Alkalide
Template:Short description 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), Page Module:Chem2/styles.css has no content.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 Page Module:Chem2/styles.css has no content.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:[3]
- Sodide or natride, Page Module:Chem2/styles.css has no content.Na−
- Potasside or kalide, Page Module:Chem2/styles.css has no content.K−
- Rubidide, Page Module:Chem2/styles.css has no content.Rb−
- Caeside, Page Module:Chem2/styles.css has no content.Cs−
Alkalides of the other alkali metals have not yet been discovered:
- Lithide, Page Module:Chem2/styles.css has no content.Li−
- Francide, Page Module:Chem2/styles.css has no content.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.[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 Page Module:Chem2/styles.css has no content.H+Na−), has been observed.[7]
- Sodium-crypt natride, [Na(cryptand[2.2.2])]+Na−, has been observed. This salt contains both Page Module:Chem2/styles.css has no content.Na+ and Page Module:Chem2/styles.css has no content.Na−. The cryptand isolates and stabilizes the Page Module:Chem2/styles.css has no content.Na+, preventing it from being reduced by the Page Module:Chem2/styles.css has no content.Na−.
- Barium azacryptand-sodide, Ba2+[H5Azacryptand[2.2.2]]−Na−⋅2CH3NH2, has been synthesized.[5]
- Anionic sodium dimers Page Module:Chem2/styles.css has no content.(Na2)2− have been observed.[5]
References
Page Template:Reflist/styles.css has no content.
- ^ Page Module:Citation/CS1/styles.css has no content.J. L. Dye; J. M. Ceraso; Mei Lok Tak; B. L. Barnett; F. J. Tehan (1974). "Crystalline salt of the sodium anion (Na−)". J. Am. Chem. Soc. 96 (2): 608–609. Bibcode:1974JAChS..96..608D. doi:10.1021/ja00809a060.
- ^ Page Module:Citation/CS1/styles.css has no content.F. J. Tehan; B. L. Barnett; J. L. Dye (1974). "Alkali anions. Preparation and crystal structure of a compound which contains the cryptated sodium cation and the sodium anion". J. Am. Chem. Soc. 96 (23): 7203–7208. Bibcode:1974JAChS..96.7203T. doi:10.1021/ja00830a005.
- ^ a b Page Module:Citation/CS1/styles.css has no content.J. L. Dye (1979). "Compounds of Alkali Metal Anions". Angew. Chem. Int. Ed. Engl. 18 (8): 587–598. doi:10.1002/anie.197905871.
- ^ Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. Template:ISBN.
- ^ a b c Page Module:Citation/CS1/styles.css has no content.M. Y. Redko; R. H. Huang; J. E. Jackson; J. F. Harrison; J. L. Dye (2003). "Barium azacryptand sodide, the first alkalide with an alkaline Earth cation, also contains a novel dimer, (Na2)2−". J. Am. Chem. Soc. 125 (8): 2259–2263. Bibcode:2003JAChS.125.2259R. doi:10.1021/ja027241m. PMID 12590555.
- ^ Page Module:Citation/CS1/styles.css has no content.J. Kim; A. S. Ichimura; R. H. Huang; M. Redko; R. C. Phillips; J. E. Jackson; J. L. Dye (1999). "Crystalline Salts of Na− and K− (Alkalides) that Are Stable at Room Temperature". J. Am. Chem. Soc. 121 (45): 10666–10667. Bibcode:1999JAChS.12110666K. doi:10.1021/ja992667v.
- ^ Page Module:Citation/CS1/styles.css has no content.M. Y. Redko; M. Vlassa; J. E. Jackson; A. W. Misiolek; R. H. Huang RH; J. L. Dye (2002). ""Inverse sodium hydride": a crystalline salt that contains H+ and Na−". J. Am. Chem. Soc. 124 (21): 5928–5929. doi:10.1021/ja025655+. PMID 12022811.
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