Metal-ligand pair anisotropy of the erbium-cyclooctatetraenide motif

A magnetostructural study on the erbium–cyclooctatetraenide (Er–COT) motif was conducted. This molecular fragment was shown to generate magnetic anisotropy, and consequently slow magnetic relaxation, in a series of example coordination complexes. The generality of this effect led to creation of the idea that certain metal-ligand pairs can act as magnetic synthons toward the development of single-molecule and molecular magnets. Chapter 1 provides a brief introduction to the study of single-molecule magnetism. It includes a discussion on the historical development of the field, as well as some of the basic theoretical framework required to understand magnetic relaxation on a molecular level. The chapter concludes with the motivation for and introduction of the metal-ligand pair anisotropy design (MLPA) principle.Chapter 2 discusses the development of a technique for measuring the magnetic relaxation time. Relaxation time measurements have historically been carried out using two separate approaches depending on the timescale being studied. A new impedance-based method toward measuring a system's relaxation dynamics at the long timescale is presented which obviates the necessity of two separate measurement approaches.Chapter 3 presents the results of a magnetostructural study conducted on a series of mononuclear Er–COT complexes. A combined magnetic and computational evaluation of Er(COT)I(THF)₂, Er(COT)I(Py)₂, Er(COT)I(MeCN)₂, and Er(COT)(Tp*) (THF = tetrahydrofuran, Py = pyridine, MeCN = acetonitrile, Tp* = tris(3,5-dimethyl-1-pyrazolyl)borate) reveal that each behave as a single-molecule magnet and thus a degree of coordinative robustness within the Er–COT metal-ligand pair is evinced. Chapter 4 introduces the idea of coupling Er–COT units. Therein a dinuclear erbium complex, [Er(COT)(μ-Cl)(THF)]₂, is shown to display a net-ferromagnetic interaction between metal centers while also maintaining magnetic anisotropy. A brief discussion is given on the relevance of this result toward making higher-order structures.Chapter 5 discusses the results of a magnetic coupling optimization study performed on a series of structurally similar MLPA compounds. Mononuclear Er(COT)I(DMPE) (DMPE = 1,2-bis(dimethylphosphino)ethane), and dinuclear [Er(COT)(μ-I)]₂(μ-DPPE), [Er(COT)(μ-I)]₂(μ-DPPM), and [Er(COT)(μ-I)(MDPP)]₂ (DPPE = 1,2-bis(diphenylphosphino)ethane, DPPM = bis(diphenylphosphino)methane, MDPP = methyldiphenylphosphine) were prepared. The effects of nuclearity and anisotropy axis orientation on the low-temperature relaxation time resulted in a million-fold improvement across this series