Sifu Tang

High gas storage capacities and stepwise adsorption in a UiO type metal–organic framework incorporating Lewis basic bipyridyl sites

A UiO type MOF with Lewis basic bipyridyl sites was synthesized and structurally characterized. After being activated by Soxhlet-extraction, this MOF exhibits high storage capacities for H2, CH4 and CO2, and shows unusual stepwise adsorption for liquid CO2 and solvents, indicating a sequential filling mechanism on different adsorption sites.

Efficient quantum cutting in hexagonal NaGdF4:Eu3+ nanorods

An ionic liquid (IL) assisted solvothermal method is employed to prepare single phase, oxygen free, hexagonal NaGdF4:Eu3+ (2 mol%) nanorods with a visible quantum efficiency of 187%. In contrast, for mixed materials containing cubic and hexagonal NaGdF4:Eu3+, the quantum efficiency is much less (127%). Thus, synthesis parameters have to be carefully chosen in order to get the high performance hexagonal material. Not only the influence of the IL but also of the Gd:F ratio during synthesis as well as the temperature were studied. It is found that the IL stabilizes the formation of hexagonal NaGdF4:Eu3+, likewise a fluoride excess (Gd:F = 1:8) and elevated reaction temperatures (200 °C).

Enhanced Uptake and Selectivity of CO2 Adsorption in a Hydrostable Metal-Organic Frameworks via Incorporating Methylol and Methyl Groups

A new methylol and methyl functionalized metal-organic frameworks (MOFs) QI-Cu has been designed and synthesized. As a variant of NOTT-101, this material exhibits excellent CO2 uptake capacities at ambient temperature and pressure, as well as high CH4 uptake capacities. The CO2 uptake for QI-Cu is high, up to 4.56 mmol g(-1) at 1 bar and 293 K, which is top-ranked among MOFs for CO2 adsorption and significantly larger than the nonfunctionalized NOTT-101 of 3.93 mmol g(-1). The enhanced isosteric heat values of CO2 and CH4 adsorption were also obtained for this linker functionalized MOFs. From the single-component adsorption isotherms, multicomponent adsorption was predicted using the ideal adsorbed solution theory (IAST). QI-Cu shows an improvement in adsorptive selectivity of CO2 over CH4 and N2 below 1 bar. The incorporation of methylol and methyl groups also greatly improves the hydrostability of the whole framework.

Tuning the structure of metal phosphonates using uncoordinating methyl group: syntheses, structures and properties of a series of metal diphosphonates

Eight new transition metal diphosphonates, namely, [Mn(H2L)(H2O)2][(H2O)2] (1), [Co(H2O)6][H2L][(H2O)2] (2), [Co(H2O)6][(H3L)2][(H2O)2] (3), [Ni(H2O)6][H2L][(H2O)2] (4), [Cu(H2L)][(H2O)2] (5), [Zn(H2O)6][(H3L)2][(H2O)2] (6), [Zn(H2L)(H2O)2] (7) and [Cd(H2L)(H2O)2] (8), have been synthesized hydrothermally from 2,5-dimethyl-1,4-phenylenediphosphonic acid (H4L) and thoroughly characterized using EA, IR, TGA, powder and single-crystal XRD, luminescence and magnetism methods. The single-crystal X-ray diffraction measurements indicate that the diphosphonate ligands adopt three kinds of coordination modes which have a huge influence on the structure formation. Compounds 1 and 8 are isostructural and feature 3D framework structures which are constructed by the connectivity of MO6 (M = Mn and Cd) octahedrons and tetradentate organic linkers. Compounds 2 and 4, 3 and 6 are also isostructural, but have isolated mononuclear structures. Compound 5 exhibits 2D layered structure, in which four-connected copper(II) centers are bridged by tetradentate diphosphonate ligands. Compound 7 has a 1D infinite chain structure which is constructed from ZnO4 tetrahedrons and bidentate bridging diphosphonate ligands. It is also found that compounds 6–8 display interesting luminescent properties, whereas 1 shows an antiferromagnetic property.

An rht type metal-organic framework based on small cubicuboctahedron supermolecular building blocks and its gas adsorption properties

A metal–organic framework NPC-5 was synthesized via reaction of a methyl-functionalized ligand 2,4,6-trimethyl benzene-1,3,5-triyl-isophthalate (TMBTI) with Co(NO3)2·6(H2O) under solvothermal conditions. The steric hindrance induced by the methyl groups on the central phenyl ring led to a non-planar configuration of the ligand and further resulted in a small cubicuboctahedron SBB sustained (3, 24)-connected rht network, which comprised three types of cages and exhibited high porosity. Experimental results showed that despite the use of different synthetic methods the same structure was obtained. Gas sorption study of this MOF revealed high CO2 and CH4 uptake capacities and relatively low adsorption enthalpies.

Highly Luminescent Salts Containing Well-Shielded Lanthanide-Centered Complex Anions and Bulky Imidazolium Countercations

Four salts containing imidazolium cations and europium(III)- or terbium(III)-centered complex anions have been successfully synthesized from an ethanol/H2O solution. The single-crystal X-ray diffraction analyses reveal that these compounds have a common formula of [R][Ln(DETCAP)4] [R = 1-ethyl-3-methylimidazolium (C2mim), Ln = Eu (1) and Tb (2); R = 1-butyl-3-methylimidazolium (C4mim), Ln = Eu (3) and Tb (4); DETCAP = diethyl-2,2,2-trichloroacetylphosphoramidate], in which the lanthanide centers are chelated by four chelating pseudo-β-diketonate ligands (DETCAP)(-), forming the respective complex anions. Their thermal behaviors and stabilities were also investigated to study the role of the length of the side chain in the cations. Fluorescence measurements at both room temperature and liquid-nitrogen temperature show that these materials show intense characteristic europium(III) or terbium(III) emissions and have long decay times. Their overall quantum yields were determined to be in the range of 30-49%.

