Crystal structure, luminescence and other properties of some lanthanide complexes of the polypyridine ligand 6,6′-bis[bis(2-pyridylmethyl)aminomethyl]-2,2′-bipyridine

Abstract

Europium(III) and gadolinium(III) form 1 : 1 complexes with the octadentate polypyridine ligand 6,6′-bis[bis(2-pyridylmethyl)aminomethyl]-2,2′-bipyridine L². The crystal structure of the complex [GdL²Cl₂]Cl·2H₂O·0.5EtOH has been determined. The gadolinium atom is co-ordinated to seven nitrogen atoms of the L² ligand and two chloride ligands. One of the pyridine groups of L² is dangling unco-ordinated. Irradiation of water or MeOH solutions of the [EuL²]Cl₃ complex with UV light led to a metal-centred luminescence. The luminescence lifetimes at 296 K in water, D₂O, MeOH and CD₃OD were 0.78, 1.28, 0.98 and 1.25 ms, respectively. From these data the average number of co-ordinated solvent molecules (water or MeOH) was calculated to be 0.5 according to earlier empirical correlations. The luminescence consists of a series of narrow lines corresponding to the envelopes of ⁵D₀ → ⁷F_J transitions, the most intense occurring at 613 nm (→⁷F₂). The integrated intensities of these emission lines give the respective quantum yields of 0.046 and 0.089 in water and D₂O. The equilibrium constant for formation of the europium complex in MeOH, I = 0.100 mol dm^-3 NBu₄ClO₄, was determined to be 10^{7.09 ± 0.09} dm³ mol^-1.

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