Magnetic Studies of Rare and Highly Symmetric Geometries in 3d and Lanthanide Metal Single Molecule Magnets

Abstract

Mnv12[Mnv12(CHv3COO)v16(Hv2O)v4Ov12]•2CHv3COOH•2Hv2O (Mnv12OAc). This molecule was remarkable in that it exhibits hysteresis similar to that of a bulk magnetic material. In this case, however, rather than an extended structure property with long range ordering as in solid state magnetic materials, each Mnv12OAc molecule behaves as a tiny magnet with a thermal barrier to the reversal of the magnetization. This discovery led to the realization that such materials are promising for the study for applications such as data storage and spintronics. In Mnv12OAc, hysteretic behavior was only be observed up to 4 K, making practical applications impossible. Since this time, the field has focused on increasing the blocking temperature for SMMs, and much progress has been made. Recently, the field has focused on low spin, highly symmetric molecules, some with only one paramagnetic metal center responsible for the magnetic behavior. The work in this dissertation is involved in this pursuit, with the goal of testing predictions and lending credence to future synthetic pathways for better SMMs. The first part of the work focuses on trigonally symmetric 3d SMMs using highly bulky ligands. Chapter II focuses on a direct comparison of two geometries, namely trigonal monopyramidal and bipyramidal. A series of divalent iron, cobalt, and nickel complexes were synthesized in both geometries through use of a tris-anionic, tetradentate ligand, and in the case of the bipyramidal structures, a water molecule. Additionally, the effect of electron donating and withdrawing substituents on the Co(II) trigonal bipyramidal structures was investigated. The third chapter is a study of the differences in magnetic behavior between partial and complete metal encapsulation through neutral, tetradentate based ligands which coordinate one or two Co(II) metal centers. The fourth chapter describes a series of octahedral 3d metal molecules that employ Ti(IV) as a new diamagnetic capping ligand. The fifth chapter focuses on lanthanide based SMMs in a geometry never before observed for SMM behavior, namely cubic. The goal was to observe how this highly symmetric geometry would affect the magnetic behavior of trivalent Dy, Er, and Tb complexes.