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1
Morello, Glenn R. "Stereoselectivity in organometallic catalysis : analysis by means of computational and mathematical chemistry /." Electronic version (Microsoft Word), 2003. http://dl.uncw.edu/etd/2003/morellog/glennmorello.doc.
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Wong, Heng Vee. "Structural, electronic and kinetic studies on organometallic intercalates of metal dichalcogenides." Thesis, University of Oxford, 1993. http://ora.ox.ac.uk/objects/uuid:aad80a5e-a1bb-4eea-80e8-ce079e0b1204.
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Large single crystals of the metal dichalcogenide hosts ZrS2 and 811X2 (X = S, Se) have been successfully intercalated with a variety of organometallic guests {C0(η-C5H5)2, CO(η-C5H4CH3)2, Mo(η-C6H6)2, Mo(η-C7H7)(η-C5H5), W(η-C7H7)(η-C5H5), Ti(η-C8H8)(η-C5H5)}. The structural and electronic properties of these materials have been studied, as well as the intercalation kinetics of these organometallic species into the tin dichalcogenides. X-ray and neutron diffraction experiments have been used to obtain 001 reflections in order to obtain a one-dimensional profile of electron and neutron scattering in these disordered layered materials (Chapter Two). Refinement of the data shows that for all the organometallic guests, the majority of the intercalant adopts an orientation in which the principal molecular axis lies parallel to the layer planes of the host. These findings are confirmed by 2H NMR spectroscopy on single crystals of deuterated cobaltocene intercalates of ZrS2 and SnSe2, where it has been shown that rapid C5, but not C2, rotation of the metallocene occurs in the interlamellar van der Waals space. To study the electronic properties of these intercalates, electrical resistivity and magnetic susceptibility measurements have been performed (Chapter Three). An apparatus has been built to measure the resistivity of these crystal intercalates down to 4.2K. The resistivity measurements show that intercalation of various organometallic complexes confers metallic properties upon ZrS2 while SnS2{Co(η-C5H5)2} 0.3 becomes a superconductor with a Tc of 8.3K. The magnetic susceptbility measurements confirm the presence of guest-host charge transfer. Estimates of its extent, as well as the magnitude of the Pauli susceptibility in these intercalates, have been attempted. Studies on the rate and mechanism for the intercalation of cobaltocene into the disulfides and diselenides of tin have been performed (Chapter Four). An apparatus has been designed and constructed for in situ diffraction using synchrotron X-rays in order to monitor the progress of these rapid intercalation reactions. The results indicate that the rate of intercalation of cobaltocene into the tin dichalcogenides is very much dependent on the solvent used, being significantly faster in dimethoxyethane than in toluene. Analyses of the kinetic rate expressions for the tin dichalcogenide intercalation in dimethoxyethane suggests that diffusion of cobaltocene molecules into the interlamellar space constitutes the rate limiting step. The choice of solvent also dramatically affects the mechanism of the intercalation. When a solution of cobaltocene in dimethoxyethane is used, the host transforms directly to the final product but in toluene, staged intermediates are observed during the intercalation process. The apparatus and techniques that have been developed for the in situ kinetics experiments are general and permit dynamic structural transformations in air- and moisture-sensitive suspensions of solids to be effectively studied.
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Assoua, Mebi Charles. "Half-sandwich ruthenium (II) complexes of 1,3,5-triaza-7-phosphaadamantane syntheses, reactivity, and catalytic application /." abstract and full text PDF (free order & download UNR users only), 2007. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3258845.
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Hoppe, Martin Louis. "Characterization of the electronic structure of complexes containing metal-heteroatom multiple bonds." Diss., The University of Arizona, 1988. http://hdl.handle.net/10150/184616.
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The electronic structure of a variety of metal-heteroatom multiply bonded complexes, including some active alkyne metathesis catalysts, have been investigated using He(I) and He(II) ultraviolet photoelectron spectroscopy (UPS), X-ray photoelectron spectroscopy (XPS) and Fenske-Hall molecular orbital calculations. Utilizing this electronic structure information, confirmation of the proposed mechanism for the alkyne metathesis reaction which involves formation of a metallacyclobutdienyl intermediate was ascertained. Also, the important relationships between metallatetrahedral and metallacyclobutadienyl complexes, both of which have been mentioned as possible intermediates in the alkyne metathesis reaction and for which examples have been prepared and isolated, are discussed in significant detail. In the final chapters the electronic structure of some corresponding metal-nitrogen triply bonded complexes are discussed as well as the results probing the charge distribution in metal-heteroatom multiply bonded systems as determined by the XPS experiment.
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Luten, Henry Alney III. "Preparation and characterization of metalorganic compounds as precursors for the preparation of electronic materials by chemical vapor deposition." Diss., Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/31016.
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Blewett, Gavin. "Novel palladium (II) complexes belonging to a family of potential catalytic precursors." Thesis, Stellenbosch : Stellenbosch University, 2006. http://hdl.handle.net/10019.1/21796.
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Thesis (MSc)--University of Stellenbosch, 2001.<br>ENGLISH ABSTRACT: This study comprises the preparation and characterization of various novel
organometallic complexes of palladium(ll) which contain symmetric and
unsymmetric (heteroatom-containing) r..-dicarbonyl-type ligands, T]3-heteroallyl
ligands and T]3-coordinated trimethylsilyl-containing ligands.
