Homoleptic Lanthanide 1,2,3-Triazolates ∞ 2–3[Ln(Tz)3] and Their Diversified Photoluminescence Properties

The series of homoleptic lanthanide 1,2,3-triazolates ∞ 3[Ln(Tz*)3] (Ln3+ = lanthanide cation, Tz*– = 1,2,3-triazolate anion, C2H2N3 –) is completed by synthesis of the three-dimensional (3D) frameworks with Ln = La, Ce, Pr, Nd, and Sm, and characterization by X-ray powder diffraction, differential thermal analysis-thermogravimetry (DTA/TG) investigations and molecular vibration analysis. In addition, α-∞ 2[Sm(Tz*)3], a two-dimensional polymorph of 3D β-∞ 3[Sm(Tz*)3], is presented including the single crystal structure. The 3D lanthanide triazolates form an isotypic series of the formula ∞ 3[Ln(Tz*)3] ranging from La to Lu, with the exception of Eu, which forms a mixed valent metal organic framework (MOF) of different structure and the constitution ∞ 3[Eu(Tz*)6+x (Tz*H)2–x ]. The main focus of this work is put on the investigation of the photoluminescence behavior of lanthanide 1,2,3-triazolates ∞ 3[Ln(Tz*)3] and illuminates that six different luminescence phenomena can be found for one series of isotypic compounds. The luminescence behavior of the majority of these compounds is based on the photoluminescence properties of the organic linker molecules. Differing properties are observed for ∞ 3[Yb(Tz*)3], which exhibits luminescence properties based on charge transfer transitions between the linker and Yb3+ ions, and for ∞ 3[Ce(Tz*)3] and ∞ 3[Tb(Tz*)3], in which the luminescence properties are a combination of the ligand and the lanthanide metal. In addition, strong inner-filter effects are found in the ligand emission bands that are attributed to reabsorption of the emitted light by the trivalent lanthanide ions. Antenna effects of varying efficiency are present indicated by the energy being transferred to the lanthanide ions subsequent to excitation of the ligand. ∞ 3[Ce(Tz*)3] shows a 5d-4f induced intense blue emission upon excitation with UV light, while ∞ 3[Tb(Tz*)3] shows emission in the green region of the visible spectrum, which can be identified with 4f-4f-transitions typical for Tb3+ ions.