Alkalide

{{short description|Chemical compound}} An '''alkalide''' is a chemical compound in which alkali metal atoms are anions (negative ions) with a charge or oxidation state of&nbsp;−1. Until the first discovery of alkalides in the 1970s,<ref>{{cite journal |journal= J. Am. Chem. Soc. |author1=J. L. Dye |author2=J. M. Ceraso |author3=Mei Lok Tak |author4=B. L. Barnett |author5=F. J. Tehan |title= Crystalline salt of the sodium anion (Na⁻) |year= 1974 |volume= 96 |issue= 2 |pages= 608–609 |doi= 10.1021/ja00809a060 |bibcode=1974JAChS..96..608D }}</ref><ref>{{cite journal |author1=F. J. Tehan |author2=B. L. Barnett |author3=J. L. Dye |title= Alkali anions. Preparation and crystal structure of a compound which contains the cryptated sodium cation and the sodium anion |journal= J. Am. Chem. Soc. |year= 1974 |volume= 96 |issue= 23 |pages= 7203–7208 |doi= 10.1021/ja00830a005 |bibcode=1974JAChS..96.7203T }}</ref><ref name="Dye1979">{{cite journal |journal= Angew. Chem. Int. Ed. Engl. |year= 1979 |author= J. L. Dye |title= Compounds of Alkali Metal Anions |volume= 18 |issue= 8 |pages= 587–598 |doi= 10.1002/anie.197905871}}</ref> alkali metals were known to appear in salts only as cations (positive ions) with a charge or oxidation state of&nbsp;+1.<ref>Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. {{ISBN|0-12-352651-5}}.</ref> 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.<ref name="Redko"/>

=="Normal" alkali metal compounds== Alkali metals form many well-known stable salts. Sodium chloride (common table salt), {{chem2|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 {{chem2|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.

==Nomenclature and known cases== There are known alkalides for some of the alkali metals:<ref name="Dye1979" /> *Sodide or natride, {{chem2|Na−}} *Potasside or kalide, {{chem2|K−}} *Rubidide, {{chem2|Rb−}} *Caeside, {{chem2|Cs−}}

Alkalides of the other alkali metals have not yet been discovered: *Lithide, {{chem2|Li−}} *Francide, {{chem2|Fr−}}

==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.<ref>{{cite journal |author1=J. Kim |author2=A. S. Ichimura |author3=R. H. Huang |author4=M. Redko |author5=R. C. Phillips |author6=J. E. Jackson |author7=J. L. Dye |year= 1999 |title= Crystalline Salts of Na⁻ and K⁻ (Alkalides) that Are Stable at Room Temperature |journal= J. Am. Chem. Soc. |volume= 121 |issue= 45 |pages= 10666–10667 |doi= 10.1021/ja992667v |bibcode=1999JAChS.12110666K }}</ref>

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 {{chem2|H+Na−}}), has been observed.<ref>{{cite journal |author1=M. Y. Redko |author2=M. Vlassa |author3=J. E. Jackson |author4=A. W. Misiolek |author5=R. H. Huang RH |author6=J. L. Dye |year= 2002 |title= "Inverse sodium hydride": a crystalline salt that contains H⁺ and Na⁻ |journal= J. Am. Chem. Soc. |volume= 124 |issue= 21 |pages= 5928–5929 |doi= 10.1021/ja025655+ |pmid= 12022811}}</ref> *Sodium-crypt natride, [Na([[2.2.2-Cryptand|cryptand[2.2.2]]])]⁺Na⁻, has been observed. This salt contains both {{chem2|Na+}} and {{chem2|Na−}}. The cryptand isolates and stabilizes the {{chem2|Na+}}, preventing it from being reduced by the {{chem2|Na−}}. *Barium azacryptand-sodide, Ba²⁺[H₅Azacryptand[2.2.2<nowiki>]]</nowiki>⁻Na⁻⋅2CH₃NH₂, has been synthesized.<ref name="Redko">{{cite journal |author1=M. Y. Redko |author2=R. H. Huang |author3=J. E. Jackson |author4=J. F. Harrison |author5=J. L. Dye |year= 2003 |title= Barium azacryptand sodide, the first alkalide with an alkaline Earth cation, also contains a novel dimer, (Na₂)²⁻ |journal= J. Am. Chem. Soc. |volume= 125 |issue= 8 |pages= 2259–2263 |doi= 10.1021/ja027241m |pmid= 12590555 |bibcode=2003JAChS.125.2259R }}</ref> *Anionic sodium dimers {{chem2|(Na2)(2-)}} have been observed.<ref name="Redko"/>

==References== {{Reflist}} {{Sodium compounds}} {{Potassium compounds}} {{Rubidium compounds}} {{Caesium compounds}}

Category:Sodium compounds Category:Potassium compounds Category:Rubidium compounds Category:Caesium compounds Category:Anions Category:Alkali metals