With the ultimate objective of preparing potential catalytic precursors similar to
known catalytic precursors which exhibit hemilabile activity, the main goals of
this study were the following: -
• Investigate the coordination mode of the aforementioned ligand-types to
the palladium of the starting compound, trans-[Pd(CeHs)CI{P(CeHshhl (1),
by physical measurements.
• Carry out single crystal structure determinations where possible.
• Investigate the influence of the properties of the ligands on the stability of
the prepared complexes.
• Investigate the existence of hemilability (if any) in the prepared complex.
The deprotonated symmetric and unsymmetric f!,-dicarbonyl-type ligands
readily bind to the palladium of the starting compound in a bidentate fashion
through the oxygens by displacing a triphenylphosphine group and producing
easily removable sodium chloride. These complexes show that a negative
charge can be accommodated in a delocalized fashion by the -S=O and -
P=O groups of these acac--type ligands in a similar manner to the carbonyl
groups of acetylacetonate. However, no evidence of hemilabile activity was
found in this series of complexes.
In a similar fashion, the deprotonated T]3-heteroallyl ligands, L = [PhzPS£],
[PhCOz-], [PhC{NSi(CH3hhl [(Ph)zP{NSi(CH3hh-], were linked to palladium
in the same starting complex, in T]3-fashion by triphenylphosphine substitution.
No evidence of hemilabilty was evident in this series of complexes, but when
L = [PhzPSz-], an exchange of the coordinated triphenylphosphine group with
the free triphenylphosphine group was observed in the reaction mixture. Finally, the preparation, isolation and spectroscopic characterization of
several T\3-allyl paliadium(lI) complexes with ligands of the type
R-TeCH2CH2CQQCH3, (R = isopropyl, t-butyl ,ethyl) were attempted with the
compound bis-( T\3-allyl )-di-~ -iodo-dipalladium( II), [T\3 -( CH2CHCH2J2Pd212J,
which had also now been crystallographically characterized. Chelate
formation by TeAQ coordination seemed possible by halide precipitation with
silver tetrafluoroborate. Unfortunately the resulting compounds were too
unstable to be isolated in the pure form for characterization.<br>AFRIKAANSE OPSOMMING: Die studie behels die bereiding en karakterisering van verskeie nuwe
palladium(lI) organometaalkomplekse met inbegrip van simmetriese en
onsimmetriese (heteroatoom bevattende) ~-dikarboniel-tipe ligande, 113-
heteroallielligande en 113_gekoordineerdetrimetielsiliel bevattende ligande.
Met die beoogde einddoel die bereiding van potensiele katalitiese
voorgangers soortgelyk aan bekende katalitiese voorgangers met hemilabiele
aktiviteit, sluit die hoof mikpunte van die studie die volgende in: -
• 'n Ondersoek na koordinasie-wyse van die bogenoemde ligand tipes aan
die palladium van die uitgangstof, trans-[Pd(C6Hs)CI{P(C6Hshhl (1), met
behulp van fisiese bepalings.
• Enkel kristal struktuur bepalings waar moontlike.
• 'n Ondersoek na die invloed van die einskappe van die ligande op die
stabilitiet van die komplekse.
• 'n Ondersoek na die bestaan van hemilabiele aktiwiteit (indien enige) in die
voorbereide complekse.
Die gedeprotoneerde simmetriese en onsimmetriese ~-dikarboniel-tipe
ligande het geredelik, bidentaat deur middel van die suurstowwe gebind aan
die palladium van die uitgangstof deur die verplasing van die trifenielfosfien
group en die vorming van verweiderbare natriumchloried. Hierdie komplekse
dui aan dat 'n negatiewe lading wei geakkommodeer kan word deur
delokalisasie by die -S=O- en -P=O-groepe van hierdie acac"-tipe Iigande,
soortgelyk aan die karbonielgroep van asetielasetonaat. Geen hemilabiliteit is
waargeneem in hierdie reeks komplekse nie.
Die gedeprotoneerde 113-heteroalliel Iigande, L = [Ph2PS£), [PhCO£),
[PhC{NSi(CH3h}£), [(PhhP{NSi(CH3hhl is op 'n soortgelyke wyse 113-
gekoppel aan palladium van dieselfde uitgangstof met trifenielfosfien
verplasing. Geen hemilabiliteit is waargeneem in hierdie reeks komplekse nie, maar wanneer L = [Ph2PS£], is 'n uitruiling van 'n gekoordineerde
trifenielfosfien met 'n vrye trifenielfosfien in die reaksiemengsel waargeneem.
Die bereiding, isolasie en spektroskopiese karakterisering van Tj3-alliel
paliadium(lI) komplekse met ligande van die tipe R-TeCH2CH2COOCH3, (R =
isopropiel, t-butiel ,etiel) is gepoog met die uitgangstof bis-(Tj3-alliel)-di-ll-iododipaliadium(
II), [Tj3-(CH2CHCH2hPd2b], wat volledig gekarakteriseer was.
