Electride

The Na is 555 pm from the nearest N and 516 pm from the nearest O, indicating that it is a separate entity in the structure. Potas-sides, rubidides and caesides have similarly been prepared. The same technique has been used to prepare solutions and even crystals of electrides, in which trapped electrons can play the role of anion. Typical examples are [K(cryptand)]+e and [Cs(18-crown-... 

Electrides, negatively charged metal ions and related phenomena. J. L. Dye, Prog. Inorg. Chem., 1984, 32, 327 (337). 

Novel anions stabilized by alkali-polyether cations The ability of a crown (such as 18-crown-6) or a cryptand (such as 2.2.2) to shield an alkali cation by complex formation has enabled the synthesis of a range of novel compounds containing an alkali metal cation coordinated to a crown or cryptand for which the anion is either a negatively charged alkali metal ion or a single electron (Dye Ellaboudy, 1984 Dye, 1984). Such unusual compounds are called alkalides and electrides , respectively. 

The electrides. Following many experimental difficulties, Dye and coworkers were able to demonstrate that reaction of 18-crown-6 with caesium in a 1 2 ratio (under specified conditions) leads to isolation of shiny, black crystals of a product of composition Cs+(18-crown-6)2 (El-laboudy, Dye Smith, 1983 Dye Ellaboudy, 1984). The solid-state 133Cs nmr spectrum, the esr spectrum, and the magnetic susceptibility of this product all indicated that it was of type Cs+(l8-crown-6).e" that is, a crystalline electride in which the anion is a single electron. In overall terms, this exotic class of compound may be considered to lie on the border between metals and non-metals. 

Role of Cation Complexants in the Synthesis of Alkalides and Electrides... 

Dye, James L., Electrides, Negatively Charged Metal Ions, and Related Phenomena. 32 327... 

Tsai, K.-L. and Dye, J.L., Synthesis, properties, and characterization of nanometer-size metal particles by homogeneous reduction with alkalides and electrides in aprotic solvents, Chem. Mater., 5, 540,1993. 

Nesper (1991) observed that a surprising consequence of such relationships may be found in the question can we invert this concept oxides as stuffed alloys into intermetallic phases as electrides In other words could the electrons find good residence regions at those points in the structure where the favoured anion positions are found ... 

The catalytic action ofalkalides and electrides will be briefly discussed in Section 7.1.3. 

Even more exotic than alkalides are electrides. They are formed instead of alkalides when an excess of a strong complexant is present ... 

Alkalides and electrides are the strongest known reducing agents in a given... 

Single-crystal cesium electride" is almost entirely diamagnetic. Reconcile this with the formulation [Cs(ligand)) e. Is there a paradox here ... 

The resulting trapped electron can absorb light in the visible region and the compound is colored (F = Ger. Farbe, color). The material may be considered a nonstoichiometric compound, Na +8C, J or as a dilute solution of sodium electride. 15... 

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)... 

In Chapter 6 it was pointed out that X rays are diffracted by electrons. Yel on page 528 h is staled that the anionic electrons of complexed cesium electride do nol show" in the structure determination. Discuss this apparent paradox. (Him Why is it hard to locale hydrogen atoms in m X-ray crystallographic determination/)... 

ELECTRIDE. An experimental compound composed of an alkali-metal cation and an electron in which the electron functions as a chemical element te.g., a halogen) in salt formation. Several such compounds have been made in (he U.S. and abroad. The phenomenon is reported to be one that challenges accepted concepts of compound formation... 

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]. 

Fig. 3. Schematic representation of the series (from the left to right) alkali-metal atom, cryptatium (expanded atom or radical contact-ion pair [Na+ c tris-bipy cryptandje ), electride (Rydberg atom or electron salt) [K+ c 9]e ).

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