Triazole-Bridged Zinc Dinuclear Complexes: Mechanochemical Synthesis, Crystal Structure, and Biological Activity.

Two zinc (Zn) complexes, [Zn2(DAT)2Cl4] (I) and [Zn2(DAT)2(NO3)4] (II), were prepared by grinding 3,5-diamino-1,2,4-triazole (C2H5N5, DAT) with Zn precursors such as ZnCl2 and Zn(NO3)2, respectively. This solid-state reaction gives the corresponding Zn complex as the sole product in over 99% yield. This mechanochemical method promotes the selective formation of Zn complexes different from those obtained using the conventional solution-based route. The crystal structures of the two complexes were analyzed by single-crystal X-ray diffraction. Complex (I) crystallizes in the monoclinic space group P21/c, whereas complex (II) crystallizes in the triclinic space group P 1̅. Each complex is characterized by the presence of a characteristic DAT-bridged dimer with one DAT ligand per Zn atom, and the DAT ligand provides a bridge between the two Zn metals. All Zn centers of (I) and (II) adopted a slightly distorted tetrahedral geometry. Both complexes contain a hexanuclear Zn2N4 ring, but their ring structures are different. Complex (I) possesses a boat geometry, while complex (II) has a nearly planar structure. The Zn-bound chlorides of complex (I) form intermolecular N-H···Cl hydrogen bonds that link neighboring molecules. In complex (II), the O atoms in the nitrate groups are hydrogen-bonded to the DAT ligand via O···H-N linkages. Both complexes exhibit blue emissions in the solid state at ambient temperature. They were evaluated as anticancer agents in HeLa, NCCIT, and MCF-7 cancer cell lines, exhibiting promising anticancer activities.

Partial oxidation of methane to methanol by isolated Pt catalyst supported on a CeO2 nanoparticle.

Catalytic transformation of methane (CH4) into methanol in a single step is a challenging issue for the utilization of CH4. We present a direct method for converting CH4 into methanol with high selectivity over a Pt/CeO2 catalyst which contains ionic Pt2+ species supported on a CeO2 nanoparticle. The Pt/CeO2 catalyst reproducibly yielded 6.27 mmol/g of Pt with a selectivity of over 95% at 300 °C when CH4 and CO are used as reactants, while the catalyst had a lower activity when using only CH4 without CO. Active lattice oxygen created on the Pt and CeO2 interface provides selective reaction pathways for the conversion of CH4 to methanol. Based on high-angle annular dark-field scanning transmission electron microscopy, x-ray photoelectron spectroscopy, x-ray absorption near-edge structure, extended x-ray absorption fine structure, catalytic studies, and density functional theory calculations, we propose a mechanistic pathway involving CH4 activation at the active site in the vicinity of Pt2+ species.

Stable carbamate pathway towards organic-inorganic hybrid perovskites and aromatic imines.

Methyl ammonium methyl carbamate (MAC), formulated as CH3NH3 +CH3NHCO2 -, was synthesized by reacting liquid methylamine with supercritical CO2, and its structure was refined by single-crystal X-ray diffraction. MAC is a white crystalline salt and is as reactive as methylamine, and is a very efficient alternative to toxic methylamine. We were able to produce hybrid perovskite MAPbI3 (MA = methyl ammonium) by grinding MAC with PbI2 and I2 at room temperature, followed by storing the mixed powder. Moreover, this one-pot method is easily scalable for the large-scale synthesis of MAPbI3 in a small vessel. We have also investigated the reactivity of MAC towards aromatic aldehydes in the absence of solvent. The solventless reactions afforded imines as exclusive products with over 97% yield, which show higher selectivity than the methylamine-based synthesis. Complete conversions were typically accomplished within 3 h at 25 °C. The results of this study emphasize the importance of solid carbamates such as MAC to develop an environmentally friendly process for the synthesis of various amine-based materials on the industrial scale.

