Cryptands sulfur-containing

Shortly after their first report of all-oxygen bridged cryptands, Dietrich, Lehn and Sauvage reported incorporation of sulfur in the strands. The experimental methods used were essentially similar to those applied in the syntheses of the parent cryptands. As in previous cases, a diacyl chloride was condensed with a diamine under high dilution conditions. In this case, however, the diamine contained sulfur atoms rather than oxygen. The synthesis of compound 5 was accomplished in two stages as illustrated below in Eq. (8.3). The first cyclization step affords the macrocyclic amine in 55% yield. The macrobicyclic product (5) is formed in 25% yield from the monocyclic diamine and the acid chloride. 

Another important type of complex is formed between metal ions and cyclic organic compounds, known as macrocycles. These molecules contain nine or more atoms in the cycle and include at least three heteroatoms, usually oxygen, nitrogen, or sulfur. Crown ethers such as 18-crown-6 and dibenzo-18-crown-6 are examples of organic macrocycles. Some macrocyclic compounds form three-dimensional cavities that can just accommodate appropriately sized metal ions. Ligands known as cryptands are examples. Selectivity occurs to a large extent because of the size and shape of the cycle or cavity relative to that of the metal, although the nature of the heteroatoms and their electron densities, the compatibility of the donor atoms with the metal, and several other factors also play important roles. 

S-donor macrocycles are typically sulfur-substituted crown ethers. The mixed donor macrocycles include those with N/S, S/0, N/O, and N/S/O combinations. Calixarenes and resorcinarenes are most often 0-donors, but may contain various functional groups and thus be classified here as mixed donor macrocycles. The macrocycles most widely used in IC and liquid membrane separations have been the crown ethers, nitrogen-substituted crown ethers, cyclen, cyclam, cryptands, calixarenes, resorcinarenes, and CDs. 

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