Phosphorescent cyclometalated iridium tris(2-phenylpyridine) derivatives were designed and incorporated into coordination polymers as tricarboxylate bridging ligands. Three different crystalline coordination polymers were synthesized using a solvothermal technique and were characterized using a variety of methods, including single-crystal X-ray diffraction, PXRD, TGA, IR spectroscopy, gas adsorption measurements, and luminescence measurements. The coordination polymer built from Ir[3-(2-pyridyl)benzoate](3), 1, was found to be highly porous with a nitrogen BET surface area of 764 m(2)/g, whereas the coordination polymers built from Ir[4-(2-pyridyl)benzoate](3), 2 and 3, were nonporous. The (3)MLCT phosphorescence of each of the three coordination polymers was quenched in the presence of O(2). However, only 1 showed quick and reversible luminescence quenching by oxygen, whereas 2 and 3 exhibited gradual and irreversible luminescence quenching by oxygen. The high permanent porosity of 1 allows for rapid diffusion of oxygen through the open channels, leading to efficient and reversible quenching of the (3)MLCT phosphorescence. This work highlights the opportunity of designing highly porous and luminescent coordination polymers for sensing other important analytes.
Metal-organic frameworks (MOFs) are an interesting class of hybrid materials that are built from metal ion connectors and polydentate bridging ligands. They have shown potential in a number of applications, such as nonlinear optics,[1] gas adsorption, [2] catalysis, [3] and even controlled drug release.[4]MOFs on the nanometer scale can offer an interesting approach to designing functional nanomaterials for biological and biomedical applications, because their compositions can be systematically tuned by judicious choice of building blocks.We have recently developed a room-temperature reversephase microemulsion procedure for the synthesis of nanoscale metal-organic frameworks (NMOFs). [5] Although such a synthetic procedure afforded NMOFs of several metal/ ligand combinations, it led to gel-like amorphous materials in many other cases, presumably as a result of rapid and irreversible metal-ligand coordination bond formation at room temperature. Alternative synthetic methods are thus needed before we can fully take advantage of the intrinsic tunability of NMOFs in designing functional NMOFs for ultimate applications in imaging, biosensing, and drug delivery. Herein we report the surfactant-assisted synthesis of two novel gadolinium NMOFs at elevated temperatures and demonstrate the potential utility of NMOFs as magnetic resonance imaging (MRI) and optical contrast agents.We chose Gd III ions as the metal connectors for their highly paramagnetic nature and the benzenehexacarboxylate moiety (bhc; the conjugate acid is also called mellitic acid) as the bridging ligand for its ability to form stable Gd NMOFs and to carry a high payload of Gd III ions. Numerous attempts at synthesizing Gd bhc NMOFs using the room-temperature reverse-phase microemulsion procedure only produced amorphous materials with ill-defined morphologies and wide size distributions. We reasoned that the bhc ligand might have too high a tendency to bridge Gd III ions, thus leading to amorphous materials by rapid irreversible crosslinking at room temperature. On the other hand, hydrothermal reactions have shown to be an excellent method for the synthesis of a variety of nanomaterials. [6,7] Presumably, the elevated temperatures alter the relative kinetics for nucleation and nanocrystal growth in favor of the formation of uniform nanomaterials under hydrothermal conditions. [8] We therefore carried out the surfactant-assisted synthesis of Gd bhc NMOFs at high temperatures with the hope of not only obtaining uniform crystalline nanomaterials but also stabilizing the resulting nanoparticles against aggregation during the synthesis. Briefly, two CTAB/1-hexanol/n-heptane/water microemulsions with W = 10 (W is defined as water-tosurfactant molar ratio; CTAB = cetyltrimethylammonium bromide) containing [NMeH 3 ] 6 [bhc] in one and GdCl 3 in the other were combined and transferred to a teflon-lined Parr reactor. The reaction mixture was then heated at 120 8C for 18 h to afford nanoparticles of [Gd 2 (bhc)(H 2 O) 6 ] (1). The nanoparticles of 1 were isolated ...