Transformation of hydrazinium azide to molecular N8 at 40 GPa.

Hydrazinium azide (HA) has been investigated at high pressures to 68 GPa using confocal micro-Raman spectroscopy and synchrotron powder x-ray diffraction. The results show that HA undergoes structural phase transitions from solid HA-I to HA-II at 13 GPa, associated with the strengthening of hydrogen bonding, and then to N8 at 40 GPa. The transformation of HA to recently predicted N8 (N≡N+-N--N=N--N-+N≡N) is evident by the emergence of new peaks at 2384 cm-1, 1665 cm-1, and 1165 cm-1, arising from the terminal N≡N stretching, the central N=N stretching, and the N-N stretching, respectively. However, upon decompression, N8 decomposes to ε-N2 below 25 GPa, but the remnant can be seen as low as 3 GPa.

Understanding CO2 capture mechanisms in aqueous hydrazine via combined NMR and first-principles studies.

Aqueous amines are currently the most promising solution for large-scale CO2 capture from industrial sources. However, molecular design and optimization of amine-based solvents have proceeded slowly due to a lack of understanding of the underlying reaction mechanisms. Unique and unexpected reaction mechanisms involved in CO2 absorption into aqueous hydrazine are identified using 1H, 13C, and 15N NMR spectroscopy combined with first-principles quantum-mechanical simulations. We find production of both hydrazine mono-carbamate (NH2-NH-COO-) and hydrazine di-carbamate (-OOC-NH-NH-COO-), with the latter becoming more populated with increasing CO2 loading. Exchange NMR spectroscopy also demonstrates that the reaction products are in dynamic equilibrium under ambient conditions due to CO2 exchange between mono-carbamate and di-carbamate as well as fast proton transfer between un-protonated free hydrazine and mono-carbamate. The exchange rate rises steeply at high CO2 loadings, enhancing CO2 release, which appears to be a unique property of hydrazine in aqueous solution. The underlying mechanisms of these processes are further evaluated using quantum mechanical calculations. We also analyze and discuss reversible precipitation of carbamate and conversion of bicarbonate to carbamates. The comprehensive mechanistic study provides useful guidance for optimal design of amine-based solvents and processes to reduce the cost of carbon capture. Moreover, this work demonstrates the value of a combined experimental and computational approach for exploring the complex reaction dynamics of CO2 in aqueous amines.

Electrocatalytic Conversion of Carbon Dioxide and Nitrate Ions to Urea by a Titania-Nafion Composite Electrode.

CO2 and nitrate ions were successfully converted to urea by a TiO2 -Nafion nanocomposite electrode under ambient conditions. The composite electrode was constructed by dropcasting the mixture of P25 titania and Nafion solution on an indium-doped tin oxide (ITO) electrode. When the electrode was electrolyzed in CO2 -saturated 0.1 m KNO3 (pH 4.5) solution at -0.98 V versus Ag/AgCl, urea was formed with a Faradaic efficiency of 40 %. The other reduced products obtained were NH3 , CO, and H2 .

A Highly Stable and Magnetically Recyclable Nanocatalyst System: Mesoporous Silica Spheres Embedded with FeCo/Graphitic Shell Magnetic Nanoparticles and Pt Nanocatalysts.

We have developed a highly stable and magnetically recyclable nanocatalyst system for alkene hydrogenation. The materials are composed of mesoporous silica spheres (MSS) embedded with FeCo/graphitic shell (FeCo/GC) magnetic nanoparticles and Pt nanocatalysts (Pt-FeCo/GC@MSS). The Pt-FeCo/GC@MSS have superparamagnetism at room temperature and show type IV isotherm typical for mesoporous silica, thereby ensuring a large enough inner space (surface area of 235.3 m(2) g(-1), pore volume of 0.165 cm(3) g(-1), and pore diameter of 2.8 nm) to undergo catalytic reactions. We have shown that the Pt-FeCo/GC@MSS system readily converts cyclohexene into cyclohexane, which is the only product isolated and Pt-FeCo/GC@MSS can be seperated very quickly by an external magnetic field after the catalytic reaction is finished. We have demonstrated that the recycled Pt-FeCo/GC@MSS can be reused further for the same hydrogenation reaction at least four times without loss in the initial catalytic activity.

