This dissertation summarizes my research in the Nuckolls group on two projects, with a central theme of achieving control of electronic coupling in various nanoscale systems. The two studies of interest aim at the study of emerging properties from alkali-doping of polyaromatic hydrocarbons (PAH), and the synthesis of novel metal chalcogen molecular clusters. Chapter 1 is divided into two parts. Part one provides a brief history of the forces we associate with bond formation. We will learn that although defining a “chemical bond” is helpful, it is limited to our incomplete understanding of what forces contribute to its existence. The behavior of an electron in externally applied magnetic fields will be discussed, where the collective behavior of electrons in a material can be measured, showing a myriad of emerging properties. The known superconducting alkali-doped PAHs are introduced, followed by the unresolved problems of reproducibility and lack of structural data to accompany superconducting samples. Finally, the proximity of AFM to superconductivity is discussed, which could give us insights on further exploration of hight temperature organic superconductors. Part two introduces atomically precise clusters of atoms, also knows as superatoms. Various synthetic approaches to create metal chalcogenide superatoms are introduced. Next, a closer look into the cobalt selenide core, [Co6Se8], is presented. The ability to selectively substitute the ligands on this superatom, achieves dimensional control. The subunit can be seen as a 0-dimensional subunit, where it readily gives away its electrons. Furthermore, assembly of the clusters into 1-, 2-, and 3-dimensional structures is described. Chapter 2 introduces a novel approach to acquire phase pure alkali-doped PAHs, p-terphenyl specifically. Previous reports of solution-processed doping of PAH have inspired highly reliable synthesis of these salts, by employing a chelating agent to stabilize the alkali metal. The first half of chapter 2 analyzes one such crystal in detail, describing emerging AFM fluctuations. The AFM coupling between nearest neighboring p-terphenyls occurs in all three crystallographic directions. Interestingly, this coupling can be seen as an unconventional bond between two terphenyl units along the hard axis, and resembles resonance structures seen in polyacetylene. The second half of the chapter further investigates the novel method, obtaining a library of alkali-doped p-terphenyls. This approach allows for selective variation of either the alkali-metal, the chelating agent, or the electronic structure of p-terphenyl. Obtaining nearly a dozen structures allows for a study of trends of doping level and accompanied magnetic properties. Lastly, Chapter 3 proves a new mechanism for ligand substitution of cobalt selenide superatomic clusters, using an easily removable carbene as the ligand. This approach grants access to new surface ligands and core shapes to expand the properties of these superatoms. Through this approach, larger atomically precise materials can be targeted, giving rise to new types of electronic properties.

1,1-Dimethyl-2-neopentylsilene reacted with the N-methylimine of benzophenone to give 1,2,2-trimethyl-3- neopentyl-4,4-diphenyl-l-aza-2-silacyclobutane, I, and 2,3,4,4a-tetrahydro-2,3,3-trimethyl-1-phenyl-4-neopentyl-2- aza-3-silanephthalene, II, in 35% and 20% yields, respectively. Compounds I and II did not serve as thermal silene precursors. Heating I and II to over 280°C did not yield 1,3-disilacyclobutanes. In the presence of 2,3- dimethyl-1,3-butadiene typical silene products were not obtained. However, I and II reacted rapidly with methanol at room temperature to give the ring-opened products (E)-2- methoxy-2,5,5-trimethyl-2-silahex-3-ene, III, 1,1- diphenyldimethylamine, IV, and 2-methoxy-2,5,5-trimethyl-3- (N-methylaminodiphenyl) methyl-2-silahexane, V.

The body of information concerning carbon-carbon spin-spin coupling constants now includes a large number of coupling constants, the establishment of a dihedral angular dependence on 3JCC, and the application of 3JCC to conformational analysis. This study adds another dimension to the growing wealth of information associated with 13 C-NMR: the influence of some non-bonded interactions on 3JCC Four types of non-bonded interactions that could influence vicinal carbon-carbon NMR coupling constants were investigated. To facilitate the NMR studies, a variety of 13C-labeled compounds were synthesized.

