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    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
    (Massey University, 2023) Woodhouse, Sidney
    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.
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    From triangles to rings : colourful clusters of substituted naphthalenediols : a thesis submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Chemistry, School of Natural Sciences at Massey University
    (Massey University, 2022) Dais, Tyson
    Coordination chemistry is perhaps one of the most base-level fields within chemistry, with a rich past and an ever expanding future. Existing in a relatively newer niche, however, is the field of single molecule magnetism, sitting at an intersection between synthetic chemistry and chemical physics with an aspiring road leading to materials chemistry and advanced information technology. While the fundamentals of the field are established, it has not yet reached the stage of implementing single molecule magnet technology, for which a broader understanding is needed. A crucial part of this is the ability to interpret magneto-structural correlations, to understand the ways in which molecular structure effects the electronic structure of the metal ions, and hence their performance as single molecule magnets. A series of new homo- and heterometallic complexes are reported; which, where possible, have been magnetically characterized. A non-macrocyclic triangular complex featuring a planar Cu₃TbO₆ core represents the first of its class to exhibit slow relaxation of magnetization in zero applied field, a characteristic of single molecule magnets, while similar Cu₃Gd, Cu₃Dy, and Ni₃Gd complexes show field supported magnetic properties. The regularity with which the Cu₃Ln and Ni₃Ln complexes crystallize, and the observation of ferromagnetic ground states for each, exemplifies the reliability of the present synthetic strategy to produce potential single molecule magnets. The Co₃Ln complexes presented here were found to have variable cobalt coordination geometries, a subtle effect induced by the size of each lanthanide, with the Co₃Dy complex being the sole example of purely octahedral cobalt centres. Magnetic measurements of Co₃La revealed a ground state spin of S = 3/2 with a relatively large zero-field splitting parameter, likely associated with the presence of a trigonal bipyramidal cobalt centre. A number of higher nuclearity complexes are also reported. Four variations of a Ni₁₆ molecular wheel have been crystallographically identified, three of which are nearly-isostructural acetate containing polymorphs and the last of which is a formate analogue. One polymorph exhibited a capsule like packing arrangement within its crystal structure, however, attempts to drive the inclusion of a guest molecule were unsuccessful. Synthetic efforts to produce a copper based analogue resulted in the unexpected formation of a Cu₁₄ cluster which exhibited the same binding pattern as Ni₁₆. Two manganese containing complexes, Mn₈ and MnLa₆, were also obtained where the former exhibited the relatively uncommon homometallic square-in-square architecture.
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    Salicylaldoxime derivatives for new magnetic materials : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Chemistry at Massey University, Manawatu, New Zealand
    (Massey University, 2019) Woodhouse, Sidney
    Salicylaldoxime (H₂Sao) is an appealing unit for metal ion coordination, specifically that of transition metal (3d) ions. During this research, four ligands were synthesised, of which two were previously unknown (L2 and L3). These ligands differed by the secondary amine added to the simple H₂Sao molecule. These H₂Sao derived ligands were complexed with a variety of 3d ions, resulting in three distinct topologies: mononuclear, triangular, and defective dicubane. The nine new complexes (C1-C9) synthesised were all structurally characterised, with Mössbauer spectroscopy performed on the iron complexes, and magnetic characterisation performed on complexes C1-C6, C8-C9. Analysis of the synthesised complexes has led to new insights into magnetostructural correlations and new pathways to unique ligand designs.
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    Magneto-structural correlations of iron-salicylaldoxime clusters : a dissertation presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Chemistry at Massey University, Turitea Campus, New Zealand
    (Massey University, 2015) De Silva, Dunusinghe Nirosha Tharangani
    The syntheses and characterisation of polynuclear metal clusters using a series of derivatised salicylaldoxime ligands are described in this thesis. The polynuclear iron clusters contain metallic cores consisting of oxo-centred triangles. It was found that slight modifications of the phenolic oxime ligands can lead to metal clusters with different nuclearities, thus producing a variety of magnetic properties within the materials. The predominant building block in the complexes is a triangular [Fe3O(Rsao) 3]+ (R = alkyl derivative, sao = salicylaldoxime) unit which can self-assemble into more complicated arrays depending on reaction conditions. A number of ligands containing a single phenolic oxime unit has been synthesised. These ligands have been used to form di-iron (C1), hexairon (C2), and heptairon (C3) complexes. A second series of ligands containing two double-headed phenolic oxime units linked by diamine straps has been synthesised and fully characterised. Two copper complexes C5 and C7 were crystallised and pyridine also took part in coordination to the copper centres. Three of the iron complexes formed with double-headed oxime ligands are heptairon compounds. The heptairon compounds were all analogous in their iron coordination environment. The hexairon complex (C8) formed from a double-headed oxime was analogous to the complex C2 formed from a single-headed oxime ligand in its iron coordination environment. The tri-iron complex (C10) also contains a metaborate ion. In each case of the heptairon complexes and the hexairon complex, the metallic skeleton of the cluster was based on a trigonal prism in which two [ O] triangles are fastened together via three helically twisted double-headed oxime ligands. Each of these ligands is present as (L-2H) where the oximic and phenolic O-atoms are deprotonated and the amino N-atoms protonated, with the oxime moieties bridging across the edges of the metal triangles. The identity of the metal ion has a major impact on the nuclearity and topology of the resultant cluster. The magnetic susceptibility measurements of these iron complexes suggest the presence of strong antiferromagnetic interactions between the metal centres and the Mössbauer analyses confirm the oxidation state of all the iron centres is 3+. The CHN analyses and other general characterisation allowed verifying and / or modifying the formulae generated by the X-ray analyses.
