Wei-Guang Zhang

The construction of coordination networks based on imidazole-based dicarboxylate ligand containing hydroxymethyl group

Reaction of Cd(II), Fe(II), and Cu(II) with a new ligand 2-(hydroxymethyl)-1H-imidazole-4,5-dicarboxylic acid (H4hmIDC) and 4,4′-bipyridine (bpy) affords three coordination polymers of {[Cd(H2hmIDC)(bpy)]·0.5bpy·H2O}n (1), [Fe2(HhmIDC)2]n (2), and {[Cu2(ITC)(bpy)(H2O)3]·2.5H2O}n (3) (ITC = imidazole-2,4,5-tricarboxylic acid), respectively. Complex 1 and complex 3 are (4,4) nets in topological view and display in different packing mode, while hydroxymethyl group in complex 3 is oxidized to carboxylic groupin situ. Complex 2 is a rare example of a cdl-e network containing both tetrahedral and square nodes. The hydroxymethyl groups act as a precursor and undergo different reactions directed by metal ions.

Tubular metal-organic framework-based capillary gas chromatography column for separation of alkanes and aromatic positional isomers.

In this work, a tubular metal-organic framework, MOF-CJ3, with a large one-dimensional channel was chosen as stationary phase to prepare a capillary gas chromatographic column via a verified dynamic coating procedure. The column offered good separations of linear and branched alkanes, as well as aromatic positional isomers (ethylbenzene, xylene, cresol, hydroquinone, dichlorobenzene, bromobenzonitrile, chloronitrobenzene, and nitrotoluene) based on a combination of host-guest interactions and adsorption effects. Elution sequence of most of the analytes followed an increasing order of their boiling points, except for the separation of n-heptanes/isooctane, cresol, and hydroquinone isomers. Separation behavior of the column upon different organic substances may be related to the tubular pore structure of MOF-CJ3, in which the van der Waals forces between the alkanes and the hydrophobic inner surfaces might have great effect on separation of n-heptanes and isooctane, whereas the separation of cresol and hydroquinone isomers were affected by (OH⋯O) hydrogen bonds formed between the analytes and the 1,3,5-benzenetricarboxylate ligands on the pore wall. The effects of temperature on separation of aromatic positional isomers were investigated to elucidate entropy and enthalpy controlling of the separation process.

An unprecedented (3,4,14)-connected 3D metal–organic framework based on planar octanuclear lead(II) clusters as a secondary building unit

An unprecedented trinodal (3,4,14)-connected 3D metal–organic framework formed by planar octanuclear lead(II) clusters as 14-connected nodes and 2-(Pyridin-3-yl)-1H-imidazole-4,5-dicarboxylate ligands as 3- and 4-connected nodes has been hydrothermally made. It provides a novel topological structure of metal–organic frameworks.

Anion-dependent assembly and solvent-mediated structural transformations of three Cd(II) coordination polymers based on 1H-imidazole-4-carboxylic acid

Three new Cd(II) coordination polymers with 1H-imidazole-4-carboxylic acid (Himc), [Cd(Himc)2(H2O)]n (1), [Cd(Himc)2]n (2) and [Cd2(Himc)2(SO4)(H2O)2]n (3) were perpared by solvothermal reactions and structurally characterized, which all comprised metal–negative ligand systems. Compound 1 exhibit a 1D zigzag chain; compound 2 features a 3D diamondoid work; while compound 3 possesses a 2D layer structure consisting of rhomboid grids. When 1 or 2 was left in a water/ethanolic solution of Na2SO4, their 1D or 3D framework was transformed into a 2D framework of 3. All compounds also displayed structure-related photoluminescent properties in the solid state.

Assembly of Cd(II) coordination polymers: structural variation, supramolecular isomers, and temperature/anion-induced solvent-mediated structural transformations

