Английская Википедия:Alkalide
An alkalide is a chemical compound in which alkali metal atoms are anions (negative ions) with a charge or oxidation state of −1. Until the first discovery of alkalides in the 1970s,[1][2][3] alkali metals were known to appear in salts only as cations (positive ions) with a charge or oxidation state of +1.[4] These types of compounds are of theoretical interest due to their unusual stoichiometry and low ionization potentials. Alkalide compounds are chemically related to the electrides, salts in which trapped electrons are effectively the anions.[5]
"Normal" alkali metal compounds
Alkali metals form many well-known stable salts. Sodium chloride (common table salt), Шаблон:Chem2, 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 Шаблон:Chem2 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.
Inverse metallic salts would be harder to form due to the high reactivity by the alkalide. By this measure as an example, the inverse salt of sodium chloride, known as chloranium sodide or chloranium natride, Шаблон:Chem2, would be extremely hard to synthesize not only due to the highly electrophilic nature of chloranium, but also the reductivity of the sodide ion.
Nomenclature and known cases
There are known alkalides for some of the alkali metals:[3]
- Sodide or natride, Шаблон:Chem2
- Potasside or kalide, Шаблон:Chem2
- Rubidide, Шаблон:Chem2
- Caeside, Шаблон:Chem2
Alkalides of the other alkali metals have not yet been discovered:
- Lithide, Шаблон:Chem2
- Francide, Шаблон:Chem2
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.[6]
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 Шаблон:Chem2), has been observed.[7]
- Sodium-crypt natride, [Na(cryptand[2.2.2])]+Na−, has been observed. This salt contains both Шаблон:Chem2 and Шаблон:Chem2. The cryptand isolates and stabilizes the Шаблон:Chem2, preventing it from being reduced by the Шаблон:Chem2.
- Barium azacryptand-sodide, Ba2+[H5Azacryptand[2.2.2]]−Na−⋅2CH3NH2, has been synthesized.[5]
- Dimers of cationic and anionic sodium have been observed.[5]
References
Шаблон:Reflist Шаблон:Sodium compounds Шаблон:Potassium compounds Шаблон:Rubidium compounds Шаблон:Caesium compounds
- ↑ Шаблон:Cite journal
- ↑ Шаблон:Cite journal
- ↑ 3,0 3,1 Шаблон:Cite journal
- ↑ Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. Шаблон:ISBN.
- ↑ 5,0 5,1 5,2 Шаблон:Cite journal
- ↑ Шаблон:Cite journal
- ↑ Шаблон:Cite journal
