Effects of Zinc(II) on the Luminescence of Europium(III) in Complexes Containing beta-Diketone and Schiff Bases

The UV, excitation, and luminescence spectra of tris(pivaloyltrifluoroacetonato)europium(III) ([Eu(pta)(3)]; Hpta = 1,1,1-trifluoro-5,5-dimethylhexane-2,4-dione = HA) were measured in the presence of bis(salicylidene)trimethylenediamine (H(2)saltn), bis[5-(tert-butyl)salicylidene]trimethylenediamine (H(2)('Bu)saltn), or bis(salicylidene)cyclohexane-1,2-diyldiamine (H(2)salchn), and the corresponding Zn(II) complexes [ZnB] (B = Schiff base). The excitation and luminescence spectra of the solution containing [Eu(pta)(3)] and [Zn(salchn)] exhibited much stronger intensities than those of solutions containing the other [ZnB] complexes. The introduction of a 'Bu group into the Schiff base was not effective in sensitizing the luminescence of [Eu(pta)(3)]. The luminescence spectrum of [ZnB] showed a band around 450 nm. The intensity decreased in the presence of [Eu(pta)(3)], reflecting complexation between [Eu(pta)(3)] and [ZnB]. On the basis of the change in intensity against the concentration of [ZnB], stability constants were determined for [Eu(pta)(3)Zn(saltn)], [Eu(pta)(3)Zn{('Bu)saltn}], and [Eu(pta)(3)Zn(salchn)] as 4.13, 4.9 and 5.56, respectively (log (beta) over bar, where (beta) over bar-=[[Eu(pta)(3)ZnB]]([[Eu(pta)(3)]][[ZnB]])(-1)). The quantum yields of these binuclear complexes were determined as 0.15, 0.11, and 0.035, although [Eu(pta)(3)Zn(salchn)] revealed the strongest luminescence at 613 nm. The results of X-ray diffraction analysis for [Eu(pta)(3)Zn(saltn)] showed that Zn(II) had a coordination number of five and was bridged with Eu(III) by three donor O-atoms, i.e., two from the salicylidene moieties and one from the ketonato group pta.