Controlled synthesis of monodisperse SiO(2)--TiO(2) microspheres with a yolk-shell structure as effective photocatalysts.

Monodisperse yolk-shell SiO(2) -TiO(2) microspheres were synthesized using core-shell silica microspheres as templates. In the absence of prior surface modifications, a uniform coating of the TiO(2) layer on the core-shell silica was achieved through a sol-gel route. Mesoporous silica shells between the outer TiO(2) shell and the SiO(2) core were selectively removed by using a weak base, yielding yolk-shell SiO(2) -TiO(2) microspheres (ys-SiO(2) @TiO(2) ). Using the same templates, we synthesized Pt-encased microspheres (SiO(2) @Pt-TiO(2) ), in which Pt nanoparticles are embedded between the SiO(2) core and the TiO(2) shell. Selective etching of the silica shells in SiO(2) @Pt-TiO(2) yields Pt-encased yolk-shell SiO(2) -TiO(2) microspheres (ys-SiO(2) @< Pt >TiO(2) ), which contain void spaces suitable for use as nanoreactors. The ys-SiO(2) @< Pt >TiO(2) catalyst shows enhanced hydrogen production from water under UV-light irradiation presumably as a result of multiple reflections within the void spaces and can be reused without losing their activity. Moreover, this core-shell template method is effective for the synthesis of other yolk-shell microspheres with different metal oxides.

Dual Pd and CuFe2O4 nanoparticles encapsulated in a core/shell silica microsphere for selective hydrogenation of arylacetylenes.

A dual catalyst containing Pd and CuFe(2)O(4) nanoparticles in a silica shell exhibits >98% conversion of arylacetylenes to related styrenes with selectivity greater than 98%, which are better than those obtained using a commercial Lindlar catalyst. The excellent synergy was likely a result of the proximal interaction between Pd and CuFe(2)O(4) nanoparticles.

Synthesis of azines in solid state: reactivity of solid hydrazine with aldehydes and ketones.

Highly conjugated azines were prepared by solid state grinding of solid hydrazine and carbonyl compounds such as aldehydes and ketones, using a mortar and a pestle. Complete conversion to the azine product is generally achieved at room temperature within 24 h, without using solvents or additives. The solid-state reactions afford azines as the sole products with greater than 97% yield, producing only water and carbon dioxide as waste.

Isolation and structural characterization of the elusive 1:1 adduct of hydrazine and carbon dioxide.

A solid hydrazine was isolated as a crystalline powder by reacting aqueous hydrazine with supercritical CO(2). Its structure determined by single crystal X-ray diffraction shows a zwitterionic form of NH(3)(+)NHCO(2)(-). The solid hydrazine is remarkably stable but is as reactive as liquid hydrazine even in the absence of solvents.

Copper nitride nanoparticles supported on a superparamagnetic mesoporous microsphere for toxic-free click chemistry.

Copper nitride nanoparticles supported on a mesoporous superparamagnetic silica microsphere exhibit superior activity toward the Huisgen cycloaddition of azides and alkynes. The nitride catalyst offers significant advantages over homogeneous Cu catalysts.

New heteroleptic iridium complexes having one biphenyl-2,2'-diyl and two bipyridyl based ligands.

The structural and spectroscopic properties of new heteroleptic iridium complexes having a biphenyl and two bipyridyl based ligands are reported; DFT calculations reveal that the HOMO is composed of the biphenyl and iridium d orbitals while the LUMO is localized mainly on the two bipyridyl based ligands.

Ligand effects on luminescence of new type blue light-emitting mono(2-phenylpyridinato)iridium(III) complexes.

