Computational study of the boron-nitrogen dative bond

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dc.contributor.advisorDillen, J.en_ZA
dc.contributor.authorZhao, Hailiangen_ZA
dc.contributor.otherStellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.
dc.date.accessioned2008-09-02T08:53:31Zen_ZA
dc.date.accessioned2010-06-01T08:59:52Z
dc.date.available2008-09-02T08:53:31Zen_ZA
dc.date.available2010-06-01T08:59:52Z
dc.date.issued2008-12en_ZA
dc.descriptionThesis (MSc (Chemistry and Polymer Science))--Stellenbosch University, 2007.en_ZA
dc.description.abstractIn 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.identifier.urihttp://hdl.handle.net/10019.1/2846
dc.language.isoenen_ZA
dc.publisherStellenbosch : Stellenbosch University
dc.rights.holderUniversity of Stellenbosch
dc.subjectBoron compoundsen_ZA
dc.subjectNitrogen compoundsen_ZA
dc.subjectElectrostatic effecten_ZA
dc.subjectSolid stateen_ZA
dc.subjectData processing in chemistryen_ZA
dc.subjectDissertations -- Chemistryen_ZA
dc.subjectTheses -- Chemistryen_ZA
dc.subject.otherChemistry and Polymer Scienceen_ZA
dc.titleComputational study of the boron-nitrogen dative bonden_ZA
dc.typeThesisen_ZA
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