Wen-Wei Zhang

Structural, morphological, and magnetic study of nanocrystalline cobalt-nickel-copper particles

Nanocrystalline Co(x)Ni(y)Cu(100-x-y) particles were synthesized by the reduction of metal acetates in a mixture of polyol and Tween 80. Inductively coupled plasma (ICP) analysis revealed that the actual wt% of Co, Ni, and Cu in these nanoparticles was nearly the same as in the starting solutions. The structures of the particles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED) spectroscopy, and vibrating sample magnetometry (VSM). The results of XRD and VSM confirmed that there was no metastable alloying in the particles. The particles were composites, consisting of nanoscale crystallites of face-centered cubic (fcc) Cu, face-centered cubic (fcc) Ni, and face-centered cubic (fcc) Co. During preparation the nucleation of Cu occurred first; then small Cu nuclei acted as cores for the precipitation of Co and Ni. The particles showed an increase in saturation magnetization (M(s)) as the concentration of Co or Ni in the particles was increased. The changes of both M(s) and coercivity of the particles with increasing annealing temperatures were studied. The coercivity of the particles was very high; it could reach as high as 489 Oe for Co34.3Ni31.2Cu34.5) .

Preparation and electrochemistry of azobenzene self-assembled monolayers on gold-long range tunneling and end-group hydrogen bonding effect

A series of thiol-functionalied azobenzene derivatives (RAzoCnSH: R=H for n=3-6, abbreviated as AzoCnSH; R=CH(3)CONH for n=4, abbreviated as aaAzoC4SH) on gold electrodes were prepared and their self-assembly and electrochemical properties were studied by cyclic voltammetry. They all formed uniform and reproducible self-assembled monolayers (SAMs) on gold and showed well-behaved voltammetric responses in aqueous solution. Both the length of the alkyl chain spacer and the H-bonding of the end acetamino group had effects on the stability and the electrochemical kinetics of the SAMs, and the effect of the H-bonding was dominant. The surface coverage of the SAMs (AzoCnSH) is gradually increased with an increase of the alkyl chain spacer length, whereas the presence of the terminal acetamino group leads to a greater increase of the surface coverage. At a low scan rate, voltammetric responses corresponding to an irreversible two-electron, two-proton reduction/oxidation of the trans-azobenzene redox center were obtained in the range of +300 mV and -800 mV, which exhibited very large peak-to-peak splitting. At a high scan rate of 500 mV/s, two steps of reversible one-electron, one-proton reduction/oxidation corresponding to the cis-isomer in azobenzene-thiol SAMs (n is odd) was clearly observed between +300 and -200 mV. The apparent electron-transfer rate is decreased with increasing distance between the azobenzene redox center and the gold electrode. The existence of the end acetamino group which restricted the conformational change during the redox process also led to a decrease of the standard rate constant, and this restriction effect is more predominant than the distance effect.

Synthesis, crystal structure and magnetic studies of cis-configuration copper(II)—M(II) (M = Ba, Ca) complexes of novel Schiff bases derived from salicylaldehyde and dipeptides

The novel heteronuclear complexes [M(CuL)2]2 · nH2O [M = Ba (1), Ca (2); H2L = N-salicylideneglycylglycine] were synthesized and characterized, and the crystal structure of complex (1) was determined by X-ray diffraction. The entire structure is held together by an extensive network of H-bonds and π–π interactions. Variable-temperature magnetic susceptibility measurements (75–300 K) revealed the occurrence of an intramolecular antiferromagnetic interaction in (1) and (2).

Syntheses and crystal structures of two maleonitriledithiolate complexes containing the 1-(R-benzyl)pyrazinium cation (R = 4′-nitro or 4′-bromo)

The complexes [NO2BzPz]2[Ni(mnt)2] (1) and [BrBzPz]2[Pd(mnt)2] (2) have been prepared by reaction of Na2mnt, NiCl2·6H2O or PdCl2, and the corresponding 1-(R-benzyl)pyrazinium bromide salt (R = 4′-nitro, R = 4′-bromo). Crystallographic data for 1: monoclinic, P21/n, a = 7.3494(15), b = 15.223(3), c = 15.054(3) Å, β = 102.42(3)°, V = 1644.8(6) Å3, Z = 2. Data for 2: monoclinic, P21/n, a = 7.399(2), b = 19.024(4), c = 12.224(2) Å, β = 94.62(3)°, V = 1715.0(7) Å3, Z = 4. In both complexes, the [M(mnt)2]2− anion has a centre of symmetry at the metal atom and two cations are related to each other by the symmetry centre. The [M(mnt)2]2− anion exhibits a quasi-planar structure in both complexes, which show similar crystal packing.

