Sodide anion

On page 528 the statement is made that "crystalline [Naclosest packed, large, complex cations with sodide anions in the octahedral holes (Fig. 2-50a). Review the discussion of closest packing in Chapter A and label the atoms in Fig. 12.50 as belonging to layers A and B and indicate the octahedral holes. 

Aside from the effects of ligand stoichiometry and the nature of the solvent, there are also differences in stability of the alkalide ions. The sodide anion is the most stable, and the ceside ion the leash Because of differential stabilities of the alkalide ions and... 

Figure 22 The structure of the inverse sodium hydride 3 AdzH+Na . The sodide anion is drawn...

A particularly imaginative application of this concept has led to the isolation of compounds which contain monatomic alkali metal anions. For example, Na was reacted with cryptand in the presence of EtNHi to give the first example of a sodide salt of... 

Of particular significance in this respect has been the ability to prepare, characterize and study most intriguing species, the alkalides [2.79, 2.80] and the electrides [2.80, 2.81] containing an alkali metal anion and an electron, respectively, as counterion of the complexed cation. Thus, cryptates are able to stabilize species such as the sodide [Na+ c 9]Na- and the electride [K+ c 9]e-. They have also allowed the isolation of anionic clusters of the heavy post-transition metals, as in ([K+ c cryp-tand]2 Pb52-) [2.82]. 

Since X-ray crystallography cannot observe the lone electron directly (Box 2.1), it is questionable whether it is really situated at such a distance from the Cs+ cation. If true, this would represent a very extreme example of the naked anion effect (Section 3.8.2). An alternative explanation localises the electron on the Cs+ cation, which would also account for the observed low conductivity. However, convincing evidence for the separation of cation and electron comes from the nearly isostructural sodide (Na ) and kalide (K ) analogues of [Cs ([18] crown-6) 2] + -e-. In these, species the alkali metal anions are situated in the same localised cavities as their electride analogues. 

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... 

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