Photoluminescence of LaI3 switched on and off by association and dissociation of non-luminescent tetrahydrofuran

Expanding the Coordination of f-Block Metals with Tris[2-(2-methoxyethoxy)ethyl]amine: From Molecular Complexes to Cage-like Structures

Low-valent f-block metals have intrinsic luminescence, electrochemical, and magnetic properties that are modulated with ligands, causing the coordination chemistry of these metals to be imperative to generating critical insights needed to impact modern applications. To this end, we synthesized and characterized a series of twenty-seven complexes of f-metal ions including EuII, YbII, SmII, and UIII and hexanuclear clusters of LaIII and CeIII to study the impact of tris[2-(2-methoxyethoxy)ethyl]amine, a flexible acyclic analogue of the extensively studied 2.2.2-cryptand, on the coordination chemistry and photophysical properties of low-valent f-block metals. We demonstrate that the flexibility of the ligand enables luminescence tunability over a greater range than analogous cryptates of EuII in solution. Furthermore, the ligand also displays a variety of binding modes to f-block metals in the solid state that are inaccessible to cryptates of low-valent f-block metals. In addition to serving as a ligand for f-block metals of various sizes and oxidation states, tris[2-(2-methoxyethoxy)ethyl]amine also deprotonates water molecules coordinated to trivalent triflate salts of f-block metal ions, enabling the isolation of hexanuclear clusters containing either LaIII or CeIII. The ligand was also found to bind more tightly to YbII and UIII in the solid state compared to 2.2.2-cryptand, suggesting that it can play a role in the isolation of other low-valent f-block metals such CfII, NpIII, and PuIII. We expect that our findings will inspire applications of tris[2-(2-methoxyethoxy)ethyl]amine in the design of light-emitting diodes and the synthesis of extremely reducing divalent f-block metal complexes that are of interest for a wide range of applications.

S-Heptazine N-ligand based luminescent coordination materials: synthesis, structural and luminescent studies of lanthanide-cyamelurate networks

Various series of lanthanide metal-organic networks denoted Ln-Cy (Ln = La, Ce, Pr, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb), were synthesized under solvothermal conditions using potassium cyamelurate (K₃Cy) and lanthanide nitrate salts. All obtained materials were fully characterized, and their crystal structures were solved by single-crystal X-ray diffraction. Four types of coordination modes were elucidated for the Ln-Cy series with different Ln³⁺ coordination geometries. Structural studies were performed to compare the various coordination compounds of the Ln-Cy series. Moreover, the cyamelurate linkers of rich π-conjugated and uncoordinated Lewis basic sites were used as an absorbing chromophore to enhance the luminescence quantum efficiency, the band emission and the luminescence lifetime of the coordinated Ln metal centers. Solid-state UV-visible measurements combined with density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations were performed to further explore luminescent features of the Ln-Cy series and their origins.

The Lanthanide Contraction Is a Variable

Upon examination of the bond distances of the recently reported series of [Ln(SST)₃(THF)₂] [Ln = lanthanides, SST = tris(trimethylsilyl)siloxide (OSi(SiMe₃)₃), and THF = tetrahydrofuran] compounds, it was found that over the Ln-series (La through Lu), the Ln-O(THF) bond changed by 0.257 Å, whereas the Ln-O(SST) bond varied by 0.164 Å. Examination of all similarly ligated Ln-O(THF) (Ln = La vs Lu) structures available in the Cambridge Structural Database (CSD) revealed that this previously unreported, increased Ln-contraction is pervasive. Further evaluations showed that this enhanced Ln-contraction also occurs for pyridine (py) in the [Ln(SST)₃(py)₂] family as well as the average Ln-N(py) (La vs Lu) structure distances recovered from the CSD. Additional ligands, such as halides (Cl and I) were found to display this enhanced Ln-contraction, while other species (i.e., cyclopentadienide, alkoxide, SST, and dimethyl sulfoxide) yielded a "normal" Ln-contraction (La-L vs Lu-L). Gas-phase electronic structure density functional theory calculations were carried out to evaluate the molecular orbital influence on the Ln-contraction between Ln-O(SST) and Ln-O(THF). The calculated [Ln(SST)₃(THF)₂] structures were found to demonstrate the same capricious Ln-contraction. Based on these studies, one can say that the variability of the Ln-contraction noted in the [Ln(SST)₃(THF)₂] experimental data is due to the different bonding types, ion-ion for the Ln-SST bond versus ion-dipole for the Ln-THF bond.