Di‐Benzo‐18‐Crown‐6 and its Derivatives as Ligands in the Search for Ion Channels

Based on the previously reported one‐dimensional channel system [(H2O)⊂(DB18C6)(μ2‐H2O)2/2][(H3O)⊂(DB18C6)(μ2‐H2O)2/2]I3 (2), which is realized by stacking of crown ether molecules (DB18C6 = dibenzo‐18‐crown‐6), other synthetic approaches towards ionic channels and their results are presented in this paper. The “cutting out” approach using DB18C6 as scissor, applied on NaI, yields the compound [Na⊂(DB18C6)I(THF)][Na⊂(DB18C6)(H2O)2]I(THF)2(CHI3) (1), in high yield. It is based on a neutral and a cationic complex of sodium by DB18C6 linked via H‐bonding to give short chain fragments. The anion exchange approach, trying to replace I3− by Br3− leads to the intercalation of a cation into a DB18C6 chain in [(Me3NPh)(DB18C6)]Br3 (3). A similar reaction as for the synthesis of 2, but replacing iodide with bromine, yields finally a brominated DB18C6 ligand. In the presence of iron, the compound [(H5O2)⊂(Br4‐DB18C6)2][FeBr4], 4, is observed, in which a H5O2+‐cation is encapsuled by two brominated crown ether molecules. The absence of Fe and an excess of Br2 leads to the complexation of H3O+, and co‐crystallisation of bromine in [(H3O)⊂(Br4‐DB18C6)]Br3Br2 (5).