Spectroelectrochemical Studies of Bipyridyls and Related Species

Song, Jae-Inh (1989) Spectroelectrochemical Studies of Bipyridyls and Related Species. PhD thesis, University of Glasgow.

Abstract

This thesis is devoted to the characterisation of redox-active ligand and metal-coordination complexes which contain the M-L chromophore, where M = metal and L = polypyridyls and their derivatives. The materials studied include simple and quaternised bipyridyls, and their complexes with Fe(II), Ru(II), and Pt(II), and bipyrimidine and its complexes. The redox changes were generally achieved by controlled potential electrolysis using an optically transparent thin layer electrode (O. T. T. L. E. ) cell and the required potentials can conveniently be determined by cyclic voltammetry. The O. T. T. L. E cell was placed in the spectrophotometer beam, and parent materials were electrolytically regenerated, so that the absorption spectra of the unstable low-oxidation state complexes could be unambiguously recorded. The radicals formed by one-electron reduction of most of the free ligands show similar spectra, assignable in terms of a simple Huckel molecular orbital scheme, with strong bands for the pi→pi* and pi*→pi* transitions. As required by theory, the positions of these bands are remarkably insensitive to the Coulomb energy at nitrogen. As expected, quaternisation and the incorporation of added nitrogens in the ring both lead to easier reduction. Thus N-methylation lowers the energy of the LUMO but does not alter its nature. In all of the metal complexes examined, except the [PtLL']2+ series, the reductions are based on the ligands and the oxidations are metal-based. The electronic absorption spectra of the reduced species show typical reduced ligand radical anion character. Furthermore, in the singly and doubly reduced [M(L)3]2+, it was found that the added electrons are localised on the individual bidentate ligands. Spectrochemical and electrochemical data agree in showing that the first reduction of the [PtLL']2+ species is metal-based, producing Pt(I) complexes. In this case, the MLCT transition from Pt(I) to ligand is available and this MLCT band should lie lower in energy than the corresponding transition from Pt(II). However, the first reduction of organometallic Pt(II) bipyridyl complexes is ligand-based.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Organic chemistry
• Date of Award: 1989
• Depositing User: Enlighten Team
• Unique ID: glathesis:1989-77939
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 28 Feb 2020 12:09
• Last Modified: 28 Feb 2020 12:09
• URI: https://theses.gla.ac.uk/id/eprint/77939