Synthesis, characterization and X-ray crystal structures of dinuclear nickel(II) complexes of a novel potentially hexadentate but functionally tetradentate binucleating ligand

A binucleating potentially hexadentate chelating agent containing oxygen, nitrogen and sulfur as potential donor atoms (H2ONNO) has been synthesized by condensing alpha,alpha-xylenebis(N-methyldithiocarbazate) with 2,4-pentanedione. An X-ray crystallographic structure determination shows that the Schiff base remains in its ketoimine tautomeric form with the protons attached to the imine nitrogen atoms. The reaction of the Schiff base with nickel(II) acetate in a 1:1 stoichiometry leads to the formation of a dinuclear nickel(II) complex [Ni(ONNO)](2) (ONNO2- = dianionic form of the Schiff base) containing N,O-chelated tetradentate ligands, the sulfur donors remaining uncoordinated. A single crystal X-ray structure determination of this dimer reveals that each ligand binds two low spin nickel(II) ions, bridged by a xylyl group. The nickel(II) atoms adopt a distorted square-planar geometry in a trans-N2O2 donor environment. Reaction of the Schiff base with nickel(II) acetate in the presence of excess pyridine leads to the formation of a similar dinuclear complex, [Ni(ONNO)(py)](2), but in this case comprises five coordinate high-spin Ni(II) ions with pyridine ligands occupying the axial coordination sites as revealed by X-ray crystallographic analysis. (c) 2005 Published by Elsevier B.V.

Degradation of azo-dye Orange II by a photoassisted Fenton reaction using a novel composite of iron oxide and silicate nanoparticles as a catalyst

A novel nanocomposite of iron oxide and silicate, prepared through a reaction between a solution of iron salt and a dispersion of Laponite clay, was used as a catalyst for the photoassisted Fenton degradation of azo-dye Orange II. This catalyst is much cheaper than the Nafion-based catalysts, and our results illustrate that it can significantly accelerate the degradation of Orange II under the irradiation of UV light (lambda = 254 nm). An advantage of the catalyst is its long-term stability that was confirmed through using the catalyst for multiple runs in the degradation of Orange II. The effects of the H2O2 molar concentration, solution pH, wavelength and power of the LTV light, catalyst loading, and initial Orange II concentration on the degradation of Orange 11 were studied in detail. In addition, it was also found that discoloration of Orange 11 undergoes a faster kinetics than mineralization of Orange II and 75% total organic carbons of 0.1 mM Orange II can be eliminated after 90 min in the presence of 1.0 g of Fe-nanocomposite/L, 4.8 mM H2O2, and 1 x 8W UVC.

Synthetic, EPR spectroscopic, magnetic and X-ray crystallographic structural studies on copper(II) complexes of the tridentate N2S donor ligand formed from 6-methyl-2-formylpyridine and S-methyldithiocarbazate (Hmpsme)

New copper(II) complexes of general empirical formula, Cu(mpsme)X center dot xCH(3)COCH(3) (mpsme = anionic form of the 6-methyl-2-formylpyridine Schiff base of S-methyldithiocarbazate; X = Cl, N-3, NCS, NO3; x = 0, 0.5) have been synthesized and characterized by IR, electronic, EPR and susceptibility measurements. Room temperature mu(eff) values for the complexes are in the range 1.75-2.1 mu(beta) typical of uncoupled or weakly coupled Cu(II) centres. The EPR spectra of the [Cu(mpsme)X] (X = Cl, N-3, NO3, NCS) complexes reveal a tetragonally distorted coordination sphere around the mononuclear Cu(II) centre. We have exploited second derivative EPR spectra in conjunction with Fourier filtering (sine bell and Hamming functions) to extract all of the nitrogen hyperfine coupling matrices. While the X-ray crystallography of [Cu(mpsme)NCS] reveals a linear polymer in which the thiocyanate anion bridges the two copper(II) ions, the EPR spectra in solution are typical of a magnetically isolated monomeric Cu(II) centres indicating dissociation of the polymeric chain in solution. The structures of the free ligand, Hmpsme and the {[Cu(mpsme)NO3] center dot 0.5CH(3)COCH(3)}(2) and [Cu(mpsme)NCS](n) complexes have been determined by X-ray diffraction. The {[Cu(mpsme)NO3]0.5CH(3)COCH(3)}(2) complex is a centrosymmetric dimer in which each copper atom adopts a five-coordinate distorted square-pyramidal geometry with an N2OS2 coordination environment, the Schiff base coordinating as a uninegatively charged tridentate ligand chelating through the pyridine and azomethine nitrogen atoms and the thiolate, an oxygen atom of a unidentate nitrato ligand and a bridging sulfur atom from the second ligand completing the coordination sphere. The [Cu(mpsme)(NCS)](n) complex has a novel staircase-like one dimensional polymeric structure in which the NCS- ligands bridge two adjacent copper(II) ions asymmetrically in an end-to-end fashion providing its nitrogen atom to one copper and the sulfur atom to the other. (c) 2005 Elsevier B.V. All rights reserved.