The reactions of Cd(II) salts and 5-(3-(1H-imidazol-1-yl)phenyl)-1H-tetrazolate (3-HIPT) resulted in eight new coordination polymers (CPs), namely, {[Cd(3-IPT)2(H2O)2]·H2O}n (1 and 2), {[Cd(3-IPT)2(H2O)2]·2H2O}n (3), [Cd(3-IPT)(H2O)Cl]n (4), [Cd(3-IPT)Cl]n (5), [Cd(3-HIPT)I2]n (6), [Cd(3-IPT)I]n (7), and [Cd(3-HIPT)2]n (8). Single-crystal X-ray analysis revealed that compound 1 is a 1D beaded chain, whereas compounds 2 and 3 are made of 2D networks. Compounds 1–3 are supramolecular isomers; their synthesis can be controlled under different temperatures and concentrations. The results showed that compounds 1 and 3 are the most thermodynamically and kinetically favored products, respectively. The thermodynamic stability of compound 1 may be attributed to the formation of the smallest M2L2 ring in the compound. Compounds 4–7 were obtained at higher Cl−/I− concentrations. Compound 4 is a 2D net composed of 1D [Cd(3-IPT)]n chains and μ2-Cl and μ2-H2O connectors. Compound 5 is a (3,6)-connected 3D framework with rtl topology. Compound 6 possesses a 1D chain with 3-HIPT ligands on both sides. Compound 7 is a 2D (4·82) net. Compound 8, a 3D pcu framework based on trinuclear linear SBUs, was formed when Cd(CF3CO2)2 was introduced at 170 °C. Based on a temperature-changing cycle, compounds 1 and 3 display crystal-to-amorphous-to-crystal phase transitions accompanying the dehydration–rehydration process, whereas compound 2 only displays crystal-to-amorphous phase transition when the temperature is increased and cannot go back to the crystal phase again. Interestingly, solvent-mediated structural transformations were accomplished among the selected compounds. When compounds 2, 3, 6, 7, or 8 were left in a water and NaCl solution at 170 °C, they were partly/fully transformed into compounds 1 and 5, respectively. When compound 5 was recrystallized in water at 120 and 170 °C, it was partly and fully transformed into compounds 2 and 1, respectively. Such transformations were induced by the temperature or an anion. In addition, the thermal stabilities and luminescence properties of selected compounds have also been studied in detail. The complexes exhibit intense solid-state fluorescence emission at room temperature.

The construction of Cu(I)/Cu(II) coordination polymers based on pyrazine–carboxylate: Structural diversity tuned by in situ hydrolysis reaction

The reaction of a new ligand, N,N′-(5,7-dihydro-1,3,5,7-tetraoxobenzo[1,2-c:4,5-c′]dipyrrole-2,6(1H,3H)-diyl)bis-(9CI)-3-pyrazinecarboxamide (L), with CuCl2·2H2O, CuI, or Cu(ClO4)·2H2O yields five coordination polymers. Among these polymers are three new coordination polymers, [CuII2(μ3-pzc)2(μ1-Cl)2]n (1), [CuICuII(μ2-pzc)2(μ2-Cl)(H2O)]n (2a), and {[CuI2CuII(μ2-pzc)2(μ3-I)2(H2O)]·H2O}n (3), as well as two previously reported coordination compounds, [CuICuII(μ2-pzc)2(μ2-Cl)(H2O)]n (2b) and [CuII(pzc)2] (4), in which 2-pyrazinecarboxylate (Hpzc) was obtained from in situ hydrolysis of the L ligand. Compound 1 is a two-dimensional (2D) double-layer structure, which can be viewed as a binodal (3,3)-connected network with the Schlafli symbol of (62·10) (6·102). Compounds 2a and 2b are two supramolecular isomers, both of them are (4,4) nets in topological view but showing different packing modes. Compound 3 has a 3D open framework constructed from the linkages of 1D sawtooth chains of iodide copper(I) clusters with [CuII(μ2-pzc)] subunits. Compound 4 is a mononuclear complex. Interestingly, except for compounds 2b and 4, all the other compounds cannot be directly synthesized using Hpzc and the corresponding Cu ions as initial reactants under the same reaction conditions. This finding indicates that the structural diversity of this system is tuned by the in situ hydrolysis reactions.

Construction of luminescent three-dimensional Ln(III)–Zn(II) heterometallic coordination polymers based on 2-pyridyl imidazole dicarboxylate

Four three-dimensional (3D) Ln(III)–Zn(II) heterometallic coordination polymers, {[LnZn6(μ4-mPyIDC)4Cl2(H2O)6]·Cl}n [Ln = Sm (1), Eu (2), Tb (3); H3mPyIDC = 2-(pyridine-3-yl)-1H-4, 5-imidazoledicarboxylic acid], and {[LnZn(μ5-pPyIDC)(μ2-SO4)(H2O)3]·3H2O}n [Ln = Tb (4); H3pPyIDC = 2-(pyridine-4-yl)-1H-4,5-imidazoledicarboxylic acid], were prepared under hydrothermal conditions. Isostructural complexes 1–3 were constructed using 1D [Zn3(mPyIDC)2Cl(H2O)3]n chains in a plywood-like packing mode jointed by Ln(III) ions. These compounds display unusual trinodal (3,4)-connected 3D networks with a point symbol of (4·62)4(4·63·82)4(62·82·112). Complex 4 has a highly connected framework with (36·422·516·6) network topology based on a rare planar heterometallic hexanuclear [Tb2Zn4(pPyIDC)2] secondary building block. The luminescent properties of complexes 2–4 were also investigated.

