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 L 2 . The crystal structure of the complex [GdL 2 Cl 2 ]Cl·2H 2 O·0.5EtOH has been determined. The gadolinium atom is co-ordinated to seven nitrogen atoms of the L 2 ligand and two chloride ligands. One of the pyridine groups of L 2 is dangling unco-ordinated. Irradiation of water or MeOH solutions of the [EuL 2 ]Cl 3 complex with UV light led to a metal-centred luminescence. The luminescence lifetimes at 296 K in water, D 2 O, MeOH and CD 3 OD 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 5 D 0 → 7 F J transitions, the most intense occurring at 613 nm (→ 7 F 2 ). The integrated intensities of these emission lines give the respective quantum yields of 0.046 and 0.089 in water and D 2 O. The equilibrium constant for formation of the europium complex in MeOH, I = 0.100 mol dm -3 NBu 4 ClO 4 , was determined to be 10 7.09 ± 0.09 dm 3 mol -1 .