Spin-Crossover Iron Complexes Bearing Alkyl Chain Substituents

This thesis concerns synthesis, magnetic and mesogenic properties of novel iron(II) complexes based on 2,6-bis(pyrazol-1-yl)pyridine derivatives, with short and long alkyl chains on the pyrazolyl or pyridyl rings. Chapter 1 is an introduction to the spin crossover and liquid crystal phenomena. Using significant literature examples, it outlines: their discovery and physical origin; the interplay between spin crossover and long alkyl chains; the factors that affect spin crossover; and progress towards their practical application. Chapter 2 describes a family of 2,6-bis(pyrazol-1-yl)pyridine derivatives with no long alkyl chain substituents, and explores the effect of small structural differences on their spin crossover. Chapter 3 presents two series of 2,6-bis(pyrazol-1-yl)pyridine derivatives with long alkyl chains bound to the pyridyl ring, and investigates the effect of the alkyl chain length on spin crossover and phase transitions in their iron(II) complexes. Chapter 4 discusses four series of 2,6-bis(pyrazol-1-yl)pyridine derivatives with long alkyl chains on the pyrazolyl rings. Mono- and disubstituted examples bearing saturated and unsaturated substituents are included. An unusual spin crossover exhibited by some of the complexes is described. Chapter 5 details some asymmetric 2,6-bis(pyrazol-1-yl)pyridine and isomeric 2-(1H-pyrazol-1-yl)-6-(triazolyl)pyridine derivatives. It includes a study of a coordination polymer formed from one of these ligands, using crystallography and magnetic measurements. Chapter 6 is an account of all the synthetic procedures used in this work, the standard characterisation of the new products, and the instrumentation used for the analyses.