Chelaat-vorming deur TeAO-koordinasie het moonlik blyk te wees deur halied
presipitasie met behulp van AgBF4. Die komplekse is baie onstabiel en is dit
gevolglik nie moontlik am die komplekse suiwer te isoleer en te karakteriseer
nie.
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Magwa, Nomampondo Penelope. "A spectroscopic study of the electronic effects on copper (II) and copper (I) complexes of ligands derived from various substituted benzyaldehyde- and cinnamaldehyde- based schiff bases." Thesis, Rhodes University, 2010. http://hdl.handle.net/10962/d1006712.
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Several Schiff base ligands, N, N‟-(aryl)benzyaldiimine ligands (R-BEN); N, N‟-(aryl)benzyaldiamine dihydrochloride ligands (R-BENH•2HCl); N, N‟-(aryl)benzyaldiamine ligands (R-BENH); N, N‟-bis(cinnamaldiimine) ligands (R-CA2EN) were synthesized for the investigation of the electronic effect of the substituents at para-position of the Schiff base ligands and their copper complexes. The synthesis of Schiff bases was carried out by reacting a series of para-substituted benzyaldehyde, and para-substituted cinnamaldehyde with ethylenediamine. The imine group of Schiff bases, N, N‟-(aryl)benzyaldiimine ligands and N, N‟-bis(cinnamaldiimine)ligands were reduced to corresponding amines with sodium borohydride in methanol These ligands, N, N‟-(aryl)benzyaldiamine ligands (H-BENH), N, N‟-bis(cinnamaldiimine)ligands (CA2EN) were reacted with copper(II) dihalide and copper(I) monohalide ions respectively to form complexes. The ligands and their complexes were analysed using elemental analyses, FT-IR spectroscopy (mid-IR), UV/vis in aprotic and protic solvents,while mass spectrometry, 1H-NMR and 13C-NMR were used to further analyse the ligands. By using substituent parameters, both the single and dual substituent parameters with the spectroscopic data obtained from the spectroscopic techiques mentioned above, it was hoped to monitor and determine whether the electronic effects (resonance or inductive effcets) was predominantly within the Schiff base ligands and copper complexes. The NMR studies with dual substituent parameters suggest that the effects of the substituents are transimitted through the ligands, via resonance effects and that the phenyl group is nonplanar with the azomethine in N, N‟-(aryl)benzyaldiimine ligands. The presence of an extra double bond in Schiff base {(N, N‟-bis(cinnamaldiimine) ligand)} altered the electron density. The UV/vis studies showed that the symmetry of the N, N‟-bis(4-R-benzyl)-1, 2-diaminoethanedihalidecopper(II) complexes were predominantly tetrahedral for both chloro and bromo complexes. The correlation studies from mid-infrared were beneficial in monitoring the effect experienced by N, N‟-(aryl)benzaldiimine ligands, the studies suggest that the inductive effect is more pronounced at the C=N.
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Khani, Sarah Karbalaei. "Exploring Inorganic Catalysis with Electronic Structure Simulations." Thesis, University of North Texas, 2016. https://digital.library.unt.edu/ark:/67531/metadc849685/.
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Organometallic catalysis has attracted significant interest from both industry and academia due to its wide applications in organic synthetic transformations. Example of such transformations include the reaction of a zinc carbenoid with olefins to form cyclopropanes. The first project is a computational study using both density functional and correlated wavefunction methods of the reaction between ethylene and model zinc carbenoid, nitrenoid and oxenoid complexes (L-Zn-E-X, E = CH2, NH or O, L = X = I or Cl). It was shown that cyclopropanation of ethylene with IZnCH2I and aziridination of ethylene with IZnNHI proceed via a single-step mechanism with an asynchronous transition state. The reaction barrier for the aziridination with IZnNHI is lower than that of cyclopropanation. Changing the leaving group of IZnNHI from I to Cl, changes the mechanism of the aziridination reaction to a two-step pathway. The calculation results from the epoxidation with IZnOI and ClZnOCl oxenoids suggest a two-step mechanism for both oxenoids. Another important example of organometallic catalysis is the formation of alkyl arenes from arenes and olefins using transition metal catalysis (olefin hydroarylation). We studied with DFT methods the mechanism of a novel Rh catalyst (FlDAB)Rh(TFA)(η2–C2H4) [FlDAB = N,N’ -bis(pentafluorophenyl)-2,3-dimethyl-1,4-diaza-1,3-butadiene; TFA = trifluoroacetate] that converts benzene, ethylene and air-recyclable Cu(II) oxidants to styrene. Possible mechanisms are discussed.
9
Rai, Chaudhuri Anjana. "Electronic structure and bond energy trends in silicon-hydrogen and germanium-hydrogen bond activation by transition metals." Diss., The University of Arizona, 1989. http://hdl.handle.net/10150/184731.
