Exploring methods of magnetic manipulation in defective dicubanes, dinuclear, and extended structures : a thesis submitted in fulfillment of the requirements for the degree of Doctor of Philosophy in Chemistry, School of Natural Sciences, Massey University

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Massey University
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Transition metal (3d) and lanthanide (4f) coordination clusters form a base for which many fields of research expand from. One field of interest, magnetic materials, has risen in popularity due to the discovery of single molecule magnets (SMMs), which are currently capable of operation up to 80 K. Although this field is highly researched, significant improvements are still required in order for SMMs to be stable enough for implementation into modern technological devices. One fundamental area of interest is the electron sharing pathway between metal ions, which is responsible for the magnetic properties of the molecules. Methods which optimise this to promote ferromagnetic exchange, an intrinsic property of SMMs, are an important focus. Polynuclear homometallic 3d and heterometallic 3d3d’ and 3d4f coordination clusters are reported, which explore different ways as to which the exchange pathway angles can be manipulated. Several complexes have undergone magnetic and computational analyses to explore how the different manipulations have affected the exchange pathways. A series of Niᴵᴵ₄ defective dicubanes composed of both ligand and anion based exchange pathways present a platform for manipulations based on the switching of key donor groups and solvate molecules found in the crystal lattice. The results revealed that the strongest manipulator was the introduction of lattice-bound solvent molecules, capable of hydrogen bonding to the metal ion donor groups. Moving from a combination of ligand and anion based exchange pathways to those that are solely ligand derived were explored by synthesising a series of homometallic and heterometallic 3d3d’ dinuclear complexes, and conducting a study which closely looked at how different metal ion combinations affected the magnetic properties. Transmetalation reactions were performed alongside a computational analysis to determine the stabilities of the 3d3d’ dinuclear complexes, with the most stable being that of the CuᴵᴵMnᴵᴵ complex. Unexpectedly, the Cuᴵᴵ₂ complex was found to have the largest ferromagnetic coupling, indicating the large coordination number for a Cuᴵᴵ ion to be the strongest magnetic manipulator. Expanding on the 3d3d’ dinuclear series was achieved by the introduction of 4f ions with the aim of producing a series of 3d4f dinuclear complexes, where the use of different metal ions, anions, and coordinated solvent molecules have been structurally analysed to determine the success of the manipulations. It was found that the complexes with smaller exchange angles had a common similarity, that being additional bridging groups between the metal ions. Finally, a series of clusters ranging from mononuclear to icosanuclear are reported, all of which were unexpected results. These complexes reveal unusual and uncommon properties, such as the coordination of an alkyloxime oxygen.
Metal clusters, Magnetic properties, Lattice dynamics, Ligands