Crystal engineering and bifunctionality in spin-crossover materials

This thesis focuses on crystal engineering metal salts of 2,2’:6’,2’’-terpyridine and 2,6-di(pyrazol-1’-yl)pyridine to tune and better understand the cooperative spin crossover in the solid state and incorporation of a second functionality towards bifunctional spin crossover materials. Chapter 1 can be considered an introduction to the phenomenon of spin crossover in first row transition metal complexes and outlines its discovery, recent developments and progression towards real-world application. Chaper 2 is a discussion of the methodology of synthetic efforts undertaken in the acquisition of the wealth of tris-chelating organic compounds whose coordination chemistry is the subject of later chapters. Chapter 3 details the spectroscopic, electrochemical and magnetic properties of cobalt(II) and iron(II) complexes of tris-azinyl analogues of 2,2’:6’,2’’-terpyridine in efforts towards tuning their electronic spin-equilibria. Chapter 4 presents a series of novel ruthenium(II) based materials exhibiting enhanced room temperature emission and their incorporation into an inert spin crossover host material. Retention of parent functionalities is screened for over an operable temperature regime. Chapter 5 concerns iron(II) complex salts of 2,6-di(pyrazol-1’-yl)pyridine derivatives, whose ligand backbones are modified in an attempt to tune the solid state spin crossover behaviour both electronically and sterically. Chapter 6 is an account of all synthetic procedures carried out during this work, their standard characterisation and details the instrumentation performed on all materials which are the subject of discussion in this thesis.