Crown ethers electride complexes

This general trait of crown ethers and cryptands (to be discussed later) to stabilize alkali metal salts has been extended to even more improbable compounds, the al-kalides and electrides, which exist as complexed alkali metal cations and alkalide or electride anions. For example, we saw jn Chapter 10 that alkali metals dissolve in liquid ammonia (and some amines and ethers) to give solutions of alkali electrides 10 M M+ f e" (12.38)... 

Alkalides and electrides are stoichiometric salts containing alkali metal cations complexed by crown ethers. Charge balance is provided by the alkali metal anions (alkalides) or trapped electrons (electrides). Rb and Rb NMR has been used to study a number of mbidium alkalides, electrides and related compounds (Kim et al. 

The structure of [Cs(18-crown-6)2] e has been determined. Because the electride anions are extremely poor scatterers compared to the large cesium cation (and to a lesser extent the C and O atoms of the crown ether), the structure has the odd appearance of complexed metal cations with no corresponding anions (Fig. 12.50b). However, the most likely position of the electrons can be inferred from the presence of cavities of 240-pm radius presumably the electrons are located in these cavities. 

Alkali metals can dissolve in solvating media such as ethers and amines to form blue solutions of solvated electrons. In the presence of strongly complexing ligands such as crown ethers or cryptands, electrides (complexed alkali cation and electron), or nuclides (complexed alkali cation and alkali metal anion) can be formed as shown in Scheme 7.3 [50]. Nuclides have been shown to react with monomers such as styrene and methyl methacrylate... 

The study of more concentrated alkali metal solutions in a variety of solvents became possible in 1970, when crown ethers were used to enhance the solubility of the metal. The use of crown ethers and cryptands permitted extensive studies of the optical spectra of solvated electrons and alkali metal anions in solution. After the isolation of the first sodide salt in 1974, the optical spectra of polycrystalline films of various alkalides and electrides were determined by rapid evaporation of all solvent from a liquid film on the walls of the optical cell." " Displayed in Fig. 1 are the optical spectra obtained in this way. Clearly, there is a 1 1 correspondence between the spectra in solution and in the solid state. Although the peak positions shift somewhat with temperature and with the complexant used, the optical peaks can be used to verify the presence of particular alkali metal anions or trapped electrons. In addition to rapid solvent evaporation, solvent-free alkalide and electride films can be made by codeposition of the complexant and alkali metal in high vacuum (10 torr)." This permitted the study of optical... 

Alkalides and electrides are effective reducing agents comparable to solvated electrons. Alkalides and electrides are crystalline salts consisting of crown ethers complexed with alkali ions or salts with alkali metals as anions, and consist of trapped electrons. They are of the type K+(15 — crown — 6)2Na [197-200]. The reduction is carried out in solvents such as THF under... 

---