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The electronic structure factors that control Si-H and Ge-H bond activation by transition metals are investigated by means of photoelectron spectroscopy. Molecular orbital calculations are also used to gain additional insight into the orbital interactions involved in bond activation. The complexes studied have the general molecular formula (η⁵-C₅R'₅)Mn(CO)(L)HER₃, where R' is H or CH₃, L is CO or PMe₃, E is Si or Ge and R is Ph or Cl. These compounds are interesting models for catalysts in industrial processes like hydrosilation. The compounds display different stages of interaction and "activation" of the E-H bonds with the metal. One purpose is to measure the degree of Mn, Si, H 3-center-2-electron bonding in these complexes. The three-center interaction can be tuned by changing the substituents on Si, methylating the cyclopentadienyl ring, changing the ligand environment around the metal and substituting Si with Ge. The degree of activation is measured by observing the shifts in the metal and ligand ionizations relative to starting materials and free ligand in the photoelectron spectrum. Changing the substituent on Si extensively changes the degree of activation. Photoelectron spectral studies on (η⁵-C₅H₅)Mn(CO)₂HSiPh₃ show this to be a Mn(I) system. Progressive methylation of the cyclopentadienyl ring increases the electron richness at the metal center with no substantial effect on the degree of activation. Substitution on the metal (PMe₃ for CO) is less able to control the electronic structure factors of activation than the substitution on the Si atom. The magnitude of Ge-H bond activation is found to be of the same order as the Si-H bond activation for analogous compounds as found by studying (η⁵-C₅H₅)Mn(CO)₂HGePh₃, (η⁵-CH₃C₅H₄)Mn(CO)₂HGePh₃ and (η⁵- C₅(CH₃)₅)Mn(CO)₂HGePh₃ complexes by photoelectron spectroscopy. The photoelectron spectra of CpFe(CO)₂SiCl₃ and CpFe(CO)₂SiMe₃ were measured to study the electron charge shift from the metal to the ligand in these complexes as compared to CpMn(CO)₂HSiR₃ complexes. The photoelectron spectroscopic studies include numerous perturbations of the ligand and metal center to observe the extent of bond interaction and remain one of the best techniques to detect activation products.
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Renshaw, Sharon Kintner. "Photoelectron spectroscopy and bonding of iron and rhodium organometallic compounds with metal-carbon and metal-hydrogen bonds." Diss., The University of Arizona, 1991. http://hdl.handle.net/10150/185692.
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Gas phase ultraviolet photoelectron spectroscopy was used to investigate the electronic structure of organometallic compounds. Acetylide ligands in (η⁵-C₅H₅)Fe(CO)₂CECR (R = H, ᵗBu, Ph, C=CH) compounds are found to be effective π donor ligands. There is extensive interaction between the filled acetylide π and filled dπ orbitals. The HOMO and SHOMO of the acetylide compounds are partially localized on the acetylide β carbon. Variation of the R group causes both the σ and π donor ability of the acetylide to change significantly. The dπ/pπ mixing is more extensive in the R = ᵗBu or Ph compounds than in the R = H compound. In the compound CpFe(CO)₂(C=C-C=CH), the butadiyne π system mixes extensively with the metal dπ electrons. The d1t electron density is extended across the C₄H chain. These findings explain the observed reactivity toward electrophiles and Metal/acetylide communication. The first photoelectron spectra of Rh(III) compounds were obtained. The electronic structure of (η⁵-C₅Me₅)Rh(PMe₃)(Cl)(R) compounds, where R = CI, CH₃ or C₆H₅, is sensitive to changes in the R ligand. The a donor ability of the methyl and phenyl ligands are similar, but the phenyl has an additional filled/filled interaction with a metal dn orbital. The PES of (η⁵-C₅Me₅)Rh(PMe₃)(R)₂ (R = H or CH₃) revealed an electronic structure that is not isolobal with other d⁶ organometallic compounds. The HOMO and SHOMO are ligand based, as a result of the metal orbitals mixing with the Cp ring and M-R a bond combinations. The PES spectra of the compounds (η⁵-C₅H₄X)Rh(CO)₂ (X = NO₂, CF₃, CI, H, NMe₂, CH₃) gave measures of σ (inductive) and π (resonance) effects of the X substituent. The ionization energies of the metal based orbitals correlate with the carbonyl stretching frequencies and with Hammett σ(p) parameters. The X = Cl and NMe₂ compounds have significant π overlap with the Cp ring, and also have accelerated rates of associative CO substitution. The measures of inductive and resonance effects were correlated to the rates of CO substitution. The 7t terms are crucial to the correlation and suggest stabilization of an η³-Cp slipped ring intermediate. The PES of the associative substitution products (η⁵-C₅H₅)Rh(CO)L (L = PMe₃ or PPh3) have analogous electronic structure to CpRh(CO)₂, except that the valence ionizations are destabilized due to donor properties of the phosphines. The PPh₃ ligand is a better donor than PMe₃.
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Mountford, H. Scott. "The structure and spectroscopy of compounds with 1,4,8,11-tetraazacyclotetradecane and manganese (III), nickel (II), and iron (II) : [thesis]." Scholarly Commons, 1991. https://scholarlycommons.pacific.edu/uop_etds/2221.
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This thesis involves reactions of cyclam with Mn(III), Ni(II) and Fe(II). The chemistry of each metal with cyclam will be presented in sections discussing each metal. The initial intent of this thesis was to examine and compare the structures and electronic spectra of a series of trans monomeric first row transition metal cyclam compounds. Both Mn(III) and Ni(II) form such trans monomeric complexes with cyclam and their structural and electronic characteristics are, indeed, examined in this thesis. However, in the course of our study, we found that Fe(II) and cyclam in acetonitrile in the presence of oxygen form a di-macrocycle shown here: [See PDF]
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Van, Niekerk Lizette. "Bereiding en karakterisering van dikernige komplekse uitgaande van chroomheksakarboniel en groep 4 metallosene." Thesis, Stellenbosch : Stellenbosch University, 2000. http://hdl.handle.net/10019.1/51635.
