Europium(II) complexes with unsubstituted crown ethers

Three Eu(II) complexes with crown ethers were obtained by electrochemical reduction. The complex with 12-crown-4 contains Eu bonded to four 0 crown atoms, three water molecules and a chloride anion, and shows luminescence at 429 nin at room temperature and at 410 ran at 77 K. The bis(15-crown-5)europium(II) cation has a sandwich structure with 10-coordinate metal ion. Its luminescence has the maximum at 433 nin at room temperature and at 417 nin at 77 K. The weakly luminescing (411.5 nm at 77 K) bisperchlorato(18-crown-6)europium(II) is also 10-coordinate; both perchlorate anions are bonded in a chelating bidentate fashion. The luminescence lifetimes and the excitation spectra are discussed. (C) 2002 Elsevier Science Ltd. All rights reserved.