From Hydrogen Bond to van der Waals Force: Molecular Scalpel Strategy to Exfoliate a Two-Dimensional Metal-Organic Nanosheet.

The facile exfoliation of a two-dimensional metal-organic nanosheet of {[Co(HL)(H2O)(Py)3/4]·1/2H2O·DMF}n [1-Py; H3L = 5-(1H-pyrazol-4-yl)isophthalic acid and Py = pyridine] was achieved, via a molecular scalpel strategy, by weakening intermolecular forces between adjacent layers. The resulting 1-Py/KB40 (KB = Ketjen black) shows an increased oxygen evolution reaction (OER) performance with an overpotential of 370 mV at a current density of 10 mA cm-2 and a Tafel slope of 58 mV dec-1. This work sheds light on the structure-morphology-reactivity relationship of such materials in OER.

Regulation of Chirality in Metal-Organic Frameworks (MOFs) Based on Achiral Precursors through Substituent Modification.

The generation and regulation of chirality are closely related to the origin of life. Using achiral precursors to spontaneously build chiral MOFs remains a major challenge. Here, a method to synthesize chiral MOFs from achiral precursors by utilizing chiral fragments was achieved. The transformation from chiral fragments of 1 to chiral frameworks of 2 and 3 was realized by modifying the substituents, and the enantiomer resolution of 3-P41212 and 3-P43212 was achieved by d/l camphoric acid. 3 was then further studied in applications.

Molecular engineering in a family of pillared-layered metal-organic frameworks for tuning gas adsorption behavior.

In this work, inspired by a water-assisted three-dimensional supramolecular structure 1, we use a mixed-ligand strategy to form a 3D pillared-layered matrix by the introduction of linear ligands to compete against the water molecules. The resulting analogue microporous MOFs of 2-H, 2-F and 2-N, decorated with different functional groups, similarly show the CO2 uptake. Thanks to the negligible N2 adsorption capacity, enhanced selective adsorption towards CO2 is achieved in compound 2-N. That is, we present here an alternative plan for the high CO2 selective adsorption performance. In addition, the structure stability and moderate affinity for CO2 of these microporous MOFs endow them with excellent reusability.

Three metal-organic framework isomers of different pore sizes for selective CO2 adsorption and isomerization studies.

Metal-organic frameworks (MOFs) or porous coordination polymers (PCPs) with tunable pore sizes, shapes and functionalities have excellent prospects in many applications, such as carbon capture. Molecular sieving can usually enable very high CO2 adsorption selectivity but has rarely been achieved, because it is difficult to precisely control the pore size in the range of 3-4 Å. We report here three MOF isomers built from CdII, terephthalic acid and 3,6-di(pyridin-4-yl)-1,2,4,5-tetrazine with the same stoichiometric ratio, among which 1 and 2 are framework-catenation isomers and 2 and 3 are framework-topological isomers. 1 contains 2-fold interpenetrated networks (topology of pcu) and 1D ultra-micropores and shows highly selective adsorption of CO2 over N2 and CH4, which is mainly ascribed to the molecular sieving effect of the framework. 2 contains a pcu network with 3D interconnected micropores, and 3 contains a kag network with much larger pores of 15 Å. Framework isomerization, in this case, was shown to be a feasible way of tuning the pore size of a MOF for selective CO2 adsorption. The effects of hydrothermal reaction conditions and additives on the structures and the formation of the MOF isomers were also studied.

Tetrazole-based porous metal-organic frameworks for selective CO2 adsorption and isomerization studies.

Tetrazole-based molecules have numerous bridging coordination modes which afford great synthetic possibilities for the preparation of porous metal-tetrazolate architectures for many applications, such as carbon capture. We reported here three tetrazole-based MOFs: 1, {[Cu12(ttz)8/3Cl5(H2O)16]11+·11Cl-}n (H3ttz = N2,N4,N6-tris(4-(1H-tetrazol-5-yl)phenyl)-1,3,5-triazine-2,4,6-triamine), contains highly positively charged Cu12 clusters and the largest mesopores (32 Å) among the reported MOFs based on a tri-topic tetrazole ligand. 2 and 3 are two MOF isomers built by using CuII and 2-(1H-tetrazol-5-yl)pyrimidine. 3 contains nonporous layers, while 2 contains 1D channels and showed high selectivity for adsorbing CO2, which should be attributed to the high density of free nucleophilic tetrazole N atoms on the pore surfaces. We found that the isomerization between 2 and 3 was caused by the diverse coordination modes of tetrazole-based ligands and can be controlled in synthesis processes.

Effective adsorption of Congo red by a MOF-based magnetic material.