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Lam, Wai Han. "Structural features of transition metal complexes having ligands with different electronic properties and mechanistic aspect of C-H bond activation and functionalization by transition metal complexes /." View Abstract or Full-Text, 2003. http://library.ust.hk/cgi/db/thesis.pl?CHEM%202003%20LAMW.
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Barden, Joel M. "A study of the regioselectivity in the zeolite-assisted nitration of toluene /." Electronic version (PDF), 2003. http://dl.uncw.edu/etd/2003/bardenj/joelbarden.html.
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Harris, Tyler. "Photo-induced isomerization and dimerization of various styryl quinolines." View electronic thesis (PDF), 2009. http://dl.uncw.edu/etd/2009-2/harrist/tylerharris.pdf.
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Adams, Krysten Scott. "Using computational methods to predict NMR spectra for polyether compounds /." Electronic version (PDF), 2005. http://dl.uncw.edu/etd/2005/adamsk/krystenadams.pdf.
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Smith, Lacie Marie. "Synthesis of site specific DNA methylating compounds targeting pancreatic ß-cells." View electronic thesis, 2008. http://dl.uncw.edu/etd/2008-3/smithl/laciesmith.pdf.
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Gephart, Raymond Thomas. "The highly preorganized ligand 2,9-BIS(Hydroxymethyl)-1,10-Phenanthroline, and its complexation properties with metal ions /." Electronic version (PDF), 2006. http://dl.uncw.edu/etd/2006/gephartr/raymondgephart.pdf.
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Truxal, Laura T. "Characterization of novel compounds isolated from Karenia brevis cultures." View electronic thesis, 2008. http://dl.uncw.edu/etd/2008-3/rp/truxall/lauratruxal.pdf.
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Gangopadhyay, Shruba. "Density Functional Theory Study of Molecules and Crystals Containing d and f Metals." Doctoral diss., University of Central Florida, 2011. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4897.
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Density Functional Theory (DFT) method is applied to study the crystal structure of transition metal and lanthanide oxides, as well as molecular magnetic complexes. DFT is a widely popular computational approach because it recasts a many-body problem of interacting electrons into an equivalent problem of non-interacting electrons, greatly reducing computational cost. We show that for certain structural properties like phase stability, lattice parameter and oxygen migration energetics pure DFT can give good agreement with experiments. But moving to more sensitive properties like spin state energetic certain modifications of standard DFT are needed. First we investigated mixed ionic-electronic conducting perovskite type oxides with a general formula ABO3 (where A =Ba, Sr, Ca and B = Co, Fe, Mn). These oxides often have high mobility of the oxygen vacancies and exhibit strong ionic conductivity. They are key materials that find use in several energy related applications, including solid oxide fuel cell (SOFC), sensors, oxygen separation membranes, and catalysts. Different cations and oxygen vacancies ordering are examined using plane wave pseudopotential density functional theory. We find that cations are completely disordered, whereas oxygen vacancies exhibit a strong trend for aggregation in L-shaped trimer and square tetramer structure. On the basis of our results, we suggest a new explanation for BSCF phase stability. Instead of linear vacancy ordering, which must take place before the phase transition into brownmillerite structure, the oxygen vacancies in BSCF prefer to form the finite clusters and preserve the disordered cubic structure. This structural feature could be found only in the first-principles simulations and cannot be explained by the effect of the ionic radii alone. In order to understand vacancy clustering and phase stability in oxygen-deficient barium strontium cobalt iron oxide (BSCF), we predict stability and activation energies for oxygen vacancy migration. Using symmetry constrained search and Nudged Elastic Band method, we characterize the transition states for an oxygen anion moving into a nearby oxygen vacancy site that is surrounded by different cations and find the activation energies to vary in the range 30-50 kJ/mol in good agreement with experimental data. Next we study spin alignments of single molecule magnets (SMM). SMMs are a class of polynuclear transition metal complexes, which characterized by a large spin ground state and considerable negative anisotropy. These properties lead to a barrier for the reversal of magnetization. For these reasons SMM are expected to be promising materials for molecular spintronics and quantum computing applications. To design SMM for quantum computation, we need to accurately predict their magnetic properties. The most important property is, Heisenberg exchange coupling constant (J). This constant appears in model Heisenberg Hamiltonian that can be written in general form as
H = −ΣJijSiSj
here Jij represents the coupling between the two magnetic centers i and j with the spin states Si and Sj. The positive J values indicate the ferromagnetic ground state and the negative ones indicate the antiferromagnetic ground state. We found pure DFT is not accurate enough to predict J values. We employ density functionals with a Hubbard U term that helps to counteract the unphysical delocalization of electrons due to errors in pure exchange-correlation functionals. Unlike most previous DFT+U studies, we calibrate U parameters for both metal and ligand
atoms using five binuclear manganese complexes as the benchmarks. We note delocalization of the spin density onto acetate ligands due to π-back bonding, inverting spin-polarization of the acetate oxygen atoms relative to that predicted from superexchange mechanism. This inversion may affect performance of the models assuming strict localization of the spins on magnetic centers for the complexes with bridging acetate ligands. Next, we apply DFT+U methodology for Mn12(mda) and Mn12(ada) complexes to calculate all six nearest neighbor Jij value. Our result shows both qualitative and quantitative agreement with experiments unlike other DFT studies. Using the optimized geometry of the ground spin state instead of less accurate experimental geometry was found to be crucial for this good agreement. The protocol tested in this study can be applied for the rational design of single-molecule magnets for molecular spintronics and quantum computing applications.
