| Abstract
| - We report on the hydrothermal synthesis of the [Eu(DPA)(HDPA)(H2O)2]·4H2O lanthanide-organic framework(where H2DPA stands for pyridine-2,6-dicarboxylic acid), its full structural characterization including single-crystal X-ray diffraction and vibrational spectroscopy studies, plus detailed investigations on the experimentaland predicted (using the Sparkle/PM3 model) photophysical luminescent properties. We demonstrate that theSparkle/PM3 model arises as a valid and efficient alternative to the simulation and prediction of thephotoluminescent properties of lanthanide-organic frameworks when compared with methods traditionallyused. Crystallographic investigations showed that the material is composed of neutral one-dimensionalcoordination polymers ∞[Eu(DPA)(HDPA)(H2O)2] which are interconnected via a series of hydrogen bondinginteractions involving the water molecules (both coordinated and located in the interstitial spaces of thestructure). In particular, connections between bilayer arrangements of ∞1[Eu(DPA)(HDPA)(H2O)2] are assuredby a centrosymmetric hexameric water cluster. The presence of this large number of O−H oscillators intensifiesthe vibronic coupling with water molecules and, as a consequence, increases the number of nonradiativedecay pathways controlling the relaxation process, ultimately considerably reducing the quantum efficiency(η = 12.7%). The intensity parameters (Ω2, Ω4, and Ω6) were first calculated by using both the X-ray andthe Sparkle/PM3 structures and were then used to calculate the rates of energy transfer (WET) and back-transfer (WBT). Intensity parameters were used to predict the radiative decay rate. The calculated quantumyield obtained from the X-ray and Sparkle/PM3 structures (both of about 12.5%) are in good agreement withthe experimental value (12.0 ± 5%). These results clearly attest for the efficacy of the theoretical modelsemployed in all calculations and create open new interesting possibilities for the design in silico of novel andhighly efficient lanthanide-organic frameworks.
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