Zhenzhen Xue

Effect of Functionalized Groups on Gas‐Adsorption Properties: Syntheses of Functionalized Microporous Metal–Organic Frameworks and Their High Gas‐Storage Capacity

The microporous metal-organic framework (MMOF) Zn4O(L1)2⋅9 DMF⋅9 H2O (1-H) and its functionalized derivatives Zn4O(L1-CH3)2⋅9 DMF⋅9 H2O (2-CH3) and Zn4O(L1-Cl)2⋅9 DMF⋅9 H2O (3-Cl) have been synthesized and characterized (H3L1=4-[N,N-bis(4-methylbenzoic acid)amino]benzoic acid, H3L1-CH3=4-[N,N-bis(4-methylbenzoic acid)amino]-2-methylbenzoic acid, H3L1-Cl=4-[N,N-bis(4-methylbenzoic acid)amino]-2-chlorobenzoic acid). Single-crystal X-ray diffraction analyses confirmed that the two functionalized MMOFs are isostructural to their parent MMOF, and are twofold interpenetrated three-dimensional (3D) microporous frameworks. All of the samples possess enduring porosity with Langmuir surface areas over 1950 cm(2) g(-1). Their pore volumes and surface areas decrease in the order 1-H>2-CH3 >3-Cl. Gas-adsorption studies show that the H2 uptakes of these samples are among the highest of the MMOFs (2.37 wt% for 3-Cl at 77 K and 1 bar), although their structures are interpenetrating. Furthermore, this work reveals that the adsorbate-adsorbent interaction plays a more important role in the gas-adsorption properties of these samples at low pressure, whereas the effects of the pore volumes and surface areas dominate the gas-adsorption properties at high pressure.

A series of d10 coordination polymers constructed with a rigid tripodal imidazole ligand and varied polycarboxylates: syntheses, structures and luminescence properties

Five novel Zn(II)/Cd(II) coordination polymers, [Zn2(tib)(L1)(μ2-OH)(HCOO)·2H2O]n (1), [Cd2(tib)2(L1)(NO3)2·2H2O·4DMF]n (2), [Cd2(tib)2(L2)(NO3)2·2H2O·4DMF]n (3), [Cd(tib)(L3)·H2O·2DMF]n (4) and [Cd3(tib)4(L4)·5/2NO3·1/2OH·3DMF]n (5) (tib = 1,3,5-tris(1-imidazolyl)benzene, H2L1 = terephthalic acid, H2L2 = isophthalic acid, H2L3 = 1,4-naphthalenedicarboxylic acid, H3L4 = (1α,3α,5α)-1,3,5-cyclohexanetricarboxylic acid, DMF = N,N-dimethylformamide), have been synthesized under solvothermal conditions. In compound 1, two-dimensional (2D) Zn-tib layers are pillared by L1 to afford a (3,5)-connected three-dimensional (3D) framework with topology (63)(69·8). Compound 2 displays a 2D + 2D → 2D interpenetrated bi-layer array based on a 2D (3,4) network. Compound 3 is characterized as an infinite one-dimensional (1D) chain structure, which is further extended into a 3D supramolecular architecture via weak π⋯π stacking interactions. Compound 4 possesses a 3D 2-fold interpenetrated architecture with the Schlafli symbol (42·65·83)(42·6). Compound 5 features a fascinating petal shaped (3,5)-connected network with a (42·6·84·103)3(42·6)3(83)2 topology which until now has never been documented. In this series of compounds, the diversity of the structures is tuned by the coordination geometries of the metal ions and the nature of the varied co-ligands. Furthermore, the luminescence properties of compounds 1–5 at room temperature have also been studied in detail.

Effect of anions on the self-assembly of two Cd–organic frameworks: syntheses, structural diversity and photoluminescence properties

By employing a rigid tripodal ligand 1,3,5-tris(1-imidazolyl)benzene (tib) to assemble with two different Cd(II) salts, we have obtained two distinct cationic metal–organic frameworks, [Cd(tib)2·2NO3·4DMF]n (1) and [Cd(tib)2·2ClO4·4DMF]n (2) (DMF = N,N-dimethylformamide). The compounds were structurally characterized by single-crystal X-ray diffraction analyses and further characterized by infrared spectra (IR), elemental analyses, powder X-ray diffraction (PXRD), and thermogravimetric analyses (TGA). Both compounds 1 and 2 are constructed based on 2D square lattice (sql) nets, through ligand-to-axial (L–A), pillared by triangular tib ligands, resulting in two diverse 3D pillar-layered architectures. Compound 1 features a cationic framework with a (3,6)-connected rtl topology and has rhomboid channels; while for 2, the 2D layers repeat in an ⋯ABAB⋯ staggered stacking mode pillared by tib ligands, resulting in a different cationic framework from 1 with a pyr net. The results demonstrate that counterions NO3− and ClO4− play an important role in the fabrication of structures of 1 and 2. Furthermore, the photoluminescence of compounds 1 and 2 have been investigated in the solid state at ambient temperature.

