RESUMEN
With small molecules, it is not easy to create large void spaces. Flat aromatics stack tightly, while flexible chains fold to fill the cavities. As an intuitive design to make open channels inside molecularly constructed solids, we employed propeller-shaped bicyclic triazoles to prepare a series of aromatic-rich three-dimensional (3D) building blocks. This modular approach has no previous example, but is readily applicable to build linear, bent, and branched arrays of non-stackable architectural motifs from existing flat aromatics by single-pot reactions. A letter H-shaped molecule thus prepared self-assembles into porous crystals, the highly unusual stepwise gas sorption behaviour of which prompted in-depth studies. A combination of single-crystal and powder X-ray diffraction analysis revealed multiple polymorphs, and sterically allowed pathways for their reversible interconversions that open and close the pores in response to external stimuli.
RESUMEN
The three-dimensional (3D) coordination polymers [Cd(tpmd)(NCX)2]n [X = O (1), S (2), and BH3 (3); tpmd = N,N,N',N'-tetrakis(pyridin-4-yl)methanediamine] have been determined to display their network structures through coordinated anionic ligands. Polymers 1 and 2 show nonporous structures, whereas polymer 3 shows a porous coordination framework. On the basis of the Cd(II) network structures, the 3D coordination polymer [Zn(tpmd)(NCBH3)2]n·nMeOH (4) was self-assembled. In the cases of polymers 1 and 2, pseudohalide ions acted to form nonporous network structures; however, in polymers 3 and 4, NCBH3- helps to construct porous network structures. Polymers 1-4 show strong ultraviolet luminescence emissions, depending on the pseudohalide ions present, compared to the tpmd ligands. Interestingly, coordination polymers 3 and 4 that possess NCBH3- ions exhibit high porosities and gas sorption properties. The polymers appeared to absorb N2, H2, CO2, and CH4. In the case of polymer 4, the structure is almost identical with that of polymer 3, except for the Cd(II) ion. However, polymer 4 has a larger void volume and higher gas absorption ability for N2 gas than polymer 3. For the sorption of gases, polymers 3 and 4 showed similar behaviors.
RESUMEN
The efficient and selective aerobic oxidation of alcohols has been investigated with judicious combinations of europium-incorporated and/or TEMPO ((2,2,6,6-tetramethylpiperidin-1-yl)oxyl)-functionalized zirconium-based porous metal-organic frameworks (MOFs). Although MOFs are well-known catalytic platforms for the aerobic oxidation with radical-functionalities and metal nanoparticles, these systematic approaches involving metal cations and/or radical species introduce numerous interesting aspects for cooperation between metals and TEMPO for the aerobic oxidation of alcohols. The role of TEMPO as the oxidant in the heterogeneous catalytic aerobic oxidation of alcohols was revealed through a series of comparisons between metal-anchored, TEMPO-anchored, and metal and TEMPO-anchored MOF catalysis. The fine tunability of the MOF allowed the homogeneously and doubly functionalized catalysts to undergo organic reactions in the heterogeneous media. In addition, the well-defined and carefully designed heterogeneous molecular catalysts displayed reusability along with better catalytic performance than the homogeneous systems using identical coordinating ligands. The role of metal-cation fixation should be carefully revised to control their coordination and maximize their catalytic activity. Lastly, the metal cation-fixed MOF displayed better substrate tolerance and reaction efficiencies than the TEMPO-anchored MOF or mixture MOF systems.
RESUMEN
Metal-organic frameworks (MOFs) are an attractive catalyst support for stable immobilization of the active sites in their scaffold due to the high tunability of organic ligands. The active site-functionalized ligands can be easily employed to construct MOFs as porous heterogeneous catalysts. However, the existence of active sites on the external surfaces as well as internal pores of MOFs seriously impedes the selective reaction in the pore. Herein, through a simple post-synthetic ligand exchange (PSE) method we synthesized surface-deactivated (only core-active) core-shell-type MOF catalysts, which contain 2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) groups on the ligand as active sites for aerobic oxidation of alcohols. The porous but catalytically inactive shell ensured the size-selective permeability by sieving effects and induced all reactions to take place in the pores of the catalytically active core. Because PSE is a facile and universal approach, this can be rapidly applied to a variety of MOF-based catalysts for enhancing reaction selectivity.
