Shi-Yuan Zhang

A Mixed-Crystal Lanthanide Zeolite-like Metal–Organic Framework as a Fluorescent Indicator for Lysophosphatidic Acid, a Cancer Biomarker

Two lanthanide zeolite-like metal-organic frameworks (Ln-ZMOFs) with rho topology, Tb-ZMOF and Eu-ZMOF, were constructed by self-assembly of a 4-connected lanthanide molecular building block and a bipyridine-dicarboxylate ligand. Varying the Tb(3+) and Eu(3+) ratio during synthesis afforded three mixed-crystal isostructural MZMOFs with variable Eu:Tb stoichiometry. Fluorescence studies revealed that a methanol suspension of one of these mixed crystals, MZMOF-3, exhibits selective detection of lysophosphatidic acid (LPA), a biomarker for ovarian cancer and other gynecologic cancers. Linear correlation between the integrated fluorescence intensity and the concentration of LPA was observed, enabling quantitative analysis of LPA in physiologically relevant ranges (1.4-43.3 μM). MZMOF-3 therefore has the potential to act as a self-referencing and self-calibrating fluorescent indicator for LPA.

Synthesis of a Chiral Crystal Form of MOF-5, CMOF-5, by Chiral Induction

Chiral variants of the prototypal metal-organic framework MOF-5, Λ-CMOF-5 and Δ-CMOF-5, have been synthesized by preparing MOF-5 in the presence of L-proline or D-proline, respectively. CMOF-5 crystallizes in chiral space group P213 instead of Fm3̅m as exhibited by MOF-5. The phase purity of CMOF-5 was validated by single-crystal and powder X-ray diffraction, infrared spectroscopy, thermogravimetric analysis, N2 adsorption, microanalysis, and solid-state vibrational circular dichroism. CMOF-5 undergoes a reversible single crystal-to-single crystal phase change to MOF-5 when immersed in a variety of organic solvents, although N-methyl-2-pyrrolidone (NMP) does not induce loss of chirality. Indeed, MOF-5 undergoes chiral induction when immersed in NMP, affording racemic CMOF-5.

Metal–organic frameworks based on transition-metal carboxylate clusters as secondary building units: synthesis, structures and properties

Five new metal–organic frameworks, [Zn2.5(SIP)(azopy)1.5(OH)2(H2O)]n (1), {[Zn1.5(SIP)(azopy)1.5(H2O)2]·0.5(azopy)·2H2O}n (2), {[Cd1.5(SIP)(azopy)1.5(H2O)2]·0.5(azopy)·2H2O}n (3), {[Cd2.25(SIP)0.5(μ3-OH)3(H2O)]·0.5H2O}n (4), and [Cu3(SIP)(CH3COO)(μ3-OH)2(μ2-H2O)(H2O)]n (5) were produced by hydrothermal reactions of NaH2SIP (NaH2SIP = 5-sulfoisophthalic acid monosodium salt) with azopy (azopy = 4,4′-azobispyridine). They were structurally characterized by single-crystal X-ray diffraction and elemental analysis. In the formation of these compounds, transition-metal carboxylate clusters as secondary building units (SBUs) play important roles. 1 crystallizes in the triclinic P space group and exhibits a 3D metal–organic framework with typical pcu topology. 2 and 3 are isomorphic and crystallize in the monoclinic space groupP2/c, both feature an interesting 3D coordination framework with an unprecedented {62.84}{63}2{64.82}2 topological structure, which has been deposited in the Reticular Chemistry Structure Resource (RSCR) named as zlm net. 4 crystallizes in the monoclinic C2/m space group and displays a 3D architecture with interesting coordination modes. 5 crystallizes in the triclinic space group P and possesses a 2D coordination configuration with a hexanuclear Cu6O4(COO)6 cluster as the secondary building unit. The luminescence analysis on 1–3 and the magnetic analysis on 5 were performed and discussed.

Structural evolution and magnetic properties of CoII coordination polymers varied from 1D to 3D constructed by 1,4-bis(1,2,4-triazol-1-ylmethyl)benzene

Seven Co(II) coordination polymers, [Co(btx)(3)(H(2)O)(2)](ClO(4))(2)·(btx)·2H(2)O (1), [Co(btx)(3)(H(2)O)(2)](BF(4))(2)·(btx)·2H(2)O (2), [Co(btx)(2)(H(2)O)(2)](NO(3))(2)·2H(2)O (3), [Co(btx)(2)Cl(2)] (4), [Co(btx)(BA)(2)(H(2)O)(2)]·2HBA (5), [Co(btx)(IPA)] (6) and [Co(3)(btx)(3)(BTA)(2)(H(2)O)(2)] (7) (btx = (1,4-bis(1,2,4-triazol-1-ylmethyl)benzene), HBA = benzoic acid, H(2)IPA = isophthalic acid, H(3)BTA = benzene-1,3,5-tricarboxylic acid), have been hydrothermally synthesized and characterized. 1 and 2 are isostructural and show a 1D Co-μ(2)-btx-Co chain structure, in which btx acts as both a bridging and terminal ligand. 3 is also a 1D chain structure but different from 1 and 2. The Co(II) ions are bridged by double μ(2)-btx to form Co(2)-btx(2) rings, which were further connected into 1D chains by sharing the Co(II) ions of the rings. 4 exists as a 2D grid with (4,4) topology structure. When aromatic acid was introduced to the synthetic system, three other coordination polymers 5-7 were obtained. In 5, the 1D chain is as that of 1, except that the terminal ligand was replaced by BA(-). 6 shows a two-fold parallel interpenetration framework featuring a 6-c uninodal net with (3(3),4(6),5(5),6) Schlafli topological symbol. 7 is an interesting 3D framework, which contains a 2-nodal net motif with the unprecedented (3(6),4(2),5(6),6)(3(9),4(9),5(3))(2) topology structure. The influence of the varieties of the structures and magnetic properties are studied and discussed in detail.