From Pair Quadruple- to Single-Stranded Helices to Lines in a Mixed Ligand System via Adjusting the N-Substituent of l-Glu

Utilizing the mixed-ligand strategy, a novel fourfold-interpenetrated 3D homochiral metal-organic framework (1) with rare pair quadruple-stranded helices was assembled from bpee (1,2-bis(4-pyridyl)ethylene) and NCG (N-carbamyl-l-glutamate). Changing the carbamyl substituent of NCG with benzoyl group (NBzG: N-benzoyl-l-glutamate), a non-interpenetrated 3D homochiral coordination polymer (2) composed of alternate right-handed and left-handed single helix was obtained. When p-tolylsulfonyl substituent was used instead, an interesting homochiral linear structure (3) was formed from mixed-ligand bpee and NTsG (N-p-tolylsulfonyl-l-glutamate), with all individual NTsG being lined up orderly. The steric hindrance of N-substituent of l-glu has a tremendous impact on the construction of these diverse frameworks. Complexes 1-3 display second harmonic generation (SHG) efficiencies, which are approximately 0.32, 0.45, and 0.55 times as much as that of KDP powder.

Two cationic metal–organic frameworks featuring different cage-to-cage connections: syntheses, crystal structures, photoluminescence and gas sorption properties

Solvothermal reactions of a neutral rigid tripodal ligand, 1,3,5-tris(1-imidazolyl)benzene (tib), with Zn(NO3)2·6H2O and Zn(ClO4)2·6H2O produced two metal–organic frameworks, [Zn3(tib)4·6NO3·6H2O·3DMA]n (1) and [Zn2(tib)3·4ClO4·6H2O·6DMA]n (2) (DMA = N,N-dimethylacetamide), respectively, which feature different cage-to-cage connections. Both compounds 1 and 2 exhibit 3D cationic frameworks with charge-balancing extraframework anions. Interestingly, the counterions NO3− and ClO4− play an important role in the fabrication of structures of 1 and 2. Compound 1 shows 2-fold interpenetration while 2 gives a non-interpenetrated 3D porous framework. Adjacent M6L4 octahedral cages in compound 1 are further linked via vertex sharing to construct a 3D framework. For compound 2, neighboring octahedral cages connect with each other through sharing four metal ions which are in the equatorial plane to generate a 2D layer. Furthermore, the 2D layers are linked by other layers via sharing the other two metal ions which are in the axial position, finally forming a 3D supramolecular framework. The photoluminescence of compounds 1 and 2 has been investigated in the solid state. Gas sorption measurements were conducted on the activated 1, showing a H2 uptake of 1.2 wt% at 77 K and 1 bar with high initial adsorption enthalpy of 8.4 kJ mol−1.

Effect of anions on the self-assembly of Zn(II) with a hydrogenated Schiff base ligand: structural diversity and photoluminescent properties

A flexible tetradentate ligand, 1,2-bis(4′-pyridylmethylamino)ethane (L), has been used for assembly with different Zn(II) salts. Six complexes with diverse structures from zero- to two-dimensional array have been prepared under mild conditions. Complexes (Zn2LCl4·2H2O)2 (1) and (Zn2LBr4·H2O)2 (2) form novel discrete M4L2 square metallacycles, which are further linked by Cl (or Br)⋯H hydrogen bonds and weak intermolecular interactions to result in 3D frameworks. Complex [ZnL(SCN)2·2H2O]n (3) is a one-dimensional hinged chain. Different chains are stacked in a staggered pattern by the π–π interactions. Complex (ZnLCl2·2H2O)n (4) displays an infinite one-dimensional hinged chain too, but its 3D supramolecular structure is formed by the intrachain and interchain hydrogen bonds. Both complexes [ZnL(H2O)2·2ClO4·4H2O]n (5) and [ZnLAc(H2O)·Ac·2H2O]n (6) exhibit 2D networks. Structural analyses of complexes 1–6 suggest that anions Cl−, Br−, SCN−, ClO4−, and Ac− play an important role in the formation of those complexes with hydrogenated Schiff base L. Furthermore, the photoluminescence of complexes 1–6 have also been investigated in the solid state.