A series of novel organic cage compounds 1-4 were successfully synthesized from readily available starting materials in one-pot in decent to excellent yields (46-90%) through a dynamic covalent chemistry approach (imine condensation reaction). Covalently cross-linked cage framework 14 was obtained through the cage-to-framework strategy via the Sonogashira coupling of cage 4 with the 1,4-diethynylbenzene linker molecule. Cage compounds 1-4 and framework 14 exhibited exceptional high ideal selectivity (36/1-138/1) in adsorption of CO(2) over N(2) under the standard temperature and pressure (STP, 20 °C, 1 bar). Gas adsorption studies indicate that the high selectivity is provided not only by the amino group density (mol/g), but also by the intrinsic pore size of the cage structure (distance between the top and bottom panels), which can be tuned by judiciously choosing building blocks of different size. The systematic studies on the structure-property relationship of this novel class of organic cages are reported herein for the first time; they provide critical knowledge on the rational design principle of these cage-based porous materials that have shown great potential in gas separation and carbon capture applications.
Metal-organic frameworks (MOFs) are an interesting class of hybrid materials that are built from metal ion connectors and polydentate bridging ligands. They have shown potential in a number of applications, such as nonlinear optics,[1] gas adsorption, [2] catalysis, [3] and even controlled drug release.[4]MOFs on the nanometer scale can offer an interesting approach to designing functional nanomaterials for biological and biomedical applications, because their compositions can be systematically tuned by judicious choice of building blocks.We have recently developed a room-temperature reversephase microemulsion procedure for the synthesis of nanoscale metal-organic frameworks (NMOFs). [5] Although such a synthetic procedure afforded NMOFs of several metal/ ligand combinations, it led to gel-like amorphous materials in many other cases, presumably as a result of rapid and irreversible metal-ligand coordination bond formation at room temperature. Alternative synthetic methods are thus needed before we can fully take advantage of the intrinsic tunability of NMOFs in designing functional NMOFs for ultimate applications in imaging, biosensing, and drug delivery. Herein we report the surfactant-assisted synthesis of two novel gadolinium NMOFs at elevated temperatures and demonstrate the potential utility of NMOFs as magnetic resonance imaging (MRI) and optical contrast agents.We chose Gd III ions as the metal connectors for their highly paramagnetic nature and the benzenehexacarboxylate moiety (bhc; the conjugate acid is also called mellitic acid) as the bridging ligand for its ability to form stable Gd NMOFs and to carry a high payload of Gd III ions. Numerous attempts at synthesizing Gd bhc NMOFs using the room-temperature reverse-phase microemulsion procedure only produced amorphous materials with ill-defined morphologies and wide size distributions. We reasoned that the bhc ligand might have too high a tendency to bridge Gd III ions, thus leading to amorphous materials by rapid irreversible crosslinking at room temperature. On the other hand, hydrothermal reactions have shown to be an excellent method for the synthesis of a variety of nanomaterials. [6,7] Presumably, the elevated temperatures alter the relative kinetics for nucleation and nanocrystal growth in favor of the formation of uniform nanomaterials under hydrothermal conditions. [8] We therefore carried out the surfactant-assisted synthesis of Gd bhc NMOFs at high temperatures with the hope of not only obtaining uniform crystalline nanomaterials but also stabilizing the resulting nanoparticles against aggregation during the synthesis. Briefly, two CTAB/1-hexanol/n-heptane/water microemulsions with W = 10 (W is defined as water-tosurfactant molar ratio; CTAB = cetyltrimethylammonium bromide) containing [NMeH 3 ] 6 [bhc] in one and GdCl 3 in the other were combined and transferred to a teflon-lined Parr reactor. The reaction mixture was then heated at 120 8C for 18 h to afford nanoparticles of [Gd 2 (bhc)(H 2 O) 6 ] (1). The nanoparticles of 1 were isolated ...
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