sodium cation and the sodium anion". [[J. Am. Chem. Soc.]].
3. J. L. Dye. (1979). "Compounds of Alkali Metal Anions". [[Angew. Chem. Int. Ed. Engl.]].
4. Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. {{ISBN. 0-12-352651-5.
5. (1999). "Crystalline Salts of Na⁻ and K⁻ (Alkalides) that Are Stable at Room Temperature". [[Journal of the American Chemical Society.
6. (2002). ""Inverse sodium hydride": a crystalline salt that contains H⁺ and Na⁻". [[Journal of the American Chemical Society.
7. (2003). "Barium azacryptand sodide, the first alkalide with an alkaline Earth cation, also contains a novel dimer, (Na₂)²⁻". [[Journal of the American Chemical Society.