Metal-organic frameworks (MOFs) are an exciting class of porous crystallized materials, which have attracted great interest in sustainable energy and environmental remediation. Magnetite (Fe3O4) is one of the best-known magnetic materials and has been extensively studied with respect to properties involving high saturation magnetization, biocompatibility and low toxicity. The combination of MOFs and Fe3O4 has shown its potential applications in drug delivery, catalysis and wastewater treatment. However, only classical porous MOFs are used to encapsulate magnetic nanoparticles, such as MIL-100(Fe), ZIF-8, UiO-66 and so on. Herein, we firstly synthesized a new MOF ZTB-1 and surveyed its applications in magnetic materials. As a result, a highly water-stable MOF-based magnetic material Fe3O4@ZTB-1 has been obtained, and it was for the first time used as an excellent adsorbent for the fast adsorption of Congo red (CR) from aqueous solutions, exhibiting an adsorption capacity of 458 mg CR per gram. The electrostatic interactions and hydrogen bond are responsible for binding of CR with Fe3O4@ZTB-1. The magnetic material Fe3O4@ZTB-1 shows a potential application in dyeing wastewater treatment.

Two MOFs as dual-responsive photoluminescence sensors for metal and inorganic ion detection.

Two metal-organic frameworks (MOFs), [Zn(BIPA)(tfbdc)]n (1) and {[Cd(BIPA)(tfbdc)(H2O)]·DMF}n (2), were hydrothermally synthesized using the self-assembly of the "V-shape" BIPA ligand (bis(4-(1H-imidazol-1-yl)phenyl)amine) and the H2tfbdc ligand (2,3,5,6-tetrafluorobenzene-1,4-dicarboxylic acid) with Zn/Cd metal salts. 1 is a 2D hcb framework and 2 is a 2D sql network. Their applications in detecting metal and inorganic ions were also explored. The results indicate that 1 exhibits dual-responsive photoluminescence sensing for Fe3+ and Cr2O72- ions while 2 can detect Hg2+ and Cr2O72- ions.

Macrocyclic dinuclear, helical, layered and 3-D Ag(I) complexes constructed from AgX (X = NO3(-) and ClO4(-)) and flexible bis(pyridyl) ligands with a chelating spacer: syntheses, structures and photoluminescence properties.

Reaction of AgX (X = NO3− and ClO4−) and three flexible bis(pyridyl) ligands with a chelating spacer leads to the formation of eight novel Ag(I)-bis(pyridyl) coordination complexes: {[Ag2L1(NO3)2]n·2nH2O} (1), {[AgL1]n·nClO4} (2), {[AgL2]n·nNO3} (3), {[AgL2]n·nClO4} (4), [Ag2(H2L2)2]·6ClO4·9H2O (5), {[AgL3]n·nNO3·nH2O} (6), {[AgL3]n·nClO4·nH2O} (7), and {[Ag3(L3)2(ClO4)]n·2nClO4} (8) (L1 = N,N'-bis(pyridin-2-ylmethyl)propane-1,3-diamine, L2 = N,N'-bis(pyridin-3-ylmethyl)propane-1,3-diamine, L3 = N,N'-bis(pyridin-4-ylmethyl)propane-1,3-diamine), which have been characterized by elemental analysis, IR, TG, UV-Vis DRS, PL, powder and single-crystal X-ray diffraction. Complex 1 presents a (4,4) layered motif which is furnished by the bridging of L1 molecules and nitrate anions in µ4 (κ1N1:κ1N2:κ1N3:κ1N4) and µ2 (κ1O4:κ1O6) modes. With a different µ2 (κ1N1:κ1N2:κ1N3:κ1N4) mode, L1 molecules in complex 2 join the adjacent Ag(I) cations to form a helical chain structure. Complexes 3 and 4 also show helical chain structures with the L2 molecules displaying the same µ3 (κ1N1:κ1N2:κ1N3:κ1N4) mode. The protonation of ­NH­ groups in the chelating spacer leads to the formation of H2L22+ cations which further results in a macrocyclic dinuclear motif in complex 5. Complexes 6 and 7 are 3-D svi-x nets with the counter-anions and lattice water molecules being encapsulated in the 1-D channels. Complex 8 exhibits a snake-shaped chain with the L3 molecules presenting µ3 (κ1N:κ1N':κ1N″:κ1N) mode. The structural diversities of complexes 1­8 can be attributed to the coordination modes and conformations of L1­L3. The photoluminescence properties demonstrate that complexes 1, 2 and 5 exhibit ligand-based blue emission maxima from 455 to 462 nm at room temperature in the solid state.