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

Stoll I, Brodbeck R, Wiegmann S, et al. New Fluorescent Calix Crown Ethers, Part II: Synthesis and Complex Formation in Solution and the Solid State. European Journal of Organic Chemistry. 2008;2008(31):5231-5238.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. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008