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

Flor de María Ramírez, Sabi Varbanov, Corine Cécile, Gilles Muller, Nicolas Fatin-Rouge, Rosario Scopelliti, Jean-Claude G. Bünzli
2002 Journal of the Chemical Society. Dalton Transactions  
The new lower rim functionalised macrocycle 5,11,17,23,29,35-hexa-tert-butyl-37,38,39,40,41,42hexakis(dimethylphosphinoylmethoxy)calix[6]arene (B 6 bL 6 ) has been synthesised. Temperature dependent 1 H and 31 P NMR studies indicate a mixture of conformers with a time-averaged C 6v symmetry at 405 K in dmso-d 6 ; ∆G ≠ values for conformational interconversion processes are equal to 68(1) and 75(2) kJ mol Ϫ1 and reveal a semi-flexible macrocycle with alternate in-out cone conformation, a fact
more » ... ormation, 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() in acetonitrile yields stability constants log β 1 = 9.8 and log β 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() and Tb() 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() (Q abs = 4.8%, τ f = 2.1 ms, 1 : 1 complex) and Eu() (Q abs = 2.5%, τ = 2.0 ms, 1 : 2 complex) ions.
doi:10.1039/b206238k fatcat:qzf6wubglfctpalqg63jm6eqam