• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 22
  • 12
  • 2
  • 1
  • 1
  • Tagged with
  • 842
  • 69
  • 30
  • 16
  • 13
  • 12
  • 8
  • 7
  • 7
  • 7
  • 7
  • 7
  • 6
  • 6
  • 6
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Electrochemical and spectroelectrochemical studies on 2,2'-bipyridine and pyridine complexes of Pt(II) and Pd(II)

Jack, Lorna Anne January 2003 (has links)
This thesis is concerned with the synthesis, electrochemistry and spectroelectrochemistry of three different types of ligands; the 5,5’-(X)<sub>2</sub>-bpys, (bpy = 2,2’-bipyridine), the bidentate dipyridyls, (py), (where py = pyridine and X is a bridging group) and the nitro substituted bpys 4,4’-(NO<sub>2</sub>)<sub>2</sub>-bpy and 4-NO<sub>2</sub>-bpy and 4-NO<sub>2</sub>-py. The Pt(II) complexes of these ligands were also studied along with the Pd(II) complexes of the nitro substituted ligands. The ligands and complexes of general type 5,5’-(X)<sub>2</sub>-bpy and [Pt(5,5’-(X)<sub>2</sub>-bpy)Cl<sub>2</sub>] are shown by cyclic voltammetry to undergo two reversible, one electron reductions. Analysis of the absorption and epr spectra of the one electron reduction products reveal that the first reduction is localised on the bpy moiety although there is a small but significant (<i>ca</i> 10%) admixture of the Pt 5d 5d<sub>yz</sub> and 6p<sub>z</sub> and 6p<sub>z</sub> orbitals in the SOMO. Spin pairing of the two reduction electrons in the bpy p<sup>-</sup> orbital occurs. Comparison of the gradients on a plot of the Hammett parameters s<sub>m</sub> and s<sub>p</sub> <i>vs</i>. the first reduction potentials of [Pt(5,5’-(X)<sub>2</sub>-bpy)Cl<sub>2</sub>] and [Pt(4,4’-(X)<sub>2</sub>-bpy)Cl<sub>2</sub>] indicates that the 5,5’ position on bpy is electronically the more important site of substitution. The electrochemical behaviour of 4,4’-(NO<sub>2</sub>)<sub>2</sub>-bpy, [Pt(4,4]-(NO<sub>2</sub>)<sub>2</sub>-bpy)Cl<sub>2</sub>] and [Pd(4,4’-(NO<sub>2</sub>)<sub>2</sub>-bpy)Cl<sub>2</sub>] can be explained in terms of a molecular orbital scheme with a low-lying LUMO and a small LUMO/LUMO-1 energy gap. For the free ligand the 4-NO<sub>2</sub>-py rings lie orthogonal to one another and thus the two reduction electrons are localised on separate 4-NO<sub>2</sub>-py moieties. On complexation the 4,4’-(NO<sub>2</sub>)<sub>2</sub>-bpy is forced to become planar and the reduction electrons are localised over the entire ligand. However, epr studies show that the di-reduced species are paramagnetic indicating that the LUMO/LUMO-1 energy gap is still less than the spin pairing energy and di-reduction of 4,4’-(NO<sub>2</sub>)<sub>2</sub>-bpy and its Pt and Pd complexes leads to the spin-triplet species.
2

