Energy-transfer process in crystals of chiral and racemic double complex salts of [co(ethylenediamine)3][Tb(2,6-pyridinedicarboxylate)3]

Luminescence and energy-transfer reactions in double complex crystals of [Co(en)(3)][Tb(dpa)(3)] (en = ethylenediamine, dpa = 2,6-pyridinedicarboxylate) were investigated and compared to single crystals of rac-[Co(en)(3)] . rac-[Tb(dpa)(3)] (double complexes salt of racemic [Co(en)(3)](3+) and racemic [Tb(dpa)(3)](3-)) and Delta-[Co(en)(3)] . rac-[Tb(dpa)(3)] (chiral [Co(en)(3)](3+) and racemic [Tb(dpa)(3)](3-) salt). The energy-transfer rate constants from Tb3+ to Co3+ complexes were determined from the time profile of emission intensity of photo-excited Tb-III ion in the double complex crystals. The emission decay profiles of rac-[Co(en)(3) . rac-[Tb(dpa)(3)] were analyzed with single exponential curves. On the other hand, the profiles of Delta-[Co(en)(3)] . rac-[Tb(dpa)(3)] show double-exponential curves. From the X-ray analysis of crystal structures, it was found that there is only one site for [Tb(dpa)(3)](3-) in rac-[Co(en)(3)] . rac-[Tb(dpa)(3)] crystal, and there are two sites in the Delta-[Co(en)(3)] . rac-[Tb(dpa)(3)] crystal, i.e., Delta-[Tb(dpa)(3)](3-) and Lambda-[Tb(dpa)(3)](3-) are put in different sites in the crystal. The two rate constants obtained from the double-exponential curve of Delta-[Co(en)(3)] . rac-[Tb(dpa)(3)] are assigned to energy-transfer rates from Delta-[Tb(dpa)(3)](3-) and Lambda-[Tb(dpa)(3)](3-) in the crystal. A distance dependence was determined from the obtained energy-transfer rate constants and the Tb-Co distances in the crystals according to a Dexter type electron-exchange mechanism of energy-transfer model. The energy-transfer rate constants in the crystals are comparable in magnitude with energy-transfer rates in quenching experiments in the [Tb(dpa)(3)](3-)-[Co(en)(3)](3+) aqueous solution.