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
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Date
2022
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Massey University
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Abstract
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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Coordination compounds, Molecules, Magnetic properties, Metal clusters