Synthetic, spectroscopic and X-ray crystallographic structural study of the monomeric [Cu(pysme)(sac)(MeOH)] and dimeric [Cu(6mptsc)(sac)](2) complexes [pysme = anion of the pyridine-2-carboxaldehyde Schiff base of S-methyldithiocarbazate, 6mptsc=the anio

New mixed-ligand copper(II) complexes of empirical formulas [Cu(pysme)(sac) (CH3OH)] and [Cu(6mptsc)(sac)](2) have been synthesized and characterized by conductance, magnetic, IR and electronic spectroscopic techniques. X-ray crystallographic structure analyses of these complexes indicate that in both complexes the copper(II) ions adopt a five-coordinate distorted square-pyramidal geometry with an N3SO donor environment. The Schiff bases are coordinated to the copper(II) ions as tridentate NNS chelates via the pyridine nitrogen atom, the azomethine nitrogen atom and the thiolate sulfur atom. In the monomeric [Cu(pysme)(sac)(MeOH)] complex, the saccharinate anion acts as a monodentate ligand coordinating the copper(II) ion via the imino nitrogen atom whereas in the dimeric [Cu(6mptsc)(sac)](2) complex, the sac anion behaves as a bridging bidentate ligand providing the imino nitrogen donor atom to one of the copper(II) ions and the carbonyl oxygen as a weakly coordinated axial ligand atom to the other Cu(II) ion. In both complexes, the copper(II) ions have distorted square-pyramidal environments. The distortion from an ideal square-pyramidal geometry is attributed to the restricted bite angles of the planar tridentate ligand. (C) 2004 Elsevier Ltd. All rights reserved.

Stereocontrol in complexes of cyclam-like macrocycles - influences of chirality

Enforcement of chirality upon a macrocyclic tetramine ligand structure by the introduction of an asymmetric pendent arm which does not significantly modify the macrocycle conformation has no significant effect upon the geometry of the coordination sphere of a bound metal. Where substitution engendering chirality does cause a change in the ligand conformation, in particular for a ligand of restricted stereochemistry, these effects can be much greater. Thus, conversion of 3,7-diazacycloheptane to a macrocycle via attachment of chiral sidearms and ring closure through a template reaction leads to cyclam derivatives with unusual coordination properties. (C) 2004 Elsevier Ltd. All rights reserved.

Iron catalysed assembly of an asymmetric mixed-ligand triple helicate

The 2-pyridinecarbaldehyde isonicotinoyl hydrazone (HPCIH) family of ligands are typically tridentate N,N,O chelators that exhibit very high in vitro activity in mobilizing intracellular Fe and are promising candidates for the treatment of Fe overload diseases. Complexation of ferrous perchlorate with HPCIH in MeCN solution gives the expected six-coordinate complex Fe-II(PCIH)(2). However, complexation of Fe-II with 2-pyridinecarbaldehyde picolinoyl hydrazone (HPCPH, an isomer of HPCIH) under the same conditions leads to spontaneous assembly of an unprecedented asymmetric, mixed-ligand dinuclear triple helical complex Fe-2(II)(PCPH)(2)(PPH), where PPH2- is the dianion of bis(picolinoyl) hydrazine. The X-ray crystal structure of this complex shows that each ligand binds simultaneously to both metal centres in a bidentate fashion. The dinuclear complex exhibits two well separated and totally reversible Fe-III/II redox couples as shown by cyclic voltammetry in MeCN solution.