Finally we apply hybrid DFT methodology to calculate geometrical parameters for cerium oxides. We review the experimental and computational studies on the cerium oxide nanoparticles, as well as stoichiometric phases of bulk ceria. Electroneutral and nonpolar pentalayers are identified as building blocks of type A sesqioxide structure. The idealized structure of the nanoparticles is described as dioxide covered by a single pentalayer of sesquioxide, which explains the exceptional stability of subsurface vacancies in nanoceria. The density functional theory (DFT) predictions of the lattice parameters and bulk moduli for the Ce(IV) and Ce(III) oxides at the hybrid DFT level are also presented. The calculated values for both compounds agree with experiment and allow to predict changes in the lattice parameter with decreasing size of the nanoparticles. The results validate hybrid DFT as a promising method for future study the structure of oxygen vacancies and catalytic properties of ceria nanoparticles.<br>ID: 029809473; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (Ph.D.)--University of Central Florida, 2011.; Includes bibliographical references (p. 117-128).<br>Ph.D.<br>Doctorate<br>Chemistry<br>Sciences
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Pittman, Eddie LaReece. "Computed NMR shielding values of unsaturated five-membered-heterocyclic ring compounds and their benzo-analogs as a measure of aromaticity." View electronic thesis, 2008. http://dl.uncw.edu/etd/2008-2/r1/pittmane/eddiepittman.pdf.
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Chaudhary, Praveen, and University of Lethbridge Faculty of Arts and Science. "Lewis-acid and fluoride-ion donor properties of SF₄ and solid-state NMR spectroscopy of Me₃SnF." Thesis, Lethbridge, Alta. : University of Lethbridge, Dept. of Chemistry and Biochemistry, c2011, 2011. http://hdl.handle.net/10133/2621.
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Trimethyltin fluoride (Me3SnF) is a useful fluorinating agent in organometallic
chemistry. Its solid-state structure has been investigated by X-ray crystallography
showing a polymeric fluorine-bridged structure. Disorder, however, has precluded the
accurate refinement of all structural parameters. In order to obtain accurate structural
information, trimethyltin fluoride was investigated using high-resolution 13C, 19F, and
119Sn solid-state NMR spectroscopy using a four-channel HFXY capability. The
119Sn{1H} solid-state NMR spectrum agrees with pentacoordination about Sn in this
compound. The high-resolution 119Sn{19F, 1H}, 13C{1H,19F} and 19F{1H} NMR spectra offer unambiguous determination of 1J(119Sn-19F) and 1J(119Sn-13C) coupling constants. Furthermore, the analysis of the 119Sn{19F, 1H}, 119Sn{1H}, and 19F{1H} MAS spectra as a function of spinning speed allowed for the determination of the 119Sn CSA and J anisotropy, as well as the 119Sn-19F dipolar couplings. These were determined via SIMPSON simulations of the 13C, 19F, and 119Sn NMR spectra. Finally the 119Sn{19F, 1H} revealed fine structure as the result of 119Sn-117Sn two bond J-coupling, seen here for the first time. Sulfur tetrafluoride can act as a Lewis acid. Claims had been presented for the formation of an adduct between SF4 and pyridine, but no conclusive characterization had been performed. In the present study, adducts of SF4 with pyridine, lutidine, 4-picoline and triethylamine were prepared and characterized by low-temperature Raman spectroscopy. Sulfur tetrafluoride also acts as a fluoride-ion donor towards strong Lewis acids, such as AsF5 and SbF5, forming SF3
+ salts. Variable-temperature (VT) solid-state 19F NMR spectroscopy showed that SF3
+SbF6 – exists in three phases with phase transitions at ca. –45 and –85°C, while SF3
+AsF6 – exists only as one phase between +20 and –150 °C. The phases of SF3
+AsF6 – were also characterized by VT Raman spectroscopy.<br>xvi, 170 leaves : ill. (some col.) ; 29 cm
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McIver, Andrew. "Design and synthesis of DNA minor groove methylating compounds that target pancreatic ß-cells /." Electronic version (PDF), 2006. http://dl.uncw.edu/etd/2006/mcivera/andrewmciver.pdf.
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Lynch, Tera L. "Design and synthesis of DNA minor groove methylating compounds that target estrogen receptor positive cells /." Electronic version (PDF), 2006. http://dl.uncw.edu/etd/2006/lyncht/teralynch.pdf.
