Fundamental Studies of Carbon Oxygen Bond Activation in Nickel Diphosphine Ether Complexes. And, Metallomacrocycles as Ligands: Synthesis and Characterization of Aluminum-Bridged Bisglyoximato Complexes of Iron and Cobalt

<p>In order to develop better catalysts for the cleavage of aryl-X bonds fundamental studies of the mechanism and individual steps of the mechanism have been investigated in detail. As the described studies are difficult at best in catalytic systems, model systems are frequently used. To study aryl-oxygen bond activation, a terphenyl diphosphine scaffold containing an ether moiety in the central arene was designed. The first three chapters of this dissertation focus on the studies of the nickel complexes supported by this diphosphine backbone and the research efforts in regards to aryl-oxygen bond activation.</p> <p>Chapter 2 outlines the synthesis of a variety of diphosphine terphenyl ether ligand scaffolds. The metallation of these scaffolds with nickel is described. The reactivity of these nickel(0) systems is also outlined. The systems were found to typically undergo a reductive cleavage of the aryl oxygen bond. The mechanism was found to be a subsequent oxidative addition, β-H elimination, reductive elimination and (or) decarbonylation.</p> <p>Chapter 3 presents kinetic studies of the aryl oxygen bond in the systems outlined in Chapter 2. Using a series of nickel(0) diphosphine terphenyl ether complexes the kinetics of aryl oxygen bond activation was studied. The activation parameters of oxidative addition for the model systems were determined. Little variation was observed in the rate and activation parameters of oxidative addition with varying electronics in the model system. The cause of the lack of variation is due to the ground state and oxidative addition transition state being affected similarly. Attempts were made to extend this study to catalytic systems.</p> <p>Chapter 4 investigates aryl oxygen bond activation in the presence of additives. It was found that the addition of certain metal alkyls to the nickel(0) model system lead to an increase in the rate of aryl oxygen bond activation. The addition of excess Grignard reagent led to an order of magnitude increase in the rate of aryl oxygen bond activation. Similarly the addition of AlMe3 led to a three order of magnitude rate increase. Addition of AlMe₃ at -80 °C led to the formation of an intermediate which was identified by NOESY correlations as a system in which the AlMe3 is coordinated to the ether moiety of the backbone. The rates and activation parameters of aryl oxygen bond activation in the presence of AlMe3 were investigated.</p> <p>The last two chapters involve the study of metalla-macrocycles as ligands. Chapter 5 details the synthesis of a variety of glyoxime backbones and diphenol precursors and their metallation with aluminum. The coordination chemistry of iron on the aluminum scaffolds was investigated. Varying the electronics of the aluminum macrocycle was found to affect the observed electrochemistry of the iron center.</p> <p>Chapter 6 extends the studies of chapter 5 to cobalt complexes. The synthesis of cobalt dialuminum glyoxime metal complexes is described. The electrochemistry of the cobalt complexes was investigated. The electrochemistry was compared to the observed electrochemistry of a zinc analog to identify the redox activity of the ligand. In the presence of acid the cobalt complexes were found to electrochemically reduce protons to dihydrogen. The electronics of the ancillary aluminum ligands were found to affect the potential of proton reduction in the cobalt complexes. These potentials were compared to other diglyoximate complexes.</p>

Template assisted fabrication of I-D nanostructures of Nickel,Cobalt, Iron Oxide and Carbon nanotubes and a study on their structural, magnetic and nonlinear optical properties for applications

Department of Physics, Cochin University of Science & Technology

Synthesis and crystal structure characterization of iron(II), cobalt(II) and nickel(II) complexes with 1,3-bis(2-pyridylmethylthio)propane

Three new mononuclear complexes of nitrogen-sulfur donor sets, formulated as (Fe-II(L)Cl-2] (1), [Co-II(L)Cl-2] (2) and [Ni-II(L)Cl-2] (3) where L = 1,3-bis(2-pyridylmethylthio)propane, were synthesized and isolated in their pure form. All the complexes were characterized by physicochemical and spectroscopic methods. The solid state structures of complexes I and 3 have been established by single crystal X-ray crystallography. The structural analysis evidences isomorphous crystals with the metal ion in a distorted octahedral geometry that comprises NSSN ligand donors with trans located pyridine rings and chlorides in cis positions. In dimethylformamide solution, the complexes were found to exhibit Fe-II/Fe-III, co(II)/co(III) and Ni-II/Ni-III quasi-reversible redox couples in cyclic voltammograms with E-1/2 values (versus Ag/AgCl at 298 K) of +0.295, +0.795 and +0.745 V for 1, 2 and 3, respectively. (C) 2009 Elsevier Ltd. All rights reserved.