Surface free energy of a polymer is of great importance in adhesive studies. Acid/base specific interactions play pertinent roles in adhesive bond performance and polymer-polymer miscibility. In this study, the correlation between the surface characteristics of two polymers and their adhesive bond behavior as well as the compatibility of their blend systems are investigated through both the surface characterizations and bulk examinations. Inverse Gas Chromatography (IGC) is employed to determine the surface free energies, the dispersive component and acid/base specific interactions, of polyethylene terephthalate (PET), cellulose acetate (CA) and their blend. Dynamic Contact Angle (DCA) measurements are performed to obtain the surface free energies of PET and CA so that they can be compared to that from IGC. Moreover, the DCA data are used to calculate their spreading coefficients and the adhesive bond behavior between PET and CA is predicted as well. The bulk examinations on specific interactions and the miscibility of the PET/CA , PBT/CA blends are completed through Fourior Transform Infrared-Diffuse Reflectance Spectroscopy (FTIR-DRIFT), Differential Scanning Calorimeter (DSC) and Dynamic Mechanical Analyzer (DMA). Scanning Electron Microscopy (SEM) micrographs of these blends are taken to examine their morphologies. From IGC, it is deterrnined that the surfaces of PET and CA are predominantly basic. The spreading coefficients calculated from DCA data indicate the poor adhesive bond between PET and CA. The bulk examinations reveal that both PET/CA and PBT/CA blends are immiscible systems. / Master of Science

No description available.

Understanding how atoms interact is a fundamental aspect of chemistry, biology and materials science. There have been great advances in the knowledge of covalent and ionic bonding over the past twenty years but one of the major challenges for chemistry is to develop full understanding of weak interatomic/intermolecular forces. This thesis describes fundamental studies that develop the basic understanding of weak interactions between heavier polarisable elements. The chosen methodology is to constrain heavy atoms using a rigid naphthalene backbone. When substituents larger than hydrogen, are positioned at close proximity at the peri-positions of a naphthalene molecule they experience steric strain; the extent of which is dictated by intramolecular interactions. These interactions can be repulsive due to steric hindrance or attractive due to weak or strong bonding. In efforts to understand the factors which influence distortion in sterically crowded naphthalenes and study possible weak intramolecular interactions between peri-atoms, investigations focussed on previously unknown mixed 1,8-disubstituted naphthalene systems. Mixed phosphorus-chalcogenide species were initially studied; three mixed phosphine compounds of the type Nap[ER][PPh2] were prepared along with their chalcogenides and a series of metal complexes. The study of interactions between heavy atoms was progressed by investigations into a series of mixed chalcogenide compounds of the type Nap[EPh][E’Ph] (E = S, Se, Te). Subsequent reaction of the chalcogenide systems with the di-halogens, dibromine and diiodine, afforded a mixture of charge transfer and insertion adducts displaying an array of different geometries around the chalcogen atom. From molecular structural studies, a collection of intramolecular peri-interactions were found, extending from no interaction due to repulsive effects, weak attractive 3c-4e type interactions and one example containing a strong covalent peri-bond. Further weak intramolecular interactions observed include CH-π and E•••E’ type interactions plus π-π stacking between adjacent phenyl rings. It was discovered that the bulk of the peri-atoms is influential on the distance between them, but this is not the only factor determining the naphthalene geometry. Inter- and intramolecular interactions can also have an impact and furthermore the number, size and electronic properties of substituents attached to the peri-atoms can determine molecular distortion.

This work has been a study of systems, mostly of sulfa-drugs, showing polymorphic behaviour. Using different means as solid state NMR, X-ray analysis, and theoretical calculations, we have seen how it is possible to understand results obtained from the different techniques, proving how the study of polymorphic systems needs cooperative advice from the different techniques that are able to detect polymorphic differences. Within the sulfa-drugs I have been mostly concentrating on sulfanilamide, studying (^13)C and (^15)N solid state NMR spectra of the different polymorphs. The NMR parameters that have been most interesting to study, have been the relaxation times that have revealed complicated motion of the molecule despite it being a small molecule. In order to obtain detailed information from (^15)N spectra it has been necessary to enrich the samples and this has enabled a study of the shielding tensors of the nitrogens in the molecule. (^13)C spectra were also recorded of systems studied sulfathiazole solvates that proved to show some of the same solid state effects in the NMR spectra as sulfanilamide. Shielding calculations have proved to be still limited in order to obtain reliable information on the shielding of both and (^13)C (^15)N nuclei but considering hydrogen-bonded molecules, as opposed to isolated molecules, seemed to have improved the calculations quite a lot, so that some idea of intermolecular effects could be deducted. Exact positions of the hydrogen has proved to be essential as well in order to improve the calculations. Finally a case study for the REDOR pulse sequence has been carried out. Different attempts to understand the effects influencing this particular experiment have been carried out on 20% and 99% doubly enriched glycine, as well as on a particular sample, doubly enriched BRL55834, but the internuclear distances measured with this technique still displayed some uncertainties that made results not thoroughly reliable.