Macrocyclic complexes of platinum group metals

Roberts, Yvonne V. January 1991 (has links)
A series of half-sandwich complexes, [M([9]aneS<SUB>3</SUB>)*XY]<SUP>n</SUP>+ have been synthesised from MCl<SUB>2</SUB> [M = Pd, Pt,X = Y = Cl<SUP>-</SUP>(n = 0), PPh<SUB>3</SUB>0.5dppm, 0.5dppe,0.5x2, 2'-bipy(n = 2), X = Cl<SUP>-</SUP>, Y = PPh<SUB>3</SUB>(n&61 1); M = Pd, X = Y = 0.5oxytriphos, 0.5x1, 10-phen(n = 2), X = Cl<SUP>-</SUP>, Y = PCy<SUB>3</SUB>(n = 1)]. All but one of the crystal structures [M = Pd, X = Y = Cl<SUP>-</SUP>, PPh<SUB>3</SUB>, 0.5dppm, 0.5oxytriphos, 0.5x2,2'-bipy, 0.5x1,10-phen, X = Cl<SUP>-</SUP>, Y&61 PPh<SUB>3</SUB>; M = Pt, X = Y&61 PPh<SUB>3</SUB>, 0.5dppm] solved show the metal in a square-planar, S<SUB>2</SUB>XY co-ordination set, with a long-range apical interaction to the remaining S-atom of [9]aneS<SUB>3</SUB>; [Pt([9]aneS<SUB>3</SUB>)(PPh<SUB>3</SUB>)<SUB>2</SUB>]<SUP>2</SUP>+ is trigonal bipyramidal. The reductive electrochemistry of the Pd complexes shows the stabilisation of Pd(I) species by bidentate, π-acceptor X,Y ligands. A series of complexes [Ru([9]aneS_3)XYZ]^+ (X-Cl^-, Y = CO or PCy_3, Z&61 H or MeCN; X = H, Y = Z = 0.5x1,5-COD) and [Ru([n]aneS_4)*XY]^m+ (X = Cl^-, Y = PPh_3, n = 12,14,16, m&61 1; X = McCN, Y = PPh_3, n = 12,14, m&61 2; X = Y = McCN, n = 16, m = 2) have also been prepared. The crystral structures of [Ru([9]aneS_3)XYZ]^+ (X = Cl^-, Y = CO, Z&61 McCN; X = H, Y = Z = 0.5x1,5-COD) show the metal to be octahedrally co-ordinated. Such is also the case for [Ru([n]aneS_4)XY]^m+ (n = 14,16, X = Cl^-, Y&61 PPh_3; n = 16, X = Y = MeCN), with the non-macrocyclic ligands mutually <i>cis</i>. A study by nmr spectroscopy of the mechanism of formation of [Ru([9]aneS_3)Cl(PPh_3)(C_4H_3O)H^+ ]^- from [Ru([9]aneS_3)Cl_2(PPh_3)] and Et_2O/THF was undertaken. The former complex, and the dimeric intermediates [Ru([9]aneS_3)(PPh_3)Cl]_2^2+ and [Ru([9]aneS_3(PPh_3)(μ2-Cl)Tl(μ3-Cl)]_2^2+ were characterised by X-ray crystallography. Finally, the novel agostic species [Pd(H[9]aneN_3)Cl_2]_2(PF_6)_2.2([Pd(H[9]aneN_3)Cl_2]_2) is described. The X-ray structure of the dimer shows an unsupported Pd-Pd bond with mutally <i>cis</i>-Cl^- ligands. Only one of the two metal ions in the dimer forms an agostic M-H-N bond. The metal in each of the monomers also forms on M-H-N agostic bond. *[9]aneS_3 = 1,4,7-trithiacyclononane, [14]aneS_4 = 1,4,8,11-tetrathiacyclotetradecane [12]aneS_4 = 1,4,7,10-tetrathiacyclododecane, [16]aneS_4 = 1,5,9,13-tetrathiacyclohexadecane.
3

