Crystallographic and Modelling Studies of Industrially Relevant Metal Complexes

Abstract

Increasing the efficacy of ligands is crucial to many industrial processes and products. The design of new organic reagents which might find applications in automotive lubrication and extractive metallurgy are reported. Force-field based molecular modelling has been used in chapters 2 and 3 to investigate the structure of complexes of malonic acids and benzohydroxamic acids formed on binding to iron(III) oxide surfaces for which both have shown high affinity. Models were constructed in which the ligands were docked to planes in the lepidocrocite crystal structure to simulate their interaction with steel engine surfaces. The Cambridge Structural Database has been used to elucidate the structures of polynuclear complexes of carboxylic acids to define appropriate geometries for malonate complex models. The most plausible modes of surface binding involving malonic acid were modelled to establish which would show the most favourable ligand-surface and ligand-ligand secondary bonding. Modelling of hydroxamate surface binding was guided by structural motifs observed in a mononuclear trishydroxamato iron(III) complexes in a dinuclear complex [Fe2L2(μ2L)2Br2] where LH = benzohydroxamic acid. The resulting model predicted the surface activity of a range of hydroxamic acid derivatives which have been confirmed by measurements of adsorption isotherms carried out on high surface area goethite. The structures of square planar copper(II) complexes of 3-substituted salicylaldoxime ligands which are closely related to systems used in industrial hydrometallurgical processes have been investigated (chapter 4) to ascertain whether there are correlations between the solid state structures and the relative strengths of the ligands as copper extractants. It was expected that electronegative groups would enhance hydrogen bonding between ligands, pulling them towards one another with a consequent decrease in the binding cavity presented by the donor atoms. In practice the structures were found to be influenced by interactions present in the solid state. In particular, axial interactions were found to influence the inner coordination sphere geometry and these were also investigated (chapter 5) using high pressure X-ray crystal structures. Contrary to expectation, application of pressure was found to increase axial bond lengths in order to improve molecular packing efficiency so that the cell volume could decrease.