Considerations Particular to Anions

The design of preorganised, complementary anion binding hosts exhibiting maximum complexation free energy and selectivity must follow from an appreciation of some of the fundamental characteristics of anions. Listed below are some of the issues that are important to anion binding in particular. 

The vast majority of anions are Lewis bases, although there are some exceptions that do not have lone pairs (e.g. A1H4, B(C6H5)4, or are only very weak bases (e.g. B(C6F5)4 ). 

Anions are highly polarisable and so van der Waals interactions will be significant. While non-directional, these are related to the contact surface area of host and anion, and so three-dimensional encapsulation of the anion should enhance binding of all anions capable of fitting within the host. 

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