Functionalization of MOFs via a mixed-ligand strategy: enhanced CO₂ uptake by pore surface modification

Abstract

A new Zn(ii) metal-organic framework (MOF) [Me2NH2][Zn2(BDPP)(HTZ)]·4DMF (1) (H4BDPP = 3,5-bis(3,5-dicarboxylphenyl)pyridine, HTZ = 1H-tetrazole) has been constructed under solvothermal conditions by using a mixed-ligand strategy. Structural analysis demonstrates that 1 is a 3D framework based on four kinds of secondary building units (SBUs), which presents a rare structure constructed from quaternary SBUs and shows an uncommon (3,3,4,6)-connected topology. In particular, 1 contains two shapes of 1D open channels with suitable pore sizes, high porosity, and a highly polar pore system decorated with uncoordinated N atoms and carboxylic O atoms, providing a good environment for selective adsorption of CO2. Inspired by the structure of 1 and reticular chemistry, 5-amino-1H-tetrazole (ATZ) was used to replace 1H-tetrazole to enhance CO2 sorption capacity by pore surface modification; as a result, an amino-functionalized MOF, [Me2NH2][Zn2(BDPP)(ATZ)]·4DMF (1-NH2) was successfully built. 1-NH2 exhibits multipoint interactions between the CO2 molecules and the framework, resulting in better CO2 uptake and selectivity for CO2 over CH4 than 1.

Applying the Influence of Conformational Freedom on the Network Topologies Showing Impressive Proton Conductivity

“…On the other hand, generating MOFs with in-built immobilized functional groups of choice grafted inside the porous bulk surface has been extremely popular for several materials as well as physiochemical applications. ,− It is noteworthy here that insertion of immobilized proton carrier functional groups, especially of acidic natures such as sulfonic, phosphonic, carboxylic, into the pore surface is one of the most fruitful approaches to boost the proton conducting ability of the MOFs. ,,− In the presence of suitable environments, these groups also help to install proton carriers (e.g., H 2 O, NH 4 + , organic molecules like imidazole, etc.) by their hydrogen bonding abilities inside the pore and facilitate proton exchange easily. − However, grafting of free noncoordinating −COOH groups is a difficult task as metal-carboxylate coordination bonds are very strong.…”

Synthesis of 9,9-bis(4-hydroxyphenyl) fluorene catalyzed by bifunctional ionic liquids

“…ILs are considered as a new type of green solvent and catalyst, and have been widely used in separation, 16 electrochemistry, 17 and organic synthesis. 18,19 Functionalized ILs 20 take advantage of structure design, and can introduce specic functional groups into the cation and/or anion structure of the ILs for specic organic reactions. At present, many functionalized ILs are documented in the literature, and the functionalized groups include sulfonic acid groups, 21,22 hydroxyl groups, 23 alkenyl groups 24 and amino groups 25 etc.…”

Syntheses of four porous 3-D Cd(ii) metal–organic frameworks from a new multidentate ligand 5-(imidazol-1-yl)-N′-(pyridin-4-ylmethylene) nicotinohydrazide and their characterization and adsorption properties

“…Therefore, it is important to design and synthesize MOFs with suitable pore size and chemistry for the specic adsorption and separation of guest molecules. The pore size and interior surface of MOFs can be tuned and modied by changing the organic or inorganic building units via various ways, for example, changing the length and geometry of ligands, 11 introducing functional groups, 12,13 shiing counteranions, 9 using a mixed-ligand strategy, 14 and increasing the unsaturation sites of metal centers and improving the symmetry of inorganic core clusters. 15,16 Usually, the MOFs self-assembled from ligands containing multi-heteroatoms have better guest adsorption capacities due to weak host-guest interactions.…”