This thesis is concerned with the determination of the structures of the polyboron fluorides B<sub>4</sub>F<sub>6</sub>CO, B<sub>8</sub>F<sub>12</sub> and B<sub>10</sub>F<sub>12</sub> and the carboranes <i>closo-</i>2,3-C<sub>2</sub>B<sub>9</sub>H<sub>11</sub>, <i>nido</i>-2,9-C<sub>2</sub>B<sub>9</sub>H<sub>13</sub> and <i>arachno-</i>6,9-C<sub>2</sub>B<sub>8</sub>H<sub>14</sub> by experiment and theoretical calculations. B<sub>8</sub>F<sub>12</sub> is the first fully characterised higher boron fluoride and we can also report the second - B<sub>10</sub>F<sub>12</sub>. Its crystal structure contains a tetrahedron of boron atoms, each with a BF<sub>2</sub> substituent, similar to the known B<sub>4</sub>X<sub>4</sub> tetrahedra but with two additional BF<sub>2</sub> bridge bonds. <i>Ab initio</i> calculations identify a very different structure. The molecule is based upon a folded B<sub>4</sub> central core as in B<sub>8</sub>F<sub>12</sub>, but this core is highly symmetrical in B<sub>10</sub>F<sub>12</sub>. However, calculations involving sterically larger substituents such as in B<sub>10</sub>Cl<sub>12</sub>, B<sub>10</sub>Br<sub>12</sub> and B<sub>10</sub>I<sub>12</sub> show molecular structures as found in crystalline B<sub>10</sub>F<sub>12</sub>. Carboranes form a widely studied class of molecule but past structural studies have generally relied upon theoretical calculations or NMR spectroscopy whilst, due to a general inability to form single crystals, diffraction studies have been carried out on salts or derivatives of the parent cluster. To further the understanding of carborane cluster structures the compounds <i>closo-</i>2,3-C<sub>2</sub>B<sub>9</sub>H<sub>11</sub>, <i>nido</i>-2,9-C<sub>2</sub>B<sub>9</sub>H<sub>13</sub> and <i>arachno-</i>6,9-C<sub>2</sub>B<sub>8</sub>H<sub>14 </sub>have been experimentally characterised using gas-phase electron diffraction; they show structures comparable to known carboranes.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:654342 |
| Date | January 2003 |
| Creators | Mackie, Iain D. |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/12520 |
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