Neutral, cationic and anionic co-ordination complexes of ruthenium

Ruiz de Ramirez, Lena January 1974 (has links)
No description available.
4

Polymetallic complexes of substituted pyridone ligands

Grant, Craig MacIan January 1995 (has links)
The crystal structures of copper(II) pyridonate complexes are reported with the 6-bromo- (Hbhp) and 6-fluoro (Hfhp) derivatives of 2-pyridone. With Hbhp a dinuclear complex results [Cu<SUB>2</SUB>(hbp)<SUB>4</SUB>] similar to that previously reported for 6-chloro-2-pyridone (Hchp). With Hfhp a tetranuclear copper complex is obtained which consists of a dimer of dimers [{Cu<SUB>2</SUB>(fhp)<SUB>4</SUB>}<SUB>2</SUB>]. Addition of methanol to [Cu<SUB>2</SUB>(bhp)<SUB>4</SUB>] results in the formation of a tetranuclear copper complex [Cu<SUB>4</SUB>(bhp)<SUB>4</SUB>(OMe)<SUB>4</SUB>] with pyridone and methoxide bridges. The analogous reaction with [{Cu<SUB>2</SUB>(fhp)<SUB>4</SUB>}<SUB>2</SUB>] affords the polymer [{Cu<SUB>4</SUB>(fhp)<SUB>4</SUB>(OMe)<SUB>4</SUB>}<SUB>n</SUB>] with a tetranuclear repeat unit. U.V.-vis and E.P.R. spectroscopies were used to investigate the disruption of copper/pyridonate complexes by addition of methanol. Magnetochemistry (5-300 K) of all Cu(II) complexes are discussed and in general reveal antiferromagnetic coupling between Cu(II) centres. The thermolysis reactions of hydrated copper acetate with protonated pyridones gave a range of cotanuclear species, [Cu<SUB>8</SUB>(μ<SUB>4</SUB>-O)<SUB>2</SUB>(xhp)<SUB>8</SUB>(OAc)<SUB>4</SUB>] (x = Cl, Br, Me). Thermal (D.S.C./T.G.A.) studies show initial formation of the homoleptic copper species which reacts further with unreacted copper acetate in solution. N.M.R. (<SUP>1</SUP>H) studies show retention of structure in solution. A series of copper/lanthanoid complexes were synthesised by stepwise reaction of copper/pyridonate complex with hydrated lanthanoid nitrates. Structural analysis reveals three types of Cu/Ln complexes with different Cu/Ln ratios. The nature of pyridone substituent, solvent and size of lanthanoid are discussed in relation to structure type. Magnetochemistry reveals weak ferromagnetic coupling between Cu and Gd in a GdCu<SUB>3</SUB> complex with Hchp whereas antiferromagnetic exchange is observed between Gd atoms in a Cu<SUB>2</SUB>Gd<SUB>2</SUB> compound with Hfhp. The thermolysis reaction between hydrated nickel acetate and Hchp was investigated by D.S.C./T.G.A. Extraction from the melt product with ROH (R = Me, Et) gave linear trinuclear species of formula [Ni<SUB>3</SUB>(chp)<SUB>4</SUB>(R'COO)<SUB>2</SUB>(ROH)<SUB>6</SUB>] (R' = Ph, Me). In contrast extraction with THF gave the metallocycle [Ni<SUB>12</SUB>(xhp)<SUB>12</SUB>(OAc)<SUB>12</SUB>(H<SUB>2</SUB>O)<SUB>6</SUB>(THF)<SUB>6</SUB>] (xhp = chp, bhp). The magnetic properties of both structure types are discussed. The reaction of hydrated manganese(II) acetate with Na(chp) in ethanol afforded the one-dimensional polymer [{Mn<SUB>2</SUB>(chp)<SUB>2</SUB>(OAc)<SUB>2</SUB>(MeOH)<SUB>2</SUB>}<SUB>n</SUB>]. Magnetochemistry shows antiferromagnetic coupling between the Mn(II) centres.
5

Kinetic, spectroscopic and X-ray diffraction studies of D⁶ transition metal complexes

Haines, Robert I. January 1977 (has links)
The work in this thesis is concerned in the main with solvent effects on the kinetic, thermodynamic and spectroscopic properties of several d6 transition metal complexes, and their reactions with various species. Several reactions, which proceed via known mechanisms, have been analysed in terms of the solvation trends of the participant species in the various solvent mixtures studied. For example, the solvent effects on (i) the nucleophilic substitution reactions of the penta-cyanoferrate (II) anions, [Fe(CN)5L]n- (D mechanism), (ii) the acid aquation of the [Fe(5-NO2phen)3]2+ cation (Id), and (iii) mercury(II)- catalyzed aquation of the ReC162- anion, and related complexes (SE2 at Hg2+, dissociative with respect to Re (IV) centre). (iv) The peroxo-disulphate oxidation of the [Fe(phen)3]2+ and related cations has also been studied, in binary aqueous mixtures, together with the acid aquation of the [Fe(phen)3]3+ cation, and its ligand-substituted derivatives, the latter study being in aqueous solution only. In order to quantify such thermodynamic analyses, the solubilities of several pertinent compounds in ranges of binary aqueous mixtures have been measured, and the free energies of transfer of these compounds, and the appropriate single-ion values have been determined. Changes in solvent have a profound effect on the UV/visible spectra of certain inorganic complexes, and a study of such solvatochromism has been undertaken (a) to provide greater understanding of the phenomenon, and (b) to qualitatively analyse selected compounds in terms of their solvatochromic properties, relative to those of compounds of known structure. In this vein, the X-ray crystal structure of trans-di-iso-thiocyanato(cyclam)cobalt(III) thiocyanate (see chapter 7) has been determined, in an attempt to correlate its solvatochromic behaviour with its absolute stereochemistry. Finally, nucleophilic substitution reactions at low-spin iron(II) complexes have been studied, to try to clarify some mechanistic complications which have arisen in such systems.
6

