SYNERGISTIC COORDINATION IN TERNARY COMPLEXES OF EU3+ WITH AROMATIC BETA-DIKETONE LIGANDS AND 1,10-PHENANTHROLINE

Ternary Eu3+ complexes with aromatic beta-diketone ligands and 1,10-phenanthroline are observed in aqueous solution by Eu3+ luminescence spectroscopy, as revealed by a large shift in the position of the 7F0 - 5D0 transition as well as a large increase in intensity. Formation of the ternary complexes also results in a dramatic increase in the sensitized emission of Eu3+ as well as a change in the excitation band profile from that of the parent Eu3+ beta-diketone complex. These complexes are unusual in light of the fact that beta-diketone ligands bind Eu3+ only weakly, and 1,10-phenanthroline does not coordinate Eu3+ at all in aqueous solution by itself. The beta-diketone ligands that were observed to form these ternary complexes are 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione (Htta), 4,4,4-trifluoro-1-phenyl-1,3-butanedione (Hbtfa), and 1,3-diphenyl-1,3-propanedione (Hdbm). Several other beta-diketone ligands did not from ternary complexes with 1,10-phenanthroline including 2,4-pentanedione (Hacac), 1,1,1,5,5,5-hexafluoro-2, 4-pentanedione (Hhfacac), and I-phenyl-1,3-butanedione (Hba). Likewise, when 2,2'-dipyridyl or 1,7-phenanthroline was substituted for 1,10-phenanthroline, the ternary complex was not observed to form. The F-7(0) --> 5D0 excitation band of the ternary complexes can be resolved into two component bands, revealing two distinct Eu3+ environments. Likewise, the lifetime recorded at the peak maximum is a double exponential with lifetimes much longer than the parent Eu3+ beta-diketone complex. The observation of energy transfer from Eu3+ to Nd3+ in the ternary complexes shows that they are multinuclear with respect to the metal ion. The stoichiometries of the complexes were determined by monitoring the intensity of Eu3+ luminescence as a function of added ligand.