Coordination-directed one-dimensional coordination polymers generated from a new unsymmetrical oxadiazole bridging ligand and transition metal ions

Three one-dimensional coordination polymers, namely [ZnL₂(NO₃)₂]_n (1), [CdL₂(NO₃)₂]_n (2) and {[ZnL₂(H₂O)₂](ClO₄)₂?2L?2(H₂O)}_n (3), have been successfully synthesized based on a new unsymmetrical oxadiazole bridging ligand 2-[2-((3-pyridyl)methoxy)phenyl]-5-[(4-pyridyl)]-1,3,4-oxadiazole (L). Compounds 1–3 feature a similar one-dimensional infinite chain that consists of M₂L₂ building block (M = Zn(II) and Cd(II)). In 3, the uncoordinated L ligands are located between the [M₂L₂]_n chains and serve as the agents to cross-link the chains by weak π–π and H-bonding interactions into a 2D network. In addition, the luminescent properties of L and 1–3 were primarily investigated in the solid state.     

Vapour synthesis: A new technique in synthetic chemistry

Vapour synthesis is the use, as reagents, of vapours which are formed at high temperatures. Typically, vapours, such as those of transition metal atoms, are brought into contact on a cold surface with a substrate, for example an unsaturated hydrocarbon. The ensuing reaction can form compounds, typically organo-transition metal complexes. The principles and methodology are discussed critically to show the applicability of this technique to synthesis and research. A review of recent research illustrating the scope of vapour synthesis is given.     

First use of the maleamate(−1) ligand in coordination chemistry: Dinuclear copper(II) complexes with N-donors and their interesting ‘organic’ chemistry

A systematic investigation of the reactions of 3d-metal ions with the maleamate(−1) ligand (HL⁻) in the presence of mono- , bi- or tridentate chelating N-donors has been initiated and the first results are described. Reaction schemes involving Cu(ClO₄)₂ · 6H₂O, HL⁻ and 1,10-phenanthroline or 2,6-bis(pyrazol-1-yl)pyridine (bppy) in MeCN gave complexes [Cu₂(HL)₃(phen)₂](ClO₄) (1) and [Cu₂(HL)₂(bppy)₂](ClO₄)₂ (3), respectively. The same reaction systems in MeOH afforded the new complexes [Cu₂L′₂(ClO₄)(phen)₂(MeOH)](ClO₄) (2b) and [Cu₂L′₂(bppy)₂](ClO₄)₂ (4) in which the maleamate(−1) ion has been transformed to the monomethyl maleate(−1) ligand L′⁻ via a novel, metal ion-assisted process. The reaction that leads to 2b takes place through the formation of the 1D coordination polymer [Cu(ClO₄)(phen)(MeOH)₂]_n(ClO₄)_n (2a), whose structure was assigned on the basis of its spectral similarity with the structurally characterized complex [Cu(ClO₄)(phen)(MeCN)₂]_n(ClO₄)_n (2c). Only the carboxylate oxygen atoms of HL⁻ and L′⁻ are coordinated to copper(II) in 1, 2b, 3 and 4.     

Advances in metal chemistry of quinonoid compounds: new types of interactions between metals and aromatics

This Account presents an overview of current research activities that focus on novel types of interactions between cationic transition metal complexes and arene systems and on unprecedented quinonoid complexes which result from such interactions. When a negatively charged phenoxy group is present in a position para to the metal in a high oxidation state, intramolecular charge transfer occurs, giving the corresponding metallaquinones or quinone methide complexes. In addition, two types of interactions involving low-valent metal compounds have been observed: methylene arenium complexes which result from positive charge transfer to the aromatic ring and sigma-bonded C-H and C-C agostic complexes of cationic metals. These sigma-complexes are proposed as intermediates in metal-based bond activation processes.     

Exploiting the synergy between coordination chemistry and molecular imprinting in the quest for new catalysts

The synthesis of transition metal active sites by the molecular imprinting of polymerizable metal complexes into highly cross-linked organic polymers is described. The emphasis of this Account is on the synergy between the long-term goals associated with new catalyst development and the more short-term goal of addressing fundamental questions in coordination chemistry, particularly emphasizing stereochemistry and structure. An argument is presented that the latter is necessary for ultimately achieving the more difficult but more important goal of designer catalysts that achieve reaction selectivities and reactivities not obtainable with traditional homo- or heterogeneous catalysts.     

