Jean-Claude Bunzli - A p-tert-butylcalix[6]arene bearing phosphinoyl pendant arms for the complexation and sensitisation of lanthanide ions

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  Ramirez,F.D., Varbanov,S., Cecile,C., Muller,G., Fatin-Rouge,N.,   Scopelliti,R., Bunzli,J.C.G. Journal of the Chemical   Society-Dalton Transactions 2002 (23)   4505-4513

  Abstract: The new lower rim functionalised   macrocycle   5,11,17,23,29,35-hexa-tert-butyl-37,38,39,40,41,42-hexakis(dimethylphosphinoylm ethoxy)calix[6]arene   (B(6)bL(6)) has been synthesised. Temperature dependent H-1 and   P-31 NMR studies indicate a mixture of conformers with a   time-averaged C-6v, symmetry at 405 K in dmso-d(6); DeltaGdouble   dagger values for conformational interconversion processes are   equal to 68(1) and 75(2) kJ mol(-1) and reveal a semi-flexible   macrocycle with alternate in-out cone conformation, a fact   confirmed by molecular mechanics and dynamics calculations.   B(6)bL(6) crystallises as a dimer where the two calixarenes are   linked through hydrogen bonding and surrounded by water and   toluene molecules in the lattice. UV-Vis spectrophotometric   titration of B(6)bL(6) with La(III) in acetonitrile yields   stability constants logbeta(1) = 9.8 and logbeta(2) = 19.6 for   the 1 : 1 and 1 : 2 (Ln : B(6)bL(6)) species, respectively. The   corresponding complexes with La, Eu, Gd and Tb have been isolated   and characterised. Lifetime determinations of the Eu(III) and   Tb(III) complexes in acetonitrile solution are consistent with no   or little interaction of water molecules in the inner   co-ordination sphere. The new ligand sensitises reasonably well   the luminescence of the Tb(III) (Q(abs) = 4.8%, tau(f) = 2.1 ms,   1 : 1 complex) and Eu(III) (Q(abs) = 2.5%, tau = 2.0 ms, 1 : 2   complex) ions

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