ChemInform Abstract: Alkalides, Electrides and Expanded Metals

A few decades ago the phrase organic materials brought to mind only insulating polymers. Organic metals and organic superconductors have dramatically changed that perception and opened the materials science field to the full range of molecular architecture manipulation that is the forte of organic chemists. In a similar vein, the term salts generally con­ veyed a picture of insulating inorganic crystals with simple cations and anions, although many organic ions were known. With the synthesis by Pedersen, Lehn, Cram, and others of large organic complexants for metal cations, new classes of salts with thousands of different complex ions became available ( 1-7). When a suitable non-reducible organic complexant, L, is combined with an alkali metal, M, the formation of the complexed alkali cation, M+L, releases an electron. This electron can either combine with an alkali metal to form the alkali metal anion, M-, or become trapped in the solvent or in the ionic lattice to form the solvated electron, or a crystalline electride, respectively. Crystalline electrides sometimes behave as saits, in which the electrons are localized in the vicinity of the anionic sites, and sometimes as expanded metals (or near metals), in which the electrons are itinerant. This review focuses on the optical, magnetic, and electronic properties of these unusual new compounds (8, 8a-f).