Oxidation of nickel(II) cyclam and tetraglycine complexes by dissolved oxygen in the presence of sulfur(IV). Synergistic effects of manganese(III) and cobalt(III)

The autoxidation of [Ni-II(cyclam)](2+) (cyclam = 1,4,8,11-tetraazacyclotetradecane) and Ni(II)tetraglycine, accelerated by S-IV is studied spectrophotometrically by following the formation of Ni-III complexes.

Selective Transport of Zinc, Manganese, Nickel, Cobalt and Cadmium in the Root System and Transfer to the Leaves in Young Wheat Plants

• Background and Aims The uptake, translocation and redistribution of the heavy metals zinc, manganese, nickel, cobalt and cadmium are relevant for plant nutrition as well as for the quality of harvested plant products. The long-distance transport of these heavy metals within the root system and the release to the shoot in young wheat (Triticum aestivum ‘Arina’) plants were investigated. • Methods After the application of 65Zn, 54Mn, 63Ni, 57Co and 109Cd for 24 h to one seminal root (the other seminal roots being excised) of 54-h-old wheat seedlings, the labelled plants were incubated for several days in hydroponic culture on a medium without radionuclides. • Key Results The content of 65Zn decreased quickly in the labelled part of the root. After the transfer of 65Zn from the roots to the shoot, a further redistribution in the phloem from older to younger leaves was observed. In contrast to 65Zn, 109Cd was released more slowly from the roots to the leaves and was subsequently redistributed in the phloem to the youngest leaves only at trace levels. The content of 63Ni decreased quickly in the labelled part of the root, moving to the newly formed parts of the root system and also accumulating transiently in the expanding leaves. The 54Mn content decreased quickly in the labelled part of the root and increased simultaneously in leaf 1. A strong retention in the labelled part of the root was observed after supplying 57Co. • Conclusions The dynamics of redistribution of 65Zn, 54Mn, 63Ni, 57Co and 109Cd differed considerably. The rapid redistribution of 63Ni from older to younger leaves throughout the experiment indicated a high mobility in the phloem, while 54Mn was mobile only in the xylem and 57Co was retained in the labelled root without being loaded into the xylem.

Redistribution of Nickel, Cobalt, Manganese, Zinc, and Cadmium via the Phloem in Young and Maturing Wheat

The phloem mobility of heavy metals is relevant to the redistribution of micronutrients and pollutants and, ultimately, to the quality of harvested plant parts. The relative mobility in wheat may vary considerably between different cations. In the study reported here, radio-labeled nickel (Ni), cobalt (Co), manganese (Mn), zinc (Zn) and cadmium (Cd) were introduced into either intact young winter wheat (Triticum aestivum L. cv. Arina) via a leaf flap, or detached maturing shoots via the cut stem. Elements fed into the lamina of the second leaf of 21-day-old plants were translocated to the younger (expanding) leaves and to the roots but not or only in trace amounts to the first (already fully expanded) leaf. The 63Ni and 65Zn were exported more rapidly compared with the other heavy metals. Most of 54Mn was retained in the originally labeled leaf. The peduncle of some maturing shoots was steam-girdled below the ear to distinguish between xylem and phloem transport. This phloem interruption reduced the content of 63Ni in the ear to about 25%. Intermediate effects were observed for 65Zn, 57Co, and 109Cd. Total 54Mn accumulation in the ear was hardly affected by steam-girdling, indicating a transport of this element within the xylem to the ear. These results suggest that the relative phloem mobility of Ni and Zn in young wheat plants and in maturing wheat shoots is higher than the mobility of Co and Cd, whereas the mobility of Mn is very low.

(Table 1, page 146) Iron, manganese and nickel contents of 21 ferromanganese nodules from Combe D'Izame and Mont Peyroux, Montagne Noire

Ferromanganese nodules (equivalent to Recent manganese nodules) are described from the Upper Devonian griotte (red pelagic limestone) of the Montagne Noire (S. France) and the Cephalopodenkalk of the Rheinisches Schiefergebirge, West Germany. They occur as encrustations, commonly exhibiting colloform structures, around skeletal material and limestone clasts. The nodules are associated with encrusting foraminifera and a development in the sublittoral environment is envisaged. Chemically, the ferromanganese nodules are depleted in manganese relative to iron, compared with Recent nodules, a loss which is attributed to diagenetic migration of manganese. Electron probe studies show that manganese covaries positively with calcium, but negatively with iron and silicon. Diagenetic enrichment of hematite occurs in the griotte at hardground horizons where two periods of mineralization can be established. The Devonian ferromanganese nodules show that solution of nodules has not occurred on burial.

