Jean-Claude Bunzli - Complexes of p-tert-butylcalix[5]arene with lanthanides: synthesis, structure and photophysical properties

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  Charbonniere,L.J., Balsiger,C., Schenk,K.J., Bunzli,J.C.G.   Journal of the Chemical Society-Dalton Transactions  1998 (3) 505-510

  Abstract: Spectrophotometric pK(a) determination   for p-tert-butylcalix[5]arene (H5L) in acetonitrile (pK(a1) =   11.5 +/- 0.7, pK(a2) = 154 +/- 1.0 at 298 K) evidenced both   intra-and inter-molecular stabilisation of the deprotonated   forms. Dimeric complexes [Ln(2)(H2L)(2)(dmso)(4)] (Ln = Eu-III,   Gd-III, or Tb-III; dmso = dimethyl sulfoxide) were isolated from   tetrahydrofuran (thf) in the presence of NaH as base. A   single-crystal analysis of [Eu-2(H2L)(2)(dmso)(4)]. 10thf showed   the deformation of the cone conformation of the calixarene upon   complexation and co-ordination of dmso molecules by inclusion   through the hydrophobic cavity of the ligand. A photophysical   investigation revealed a total quenching of the metal   luminescence by a ligand-to-metal charge-transfer state in the   case of Eu-III while luminescence of Tb-III is sensitised   (quantum yield in thf: 5.1%). The temperature-dependent lifetime   of Tb-III is analysed in terms of a potential metal-to-ligand   back-transfer process

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