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

Abstract

A series of brightly luminescent new mononuclear Tp^PyLn(An)₂(H₂O) (where An^- = carboxylate anion, Ln = Eu or Tb and Tp^Py- = tris(3-(2'-pyridyl)pyrazolyl)borate) and dinuclear (Tp^PyLn)₂pma(MeOH)₂ (Ln = Eu, Tb, pma^4- = 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 (Tp^PyEu)(pma)(TbTp^Py)(MeOH)₂, (Tp^PyEu)₂(pma)(MeOH)₂ and (Tp^PyTb)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.