Kinetic, spectroscopic and x-ray diffraction studies of d6 transition metal complexes.

The work in this thesis is concerned in the main with solvent effects on the kinetic, thermodynamic and spectroscopic properties of several d6 transition metal complexes, and their reactions with various species. Several reactions, which proceed via known mechanisms, have been analysed in terms of the solvation trends of the participant species in the various solvent mixtures studied. For example, the solvent effects on (i) the nucleophilic substitution reactions of the penta-cyanoferrate (II) anions, [Fe(CN)5L]n- (D mechanism), (ii) the acid aquation of the [Fe(5-NO2phen)3]2+ cation (Id), and (iii) mercury(II)- catalyzed aquation of the ReC162- anion, and related complexes (SE2 at Hg2+, dissociative with respect to Re (IV) centre). (iv) The peroxo-disulphate oxidation of the [Fe(phen)3]2+ and related cations has also been studied, in binary aqueous mixtures, together with the acid aquation of the [Fe(phen)3]3+ cation, and its ligand-substituted derivatives, the latter study being in aqueous solution only. In order to quantify such thermodynamic analyses, the solubilities of several pertinent compounds in ranges of binary aqueous mixtures have been measured, and the free energies of transfer of these compounds, and the appropriate single-ion values have been determined. Changes in solvent have a profound effect on the UV/visible spectra of certain inorganic complexes, and a study of such solvatochromism has been undertaken (a) to provide greater understanding of the phenomenon, and (b) to qualitatively analyse selected compounds in terms of their solvatochromic properties, relative to those of compounds of known structure. In this vein, the X-ray crystal structure of trans-di-iso-thiocyanato(cyclam)cobalt(III) thiocyanate (see chapter 7) has been determined, in an attempt to correlate its solvatochromic behaviour with its absolute stereochemistry. Finally, nucleophilic substitution reactions at low-spin iron(II) complexes have been studied, to try to clarify some mechanistic complications which have arisen in such systems.