RESUMEN
An isostructural series of flexible metal-organic frameworks based on macrocycles having diverse pendant arms was developed to tune flexibility depending on functional groups. The pendant arms directing into the pores were found to play a key role in imparting different gate-opening behaviours in the threshold pressure and sorption capacity upon interaction with guest molecules.
RESUMEN
We report a three-dimensional Fe(ii) porous coordination polymer that exhibits a spin crossover temperature change following CO2 sorption (though not N2 sorption). Furthermore, single crystals of the desolvated polymer with CO2 molecules at three different temperatures were characterised by X-ray crystallography.
RESUMEN
Nanostructured materials such as porous metal oxides, metal nanoparticles, porous carbons, and their composites have been intensively studied due to their applications, including energy conversion and storage devices, catalysis, and gas storage. Appropriate precursors and synthetic methods are chosen for synthesizing the target materials. About a decade ago, metal-organic frameworks (MOFs) and coordination polymers (CPs) emerged as new precursors for these nanomaterials because they contain both organic and inorganic species that can play parallel roles as both a template and a precursor under given circumstances. Thermal conversions of MOFs offer a promising toolbox for synthesizing functional nanomaterials that are difficult to obtain using conventional methods. Although understanding the conversion mechanism is important for designing MOF precursors for the synthesis of nanomaterials with desired physicochemical properties, comprehensive discussions revealing the transformation mechanism remain insufficient. This Account reviews the utilization of MOFs/CPs as precursors and their transformation into functional nanomaterials with a special emphasis on understanding the relationship between the intrinsic nature of the parent MOFs and the daughter nanomaterials while discussing various experimental approaches based on mechanistic insights. We discuss nanomaterials categorized by materials such as metal-based nanomaterials and porous carbons. For metal-based nanomaterials transformed from MOFs, the nature of metal ions in the MOF scaffolds affects the physicochemical properties of the resultant materials including the phase, composite, and morphology of nanomaterials. Organic ligands are also involved in the in situ chemical reactions with metal species during thermal conversion. We describe these conversion mechanisms by classifying the phase of metal components in the resultant materials. Along with the metal species, carbon is a major element in MOFs, and thus, the appropriate choice of precursor MOFs and heat treatment can be expected to yield carbon-based nanomaterials. We address the relationship between the nature of the parent MOF and the porosity of the daughter carbon material-a controversial issue in the synthesis of porous carbons. Based on an understanding of the mechanism of MOF conversion, morphologically or compositionally advanced materials are synthesized by adopting appropriate MOF precursors and thermolysis conditions. Despite the progressive understanding of conversion phenomena of MOFs/CPs, this research field still has rooms to be explored and developed, ultimately in order to precisely control the properties of resultant nanomaterials. In this sense, we should pay more attention to the mechanism investigations of MOF conversion. We believe this Account will facilitate a deeper understanding of MOF/CP conversion routes and will accelerate further development in this field.
RESUMEN
Flexible metal-organic frameworks (MOFs) show the structural transition phenomena, gate opening and breathing, upon the input of external stimuli. These phenomena have significant implications in their adsorptive applications. In this work, we demonstrate the direct capture of these gate-opening and breathing phenomena, triggered by CO2 molecules, in a well-designed flexible MOF composed of rotational sites and molecular gates. Combining X-ray single crystallographic data of a flexible MOF during gate opening/closing and breathing with in situ X-ray powder diffraction results uncovered the origin of this flexibility. Furthermore, computational studies revealed the specific sites required to open these gates by interaction with CO2 molecules.
RESUMEN
The conversion reaction of metal-organic frameworks (MOFs) was adopted as a synthetic method to produce an advanced CO2 absorbent. A Li- and Si-containing MOF is a good precursor for lithium orthosilicate (Li4SiO4); the resulting solid has an unusual coral-like morphology, which provides an enhanced CO2-sorption performance (high uptake and fast absorption).
