Caffeine Confinement into a Series of Functionalized Porous Zirconium MOFs: A Joint Experimental/Modeling Exploration

A multitechnique approach was conducted to investigate the confinement of caffeine in a series of UiO-66­(Zr)-type MOFs, functionalized with −H, −NH₂, −Br, and −2OH groups. DFT calculations were first undertaken to elucidate the preferential geometries of the drug within the pores and the resulting drug/host framework interactions. It was shown that the caffeine molecules are preferentially located in the smaller cages, giving rise to only weak interactions with the function groups grafted on the organic linker. These host/guest interactions were concomitantly probed by advanced 1D and 2D high-field/ultrafast MAS NMR and FTIR spectroscopies, which allowed us to not only validate the DFT predictions but also to bring complementary insight into the nature of the interacting sites of both the caffeine and the MOFs. Dielectric relaxation measurements further revealed significant modifications of the ligand dynamics upon the drug encapsulation for all UiO-66­(Zr) solids. It was demonstrated that the perturbation of the ligand flip strongly depends on the nature of the grafted function. While the dynamics of the ligand is slightly enhanced in the case of the −NH₂ form, it is significantly slower for the −Br analogue. Such specific behaviors were then interpreted in light of the conclusions drawn from the DFT calculations and NMR observations

Series of Porous 3-D Coordination Polymers Based on Iron(III) and Porphyrin Derivatives

A new series of 3-D coordination polymers based on iron(III) and nickel(II) tetracarboxylate porphyrin (Ni-TCPP) have been produced using solvothermal conditions. MIL-141(A) solids (MIL stands for Material from Institut Lavoisier), formulated Fe(Ni-TCPP)A•(DMF)_<i>x </i>(A = Li, Na, K, Rb, Cs, DMF = N,N-dimethylformamide, <i>x</i> ∼ 3), are built up from three anionic interpenetrated PtS-type networks charge-balanced by alkali cations (A) entrapped inside the pores. MIL-141(A) thus includes three types of cations, two of which may act as coordinatively unsaturated metal sites (Ni²⁺ and A⁺). These solids all present a permanent porosity with a reasonably high surface area (S_BET = 510–860 m² g^–1) as well as some structural flexibility toward adsorption/desorption processes, modulated in both cases by the nature of A. Thermally Stimulated Current (TSC) measurements indicated that alkali cations are rather homogeneously distributed within the pores, while their interaction with the framework is stronger in MIL-141(A) than in the analogous cation-containing Faujasites X and Y zeolites. Finally, high pressure adsorption isotherms of N₂ and O₂ were measured. Whereas alkali ion-containing zeolites adsorb selectively N₂ toward O₂, the opposite is observed for MIL-141(A). This result is interpreted in light of the TSC data and the possible preferential interaction of the porphyrinic linker with O₂

Series of Porous 3-D Coordination Polymers Based on Iron(III) and Porphyrin Derivatives

A new series of 3-D coordination polymers based on iron(III) and nickel(II) tetracarboxylate porphyrin (Ni-TCPP) have been produced using solvothermal conditions. MIL-141(A) solids (MIL stands for Material from Institut Lavoisier), formulated Fe(Ni-TCPP)A•(DMF)_<i>x </i>(A = Li, Na, K, Rb, Cs, DMF = N,N-dimethylformamide, <i>x</i> ∼ 3), are built up from three anionic interpenetrated PtS-type networks charge-balanced by alkali cations (A) entrapped inside the pores. MIL-141(A) thus includes three types of cations, two of which may act as coordinatively unsaturated metal sites (Ni²⁺ and A⁺). These solids all present a permanent porosity with a reasonably high surface area (S_BET = 510–860 m² g^–1) as well as some structural flexibility toward adsorption/desorption processes, modulated in both cases by the nature of A. Thermally Stimulated Current (TSC) measurements indicated that alkali cations are rather homogeneously distributed within the pores, while their interaction with the framework is stronger in MIL-141(A) than in the analogous cation-containing Faujasites X and Y zeolites. Finally, high pressure adsorption isotherms of N₂ and O₂ were measured. Whereas alkali ion-containing zeolites adsorb selectively N₂ toward O₂, the opposite is observed for MIL-141(A). This result is interpreted in light of the TSC data and the possible preferential interaction of the porphyrinic linker with O₂