Guests size, thermodynamic recognition

Coordination chemistry complex stability. The sizes of the hydrophilic cavities of the macrocyclic poly ethers (13) can be compared with the radii of unsolvated ions of alkali metal ions (1,4) (Table 2.1). The predicted Optimal Spatial Fit Concept (circular recognition) between 12-crown-4 (3) and Li" ", 15-crown-5 (16) and Na", 18-crown-6 (15) and is confirmed by experimentally determined thermodynamic stability constants (15) (iCJ, i.e. the better the fit of the guest cation into the cavity of the host the larger Kg. Figure 2.3 clearly demonstrates the relationship between cation radius/cavity radius size and the stability constant of the respective complexes (15). 

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