Jean-Claude Bunzli - Structural and photophysical behaviour of lanthanide complexes with a tetraazacyclododecane featuring carbamoyl pendant arms

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  Publication Details (including relevant citation   information):

  Zucchi,G., Scopelliti,R., Pittet,P.A., Bunzli,J.C.G., Rogers,R.D.   Journal of the Chemical Society-Dalton Transactions  1999 (6) 931-938

  Abstract: The crystal and molecular structure of   1,4,7,10-tetrakis(N-benzylcarbamoylmethyl)-1,4,7,10-tetraazacyclododecane,   L-1, revealed an S-2-symmetric molecule. One pair of pendant arms   is involved in intramolecular hydrogen bonding while the other   interacts with two other ligand molecules through strong   intermolecular hydrogen bonds. In solution, the ligand adopts a   similar geometrical arrangement at low temperature but complexes   with Eu-III and Lu-III display an averaged C-4-symmetry on the   NMR timescale. One isomer only was detected, as reported for   similar complexes, and the arrangement around Eu-III and Lu-III   appears to be rigid while it is more fluxional around La-III.   Rotation of the benzyl group around the amide function was   observed for Eu-III and a dynamic NMR study in the range 253-333   K yielded Delta H double dagger = 43.0 +/- 0.1 kJ mol(-1), Delta   S double dagger = -49.3 +/- 0.4 J K-1 mol(-1) and k(298) = 47.7   +/- 1.1 s(-1). In the solid state, anhydrous eight-co-ordinate   complexes were isolated and high resolution luminescence   spectroscopy of Eu-III in the europium and Eu-doped compounds of   La, Gd and Lu confirmed a site symmetry close to C-4 along the   lanthanide-series. Energy transfer from the L-1 (3)pi pi* state   to the Tb(D-5(4)) excited state is sizable leading to an absolute   quantum yield of 6.4% in MeCN, while the Eu-III luminescence is   only poorly sensitized, possibly because of photoinduced electron   transfer processes. The Tb(D-5(4)) and Eu(D-5(0)) lifetimes for   both solid state samples and solutions in MeCN are consistent   with no water molecule in the inner co-ordination sphere but   addition of water results in the ninth co-ordination site being   bound to H2O: number of bound waters, q = 0.96 (Eu) and 0.71 (Tb)   in MeCN + 2 M H2O and 1.19 (Eu) and 1.30 (Tb) in water. The   relaxivity r(1) of the gadolinium(III) complex is pH dependent   and varies between 4.08 (pH 0.8), 1.88 (6.7) and 6.14 (11.1)   mM(-1) s(-1)

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