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

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 . O.0.5EtOH has been determined. The gadolinium atom is co-ordinated to seven nitrogen atoms of the L(2) Iigand 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 al 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 D-5(0) --> F-7(J) transitions, the most intense occurring at 613 nm (--> F-7(2)). 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 fdr 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).