Synthesis, structure, characterization, and multifunctional properties of a family of rare earth organic frameworks

A series of isomorphic 3D layered rare earth hydroxide (LREH) frameworks RE3(OH)7(1,5-NDS) (RE = Y (1), Gd (2), Er (3), Yb (4); 1,5-NDS = 1,5-naphthalenedisulfonate) has been synthesized under hydrothermal conditions. The crystal structures, thermal stabilities, photoluminescence, and magnetic properties of these compounds have been investigated. The results demonstrate that the compounds are highly stable even at 351 °C and emit strong purple fluorescence, whose colour can be tuned by the coordinated rare earth ions. Their magnetic susceptibilities have also been measured, leading the compounds to be promising multifunctional materials.

A series of metal–organic frameworks containing diverse secondary building units derived from a flexible triazine-based tetracarboxylic ligand

Five new coordination polymers, {[Zn2(CCTA)(DMF)2]·(DMF)·(H2O)2}n (1), {[Zn2.5(CCTA)(OH)(H2O)]·(DMF)·(H2O)}n (2), {[Zn2(CCTA)(H2O)3]·(NMP)2·(H2O)3}n (3), {[Cd4(CCTA)2(DMF)4(H2O)2]·(H2O)6}n (4) and {[Cd4(CCTA)2(H2O)4]·(H2O)4}n (5), (H4CCTA = 2,4-bis(4-carboxyphenylamino)-6-bis(carboxymethyl)amino-1,3,5-triazine, DMF = N,N′-dimethylformamide, NMP = N-methyl-2-pyrrolidone), have been solvothermally synthesized and contain diverse secondary building units (SBUs). Due to various coordination modes and different conformations of the flexible H4CCTA ligand, the five complexes exhibit different topologies. Complex 1 has a two-dimensional (2D) structure with (4,4)-sql topology constructed with tetranuclear zinc clusters. Complex 2 also possesses a 2D framework with an unprecedented (418·610)(45·6)2 point symbol based on pentanuclear zinc clusters. Complex 3 shows a three-dimensional (3D) framework with PtS topology, containing linear tetranuclear zinc clusters. Both complexes 4 and 5 with 3D frameworks are built with rare infinite Cd–O–Cd and Cd2O2 rod-shaped SBUs, respectively. Furthermore, complex 4 could be described as a 4-connected uninodal umc net, instead of the pillared-layer structure of complex 5.

Homochiral Metal–Organic Frameworks with Tunable Nanoscale Channel Array and Their Enantioseparation Performance against Chiral Diols

Enantioseparation is an integral process in the pharmaceutical industry, considering the ever-increasing demand for chiral medicine products. As a new material, porous metal-organic frameworks (MOFs) have shown their potential application in this field because their structures are easy to adjust and control. Though chiral recognition between racemic substrates and frameworks has made preliminary progress, discussions of their size-matching effects are rare. Herein with the help of channel-tunable homochiral MOFs (HMOFs), diols of different sizes have been separated in good enantiomeric excess (ee%). In addition, the ee% reaches 67.4% for the first time for diols as large as 1,1,2-triphenyl-1,2-ethanediol, which turns out to be the most effective value so far.

Synthesis, crystal structure and MMCT of new cyanide-bridged complexes cis-MII(dppm)2(CN)2(FeIIIX3)2 (M = Ru, Os)

The syntheses, crystal structures, IR and electronic absorption spectroscopy of two cyanide precursors cis-MII(dppm)2(CN)2 (M = Ru, 1; Os, 2) (dppm = bis(diphenylphosphino)methane) and four new cyanide-bridged complexes cis-MII(dppm)2(CN)2(FeIIIX3)2 (M = Ru, X = Cl, 3; M = Ru, X = Br, 4; M = Os, X = Cl, 5; M = Os, X = Br, 6) are reported. The crystal structural data, IR and the MMCT (metal-to-metal charge transfer) in the electronic absorption spectroscopy indicate the existence of some electron delocalization along FeIII–NC–MII arrays in complexes 3–6. The presence of a newer MMCT band of the Os-based complexes (5 and 6) than the Ru-based complexes (3 and 4) should result from the larger spin–orbit coupling (SOC) of OsII. Also the theoretical calculated values of the crystal structural data and IR spectra are consistent with the experimental values. Temperature-dependent magnetic properties of complexes 3–6 reveal the presence of the very weak metal–metal interaction between distant FeIII ions.