Development of a new synthetic method based on in situ strategies for polyethylene/clay composites

Methods to make polymer composites comprise melt and solution blending, but in the particular case of polyolefins they are not appropriate due to the weak interfacial adhesion. In the present work, in situ blended (ISB) together with in situ polymerization (ISP) processes have been employed and compared using MAO/(nBuCp)₂ZrCl₂ as catalytic system and sepiolite clay as additive in ethylene polymerization. A new method as a combination of the previous ones (ISB + ISP) has been developed and applied to the synthesis of linear low‐density polyethylene (LLDPE). When ISB + ISP method is employed high catalytic activities are observed and this combination allows to increase the storage modulus at 25°C up to 26% with 2.8 wt % of clay in LLDPE when silica is employed as catalyst carrier; in that way, copolymer particles with good morphology with higher storage modulus are obtained, useful properties for their use in specific applications. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Polymer-supported analogues of t-butyl hypohalites. Preparation and applications in synthetic organic chemistry

Crosslinked polymer-supported analogues of t-butyl hypochlorite and t-butyl hypobromite were prepared and developed as a new class of recyclable solid-phase oxidizing and halogenating reagents. The preparation of these new reagents involved a three-step polymer-analogous reaction starting from styrene-divinylbenzene crosslinked polymer. A ketone functional group was introduced into the copolystyrene-2% divinylbenzene resin beads by a Friedel-Crafts reaction with bromoacetone. This functional group was then converted to a tertiary alcoholic function on the polymer support by a Grignard reaction with methylmagnesium iodide. The treatment of this tertiary alcohol resin with sodium hypochlorite or sodium hypobromite yielded the polymeric t-butyl hypochlorite or hypobromite. These hypohalites were estimated iodometrically. These reagents were found to oxidize primary and secondary alcohols to the corresponding carbonyl compounds in high yields. They were also found to be suitable for halogenation of carbonyl compounds and amides. The spent polymeric reagent after the oxidation or halogenation step can be easily removed by filtration and can be regenerated many times by treating with the sodium hypohalite without any loss of capacity.     

Improved ORR activity of non-noble metal electrocatalysts by increasing ligand and metal ratio in synthetic complex precursors

In an effort to improve oxygen reduction reaction (ORR) activity by increasing the catalytic active site density in carbon-supported non-noble metal catalysts, several nitrogen-containing catalysts were synthesized through a heat treatment process at 900 °C using precursor complexes of Fe(II) and tripyridyl triazine (TPTZ). Fe to TPTZ mole ratios of 1:2, 1:3, 1:4, 1:5, 1:6, and 1:7 were used to prepare the precursor complexes. X-ray diffraction and surface electrochemical techniques were used to characterize these catalysts (Fe–N_x/C), and revealed that when the amount of TPTZ in the precursor complex was increased, the decomposition of Fe–N_x sites, which are considered active sites for the ORR, was effectively reduced, resulting in higher Fe–N_x site density and thus improving the catalysts’ ORR activity. This beneficial effect was validated through rotating disk electrode tests and analysis of the ORR kinetics catalyzed by these catalysts. The obtained results showed that as the Fe to TPTZ mole ratio in the precursor complex was decreased, the catalytic ORR activity of Fe–N_x/C increased monotonically in the mole ratio range of 1:2–1:6. Therefore, increasing the amount of ligand in the precursor metal complex was demonstrated to be an effective way to reduce the decomposition of ORR active site density and thereby enhance the ORR activity of non-noble metal catalysts.     

Polystyrene supported pyrazolinium Cr(VI) reagents: preparation and use in synthetic organic chemistry

Divinylbenzene (DVB) and ethyleneglycol dimethacrylate (EGDMA) crosslinked polystyrenes (2%) were functionalized to generate pyrazolinium chromate, chlorochromate and pyrazole–CrO₃ complex functionalities. These were found to oxidize primary and secondary alcohols to the corresponding carbonyl compounds in high yields. The influence of solvent, temperature, catalyst and molar excess of the reagent in these oxidation reactions was investigated to find out the optimum conditions for effective oxidation reactions. EGDMA crosslinked polystyrene supported reagents showed higher reactivity in terms of functional group capacity and percentage yield. Also, chlorochromate reagent was found to be very efficient in oxidizing alcohols to carbonyl compounds. The spent polymeric reagent after the oxidation step can be easily removed by filtration and can be regenerated many times. © 1998 SCI.     

Synthesis and characterization of a novel 3D copper(I) coordination polymer with a ligand generated in situ

Hydrothermal reaction of CuCl₂ · 2H₂O, NaN₃ with 1,4-dicyanobenzene in water/ethanol yielded a novel Cu(I)-tetrazolate, {Cu(cptz)}_n, (1) (Hcptz is 5-(4-cyanophenyl)-tetrazole). The cptz ligand in the complex was generated in situ through the [2 + 3] cycloaddition reaction involving one of the two cyano-groups of the precursor 1,4-dicyanobenzene. The structure characterization shows that 1 possesses a 3D 4-connected SrAl₂ topological network. Additionally, complex 1 exhibits strong yellow fluorescence at room temperature in the solid state.     