Zr-Laponite pillared clay-based nickel catalysts for methane reforming with carbon dioxide

Zr-Laponite pillared clays were prepared and used as supports of nickel catalysts for the methane reforming reaction with carbon dioxide to synthesis gas. The structural and textural characteristics of supports and catalysts were systematically examined by N-2 adsorption/desorption and X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron spectroscopy (TEM) techniques. The catalytic performance and carbon deposition were investigated. It is found that Zr-Laponite pillared clays are promising catalyst supports for carbon dioxide reforming of methane. The pore structure and surface properties of such supports greatly affect the catalytic behaviors of catalysts derived. Carbon deposition on catalysts was also affected by the property and structure of supports. The sintering of nickel metal and zirconia was another factor responsible for catalyst deactivation. This new-type nickel supported catalyst Ni/Zr-Laponite(8), with well-developed porosity, gave a higher initial conversion and a relatively long-term stability, and is therefore a promising catalyst for potential application to carbon dioxide reforming of methane to synthesis gas. (C) 2002 Elsevier Science B.V All rights reserved.

Layered silicate nanocomposites based on various high-functionality epoxy resins. Part II: The influence of an organoclay on the rheological behavior of epoxy prepolymers

The effect of an organically surface modified layered silicate on the viscosity of various epoxy resins of different structures and different functionalities was investigated. Steady and dynamic shear viscosities of the epoxy resins containing 0-10 wt% of the organoclay were determined using parallel plate rheology. Viscosity results were compared with those achieved through addition of a commonly used micron-sized CaCO3 filler. It was found that changes in viscosities due to the different fillers were of the same order, since the layered silicate was only dispersed on a micron-sized scale in the monomer (prior to reaction), as indicated by X-ray diffraction measurements. Flow activation energies at a low frequency were determined and did not show any significant changes due to the addition of organoclay or CaCO3. Comparison between dynamic and steady shear experiments showed good agreement for low layered silicate concentrations below 7.5 wt%, i.e. the Cox-Merz rule can be applied. Deviations from the Cox-Merz rule appeared at and above 10 wt%, although such deviations were only slightly above experimental error. Most resin organoclay blends were well predicted by the Power Law model, only concentrations of 10 wt% and above requiring the Herschel-Buckley (yield stress) model to achieve better fits. Wide-angle X-ray measurements have shown that the epoxy resin swells the layered silicate with an increase in the interlayer distance of approximately 15 Angstrom, and that the rheology behavior is due to the lateral, micron-size of these swollen tactoids.

Preparation and catalytic properties of ZrO2-Al2O3 composite oxide supported nickel catalysts for methane reforming with carbon dioxide

ZrO2-Al2O3 composite oxides and supported Ni catalysts were prepared, and characterized by N-2 adsorption/desorption, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques. The catalytic performance and carbon deposition was also investigated. This mesoporous composite oxide is shown to be a promising catalyst support. An increase in the catalytic activity and stability of methane and carbon dioxide reforming reaction was resulted from the zirconia addition, especially at 5wt% ZrO2 content. The Ni catalyst supported ZrO2-Al2O3 has a strong resistance to sintering and the carbon deposition in a relatively long-term reaction.

A novel laponite clay-based Fe nanocomposite and its photo-catalytic activity in photo-assisted degradation of Orange II

A novel laponite RD clay-based Fe nanocomposite (Fe-Lap-RD) has been successfully synthesized through a reaction between a solution of iron salt and an aqueous dispersion of laponite RD clay. The X-ray diffraction (XRD) results reveal that the Fe-Lap-RD mainly consists of Fe2O3 (maghemite) and Fe2Si4O10(OH)2 (iron silicate hydroxide), which have tetragonal and monoclinic structures, respectively, and has a high specific surface area as well as a high pore volume. The photo-catalytic activity of the Fe-Lap-RD was examined in the photo-assisted degradation of an organic azo dye Orange II. It was found that the mineralization of Orange 11 undergoes a slower kinetics than discoloration, and 70% total organic carbon (TOC) of 0.2 mM Orange 11 can be removed in 90 min, implying that the Fe-Lap-RD exhibited a high photo-catalytic activity in the presence of H2O2 and UV light (254 nm) in the photo-assisted degradation of Orange II. In addition, our experiments also illustrate that the Fe-Lap-RD has a long-term stability but is of low cost. This study illustrates the possibility of photo-assisted degradation of organic compounds without the requirements to remove the Fe ions after reaction. Two possible catalytic reaction mechanisms are also proposed. (C) 2003 Elsevier Science Ltd. All rights reserved.