Cation-binding hosts lariat ethers

Other molecules include cryptophanes, for example, 24, hemispherands (an example is 25 " ), and podands The last-named are host compounds in which two or more arms come out of a central structure. Examples are 26 and 27 " and the latter molecule binds simple cations, such as Na, K, and Ca. Lariat ethers are compounds containing a crown ether ring with one or more side chains... 

Lariat ethers are a class of compounds that contain a single side arm attached to a macrocycle, often by the nitrogen atom of an azacrown. This side arm is flexible (as in a podand) but contributes to the envelopment of the guest cation in a three-dimensional array, as in the cryptands, while the macrocycle exerts stronger complexation than in podand systems. The pseudo-podand arm comes over the face of the macrocycle and binds to the cation that has been encapsulated within the host, as demonstrated in Figure 2.4. 

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