Unusual metal–organic network constructed from Zn(II), benzenetricarboxylate and bis(1,2,4-triazolyl)pyridine

Hydrothermal reaction of ZnSO₄ · 7H₂O with 1,3,5-benzenetricarboxylic acid (H₃btc) and 2,6-bis(1,2,4-triazolyl)pyridine (btp) afforded a novel metal–organic network {[Zn₃(btc)₂(btp)₂(H₂O)₂] · 4H₂O}_n (1) with a supramolecular cocrystal [H₃btc · btp · H₂O]_n (2). The complex 1 exhibits an unusual network containing two molecular squares and a rectangle. The networks interpenetrate to make a 3D metal–organic framework, which is quite thermal stable. Compound 2 shows a 2D supramolecular network assembled through strong hydrogen bonds.     

A novel 2D metal-organic framework with Lewis basic sites as a heterogeneous base catalysis

A 2D metal-organic framework, [(Nd₂(TATMA)₂·4DMF·4H₂O]_n (namely NdTATMA), was successfully assembled from a semi-rigid organic ligand 4,4,4″-s-triazine-1,3,5-triyltri-m-aminobenzoate (H₃TATMA) and Nd(III) ion. NdTATMA has binuclear {Nd₂(COO)₆} inorganic clusters and completely deprotonated organic ligands. In the topology view, NdTATMA can be simplified as a 3,6-connected kgd topology with the Schläfli symbol of (4³)₂(4⁶ · 6⁶ · 8³). This resultant sample has been fully characterized by single crystal and powder X-ray diffractions, elemental analysis and thermogravimetric analyses. Due to abound Lewis basic sites in the structure, NdTATMA can be served as a good heterogeneous base catalysis to catalyse Knoevenagel condensation reaction. The resultant sample is able to recycle four times without significant activity decrease.     

Microporous metal–organic frameworks constructed by Cu(I)/Zn(II), Tpt and 1,4-benzenedicarboxylate

Two novel metal–organic frameworks, [Cu(tpt)(bdc)_1/2]_n · nH₂O (1) and [Zn(tpt)(bdc)_1/2I]_n (2) (tpt = 2,4,6-tris(4-pyridyl)-1,3,5-triazine, H₂bdc = 1,4-benzenedicarboxylic acid), have been prepared by hydrothermal reactions. In complex 1, Cu(I) center is in a trigonal coordination environment with bidentate tpt coordinating Cu(I) atoms to form 1D zigzag chains, and bdc ligand links the zigzag chains to form a 2D layered structure. In complex 2, Zn(II) center is in a trigonal–pyramidal environment with bidentate tpt coordinating Zn(II) atoms to form zigzag chains, and bdc links the zigzag chains to form metal–organic framework which contains interesting hexagonal nano-channels.     

A luminescent coordination polymer with potential active site for the sensing of metal cation,anion and nitrobenzene explosive

A new 1D Zn-based coordination polymer (CP), {[Zn(HBTB)(pdp)]·H₂O} (1) (H₃BTB = 1,3,5-benzenetribenzoic acid and pdp = 2-(4,6-di(pyridine-2-yl)pyridine- 2-yl)pyridine), has been synthesized under solvothermal condition and structurally characterized. The compound displays intense luminescence in solid state at room temperature with high thermal stability. Interestingly, Luminescent studies indicate that 1 could be an efficient multifunctional fluorescence material for high sensitivity metal ions, anions and organic small molecules, especially for Cu^2 +, CrO₄^2 − and nitrobenzene (NB) by luminescent quenching. The probable quenching mechanism of different analytes was also discussed.     

