Alkaline earth metal cations, nuclear

The transport of alkali and alkaline earth metal cations by many crown ethers and their derivatives has been extensively studied. Much effort has been paid to increase their selectivity as well as their efficiency. Making highly Li selective ionophores is a primary concern in this field, because large quantities of lithium could be extracted from sea water for use to nuclear fusion generators... 

Cations are usually smaller than anions, the main exceptions being the largest alkali metal and alkaline earth metal cations, all larger than the fluorine ion F . The reason for this is that removal of electrons to form cations leads to a contraction of the electron orbital clouds as a result of the relative increase in nuclear charge. Similarly, addition of electrons to form anions leads to an expansion of the charge clouds as a result of a relative decrease in the nuclear charge. 

Thus, the electronegativity values are linearly dependent on a parameter similar to the polarizing action of the cation. The dependence of the solubility on the Allred-Rochow electronegativity is divided into two sharply bounded and practically linear plots with close slopes for 3d-elements and for alkaline-earth metal-oxides (see Fig. 3.7.13). Since the slopes of these dependences are close, different positions of these plots may be explained by different relationships between the nuclear charge and Z for metals characterized by different electronic configurations. From the above-said it may be concluded that in high-temperature alkali-metal halide melts a correlation of metal-oxide solubilities with the crystal-lochemical radii of the cations is considerably simpler, i.e. it does not require the introduction of any corrections of the nucleus charge, such as Z. ... 

Hetero-multi-nuclear complexes are obtained easily due to this coordination ability. Lanthanide ions and alkali and alkaline earth metal ions can interact with these oxygen atoms. Metallohosts containing salen analogues for cations are designed and constructed on the basis of these binding properties. 

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