Potassium atom, electron localization

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. 2.29 The electron localization function of the potassium atom, adapted from Ref. [106].

Such simple approaches break down close to the critical region where additional physical processes play an essential role. The MNM transition, for example, leads to electron localization at the parent atoms, and dimer formation must also be taken into consideration. Indeed, the equation-of-state data of cesium, rubidium, and potassium imply an appreciable concentration of molecule-like associations in the critical regions. This is illustrated in Table 3.1 where the measured critical compressibility factors Zp = p V jRT are compared with that of the hard sphere van der Waals fluid (Hoover et al., 1975). 

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