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Felts, Jennifer Elaine. "An evaluation of extraction parameters and LCMS analysis of oligonucleotides from biological matrices." View electronic thesis, 2008. http://dl.uncw.edu/etd/2008-3/r1/feltsj/jenniferfelts.pdf.
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Perry, Heather N. "Synthesis of compounds capable of producing cytotoxic N3-methyladenine DNA adducts in estrogen receptor positive cells /." Electronic version (PDF), 2007. http://dl.uncw.edu/etd/2007-3/perryh/heatherperry.pdf.
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Magolan, Kathleen M. "Analysis of methanol, ethanol and propanol in aqueous environmental matrices /." Electronic version (PDF), 2005. http://dl.uncw.edu/etd/2005/magolank/kathleenmagolan.pdf.
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Cirera, Fernández Jordi. "Mesures de forma, estereoquímica i estructura electrònica de compostos de metalls de transició." Doctoral thesis, Universitat de Barcelona, 2006. http://hdl.handle.net/10803/665755.
Full textAbstract:
Els objectius d'aquest treball són donar una perspectiva general de la metodologia de les mesures continues de forma, que permeten una descripció senzilla, però acurada, de l'entorn de coordinació en compostos de metalls de transició. S'introduirà una nova eina associada a la metodologia de les mesures de forma pel seguiment d'estructures que es troben en camins d'interconversió entre poliedres. Les mesures de forma seran emprades per analitzar 1'esteroquímica de compostos organometàl·lics, comparant aquests compostos i els seus lligands típics amb els anàlegs de química de coordinació. S'estudiarà l'estereoquímica de compostos tetracoordinats i pentacoordinats en funció de la configuració electrònica del metall i de les restriccions estereoquímiques imposades per lligands amb diferent denticitat. Pels compostos tetracoordinats, es farà un estudi de les corbes d'energia per totes les configuracions electròniques i pels diferents estats de spin, per correlacionar la distribució de les estructures experimentals amb les geometries i estats de spin predits a nivell teòric. Es mostrarà com es poden obtenir un conjunt de regles senzilles per la predicció de l'entom de coordinació en compostos tetracoordinats en funció de l'estructura electrònica del metall, i quins són els factors que poden modificar l'estat de spin del metall. Finalment, i donada la relació intima que hi ha entre estructura i propietats, es farà un estudi de la correlació entre el paràmetre de desdoblarnent a camp zero, calculat teòricament, i l'entom de coordinació del metall.
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Storton, Mark Lee. "Chromatographic speciation of organometallic compounds in the marine food web." 2001. https://scholarworks.umass.edu/dissertations/AAI3027262.
Full textAbstract:
The introduction and presence of metals in the marine environment and their reaction and bioaccumulation in organisms and in the marine food web is of environmental importance. The identification and quantification of inorganic and organometallic compounds in marine samples is of importance in studies of the marine food chain and the accumulation of both nutrients and potentially toxic compounds in higher order marine organisms in the marine ecosystem. The goal of this doctoral research was to develop and apply analytical methodology to the sampling, isolation, speciation and determination of metals and organometallic compounds, notably those of the carbon-bonding main group elements such as mercury, tin and selenium in marine samples. The introduction of metals into the marine environment was investigated by analysis of phytoplankton samples cultured by the National Marine Fisheries Service. Procedures for extraction, fractionation and gas chromatographic determination by derivatization and element-specific detection by microwave plasma emission spectrometry (GC-AED) were developed. The biological pathways and transfer of elements along the food chain was investigated on a variety of marine samples including dogfish liver, mussel and lobster heptopancreas. This study was conducted in part at the National Institute of Standards and Technology (NIST), Gaithersburg, MD. Specifically this research centered around providing an alternative procedure to existing methodology for the determination of organomercury compounds in marine samples. Derivatization procedures developed in this research were exhaustively compared with direct gas chromatography of methylmercury chloride, as previously used by NIST. A modified version of the method developed for the analysis of phytoplankton samples allowed both inorganic and organomercury to be simultaneously measured at the μg/g level and below.
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Blais, Matthew S. "Organometallic synthesis and catalysis of organotitanium and organonickel compounds and synthesis and physical chemical studies of mono, functionally substituted cyclopentadienyldicarbonyliridium compounds." 1998. https://scholarworks.umass.edu/dissertations/AAI9823720.
