This thesis is concerned with the synthesis, electrochemistry and spectroelectrochemistry of three different types of ligands; the 5,5’-(X)<sub>2</sub>-bpys, (bpy = 2,2’-bipyridine), the bidentate dipyridyls, (py), (where py = pyridine and X is a bridging group) and the nitro substituted bpys 4,4’-(NO<sub>2</sub>)<sub>2</sub>-bpy and 4-NO<sub>2</sub>-bpy and 4-NO<sub>2</sub>-py. The Pt(II) complexes of these ligands were also studied along with the Pd(II) complexes of the nitro substituted ligands. The ligands and complexes of general type 5,5’-(X)<sub>2</sub>-bpy and [Pt(5,5’-(X)<sub>2</sub>-bpy)Cl<sub>2</sub>] are shown by cyclic voltammetry to undergo two reversible, one electron reductions. Analysis of the absorption and epr spectra of the one electron reduction products reveal that the first reduction is localised on the bpy moiety although there is a small but significant (<i>ca</i> 10%) admixture of the Pt 5d 5d<sub>yz</sub> and 6p<sub>z</sub> and 6p<sub>z</sub> orbitals in the SOMO. Spin pairing of the two reduction electrons in the bpy p<sup>-</sup> orbital occurs. Comparison of the gradients on a plot of the Hammett parameters s<sub>m</sub> and s<sub>p</sub> <i>vs</i>. the first reduction potentials of [Pt(5,5’-(X)<sub>2</sub>-bpy)Cl<sub>2</sub>] and [Pt(4,4’-(X)<sub>2</sub>-bpy)Cl<sub>2</sub>] indicates that the 5,5’ position on bpy is electronically the more important site of substitution. The electrochemical behaviour of 4,4’-(NO<sub>2</sub>)<sub>2</sub>-bpy, [Pt(4,4]-(NO<sub>2</sub>)<sub>2</sub>-bpy)Cl<sub>2</sub>] and [Pd(4,4’-(NO<sub>2</sub>)<sub>2</sub>-bpy)Cl<sub>2</sub>] can be explained in terms of a molecular orbital scheme with a low-lying LUMO and a small LUMO/LUMO-1 energy gap. For the free ligand the 4-NO<sub>2</sub>-py rings lie orthogonal to one another and thus the two reduction electrons are localised on separate 4-NO<sub>2</sub>-py moieties. On complexation the 4,4’-(NO<sub>2</sub>)<sub>2</sub>-bpy is forced to become planar and the reduction electrons are localised over the entire ligand. However, epr studies show that the di-reduced species are paramagnetic indicating that the LUMO/LUMO-1 energy gap is still less than the spin pairing energy and di-reduction of 4,4’-(NO<sub>2</sub>)<sub>2</sub>-bpy and its Pt and Pd complexes leads to the spin-triplet species.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:652875 |
| Date | January 2003 |
| Creators | Jack, Lorna Anne |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/12210 |
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