Polymer pendant ligand chemistry, 4. Recovery of precious metal ions from strongly acidic solution with a polymer-supported o-phenylenediamine hydrochloride ligand

We report on the synthesis and reactivity of a polymer-supported o-phenylenediamine hydrochloride ligand, PS-PDHC, using macroporous 6% crosslinked polystyrene-divinylbenzene beads. The PS-PDHC ligand was found to be highly selective to AuCl₄⁻ ions in strongly acidic solutions in the presence of other precious metal ions, PdCl₄²⁻, PtCl₄²⁻, RhCl₆³⁻, and RuCl₅²⁻ (selectivity values: 2.5, Au/Pd; 7.5, Au/Pt; 7, Au/Rh; 2.2, Au/Ru) as well as other transition metal ions, Fe ³⁺, Cr³⁺, CU²⁺, Nit+, and Mn²⁺. The sorption capacity, selectivity, kinetics of removal and recovery, and solution isotherms have been determined for AuCl₄⁻ ions in competition with the above-mentioned metal ions. The relative ease of formation of the anionic complex in 0.5 M HCI, AuCl₄⁻ was thought to be the primary reason for its selective ability to bind to the PS-PDHC ligand by an anion-exchange mechanism. Therefore, the effect of the HCI concentration on the kinetics of AuCl₄⁻ ion removal from solution was also investigated to clearly show that raising the pH from 0 to 5 caused a dramatic decrease in rate. The AuCl₄⁻ ion can be recovered quantitatively from the PS-PDHC beads using a 5% thiourea solution in 0.1 M HCl, allowing the polymer-supported ligand to be reused.     

Metal-directed syntheses of coordination polymers via in situ ligand reactions from the same precursor, 2-(1H-benzeimidazol-2-yl)-acetonitrile

Three new coordination polymers, [Co(HBit)₂]_n (1), [Mn(HBit)₂]_n (2) (H₂Bit = 2-((1H-tetrazol-5-yl)methyl)-1H-benzo[d]imidazole), and [CdCl(MBi)(HMBi)]_n (3), (HMBi = 2-methyl-1H-benzo-[d]imidazole), have been hydrothermally synthesized via in situ ligand reaction. Compounds 1 and 2 are isomorphous and display interesting 3D chiral supramolecular frameworks constructed from one-dimensional 4₁ helical chains. Complex 3 possesses a one-dimensional coordination chain, which is further connected to a 2D layer by intermolecular hydrogen bonds. More interestingly, both H₂Bit and HMBi ligands are in situ generated from the same precursor, 2-(1H-benzo[d]imidazol-2-yl)-acetonitrile, and the formation may depend on the kind of metal ion. Furthermore, the solid-state luminescence of complex 3 was investigated at room temperature.     

Wavelet: a new trend in chemistry

Since 1989, wavelet transform (WT) has attracted much interest of chemists working on signal and image processing, and the WT-based techniques have been successfully applied to the chemical signal processing. This approach has been demonstrated as fast in computation with localization and having quick decay properties, in contrast to the popular methods existing, especially to the fast Fourier transform. More than 370 papers have been published up to the year 2002 which covered applications of WT in various fields of chemistry, including analytical chemistry, chemical physics, and quantum chemistry. In this paper, we report on applications of WT to data compression, data smoothing and denoising, baseline and background correction, resolution of multicomponent overlapping signals, regression and classification, and analytical images processing in analytical chemistry. Through this report we wish to induce greater interest of chemists in WT and to obtain greater benefits from using the WT-based techniques.     

Binding metal cations and nitrate anions by new synthetic support: Castor Oil-AAc-AAm

Summary A new synthetic gel was obtained by bulk polymerization of castor oil, acrylic acid and acrylamide. This paper describes the ability of this gel to uptake heavy metals and nitrate ions from aqueous solutions as demonstrated in our laboratory. Determinations, before and after batch experiments, were carried out using atomic absorption and UV spectroscopy. These results showed that Al⁺³, Fe⁺³ and Pb⁺² ions were effectively adsorbed. Received: 28 December 2000/Revised version: 25 April 2001/Accepted: 26 April 2001     

A new helical coordination polymer constructed on flexible dicarboxylate ligand and CdII center: Structure and luminescence

A novel cadmium coordination polymer [Cd₂L₂(bpp)₂]_n (1) (H₂L = 1,3-adamantanediacetic acid and bpp = 1,3-di-4-pyridylpropane) was prepared under hydrothermal condition. The three-dimensional (3D) structure is built from the interlinking lamellars. The Cd^II ions are six- and seven-coordinated and linked by L^2? ligands, which results in the right- and left-handed helical chains. The layers are stacked with each other via bpp to generate a 3D architecture. At room temperature, the complex 1 shows the strong fluorescent emission bands in the solid state.     

现代有机生物分析的新方法与新技术及在酶化学环境科学等测检方面的应用

简要介绍了现代有机分析化学的发展及应用,重点综述了现代有机分析在酶化学检测方面的应用;现代有机分析在生命科学及环境科学中的应用;现代有机分析在日常生活中的应用。并对现代有机与生物分析的发展进行了展望。