Some reactions of acetylenes with group VIII metal complexes

Howden, Martin Edmund January 1977 (has links)
Chapter 1 presents an outline of the bonding in [special character omitted]-bonded acetylene complexes of metals, and also contains a survey of mono-acetylene complexes of four Group VIII metal systems---rhodium(I), iridium(I), palladium(O) and platinum(O). In chapter 2, some reactions of rhodium(I)-[special character omitted]-ketoenolate complexes with the electrophilic acetylene hexafluorobut-2-yne are described. Compounds of the type (Rh([special character omitted]-ketoenolate)(C2H4)2) as well as (Rh(apeo) (C2H4)2) (Rh(apemino)(C2H4)2), react with C4F6 to give products in which the acetylene adds 1,4 across the rhodium-chelate ring. In addition, the C4F6 is either trimerised to give a hexakis (trifluoromethyl)benzene ring, or dimerised, with incorporation of ethylene, to a 1,2,3,4-tetrakis-(trifluoromethyl)cyclohexa-1,3-diene ligand. These ligands become coordinated to the rhodium, with the [special character omitted]-bonded ethylene ligands being displaced, and it is found that the basicity of the chelating anion is influential in determining which ligand is formed. With (Rh (acac) (C8H14)2), a 9,10,11,12-tetrakis(trifluoromethyl)-bicyclo(6,4,0)dodeca-9,11-diene ligand is formed by combination of two C4F6 molecules and one cyclo-octene molecule. Low temperature (-78 C) reactions of C4F6 with the compounds (Rh ([special character omitted]-ketoenolate) (olefin)2) give a new class of complexes, (Rh ([special character omitted]-ketoenolate) (olefin) (C4F6)), containing both a [special character omitted]-bonded olefin and a [special character omitted]-bonded acetylene ligand. These complexes are probable intermediates in the room temperature formation of cyclohexa-1,3-diene and bicyclododeca-9,11-diene ligands, and may also be involved in the build-up of the benzene-type ligands. The crystal structures of two of these compounds, (Rh (acac) (C2H4) (C4F6)) and (Rh (acac) (C8H14) (C4F6)) are described. Starting from (Rh (dpm) (C2H4) (C4F6)), a series of complexes (Rh (dpm) (Eph3)2(C4F6)) (E = P,As,Sb) can be prepared; it is found that one of the Eph3 ligands is dissociated in chloroform solution. A preliminary investigation of the reactions of (Rh (dpm) (C2H4) (C4F6)) with other acetylenes is also reported. Chapter 3 contains the results of an investigation into the reactions of phenylhaloacetylenes with complexes of platinum(O), palladium(O), rhodium(I) and iridium(I). These results are compared with those obtained for halo-olefins, which have been previously reported. In the case of phenylhaloacetylenes, the products are largely metal-acetylide complexes, many of them previously unknown. Two [special character omitted]-bonded acetylene complexes are obtained, these being (Pt (PPh3)2 (PhC=CCl) ) and (RhCl (PPh3)2 (PhC=CCl) ), and gentle warming of these in hydroxylic solvents results in isomerisation to metal-acetylide compounds. In chapter 4 the kinetics of these two metal-acetylene to metal-acetylide isomerisations are described. In both cases, the reaction is found to exhibit considerably more intramolecular character than is found for metal-olefin to metal-vinyl rearrangements. This result is related to the greater strength of the carbon-halogen bond being broken in acetylene-acetylide isomerisation. Chapter 5 discusses the preparation of some platinum and palladium acetylide and [special character omitted]-allene complexes containing dimethyl- dithiocarbamate as a ligand. In the case of the palladium complex, (Pd (dmdtc) (C=CPh) (PPh3) ), stable products, involving insertion of the acetylene into the palladium-carbon bond, are formed in reactions with hexafluorobut-2-yne and dimethylacetylenedicarboxylate. No reactions occur in the case of the platinum analogue. These results are compared with those for reactions of the acetylenes with (PdX (C=CPh) (PPh3)2) (X = halogen), in which no stable mono-insertion products are formed, although multiple insertion into the palladium-carbon bond may be occurring. Reaction of C4F6 with (Pd (HC=C=CH2) (dmdtc)(PPh3)) is postulated to give a product derived from insertion of the acetylene into the palladium-[special character omitted]-allene bond, followed by rearrangement of the allene moiety to an acetylenic group.
7