A metal–organic framework containing meso-helical chains: Synthesis,characterization and luminescent property

A new metal–organic frameworks (MOFs), [Cd₃(pmb)₂(bpdc)₂] 2H₂O (1) (pmb = 3,5-bis(4-pyridylmethylenoxyl)benzoate, bpdc = 2,2′-biphenyldicarboxylate), has been synthesized by hydrothermal method and structurally characterized through IR, TG and single-crystal X-ray analysis. The infinite wave-like 1D metal–oxygen chains made by Cd₃N₄O₁₂ clusters in 1 bridged by the carboxylate of bpdc ligand, construct a 2D framework in which interesting meso-helical chains are constructed by metal centers and pmb ligands. Solid state luminescent spectrum of 1 also has been investigated at room temperature.     

Isostructural 3D Ln–Ag (Ln = Eu; Dy; Ho) coordination frameworks based on mixed nicotinate and oxalate ligands: Synthesis,crystal structures and luminescence

By control of mixed organic ligands with different geometries, three unusual 4d–4f heterometallic coordination polymers, [AgLn(nic)₂(ox)] · 2H₂O [Ln = Eu (1); Dy (2); Ho (3)] [nic = nicotinate; ox = oxalate] have been synthesized under hydrothermal reaction. Three structures represent 3D open heterometallic coordination frameworks that are constructed from rare zigzag lanthanide-ox-silver chains and nic linkers. Furthermore, the luminescent property of complex 1 was discussed.     

Novel magnetic nanoparticles Fe3O4-immobilized domino Knoevenagel condensation,Michael addition,and cyclization catalyst

The synthesis, characterization and applications of guanidine supported on magnetic nanoparticles Fe₃O₄ (MNPs–Guanidine) as a novel magnetically separable base nanocatalyst are described. We have studied the application of this new catalyst for the Knoevenagel condensation reaction of aromatic aldehydes with malononitrile or cyanoacetate in PEG/water = 1:1 at room temperature. Also, the three-component and one-pot synthesis of 2-amino-4H-chromenes and 2-amino-4H-benzo[h]chromenes by condensing aldehydes, malononitrile and cyclic 1,3-dicarbonyl/α-naphthol, in the presence of catalytic amount of MNPs–Guanidine under same conditions is investigated. The supported catalyst could simply be separated and recovered from the reaction mixture with the assistance of an external magnet and reused several times.     

Construction of three isostructural 3d–4f microporous coordination frameworks based on mixed nicotinate and oxalate ligands

The self-assembly of nicotinic acid and sodium oxalate with mixed 3d–4f metal salts under hydrothermal conditions gave three isostructural 3D 3d–4f coordination polymers, [LnCu(nic)₂(ox)] · xH₂O [Ln = La, x = 1 (1); Ln = Eu, x = 2 (2); Ln = Gd, x = 2 (3)] [ox = oxalate, nic = nicotinate]. All three structures exhibit same unusual 3D microporous heterometallic coordination frameworks that are built up by rare tetranuclear Ln₂Cu₂ clusters and mixed ox and nic linkers. Furthermore, the luminescent property of complex 2 has also been investigated.     

Two 2D metal–organic frameworks based on 2,2′-bibenzimidazole ligand with (6,3) net topology

Two 2D metal–organic frameworks (MOFs), {[Zn₄(Hbbim)₄(bbim)₂] 2H₂O}_n (1) and [Cd₂(Hbbim)₂(bbim)]_n (2) (H₂bbim = 2,2′-bibenzimidazole) were obtained by solvothermal reaction and characterized by single crystal X-ray diffraction analysis. Different metal ions, Cd(II)/Zn(II), adopt very different coordination geometries though two title compounds both have a 2D honeycomb network with (6,3) topology. The frameworks of compounds 1 and 2 are stable below 360 °C and 475 °C, respectively. Solid-state luminescent spectroscopy of compound 2 exhibits an emission peak at 407 nm.     