Construction of terpyridine–Ln(III) coordination polymers: structural diversity, visible and NIR luminescence properties and response to nerve-agent mimics

Reactions of Ln(III) salts with 4′-(2,4-disulfophenyl)-2,2′:6′2′′-terpyridine (H2DSPT) result in five types of coordination polymers, namely, {[Gd(DSPT)(OH)(H2O)2]·4H2O}n (type I, 1), {[Ln(DSPT)(ox)0.5]·H2O}n (type II, Ln = Nd (2), Eu (3), Tb (4), Er (5), Yb (6), Lu (7), ox = oxalate), {[Ln(DSPT)(ox)0.5(H2O)]·4H2O}n (type III, Ln = Yb (8), Lu (9)), {[Ln(DSPT)(pBDC)0.5·(H2O)2]·5H2O}n (type IV, Ln = Yb (10), Lu (11), H2pBDC = 1,4-benzenedicarboxylic acid), and {[Ln(DSPT)(pBDC)0.5·(H2O)2]·5H2O}n (type V, Ln = Dy (12), Er (13)). Type I is a 1D chain built from binuclear Ln2(DSPT)2 building blocks and OH− linkers. Type II is a 2D layer with (4,5)-connected topology constructed by binuclear Ln2(DSPT)2 building blocks and ox− anions. Type III is also a 2D network based on Ln(III), DSPT2−, and ox−, but with (3,4)-connected topology. The ox− anion is generated in situ from carboxylic acid precursor in type II and type III structures. The formation of Lu(III) complexes of type II or type III can be tuned by the addition of different carboxylic precursors. Type IV posseses a 2D layered structure based on the [Ln(DSPT)]n chain connected by pBDC2−. Type V exhibits a 3D framework formed by binuclear [Ln2(SO3)2(COO)2] secondary building blocks and DSPT2− and pBDC2− linkers, resulting in a uninodal 8-connected sqc4 topology. The Nd- and Yb-centered complexes show strong NIR luminescence, whereas the Tb- and Eu-centered complexes exhibit strong luminescence in the visible region at room temperature in both solid state and water emulsions. Their luminescence intensity can be strongly quenched by the addition of diethylchlorophosphonate (DCP), but significantly less influenced by dimethylmethylphosphonate (DMMP), diethylcyanophosphonate (DCNP) and other selected organophosphate, which make this material have a potential application in nerve-agent detection.

Controlled synthesis, structures and properties of one-, two-, and three-dimensional lanthanide coordination polymers based on (8-quinolyloxy)acetate

Hydrothermal reactions of Ln(NO3)3 and (8-quinolyloxy)acetic acid (HQOA) with auxiliary ligands resulted in a series of new one-, two- and three-dimensional (1D, 2D and 3D) coordination polymers, namely, [Ln(QOA)2 (H2O)2]·NO3·H2O [Ln = Eu (1), Gd (2)], [Ln2(QOA)4(ox)(H2O)]·3H2O [Ln = Pr (3), Er (4)], [Ln2(QOA)4(BDC) (H2O)]·4H2O [Ln = Sm (5)] and [Ln(QOA)(BDC)] [Ln = Sm (6), Eu (7)] [QOA = (8–quinolyloxy)acetate; ox = oxalate; BDC = 1, 4–benzenedicarboxylate], respectively. Compounds 1–2 possess 1D zigzag chains bridged by QOA anions and 3–4 contain 1D folded chains alternately bridged by oxalates and QOA anions. Complex 5 is an ordered (2,4)–connected 2D sheet-like structure. In compounds 6–7, four BDC anions bridge two adjacent metal atoms to form dinuclear lanthanide building blocks and these dinuclear blocks are further connected together to form an 8-connected 3D network. The progressive variation from 1D zigzag chains (1–2) to 1D folded chains (3–4) to a 2D layer network (5) and to 3D frameworks (6–7) is mainly attributed to the change of bridging ligands as well as the different coordination modes of organic carboxylic ligands. Moreover, the thermal stabilities and photoluminescent properties of these compounds show a remarkable difference due to the progressive variation of crystal structures.

Stereoselective quantification of triticonazole in vegetables by supercritical fluid chromatography

A highly fast analytical method though supercritical fluid chromatography (SFC) has been developed to quantify triticonazole enantiomers in cucumbers and tomatoes. Effects of organic modifier type and concentration on chiral separation and quantification of standard solution as well as matrix-matched standard solutions have been studied in detail. Among three organic modifiers, better separation of triticonazole racemate was achieved with 20% ethanol (v/v). The run time in SFC (ca 3min) with CO2-ethanol (80:20, v/v) as the mobile phase was six-fold shorter than HPLC analysis (about 18min). Then, QuEChERS (quick, easy, cheap, effective, rugged and safe) extraction procedure was used for triticonazole in vegetables. The residue analysis method was validated. Good linearity (R2≥0.9988) and recoveries (81.62-106.21%, RSD≤7.30%) for the two enantiomers were achieved. This developed method described herein is convenient and reliable for enantioselective detection of triticonazole in vegetables, which might provide additional information for reliable risk assessment of chiral pesticides.