Crystal structures and intense luminescence of tris(3-(2'-pyridyl)-pyrazolyl)borate Tb3+ and Eu3+ complexes with carboxylate co-ligands.

A series of brightly luminescent new mononuclear TpPyLn(An)2(H2O) (where An- = carboxylate anion, Ln = Eu or Tb and TpPy- = tris(3-(2'-pyridyl)pyrazolyl)borate) and dinuclear (TpPyLn)2pma(MeOH)2 (Ln = Eu, Tb, pma4- = tetraanion of pyromellitic acid) complexes were prepared and characterized by X-ray crystallography. Within each series the compounds possess similar molecular structures, which differ only by the nature of the carboxylate anions. The quantum efficiencies for metal-centered emission of the complexes were up to 29(3)% for Eu3+ and 53(5)% for the Tb3+ compounds and significantly depend on the electronic structure of the additional ligand (i.e. the carboxylate). The aliphatic carboxylate compounds' luminescence quantum yields were all similar, but different from those for the aromatic ones. The complexes with trifluoroacetate and pentafluorobenzoate unexpectedly displayed lower quantum efficiencies compared to those with the corresponding non-fluorinated analogues. Energy transfer from Tb3+ to Eu3+ occurs in a mixture of (TpPyEu)(pma)(TbTpPy)(MeOH)2, (TpPyEu)2(pma)(MeOH)2 and (TpPyTb)2(pma)(MeOH)2 but is not very efficient. The Tb3+-compounds displayed green electroluminescence, and both the Eu3+ and Tb3+ complexes exhibited bright metal-centered red (Eu3+) or green (Tb3+) triboluminescence.