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    Mercury clusters from van der Waals to the metallic solid : a thesis presented in partial fulfillment of the requirements of the degree of Doctor of Philosophy in Theoretical Chemistry at Massey University, Albany, New Zealand
    (Massey University, 2003) Gaston, Nicola
    The nature of mercury clusters is studied in an attempt to reconcile the behaviour of the solid with that of the smallest molecules. Related systems such as Zn, Cd, and Ba are investigated for comparison. A range of ab initio methods are employed, and their accuracy assessed. Density functional theory (DFT) based methods are shown to be unreliable. Different functionals vary widely in their description of a particular system, such as the dimer, while individual functionals vary in accuracy when applied across a range of system sizes. This is related to the neglect of van der Waals forces by DFT for the smaller systems, but raises interesting questions about the solid. Wavefunction-based methods are seen to be much more reliable than DFT, although a high-level description of correlation is required. Hartree-Fock (HF) calculations are shown to be consistent in their description of systems of all sizes, and therefore although inadequate on its own the addition of a correlation potential derived from the many-body perturbational (MP2) calculation for the dimer corrects HF to produce exactly the correct bond lengths (when compared to the best known data) for all sizes up to the bulk lattice. The use of higher order many-body potentials is investigated and compared to the situation observed for the noble gases, since for small sizes these are the closest analogues of the neutral mercury clusters. The question of how to simulate transitions in large clusters is addressed. Transitions of interest in clusters are the liquid to solid phase transition, the metal to non-metal transition, or a structural transition from one isomeric motif to another. Therefore the ability to calculate the properties of these clusters accurately is as important as the question of structure. Four-component DFT calculations for the mercury dimer polarisability agree well with the anisotropy derived from Raman spectroscopy. Various isomers proposed in the literature are compared for the smaller mercury clusters. The structures of cationic clusters are also optimised, and their electronic excitation spectra are investigated through CIS(D) and TD-DFT calculations and compared to experimental results. The structures of anionic zinc clusters are obtained and the density of states compared with experiment. The structures and spectra of these clusters are related to those seen for the magnesium analogues, and the effect of the d-electrons in perturbing the jellium model description of these clusters is considered.
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    A systematic search for the global minimum structures of Cs, Sn and Au clusters and corresponding electronic properties : a thesis submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at Massey University, Albany, New Zealand
    (Massey University, 2007) Assadollahzadeh, Behnam
    Clusters of atoms or molecules form the building blocks of nanoscience and are regarded as a new type of material, as they constitute a bridge between microscopic and macroscopic forms of matter. The experimental and quantum theoretical study of structures, chemical and physical properties and reactivities of nanoclusters represents an innovative and very active field of research, which has resulted in a wide range of applications. Independent of the model used to describe the bonding in these clusters, one of the prime objectives is to find the geometrical arrangement of the atoms or molecules, for a given cluster size, which corresponds to the lowest energy on the potential energy hyper-surface, the global minimum. In order to find such an arrangement, a density functional theory based genetic algorithm code, which is rooted in the Darwinian evolution concept of the survival of the fittest, is developed and utilized to systematically search for the global minimum isomers of homo-nuclear clusters consisting of up to twenty atoms of cesium, tin, gold and of nine atoms of copper. The performance of this algorithm is excellent as numerous energetically lower-lying cluster isomers (compared to those reported in the literature) are found. Extensive valence basis sets together with energy-consistent scalar-relativistic pseudopotentials are employed to optimize the geometry of these clusters and to calculate their electronic properties accurately at the density functional level of theory. Moreover, in collaboration with the Technische Universit??t Darmstadt, the mean static polarizability of tin clusters are measured by a beam deflection method. The qualitative agreement between measured and calculated dipole moments and static electric dipole polarizabilities of tin clusters up to twenty atoms is satisfactory, thus confirming the accuracy of the theoretical models used in this work. Furthermore, the performance of density functional theory in the field of metallophilicity is investigated for dimeric and trimeric [X-M-PH3] compounds (X = Cl, Br, I; M = Cu, Ag, Au) and it is found that the metallophilicity decreases down the group 11 elements of the periodic table of elements.