Preparation, Crystal structure and Luminescence Properties of Lanthanide Complexes with 2,4,6-tri(pyridin-2-yl)-1,3,5-triazine and Organic Carboxylic Acid

Five Dinuclear Lanthanide Complexes Based on 2,4-dimethylbenzoic Acid and 5,5'-dimethy-2,2'-bipyridine: Crystal Structures, Thermal Behaviour and Luminescent Property

A series of new complexes, [Ln (2,4-DMBA)3(5,5'-DM-2,2'-bipy)]2 (Ln = Sm(1), Eu (2)), [Pr (2,4-DMBA)3 (5,5'-DM-2,2'-bipy)]2·0.5(C2H5OH) (3), [Ln (2,4-DMBA)3 (5,5'-DM-2,2'-bipy)]2·0.5(2,4-DMBAH)·0.25(5,5'-DM-2,2'-bipy) (Ln = Tb (4), Dy (5)) (2,4-DMBA = 2,4-dimethylbenzoate, 5,5'-DM-2,2'-bipy = 5,5'-dimethy-2,2'-bipyridine) were synthesized via hydrothermal reaction conditions. The complexes were characterized through elemental analysis, Infrared spectra (IR), Raman (R) spectra, UV-Vis spectra, single X-ray diffraction. Single crystal data show that complexes 1-5 are binuclear complexes, but they can be divided into three different crystal structures. The thermal decomposition mechanism of complexes 1-5 were investigated by the technology of simultaneous TG/DSC-FTIR. What's more, the luminescent properties of complexes 1-2 and 4 were discussed, and the luminescence lifetime (τ) of complexes 2 and 4 were calculated.

Probing Optical Anisotropy and Polymorph-Dependent Photoluminescence in [Ln2 ] Complexes by Hyperspectral Imaging on Single Crystals

Two homodinuclear and one heterodinuclear lanthanide (Ln)-based complexes of the general formula [Ln₂ (bpm)(tfaa)₆ ] (Ln=Eu (1), Tb (2), Eu-Tb (3), bpm=2,2'-bipyrimidine, tfaa^- =1,1,1-trifluoroacetylacetonate) were synthesized and characterized by single-crystal photoluminescence spectroscopy and hyperspectral imaging. Complexes 1 and 2 crystallize in two polymorphic structures, while three polymorphs were isolated for 3, namely having needle-, plate-, and block-like morphologies. Single-crystal photoluminescence spectroscopy and imaging on Eu³⁺ -containing 1 and 3 revealed polymorph-dependent J-splitting of the hypersensitive ⁵ D₀ →⁷ F₂ Eu³⁺ transition as well as electric-to-magnetic dipole emission intensity ratios. According to these observations, the lowest symmetry chemical environment was attributed to the Eu³⁺ ions present in the needle-like polymorph, also in agreement with single-crystal X-ray diffraction analysis. More importantly, hyperspectral imaging on all three single-crystal polymorphs of 3 exhibits optical anisotropy with photoluminescence enhancement at specific crystallographic faces. This behavior was ascribed to the distinct molecular packing of the Ln-Ln dimers in each polymorphic crystal as well as to face-specific local symmetry of the Eu³⁺ centers. Overall, opto-structural relationships of three Ln-Ln dimers and their single-crystal polymorphs were established as a particularly promising avenue for control of photoluminescence by chemical crystal engineering.