Unique vapor phase synthesis of 1,2,3,5,6,7-hexahydrodicyclopenta[b,e]pyridine selectively over Co–Al-MCM-41

Cyclization of cyclopentanone, formaldehyde and ammonia in vapor phase gives 1,2,3,5,6,7-hexahydrodicyclopenta[b,e]pyridine (HHDCP) and spiro[cyclopentane-1,8′-(1′,2′,3′,5′,6′,7′,8′,8′a) octahydrodicyclopenta[b,e]]pyridine (SCOHDCP) over zeolites HY, HZSM-5, Hβ and mesoporous Al-MCM-41 molecular sieves. The preliminary screening of catalysts clearly shows that Al-MCM-41 is more suitable for the vapor phase synthesis of HHDCP. As the NH₃-TPD profiles of Al-MCM-41 show wide range distribution of acid sites in the temperature range of 200–600 °C (weak–medium–strong), Al-MCM-41 is further modified with transition metal ions like V(V), Mn(II), Fe(III), Co(III), Cu(II), La(III) and Ce(III) to fine tune the acid sites. Correlation of activity and selectivity of transition metal modified Al-MCM-41 with the NH₃-TPD profiles show that though the conversions are high, selectivity of either HHDCP or SCOHDCP is a preference of acid site strength formed on metal ion modification. Interestingly Co²⁺ ion modification of Al-MCM-41 resulted distinctly into two sets of acid sites with T_max around 218 °C (weak–medium) and 673 °C (strong). The reaction is studied on Co–Al-MCM-41 by adsorbing pyridine at 300 °C. The typical acidity available on pyridine adsorbed Co–Al-MCM-41 around 300 °C is showing cyclization activity forming only HHDCP indicating that weak–medium acid sites are responsible for the formation of HHDCP. Based on the product distribution plausible reaction mechanism is proposed.     

Two novel 3D self-threading coordination polymers with CdSO4 topology: Syntheses,structures and properties

Two new isostructural metal-organic frameworks, namely [Co(HL)(bpp)] · 0.5H₂O (1) and [Zn(HL)(bpp)] · 3H₂O (2) (H₃L = 5-(2′-carboxy-biphenyl-4-ylmethoxy)-isophthalic acid, bpp = 1,3-bis(4-pyridyl)propane), have been hydrothermally synthesized and further characterized by single crystal X-ray diffraction, powder X-ray diffraction, elemental analyses, IR spectra and TG analyses. Compounds 1 and 2 exhibit interesting 3D frameworks of (6⁵.8)-CdSO₄ topology with dangling arm (i.e. the uncoordinated 2′-carboxy-biphenyl-4-ylmethoxy group of HL ligand). The remarkable feature of these two compounds is that each dangling arm threads into two 6-membered rings belonging to the 3D net itself, displaying the self-threading character. The magnetic properties of 1 and photoluminescence of 2 have also been investigated.     

Structure and catalytic performance of Pt-promoted alumina-supported cobalt catalysts under realistic conditions of Fischer–Tropsch synthesis

The structure of alumina-supported cobalt catalysts promoted with platinum and their catalytic performance in Fischer–Tropsch synthesis were investigated under realistic reaction conditions (P = 20 bar, T = 493 K) using in situ time-resolved X-ray diffraction with simultaneous analysis of reaction products. The catalysts were prepared via incipient wetness impregnation and characterized by a wide range of ex situ techniques. Direct in situ measurements were indicative of considerable versatility of alumina-supported cobalt catalysts during Fischer–Tropsch synthesis. Cobalt sintering occurred at the first hours of the reaction and resulted in a significant drop of the catalytic activity. In addition to sintering, partially oxidized catalysts containing smaller cobalt particles (mean particle size <5 nm) were slowly reducing during Fischer–Tropsch reaction. Treatment of cobalt catalysts in pure carbon monoxide led to selective transformation of cobalt metallic phases to Co₂C cobalt carbide. Cobalt carbidization followed by hydrogenation selectively led to cobalt hcp metallic phase, which seems to be more active in Fischer–Tropsch synthesis than cobalt fcc phase. Cobalt oxidation by water was not significant in the catalysts with metal particles larger than 5 nm even at high water concentrations.     

