Effects of Zinc(II) on the Luminescence of Europium(III) in Complexes Containing β ‐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 ( t 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 t 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{( t Bu)saltn}], and [Eu(pta) 3 Zn(salchn)] as 4.13, 4.9 and 5.56, respectively (log  $\rm{\overline \beta }$ , where $\rm{\overline \beta }$ =[[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.