In Situ Ligand Transformation for the Development of Luminescent 3D Metal-Organic Frameworks with Diamond-like...

Here, the synthesis by a soft solvothermal route of two novel isoreticular compounds based on the in situ generated (by a nucleophilic aromatic substitution) 2-hydroxi-5-(trifluoromethyl)-pyrimidine (H₁L) ligand and Zn-(II) and Cd-(II) as metallic centers (with the general formula [ML₂]_n and labeled as GR-MOF-30 for M = Zn and GR-MOF-31 for M = Cd) is reported, together with their detailed structural and photoluminescent characterization. These metal-organic frameworks are the first examples of coordination compounds based on Zn-(II) and Cd-(II) constructed with this novel ligand. Structures show remarkable intermolecular interactions, including C-F···π and π···π stacking, which not only stabilize the structure but also improve the luminescent properties of the materials. DFT calculations were employed to unequivocally assign the bands observed in UV-vis solid-state spectroscopy. A photophysical study of the materials revealed that GR-MOF-30 and GR-MOF-31present fluorescence band maxima at 394 and 388 nm, respectively, with phosphorescence band maxima and emission lifetimes of 500 and 48.1 ms for GR-MOF-30 and 450 and 69.2 ms for GR-MOF-31. Interestingly, the photoluminescence properties of compound GR-MOF-30 are hardly affected by the change of temperature; meanwhile, GR-MOF-31 shows a transition from a dominating fluorescent emission at room temperature to a phosphorescent emission at 25 K.