(Table 1) Composition of manganese-iron accumulates in the Kiel Bay, western Baltic Sea

Manganese-iron accumulates in the Kiel Bay were investigated with regard to their occurence, chemical composition and formation. Three morphologically different types were identified: a) growth on mussels, b) spherical nodules (ca. 1-3 cm) and c) disshaped symetrical and asymetrical nodules (up to 10 cm). Average values from 110 accumulates representing the three types were: Mn 29.3%, Fe 10.0%, Co 77 ppm, Ni 97 ppm, Cu 21 ppm and Zn 340 ppm. Accumulates on mussels showed the highest trace metal concentrations. A growth rate of ca. 0.6 mm/yr for type (a) was estimated. Heavy metal concentrations were determined in ca. 60 sediment and 30 pore water samples, and in 110 Baltic sea water samples. During certain periods, large increases in Mn values (up to 400 (µg/l) were found in the deeper waters. These concentrations develop during periods of strong stagnant conditions in the sediments where dissolution of Mn oxides, and diffusion mobilizes the Mn into the overlying waters. The manganese is then reprecipitated close to the boundary of the O2-enriched surface waters. This critical O2-concentration was found to be 40% saturation. In the Kiel Bay, Mn-Fe-accumulates are found in a zone which marks the upper limit sometimes reached by the deep waters of lower O2-concentration. Additionally, the availability of larger particles (especially stones or mussels) on the sediment surface is necessary. These conditions are met in the Kiel Bay in a water depth of 20-28 m at several places.

The effects of manganese content and mould size on abrasion and slurry erosion behaviour of chromium-manganese iron systems investigated by positron lifetime spectroscopy

Abrasion and slurry erosion behaviour of chromium-manganese iron samples with chromium (Cr) in the range similar to 16-19% and manganese (Mn) at 5 and 10% levels have been characterized for hardness followed by microstructural examination using optical and scanning electron microscopy. Positron lifetime studies have been conducted to understand the defects/microporosity influence on the microstructure. The samples were heat treated and characterized to understand the structural transformations in the matrix. The data reveals that hardness decreased with increase in Mn content from 5 to 10% in the first instance and then increase in the section size in the other case, irrespective of the sample conditions. The abrasion and slurry erosion losses show increase with increase in the section size as well as with increase in Mn content. The positron results show that as hardness increases from as-cast to heat treated sample, the positron trapping rate and hence defect concentration showed opposite trend as expected. So a good correlation between defects concentration and the hardness has been observed. These findings also corroborate well with the microstructural features obtained from optical and scanning electron microscopy. (C) 2009 Elsevier B. V. All rights reserved.

A convenient and high-yield synthesis for pyridinium and metal hexafluorocomplexes of vanadium, chromium, iron and cobalt

Pyridinium poly(hydrogen fluoride) reacts with the oxide of vanadium(V) and chlorides of chromium(III), iron (III) and Co(II) at room temperature forming the pyridinium salts of hexafluoro vanadate(V), hexafluorochromate(III), hexafluoroferrate(III) and hexafluorocobaltate(II) in near quantitative yields (80%). These pyridinium salts are the precursors for the preparation of the alkali metal hexafluorometallates by metathetic reactions in acetonitrile medium with the corresponding metal chlorides. The prepared salts have been identified by their infrared spectral data and elemental analysis.

Chromium-manganese iron alloy system design cast in metal and sand moulds for erosion resistance: a positron lifetime study

Erosion characteristics of high chromium (Cr, 16-19%) alloy cast iron with 5% and 10% manganese (Mn) prepared in metal and sand moulds through induction melting are investigated using jet erosion test setup in both as-cast and heat-treated conditions. The samples were characterised for hardness and microstructural properties. A new and novel non-destructive evaluation technique namely positron lifetime spectroscopy has also been used for the first time to characterise the microstructure of the material in terms of defects and their concentration. We found that the hardness decreases irrespective of the sample condition when the mould type is changed from metal to sand, On the other hand, the erosion volume loss shows an increasing trend. Since the macroscopic properties have a bearing on the microstructure, good credence is obtained from the microstructural features as seen from light and scanning electron micrographs. Faster cooling in the metal mould yielded fine carbide precipitation on the surface. The defect size and their concentration derived from positron method are higher for sand mould compared to metal mould. Lower erosion loss corresponds to smaller size defects in metal mould are the results of quicker heat transfer in the metal mould compared to the sand mould. Heat treatment effects are clearly seen as the reduced concentration of defects and spherodisation of carbides points to this. The erosion loss with respect to the defects size and concentration correlate very well.

The Determination of the Surface Tensions of Liquid-Iron, Nickel and Iron-Nickel Alloys using the electromagnetic Oscillating Droplet Technique

An oscillating droplet method combined with electromagnetic levitation has been applied to determine the surface tensions of liquid pure iron, nickel and iron-nickel alloys as a function of the temperature. The natural frequency of the oscillating droplet is evaluated using a Fourier analyser. The theoretical background of this method and the experimental set-up were described, and the influence of magnetic field strength was also discussed. The experimental results were compared with those of other investigators and interpreted using theoretical models (Butler's equation, subregular and perfect solution model for the surface phase).