No description available.

The site of initial metal-carbonyl bond-breaking during ligand-exchange reactions in a series of octahedral metal carbonyls of the type (L2)M(CO)4 (M = Cr, Mo, W; L2 = diphos, phen, dipy) has been determined employing infrared spectroscopy and Fourier transform nuclear magnetic resonance spectroscopy. The results of this study reveal, for all metal carbonyl complexes of the type mentioned above, that loss of CO occurs exclusively at an axial position (cis to the bidentate ligand, I^)• The dynamic nature of the five-coordinate intermediates, such as (diphos)Mo(CO)3, (phen)M(CO)3 (M = Cr, Mo, W), and (dipy)Cr(CO)3, which are generated in solution upon CO dissociation, is reported and discussed. The results of this investigation confirm that these intermediates are fluxional on the time scale of CO-exchange process. A mechanism which describes the site of initial metal-carbonyl bond-breaking and the fluxionality of the five-coordinate intermediate during ligand-exchange reactions in the complexes (L2)M(CO)4 is proposed. A kinetic study of reactions of W(CO)6 with pseudo-halide anions (NCS-, NCO-, CN-) has been initiated. The results indicate that these reactions proceed via a bimolecular path, which involves initial attack of the pseudo-halide anion at a carbonyl carbon of W(CO)6,

Submitted by (lucia.rodrigues@ufrpe.br) on 2016-11-08T13:02:43Z No. of bitstreams: 1 Janaina Rodrigues da Silva.pdf: 1872104 bytes, checksum: 431b7b8583753aa995b3ae518e125d06 (MD5) / Made available in DSpace on 2016-11-08T13:02:43Z (GMT). No. of bitstreams: 1 Janaina Rodrigues da Silva.pdf: 1872104 bytes, checksum: 431b7b8583753aa995b3ae518e125d06 (MD5) Previous issue date: 2008-11-10 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / The words analogies and metaphors etimologically mean the relationship of similarity between things and change of meaning from the proper to the figurative. They have been utilised on a day to day basis, in the evolution of Science and as teaching tools to facilitate communication. Given this pressuposition, the objective of this paper is to analyse the use of analogies and metaphors in the process of constructing knowledge regarding the scientific concept of chemical bonds. To this end three Chemistry teachers from the state public system had their classes monitored. They were also interviewed and had to answer a questionary. The results showed that among the teachers being monitored one made use of analogies while the other two used analogies and metaphors. The use of analogies and metaphors by the teachers being monitored was spontaneous and without definite planning. We also observed that the use of analogies and metaphors as teaching tools was less frequent. This fact may be due to the absence of planning as well as of discussions that may increase the use of analogies and metaphors as teaching tools in such a way that they can be a part of the process of teaching and learning. / Analogias e metáforas, que etimologicamente significam relações de semelhança entre coisas e transposição do sentido próprio ao figurado, têm sido utilizadas no cotidiano, na evolução da Ciência e como ferramentas didáticas, com o intuito de facilitar na comunicação. Diante do presente pressuposto, o objetivo deste trabalho foi analisar a utilização de analogias e metáforas na construção do conhecimento sobre o conceito científico de ligações químicas. Para tanto, foram considerados três professores de Química da rede pública estadual, que tiveram suas aulas observadas, responderam a um questionário e a uma entrevista. Os resultados mostraram que dos professores investigados, um fez uso das analogias, enquanto que dois aplicaram as mesmas e as metáforas. Dessa forma, os professores empregaram as analogias e metáforas de modo espontâneo sem que houvesse planejamento definido. Vimos ser ainda pouco freqüente o uso das mesmas como ferramentas didáticas, talvez pela ausência de planejamento e de discussões que possam permeá-las como recurso didático de modo a subsidiar no processo de ensino-aprendizagem.