Computational study of the boron-nitrogen dative bond

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dc.contributor.advisor Dillen, J. en_ZA Zhao, Hailiang en_ZA
dc.contributor.other Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science. 2008-09-02T08:53:31Z en_ZA 2010-06-01T08:59:52Z 2008-09-02T08:53:31Z en_ZA 2010-06-01T08:59:52Z 2008-12 en_ZA
dc.description Thesis (MSc (Chemistry and Polymer Science))--Stellenbosch University, 2007. en_ZA
dc.description.abstract In this study, ten selected boron-nitrogen compounds and three borane carbonyl complexes were investigated by a number of computational methods. It is well known that the B-N dative bond is shorter in the solid state than in the gas phase. The B-CO distance, on the other hand, displays the opposite effect. Quantum mechanical techniques at the Hartree-Fock, Møller-Plesset second-order and Density Functional Theory level were used to calculate the geometries of the isolated molecules and to compare them with those found in molecular clusters built to model the solid state. It was found that calculated geometries were very sensitive to the choice of the basis set. The effects of dipole-dipole interactions were further investigated by applying an external electric field with varying strength to isolated molecules, and by replacing the central molecule in a cluster with a different compound. The B-N bond was found to respond much more to the applied field than the B-CO bond. An effort was made to correlate the lengthening or shortening of the dative bond to the strength of the crystal field, the latter being calculated classically from point charges. Unfortunately, large differences were noted between the charges calculated with common methods like Mulliken or Merz-Kollman-Singh. Furthermore, an analysis of 67 crystal structures taken from the Cambridge Structural Database did not reveal a correlation between the length of the B-N bond and the crystal field calculated with Charge Equilibration charges. Finally, a valence force field was developed for H3N-BH3. It was shown that a much better fit of the vibrational spectrum can be obtained if the B-N stretching mode is assigned to the 603 cm-1 band rather than the peak observed at 968 cm-1. en_ZA
dc.language.iso en en_ZA
dc.publisher Stellenbosch : Stellenbosch University
dc.subject Boron compounds en_ZA
dc.subject Nitrogen compounds en_ZA
dc.subject Electrostatic effect en_ZA
dc.subject Solid state en_ZA
dc.subject Data processing in chemistry en_ZA
dc.subject Dissertations -- Chemistry en_ZA
dc.subject Theses -- Chemistry en_ZA
dc.subject.other Chemistry and Polymer Science en_ZA
dc.title Computational study of the boron-nitrogen dative bond en_ZA
dc.type Thesis en_ZA
dc.rights.holder University of Stellenbosch
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