Dual-Functionalized Metal–Organic Frameworks Constructed from Hexatopic Ligand for Selective CO2 Adsorption

A ligand design approach, which requires rational design of ligand based on the knowledge of specific target, was applied for the synthesis of two interesting and robust MOFs 1 and 2 containing unusual several types of copper(II) secondary building units (SBUs). Thanks to unsaturated metal centers (UMCs) and azo group, microporous material 1 exhibited not only high CO2 uptake but also an impressive selective adsorption of CO2 over CH4 and N2. Moreover, a high H2 uptake of 1 was also observed.

From 1D zigzag chains to 3D chiral frameworks: synthesis and properties of praseodymium(III) and neodymium(III) coordination polymers

Reaction of H3TDA with PrIII/NdIII salts resulted in two coordination polymers, [Ln(H2O)4(HTDA)(H2TDA)]·H2O (Ln = Pr(1) and Nd(2), H3TDA = 1H-[1,2,3]-triazole-4,5-dicarboxylic acid), crystallizing in the monoclinic P21/c space group with a one-dimensional zigzag chain structure. The number of ligands and water molecules coordinated to the LnIII ions can be reduced by a hydrothermal method and the products transformed into {[Ln(TDA)(H2O)]·2.5H2O}n (Ln = Pr(3) and Nd(4)), crystallizing in the trigonal P3121 space group with a three-dimensional chiral framework structure. The compounds were characterized by elemental analysis, IR, PXRD, circular dichroism spectra and single crystal X-ray diffraction. The variable temperature magnetic susceptibility studies indicated that there are antiferromagnetic interactions between the LnIII ions in 1–4. Gas sorption and separation were studied as well.

Systematic investigation of the lanthanide coordination polymers with γ-pyrone-2,6-dicarboxylic acid

A series of lanthanide coordination polymers have been synthesized via the reaction of Ln3+ ions with γ-pyrone-2,6-dicarboxylic acid (H2CDO). Four new types of structures were segregated due to the plentiful linking modes of CDO ligands and high coordination flexibility of Ln3+ ions. The light rare earth ion (Nd3+) combined with H2CDO to yield 1D chain (type I, {[Nd2(H2O)11(CDO)3]·5H2O}n). The middle rare earth ions were linked by H2CDO to form a 2D sheet structure (type II, {[Ln2(H2O)7(CDO)3]·6H2O}n, Ln = Eu, Gd, Tb, Dy and Ho). H2CDO partly decomposed into oxalate in type III and IV. The heavy rare earth ions (Er3+, Tm3+) were chelated with CDO ligands and further bridged by oxalate ions to form a binuclear structure (type III, [Ln2(H2O)8(ox)(CDO)2]·6H2O), whereas Yb3+ ions combined with H2CDO and OX2−, respectively, to form two independent chains (type IV, {[Yb(H2O)4(ox)][Yb(H2O)4(CDO)2]·3H2O}n). The decomposition mechanism of H2CDO was preliminarily explained that the oxalate may be formed via an in situ oxidation–hydrolysis reaction of H2CDO in aqueous solution. Further experiments reveal that heavy lanthanide ions, long reaction time and high temperature may be related to this decomposition. In addition, the luminescence of Eu-2, Tb-3, and Dy-5 were studied in detail.

A Macroporous Metal-Organic Framework with Enhanced Hydrophobicity for Efficient Oil Adsorption

The applications of three-dimensional superstructures that consist of metal-organic framework (MOF) crystals are promising, but limited by spatial control over the crystallization process. Here a hydrophobic hierarchical metal-organic framework (HZIF-8) containing unusual micro-, meso-, and macropores was designed and synthesized by a template strategy, in which the polystyrene (PS) not only acted as the template to construct the macropores, but also modified the hydrophilic crystal surface of ZIF-8. When used as adsorbent for liquid oil/water separation, HZIF-8 demonstrated significantly enhanced oil adsorption performance while maintaining very low water uptake.

Modulation of Water Vapor Sorption by a Fourth-Generation Metal–Organic Material with a Rigid Framework and Self-Switching Pores

Hydrolytically stable adsorbents are needed for water vapor sorption related applications; however, design principles for porous materials with tunable water sorption behavior are not yet established. Here, we report that a platform of fourth-generation metal-organic materials (MOMs) with rigid frameworks and self-switching pores can adapt their pores to modulate water sorption. This platform is based upon the hydrolytically stable material CMOM-3S, which exhibits bnn topology and is composed of rod building blocks based upon S-mandelate ligands, 4,4-bipyridine ligands, and extraframework triflate anions. Isostructural variants of CMOM-3S were prepared using substituted R-mandelate ligands and exhibit diverse water vapor uptakes (20-67 cm3/g) and pore filling pressures ( P/ P0, 0.55-0.75). [Co2( R-4-Cl-man)2(bpy)3](OTf) (33R) is of particular interest because of its unusual isotherm. Insight into the different water sorption properties of the materials studied was gained from analysis of in situ vibrational spectra, which indicate self-switching pores via perturbation of extraframework triflate anions and mandelate linker ligands to generate distinctive water binding sites. Water vapor adsorption was studied using in situ differential spectra that reveal gradual singlet water occupancy followed by aggregation of water clusters in the channels upon increasing pressure. First-principles calculations identified the water binding sites and provide structural insight on how adsorbed water molecules affect the structures and the binding sites. Stronger triflate hydrogen bonding to the framework along with significant charge redistribution were determined for water binding in 33R. This study provides insight into a new class of fourth-generation (self-switching pores) MOM and the resulting effect upon water vapor sorption properties.