Synthesis, crystal structure and photophysical properties of mixed-ligand lanthanide complexes with 1,3-diketonates bearing pyrazole moieties and 1,10-phenanthroline

Three novel lanthanide complexes based on 1,3-bis(1,3-dimethyl-1H-pyrazol-4-yl)propane-1,3-dionate (L), namely [Ln(L)3(phen)] (Ln = Gd, Yb, Lu; phen = 1,10-phenanthroline) were synthesized and characterized by spectroscopy and single crystal X-ray study that revealed a monomeric nature for the three compounds. Comparison of the molecular parameters has been made with analogous [Ln(diketonate)3(N2-donor)] species. The peculiarities of the coordination polyhedron and the photophysical properties for the three complexes were discussed. It has been found that, despite relatively high energy of triplet state of the ligand (T1 = 22000 cm-1) unfavorable for sensibilization of Yb3+ ion, the ytterbium complex is noticeable luminescent. The emission Stark-splitted maximum in photoluminescence spectrum of [Yb(L)3(phen)] is peaked at 980 nm (NIR-region) and photoluminescence quantum yield (PLQY) is about 0.3%.