Newly prepared hydrido iridium(III) complexes [Ir(ppy)(PPh3)2(H)L](0,+) (ppy = bidentate 2-phenylpyridinato anionic ligand; L = MeCN (1b), CO (1c), CN(-) (1d); H being trans to the nitrogen of ppy ligand) emit blue light at the emission lambda(max) (452-457, 483-487 nm) significantly shorter than those (468, 495 nm) of the chloro complex Ir(ppy)(PPh3)2(H)(Cl) (1a). Replacing ppy of 1a-d with F2ppy (2,4-difluoro-2-phenylpyridinato anion) and F2Meppy (2,4-difluoro-2-phenyl-m-methylpyridinato anion) brings further blue-shifts down to the emission lambda(max) at 439-441 and 465-467 nm with CIE color coordinates being x = 0.16 and y = 0.18-0.20 to display a deep-blue photoemission. No significant blue shift is observed by replacing PPh3 of 1a with PPh2Me to produce Ir(ppy)(PPh2Me)2(H)(Cl) (1aPPh 2Me), which displays emission lambda max at 467 and 494 nm. The chloro complexes, [Ir(ppy)(PPh3)2(Cl)(L)](0,+) (L = MeCN (2b), CO (2c), CN(-) (2d)) having a chlorine ligand trans to the nitrogen of ppy also emit deep-blue light at emission lambda(max) 452-457 and 482-487 nm.

Fabrication of silica-coated magnetic nanoparticles with highly photoluminescent lanthanide probes.

Bi-functional nanoparticles (NPs) that consist of silica-coated magnetic cores and luminescent lanthanide (Ln) ions anchored on the silica surface via organic linker molecules are reported. Compared to individual Ln ions, the hybrid NPs show a drastically enhanced photoluminescence due to the efficient ligand-to-metal energy transfer in the Ln-loaded NPs: the new bi-functional NPs could be used in a variety of biological applications involving magnetic separation and optical detection.

Enhanced photocatalytic activity in composites of TiO2 nanotubes and CdS nanoparticles.

A new composite consisting of TiO(2) nanotubes and CdS nanoparticles, where CdS particles bind covalently to the titania surface through a bifunctional organic linker, was successfully fabricated; this titania nanotube-based composite shows enhanced photocatalytic activity under visible-light irradiation.

Growth of FePt nanocrystals by a single bimetallic precursor [(CO)3Fe(mu-dppm)(mu-CO)PtCl2].

A new single source approach was developed to synthesize face-centered tetragonal (fct) FePt nanoparticles using bimetallic compound (CO)3Fe(mu-dppm)(mu-CO)PtCl2, which has been characterized by single crystal X-ray diffraction and was used as the precursor to ensure the accurate stoichiometry of the final FePt product; the ability of the molecular complex to act as a single source precursor for the formation of fct FePt nanocrystals with an average diameter of 3.2 nm has been demonstrated.

Phase- and size-controlled synthesis of hexagonal and cubic CoO nanocrystals.

Highly crystalline, phase- and size-controlled CoO nanocrystals of hexagonal and cubic phases have been prepared by thermal decomposition of Co(acac)3 in oleylamine under an inert atmosphere. Kinetic and thermodynamic control for the precursor formation leads to two different seeds of hexagonal and cubic phases at higher temperatures. The crystal size of both CoO phases can be easily manipulated by changing the precursor concentration and reaction temperature.

Direct evidence for ferromagnetism of nanometer-scale palladium by contact with perovskite manganite.

Using a template method, we have synthesized hybrid Pd/La0.7Ca0.3-xSrxMnO3 (LCSMO) materials, which were evidenced by SEM, TEM, X-ray powder diffraction, and magnetization measurements. It was found that the Pd moment was induced by the rough LCSMO oxide, which was quantitatively analyzed. Our results provided direct evidence for ferromagnetism of nanosized Pd materials by contact with the perovskite manganite.