Full textAbstract:
In Chapter 1 the syntheses of a series substituted $(\eta\sp5$-cyclopentadienyl)dicarbonyliridium complexes using chlorodicarbonyl(pyridine)iridium as a starting material are described, giving yields as a high as 94%. Ring substituted compounds synthesized by this route include: chloro, benzyl, pentabenzyl, acetyl, carbomethoxy, methyl, benzoyl, trimethylsilyl, cyano, N,N-dimethylamino, tetraphenyl, N,N-dimethylamino-ethyl, (tetramethyl)N,N-dimethylaminoethyl, methoxyethyl, and pentamethyl. Also examined were the effects of the ring substituent on the asymmetric and symmetric carbonyl stretching frequencies as well as the $\sp{13}$C NMR chemical shift of the carbonyl carbon. In addition the photolysis of the pentamethyl, trimethylsilyl, dimethylaminoethyl and tetramethyldimethylamino substituted cyclopentadienyl-dicarbonyliridium compounds were studied. In Chapter 2 are presented the synthesis and polymerization properties of a series of pendent amino-substituted cyclopentadienyl titanium trichloride compounds. Specifically prepared were the picolyl and diisopropylaminocyclopentadienyl, dimethylaminoethyl, pyridylethyl and diisopropylaminoethylindenyl titanium trichlorides and triisopropoxides. In addition phenylethylcyclopentadienyltrichlorotitanium was prepared. As part of the synthetic process, three new thallium reagents were prepared and characterized. Their synthetic usefulness was demonstrated by the preparation of several new organometallic compounds of rhodium, titanium, and iridium. The catalytic properties of the pendent coordinating titanium compounds were explored by polymerizing ethylene, propylene and styrene. The polymers obtained were characterized by molecular weight via viscosity measurement and GPC and tacticity via $\sp{13}$C NMR and DSC. In Chapter 3 is described a search for new late transition metal coordination and organometalic compounds which could polymerize olefins to create high molecular weight polyolefins and co-polymerize olefins and carbon monoxide to create polyketones. Specifically diimine, $o,o\sp\prime$-dimethylaminomethylphenyl, dipyridyl, and benzamidinate compounds of nickel and palladium were prepared and tested for their ability to polymerize ethylene and propylene and co-polymerize hexene or propylene and carbon monoxide. The synthesis and catalysis were only partially successful giving one molecule (R-DABNiBr$\sb2)$ that proved to be highly active for the polymerization of oefins. In addition $o,o\sp\prime$-dimethylaminomethylphenylnickel bromide appears to oligomerize both hexene-CO and propylene-CO. In connection with our search for new nickel catalysts, (diphenylphosphinylcyclopentadienylbromonickel) $\sb2$ and (diphenylphosphinylcyclopentadienylmethylnickel) $\sb2$ were prepared and characterized by NMR and X-ray crystallography. Polymer samples obtained from various polymerization runs were characterized by $\sp{13}$C NMR, GPC and DCS.
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Muller, Alfred Johannes. "Steric and electronic effects of phosphine and phosphite ligands in vaska-type complexes of rodium." Thesis, 2008. http://hdl.handle.net/10210/1201.
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Ph.D.<br>In order for any new useful complexes to be developed, whether of catalytic, biological or of other importance, it is very important that sufficient knowledge exists regarding the fundamental principles applying to the chemistry involved. In all chemical processes involving metal complexes, the coordinated ligands govern the reactions to a great extent. It is thus very important that the properties (solubility, reactivity, steric bulk, etc.) of various ligands of these complexes is clearly understood in order to enable intelligent adjustments to be made, inducing the effects of choice. In most catalytic cycles, basic chemical reactions like substitution, addition, oxidative addition and reductive elimination are of importance. Some of the methods used to quantify ligand properties include single crystal X-ray studies as well as investigating various reactions on model square planar complexes. Several problems are normally associated with this type of investigation and are summarized below along with the aims of this study to improve upon this. (i) Very often the Vaska type compounds crystallise on an inversion centre as is shown in a generalized structure in Figure 1.1. This creates several problems ranging from less accurate bond distances/angles to problematic refinement of single crystal data. As the disorder is ruled by symmetry, the occupancies of the disordered atoms are 50%. The example shown in Figure 1.1 is also a fortunate case where the disordered atoms do not have the same positions, making refinement of the data easier, but there are examples27 such as [Pt(Me)Cl(PCy3)2] where the disordered moieties (Me- and Cl-) occupy virtually the same positions. In examples such as these restraints have to be applied, i.e. fixing bond distances to average distances from literature. The important parameter of the ligand trans effect is then meaningless and cannot be reliably compared to data from solution studies.<br>Prof. A. Roodt
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Hari, Krishna Reddy Kurre. "Electronic Structure And Bonding In Metallaboranes And Main Group Compounds." Thesis, 2012. http://hdl.handle.net/2005/2533.
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This thesis entitled “Electronic Structure and Bonding in Metallaboranes and Main Group Compounds” consists of five chapters. Chapter 1 gives an exposition of concepts and techniques used in understanding the electronic structure and bonding in some chemically interesting molecules. Heuristics concepts like isolobal analogy and electron counting rules are used in analyzing and predicting some novel chemical systems. A brief description of computational techniques such as density functional theory (DFT) based methods are used to quantitatively examine the structures and energies of these systems. In chapter 2 we present a critical analysis of bonding in neutral and dianionic stannadiphospholes and compare the potential energy surfaces with the isoelectronic Cp+ and Cp- species. The analysis indicates that Sn can be a better isolobal analogue to P+ than to BH or CH+. In chapter 3 we present new strategy to stabilize B2H4 in planar configuration using transition metal fragments. This requires the metal to donate two electrons into the empty B-B π orbital. Such complexes present a unique case study to the classical DCD model of metal-π complex. In chapter 4 we study the bonding in some recently synthesized metallaboranes which does not follow conventional electron counting rules. The complex and non-canonical nature of these metallaboranes feature some unique bonding patterns which are elucidated using theoretical techniques. In the final chapter we present new approach to build metal coated boron fullerenes. We use electron counting rules to device new structures which show enhanced metal boron bonding.