Lanthanide diphosphonates based on a V-shaped ligand: syntheses, structures, experimental and theoretical luminescence properties

One series of isostructural lanthanide phosphonates, namely [Ln2(H2L)3][(H2O)5] (H4L = (5-methyl-1,3-phenylene)bis(phosphonic acid); Ln = Eu (1), Gd (2), Tb (3), and Dy (4)), have been successfully synthesized from a V-shaped rigid ligand. Systematic characterizations using single-crystal and powder X-ray diffraction (XRD), thermogravimetric analyses (TGA), and photoluminescence spectroscopy were accomplished. It was found that these compounds all crystallize in the cubic I213 space group, showing three-dimensional framework structures. The frameworks are stable up to 350 °C and show their respective characteristic metal-centered emissions. The photoluminescence properties were also theoretically investigated by using a newly developed software program – LUMPAC. The energy transfer and back energy transfer rates were estimated, and the T1 → 5D1 and T1 → 5D0 channels were revealed to be the dominant pathways. The combination of experimental and theoretical studies on the photoluminescence properties substantially supports the understanding and design of highly luminescent inorganic–organic hybrid materials.

Investigation of the structure variation of metal diphosphonates with the changing of N-donor auxiliary ligands and their properties

Nine metal diphosphonates, [Co(H2L)(pyz)(H2O)][(H2O)0.3] (1), [Ni(H2L)(pyz)(H2O)2] (2), [Ni(H2L)(2,2′-bipy)2][(H2O)2] (3), [Ni(H2L)(4,4′-bipy)(H2O)][(H2O)2] (4), [Ni(H2L)(dpe)(H2O)2][(H2O)2] (5), [Cu(H2L)(pyz)(H2O)2] (6), [Cu(H2L)(4,4′-bipy)][(H2O)2] (7), [Zn(H2L)(2,2′-bipy)(H2O)2] (8) and [Cd(H2L)(pyz)(H2O)2] (9), have been synthesized from a diphosphonate ligand 2,5-dimethyl-1,4-phenylenediphosphonic acid (H4L) and four N-donor auxiliary ligands (pyz = pyrazine, 2,2′-bipy = 2,2′-bipyridine, 4,4′-bipy = 4,4′-bipyridine, dpe = 1,2-di(4-pyridyl)ethylene). In compound 1, pyrazine molecules behave as pillars which connect the Co(H2L) layers into a 3D network structure. Compounds 2, 6 and 9 are isostructural and also show 3D framework structures, in which metal centers are linked by the bidentate diphosphonate ligands into 1D infinite chains and are connected by the pyrazine linkers. In compounds 3 and 8, the diphosphonate ligands, showing bidentate or tetradentate coordination modes, bridge the respective metal ions (Ni2+ and Zn2+) into a 1D infinite chain or 2D layer structure, respectively, in which the 2,2′-bipy ligands chelate to the central metal ions and complete the coordination spheres. In compound 4, the 4,4′-bipy molecules also behave as pillars between the 2D layers, which are constructed from tridentate bridging diphosphonate ligands and six-coordinated Ni2+ ions. Compounds 5 and 7 have similar square grid layered structures which are constructed from bridging bidentate diphosphonate ligands and 4,4′-bipy or dpe linkers. Photophysical measurements indicate that compounds 8 and 9 display ligand centered emissions. Magnetic studies reveal that dominant antiferromagnetic interactions are propagated in compounds 1–3 between the magnetic centers.

Promotional effect of HZSM-5 on the catalytic oxidation of toluene over MnOx/HZSM-5 catalysts

A series of HZSM-5 supported MnOx catalysts with different manganese contents were prepared by an incipient impregnation method and tested for the catalytic oxidation of toluene. The catalytic results indicate that 10% MnOx/HZSM-5 exhibits the optimum catalytic activity, excellent catalytic durability in dry conditions and high regeneration capability in humid conditions. The dispersion of MnOx species on the HZSM-5 surface significantly reduces coke formation and simultaneously efficiently accelerates the oxidative decomposition of coke deposition during toluene catalytic oxidation. An obvious cooperative action is present on the MnOx/HZSM-5 catalysts for the catalytic oxidation of toluene, which is originally attributed to the excellent toluene adsorption capacity and trapping ability of HZSM-5 as well as the superior redox ability of the MnOx species. The correlation between characterizations and the catalytic results reveals that the mesoporous structure and low-temperature reducibility of MnOx are key factors responsible for the catalytic performance of toluene oxidation. Moreover, the Bronsted acid sites of the HZSM-5 zeolite, as active promoters, play a significant role in the catalytic oxidation of toluene through a comparative analysis with SiO2 and Al2O3 supported MnOx catalysts. The existence of a cooperative action between the redox ability of the MnOx species and the acidic properties of the HZSM-5 zeolite in the MnOx/HZSM-5 catalysts results in a high catalytic activity for the reaction.

Two new two-dimensional layered uranyl-bearing polycarboxylates from semi-rigid tetracarboxylic acids

Two new uranyl-bearing tetracarboxylates with interesting structures have been synthesized from two semi-rigid tetracarboxylic acids. Both compounds 1 and 2 display two-dimensional layered structures, but 1 is assembled from corner-sharing UO5F2 polyhedra and hexadentate tetracarboxylate ligands whereas 2 is constructed from discrete UO7 polyhedra and pentadentate tetracarboxylate ligands.