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

Abstract

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.