Electrides channel structures

Figure 3.77 Channel structure of the cryptand electride [K([2.2.2]cryptand)]+e. (Reprinted with kind permission from Elsevier).

It is also possible to prepare crystalline electrides in which a trapped electron acts in effect as the anion. The bulk of the excess electron density in electrides resides in the X-ray empty cavities and in the interconnecting channels. Structures of electri-dides [Li(2,l, 1-crypt)]+-e [K(2,2,2-crypt)]+-e, [Rb(2,2,2-crypt)]+-e, [Cs(18-crown-6)2]+ e , [Cs(15-crown-5)2]+-e and mixed-sandwich electride [Cs(18-crown-6)(15-crown-5) e ]6 l8-crown-6 are known. Silica-zeolites with pore diameters of 7 A have been used to prepare silica-based electrides. The potassium species contains weakly bound electron pairs which appear to be delocalized, whereas the cesium species have optical and magnetic properties indicative of electron localization in cavities with litde interaction between the electrons or between them and the cation. The structural model of the stable cesium electride synthesized by intercalating cesium in zeolite ITQ-4 has been confirmed by the atomic pair distribution function (PDF) analysis. The synthetic methods, structures, spectroscopic properties, and magnetic behavior of some electrides have been reviewed. Theoretical study on structural and electronic properties of inorganic electrides has also been addressed recently. ... 

Fig. 3 Channel structures of four electrides. The general shapes of the cavities and channels are represented. (From Ref. [29].)...

In electrides, electrons behave as anions. In a typical organic electride Cs+ (15-crown-5)2 e, the electrons occupy cavities connected by narrow channels. The first electride stable at room temperature was made by ionizing Cs into Cs+ and e within the channels of an aU-sUica zeohte. Petkov et confirmed that Cs+ and a low-density electron gas are present in the one-dimensional nanopores of the sihceous zeolite ITQ-4 (Si32064). The PDF technique provided direct structural evidence that Cs intercalated in the form of Cs+ ions arranged in short zigzag chains (see Figure 10). This structural model... 

A more iuterestiug electride, [K([2.2.2]cryptand)] e isformedby thereactiouof [2.2.2]cryptand with potassium metal in diethyl ether at -50 °C. In this material, the X-ray crystal structure shows that the [K([2.2.2]cryptand)] cations are separated by large dumbbell-shaped cavities in which pairs of electrons reside, some 5.3 A apart. Each pair of cavities is connected with adjacent cavities via channels 7.8 and 8.4 A long (Figure 3.77). The structures of the alkalide anion analogues [K([2.2.2]cryptand)] have also been reported,and show that the alkali metal anions also... 

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