Co-ordination chemistry of a series of bi- and tripodal ligands

Abstract

A structural investigation into a series of transition metal complexes forms the basis of Chapter 1. Specifically, this work focuses on the co-ordination chemistry of two bipodal ligand frameworks, L and L. Each ligand contains a ketone moiety which, in the case of L, has been shown to undergo hemi-ketal formation upon complexation in some instances, yielding dinuclear complexes of the form M2{(2-bipy)2C(OMe)0'}2 C104 2 (M = Fen or Zn11). Chapters 2 and 3 take a detailed look at a series of transition metal complexes formed by the tripodal bipyridine-based ligand frameworks, L - L. The tris-bipyridyl ligand, L, has been shown to enforce a predominantly trigonal prismatic co-ordination environment around a metal centre, even in cases where the metal has a strong stereoelectronic octahedral preference. For each ligand, the relationship between octahedral and trigonal prismatic character as the d-electron configuration of the metal centre is varied has been examined. Using the Cartesian co-ordinates obtained from crystallographic data sets, continuous shape mapping analysis (CShM) has been employed to assist in the quantification of the distortions away from these two ideal geometries. Chapters 4 and 5 report the protonation and stability constants for a series of potential MRI contrast agents which are based upon a tripodal ligand scaffold with a tris-pyridine core (L6 o - L ). This work examines how modifying the denticity of the ligands from four to six by changing the number of peripheral binding functions affects overall complex stability and the nature of species in solution. Chapter 6 investigates the efficacy of a series of gadolinium complexes as potential MRI contrast agents. This has been accomplished by measuring Tl relaxivities using a fast field- cycling (FFC) relaxometer