Dimensionality of luminescent coordination polymers of magnesium ions and 1,1′-ethynebenzene-3,3′,5,5′-tetracarboxylic acid modulated by structural inducing agents

Solvothermal reactions of aromatic 1,1′-ethynebenzene-3,3′,5,5′-tetracarboxylic acid (H4EBTC) and Mg2+ salts in the presence of different supporting ligands afforded the coordination polymers [Mg(H2EBTC)(DMF)2(H2O)2] (1), [Mg3(HEBTC)2(H2O)4]·solvent (2) and [Mg2(EBTC)(H2O)5]·solvent (3). The crystal structures of 1–3 were determined by the single crystal X-ray diffraction technique, where CP 1 showed a one-dimensional zigzag MgO6 coordination octahedral chain structure; 2 exhibited a two-dimensional MgO6 coordination octahedral framework with trinuclear [Mg3(COO)6] SBUs, and 3 featured a three-dimensional MgO6 coordination octahedral framework with binuclear [Mg2O(COO)2] SBUs. The various structures in CPs 1–3 of Mg2+ ions with the H4EBTC ligand were ascribed to the conformational flexibility and the coordination mode diversity of the H4EBTC ligand. Interestingly, the zwitterionic supporting ligand 2-aminoterephthalic acid or 4-aminobenzenesulphonic acid played a vital role in the initial formation process of nuclear crystals but only as a structural induction agent, which modulated the dimensionality of these Mg2+-based CPs. Additionally, the three CPs emitted bright blue luminescence at ambient conditions, and the emission lifetimes and absolute quantum yields were also investigated.

Dual-emission and thermochromic luminescence alkaline earth metal coordination polymers and their blend films with polyvinylidene fluoride for detecting nitrobenzene vapor

Dual emission materials show unique advantages in the areas of detecting analytes or probing a change of environment (e.g. temperature or pressure). In this study, we have harvested three coordination polymers (CPs), [Ca(H2EBTC)(DMF)2] (1), [Sr3(EBTC)2(DMSO)2] (2) and [Ba3(HEBTC)2(DMSO)2] (3) with H4EBTC = 1,1′-ethynebenzene-3,3′,5,5′-tetracarboxylic acid, which emit H4EBTC-based fluorescence and phosphorescence under ambient conditions and show thermochromic luminescence behavior in the range 10–300 K. The luminescent blend films of 1–3 with hydrophobic polyvinylidene fluoride (PVDF), labeled as X@PVDF (X = 1–3), were fabricated using a facile and effective drop-casting approach. The formation of blend films much improves the water-stability of alkaline earth metal CPs. The dual emission blend films of CPs were used as the signal transducer for nitrobenzene vapor detection for the first time. Compared to the conventional luminescence probe that used a dispersed solution of luminescent CP powder, the dual emission blend films show excellent performances, e.g. ultrafast luminescence quenching response, lower concentration limit of detection, facile manipulation and cycling utility. Such a strategy using a blend film as the probe can be easily expanded to other probe systems of luminescent CPs, thus opening up a new perspective for the development of efficient and practical film sensing materials.

Higher Symmetry Multinuclear Clusters of Metal–Organic Frameworks for Highly Selective CO2 Capture

A new approach of finely tuning multinuclear clusters of metal-organic frameworks (MOFs) through symmetry-upgradingly isoreticular transformation was first presented and a bcu-type MOF, {[Cu4(μ4-O)Cl2(IN)4][CuCl2]}∞ (NJU-Bai35; NJU-Bai for Nanjing University Bai group), with cluster [Cu4(μ4-O)Cl2(COO)4N4] of higher symmetry compared to the pristine MOF, was successfully synthesized. The symmetry upgrading implemented on the inorganic part triggers the adjustment of channels in NJU-Bai35 to fit CO2 molecules, leading to a high CO2 adsorption capacity (7.20 wt % at ∼0.15 bar and 298 K) and high selectivity of CO2 over N2 and CH4 (275.8 for CO2/N2 and 11.6 for CO2/CH4) in NJU-Bai35. Breakthrough experiments further confirmed that NJU-Bai35 might be an excellent candidate for CO2 capture and natural gas purification.

catena-Poly[[[triaqua-cobalt(II)]-μ-10-methyl-phenothia-zine-3,7-dicarboxyl-ato] monohydrate].

The polymeric title compound, {[Co(C15H9NO4S)(H2O)3]·H2O}n, consists of chains along [001] made up from Co2+ ions bridged by 10-methylphenothiazine-3,7-dicarboxylate anions. The Co2+ ion, coordinated by three O atoms from two different carboxylate groups and three water molecules, displays a distorted octahedral environment. In the crystal, π–π interchain interactions, with centroid–centroid distances of 3.656 (2) and 3.669 (2) Å between the benzene rings of the ligands, assemble the chains into sheets parallel to (100). O—H⋯O hydrogen-bonding interactions between the coordinating water molecules and carboxylate O atoms link the sheets into a three-dimensional network.