Self-assembly of highly luminescent lanthanide complexes promoted by pyridine-tetrazolate ligands

Abstract

Two tridentate pyridine-tetrazolate ligands (H₂pytz and H₂pytzc), analogues of the well-known dipicolinate (H₂dpa) ligand, have been synthesized in a straightforward manner and used for lanthanide(III) coordination. The structures of the resulting tris-ligand complexes were determined in solution (¹H-NMR), where they remain undissociated, as well as in the solid state (X-ray diffraction). The solubility of these anionic complexes can be easily tuned by changing the countercation. The bis-tetrazolate-pyridine ligand H₂pytz sensitizes very efficiently both the visible and near-IR emission of the lanthanides, with unusually high luminescence quantum yields in solid state (61% and 65% for Eu and Tb, respectively, and 0.21% for Nd) and in water (63% for Tb and 18% for Eu). Furthermore, the absorption window of the complexes is significantly extended towards the visible region up to 330 nm. The results show that the bis-tetrazolate-pyridine ligand provides a very attractive alternative to the classic dipicolinate ligand.