Jean-Claude Bunzli - Complexes of Lanthanoid Salts with Macrocyclic Ligands .40. Structural and Luminescence Study of the 3-2 Complex Between Europium Nitrate and the B-Isomer of Dicyclohexyl-18-Crown-6

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      Moret,E., Nicolo,F., Plancherel,D., Froidevaux,P., Bunzli,J.C.G.,   Chapuis,G. Helvetica Chimica Acta 1991  74 (1) 65-78

      Abstract: The crystal and molecular structure of   bis[dinitrato-(2,4,8,15,18,21-hexaoxatricyclo[,14)]hexacosane)europiu m(III)]pentakis   (nitrato)europiate(III) [Eu(NO3)2L(B)]2[Eu(NO3)5]), has been   determined at 170 K from single-crystal X-ray diffraction. The   complex crystallizes in the monoclinic space group P2(1)/n(ITC   No. 14): a = 16.338(3) angstrom, b = 15.704(3) angstrom, c =   24.474(4) angstrom, beta = 97.73(1)degrees, Z = 4. The structure   was refined to a final R value of 0.058 (R(w) = 0.060). The   asymmetric unit contains three independent ions lying on general   positions: [Eu(NO3)5]2- and two distinct [Eu(NO3)2L(B)]+ cations   with the macrocyclic ligand in the cis-anti-cis conformation   (B-isomer). The Eu(III) ions are 10-coordinate with the following   mean bond lengths: Eu-O(nitrate) = 2.48(2) angstrom in the anion   and 2.45(2) angstrom in the two cations, Eu-O(ether) = 2.56(8)   and 2.55(5) angstrom. Small but significant differences are   observed between the two complex cations, especially with respect   to the positions of the cyclohexyl substituent. A conformational   analysis performed on the six O-atoms of the complex cations   confirms the predictions of a simple model. The metal ion sites   of the complex have been probed by high-resolution excitation and   emission spectra at 296 and 77 K. The 5D0<--7F0 excitation   spectrum displays two main bands along with several other minor   components. A detailed analysis of the corresponding and   selectively excited emission spectra leads to the observation of   three types of spectra corresponding to the three   crystallographically different Eu(III) ions. Moreover, three   minor sites are identified, one anionic and two cationic, with a   population equal to ca. 10% of the population of the main sites.   We interpret this finding as reflecting the presence of molecules   with slightly different conformations

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