Assembly of a 3D chiral Cu(I) metal–organic framework based on 4,5-dicyanoimidazole: CD spectrum,luminescence and selective gas adsorption

One chiral Cu(I) metal–organic framework {[Cu(DCI)]·0.1Cyc·0.45Nbenz}_n (1) (HDCI = 4,5-dicyanoimidazole, Cyc = cyclohexanol, Nbenz = nitrobenzene), was obtained under solvothermal condition. Complex 1 presents a 3D chiral porous framework with 38.2% porosity. The 3D metal–organic framework can be regarded as a PtS net with the vertex symbol of {4².8⁴}. The gas adsorption/desorption experiments of complex 1 have been measured at 77 K. Moreover, the CD spectrum and photoluminescent behavior of complex 1 have been studied.     

Manganese(II) coordination polymer with simultaneous azide,tetrazolate and carboxylate bridges: Synthesis,structure and magnetism

The reaction of a pyridinium-containing ligand precursor with manganese(II) chloride and sodium azide yielded a Mn(II) coordination polymer, [MnLN₃]_n·1.5nH₂O, where L is 1-(tetrazolato-5-methyl)pyridinium-4-carboxylate, a bifunctional zwitterionic ligand generated in situ from a non-coordinative precursor via two organic reactions (cyano-to-azide cycloaddition and ester hydrolysis). In the compound, metal ions are connected into uniform chains by the triple bridges consisting of μ-1,1-azide, μ-2,3-tetrazolate and μ-1,3-carboxylate, and the formally anionic chains are charge compensated and interlinked into 2D layers by the cationic 1-methylenepyridinium backbone of the L ligand. The compound displays typical 1D antiferromagnetism with J = − 2.37 cm^− 1 through the triple bridges. Magneto-structural analysis indicates the antiferromagnetic interaction increases as the Mn–N–Mn angle of the azide bridge decreases.     

Synthesis and characterization,second-order nonlinear optical and photorefractive properties of new multifunctional polysiloxane with broad optical transparent pentafluorophenyl azo chromophore

A new polysiloxane P1 with pendant carbazoly groups and a high density of the pentafluorophenyl azo chromophore as side chain was synthesized in moderate yield by two successive postfunctionalization reaction including Vilsmeir formylated reaction and Knoevenagel condensation. Its structure was verified by ¹H NMR, IR, and UV–Vis spectra. The polymer P1 exhibited good solubility in common organic solvents and was thermally stable up to 282 °C. The maximum absorption appeared at about 407 nm for P1 in THF, which was blue-shifted about 87 nm compared to the corresponding polysiloxane P2 with a well-known nitro acceptor azo chromophore, resulting in a wider transparency window. The value of the NLO coefficient d₃₃ of P1 thin film, measured by in situ second harmonic generation (SHG), was 11.9 pm/V. Preliminary photorefractive experiments showed that P1 obtained diffraction efficiency of 78% and a time constant of 1.19 sec.     

Metal ions directed self-assembly based on rigid polycarboxylate ligand 5-tert-butyl isophthalic acid and flexible N-heterocyclic ligand 1,4-bis(2-methylimidazol-1-ylmethyl)-2,3,5,6-tetramethylbenzene

Two new complexes {[Cd(bmimx)_0.5(tbip)(H₂O)] · H₂O}_n (1) and [Zn(bmimx)(tbip)]_n (2) (bmimx = 1,4-bis(2-methylimidazol-1-ylmethyl)-2,3,5,6-tetramethylbenzene, H₂tbip = 5-tert-butyl isophthalic acid) based on mixed ligands have been hydrothermally synthesized by varying the metal ions. Structural analysis reveals that complex 1 displays a 2D layer structure with a 4⁴-sql topology; complex 2 exhibits a 3D 4-fold interpenetrated framework with sra topology. The structural differences between 1 and 2 indicate that metal ions have significant effects on the formation of the final architectures. In addition, the thermal stabilities and photoluminescent properties of the two complexes were also investigated.     

