New Fluorescent Calix Crown Ethers, Part II: Synthesis and Complex Formation in Solution and the Solid State

New luminescent 1‐aza‐15‐crown‐5 ethers bearing a coumarin unit were synthesised leading to the cavitand‐based calix crown ether 9 . The solid‐state structures of crown ethers 5 and 6 and the solid‐state structures of the sodium and potassium iodide complexes of crown ether 5 are presented. The association constants for the complex formation with alkali metal ions in methanol were determined. Only weak complexes were formed ( K Na = 286 M –1 , K K = 392 M –1 ). The aza‐15‐crown‐5 ether was attached by a methylene unit to a cavitand to give the new fluorescent calix crown ether 9 . The association constants for the sodium and potassium complexes in methanol were investigated as well, and an enhancement for the association constant of the sodium complex was found ( K Na = 1215 M –1 , K K = 497 M –1 ). Selected equilibrium structures of the complexes of 9 were examined by Kohn–Sham density functional calculations to give a detailed understanding of the interplay between the two involved building blocks. Based on these results, a sidewise cation binding of the host 9 can be assumed. These complex geometries are distinct from our findings in our previous work for a larger crown ether attached to a cavitand.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)