Actinide chemistry : high oxidation-state uranium fluoride and fluoride halide complexes

Benham, Emmanuel Jakob January 1992 (has links)
The preparation of UF5 has been re-investigated in detail and it has been shown that the most reliable synthetic route is a novel reaction in which UF6 is interacted with hexamethyldisiloxane at room temperature. The pure UF5 produced has been employed in an investigation of the reactions of UF5.nCH3CN and UF5.nTPPO with trimethylsilylchloride which have been claimed to yield compounds of the type UFxC15-x.nCH3CN (0?x?5 and n = 1,2) and UFxC15-x.nTPPO (TPPO = (C6H5)3PO, 0?x?5 and n = 1,2). In the process of these studies a large number of products were obtained as single crystals and the single-crystal X-ray structures of the novel compounds, [UF4.TPPO]2F, [(UF3.3TPPO)2]2+ 2[UF6]-, cis-UO2Cl2.2TPP0 and ?-trans- UO2Cl2.2TPPO have been obtained. Attempts have been made to elucidate the infrared and e.s.r. spectra of these compounds in order to try to understand the nature of the chemical reactions which give rise to them. Efforts to prepare a mixed bromide fluoride of uranium (VI) have yielded only uranium pentafluoride or uranium tetrafluoride. The preparations of UF5.SbF5.L (L = CH3CN and TPPO) and UF5.2SbF5.5CH3CN were repeated and single crystals were successfully grown for X-ray examination. An attempt to obtain the novel UF5.2SbF5.5TPP0, however, gave inconclusive results.
8

Exchange calculations between donors in silicon and metal-phthalocyanine dimer

Wu, Wei January 2007 (has links)
This thesis describes the calculation of exchange interactions for systems of electrons, and their potential uses for quantum information processing. The first part treats exchange between donor impurities (including especially deep donors) in silicon, while the second describes exchange in copper and manganese phthalocyanines. Part I uses the quantum defect method and a model central-cell correction to evaluate the exchange interaction between two deep donors by a Heitler-London-type approach. This part also describes calculations of the exchange in a three-donor complex, where one donor plays the role of a 'control atom' whose optical excitation switches the coupling strengths, and the other two are qubits embodying the quantum information. Variational calculations are described which give the control electron freedom to reside on different parts of the complex it is found that the exchange between two qubits is increased when the control electron be comes delocalized, and that it is possible for the exchange to become ferromagnetic. These observations are rationalised in terms of multi-centre exchange processes using Green's function perturbation theory. In Part II, exchange interactions between copper(II) phthalocyanine (Cu(II)Pc) and manganese (II) phthalocyanine dimers (Mn(II)Pc) are described these systems have both long excited-state lifetimes and tunable magnetic properties. The theoretical studies described include both a model Green's function calculation, to understand the roles of the competing exchange processes, and ab initio density functional theory calculations. The model calculations of Cu(II)Pc show that the dominant contribution comes from so-called indirect exchange, and depends strongly on the stacking angle. The magnitude of the exchange interaction from the ab initio calculations of Cu(II)Pc roughly agrees with the experiment.
9

Synthesis and characterisation of complex oxychalcogenides and oxypnictides

Herkelrath, Sebastian J. C. January 2009 (has links)
No description available.
10

Some aspects of the chemistry of nitrogen-bridged diphosphorus compounds

Bulloch, G. January 1976 (has links)
No description available.

Page generated in 0.0202 seconds