Catalytic wet oxidation of p-chlorophenol over supported noble metal catalysts

Heterogeneous catalytic wet oxidation of aqueous p-chlorophenol (p-CP) solution was investigated at 453 K and 2.6 MPa in a slurry reactor. The performance of noble metal catalysts was compared with that of traditional manganese catalysts. Activated carbon supported catalysts showed significant higher activities for total organic carbon (TOC) reduction than those supported on alumina or cerium oxide. Pt was found to be the most active metal for p-chlorophenol oxidation. The activities of noble metal catalysts were found to correlate with heat of formation of metal oxides. CO₂ is the predominant oxidation product with formation of minor p-benzoquinone and acetic acid as intermediate compounds. Possible reaction pathway was also discussed.     

A new self-penetrating amine-decorated microporous metal–organic framework: Crystal structure,adsorption selectivity,and luminescence properties

A new microporous metal–organic framework, [Cd(bpdc)_0.5(atz)(DMF)]·0.5DMF (1) (H₂bpdc = 4,4′-biphenyldicarboxylic acid, Hatz = 3-amino-1,2,4-triazole, DMF = N,N-dimethylformamide) has been solvothermally synthesized by employing the mixed H₂bpdc and Hatz ligands. 1 is a 3D pillared-layer framework, consisting of Cd–triazolate layer and dicarboxylate pillar, which exhibits a 6-connected (4⁶ · 6⁸ · 8) self-penetrating net. Because of the pore system functionalized by amino groups and open metal sites, this material shows high CO₂ adsorption selectivity over H₂ and N₂. In addition, 1 exhibits blue emission at ambient temperature.     

Syntheses,topological analyses and magnetic properties of two 3D supramolecular nickel-organic frameworks constructed from 1,3,5-benzenetricarboxylate and flexible imidazole-based ligands

Two supramolecular nickel-organic frameworks, [Ni(HBTC)(bix)]_n (1) and [Ni₃(BTC)₂(mbix)₃(H₂O)₄]_n · 6nH₂O (2) (bix = 1,4-bis(imidazole-l-yl-methyl)benzene, mbix = 1,3-bis(imidazole-l-yl-methyl)benzene, and H₃BTC = 1,3,5-benzenetricarboxylate), have been hydrothermally prepared by the assembly of H₃BTC, Ni²⁺ with bix or mbix. Compound 1 shows a 2D layer structure, whose 3D supramolecular structure exhibits a fsc topology when hydrogen-bonging interactions between the adjacent layers are taken into account. Compound 2 manifests an unprecedented 2D (3, 4)-connected topological net. The 3D supramolecular framework of 2 is formed through π?π stacking interactions between the adjacent layers. The magnetic studies show that 1 features overall ferromagnetic property whilst 2 presents strong zero-field splitting (ZFS) when treated as a mononuclear model. Furthermore, the IR and TGA properties of 1 and 2 were also studied.     

1D helical ZnII metal–organic polymers: Syntheses,structures and fluorescent properties

Hydrothermal reactions of 1,1′-(1,5-pentanediyl)bis-1H-benzimidazole (pbbm) with ZnCl₂ afford two 1D helical metal–organic polymers {[ZnCl₂(pbbm)] · (H₂O)_1/8}_n (1) and {[Zn(pbbm)₂] · Cl₂ · (H₂O)_1/2}_n (2). Polymer 1 features a 1D single helical architecture, whereas 2 possesses a 1D cationic double helical chain framework. Photoluminescence investigations reveal that both of them display strong emissions in the solid state at room temperature, which could originate from a ligand-to-ligand charge-transfer (LLCT) transition, as confirmed by the molecular orbital (MO) calculations.