Photoluminescent properties of three lanthanide compounds of formulae LnCl3(diphenyl((5-phenyl-1H-pyrazol-3-yl)methyl)phosphine oxide)2, Ln = Sm, Eu and Tb: X-ray structural, emission and vibrational spectroscopies, DFT and thermogravimetric studies

The synthesis and properties of a new sensitizing bidentate ligand, diphenyl((5-phenyl-1H-pyrazol-3-yl)methyl)phosphine oxide, 2, capable of demonstrating the emissive properties of lanthanide elements, is described. Two ligands are attached to LnCl3 moieties, Ln = Sm, Eu and Tb, resulting in complexes of formulae LnCl3(2)2. These complexes were structurally characterized by single-crystal X-ray crystallography and have geometries that are pentagonal bipyramidal with the two bidentate ligands in a cisoid conformation on the equatorial plane and the three chloride ligands in a mer-configuration. The coordination bond distances decrease from Sm to Tb paralleling the decrease in lanthanide ionic radii. The photoluminescent properties of these complexes were examined and, one of them, TbCl3(2)2, was assessed a ΦF of ca. 1.00. DFT calculations were conducted to understand the mechanism of proton transfer in ligand 2 for a hydrogen atom hopping between nitrogen atoms on the pyrazolyl moiety and, to assess aspects of the coordination sphere of the lanthanide complexes.