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    Synthesis and characterisation of pyrazine-based ligands for the analysis of metal-metal communication : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Chemistry at Massey University, Manawatū, New Zealand
    (Massey University, 2018) Brown, Michael James
    Pyrazine is an attractive molecule that has been incorporated as a bridging ligand between two metal centres. These complexes have been shown to exhibit both magnetic and electrochemical exchange between the metal centres through the pyrazine unit. Addition of functionality onto the 2 and 5 position of pyrazine can reinforce the coordination of 3d octahedral metal ions to the pyrazine ring. The Schiff base condensation of A1 with various primary amine reactants produced three unique ligand systems. The confirmed synthesis of these ligands was verified with a variety of characterisation techniques. A single crystal structure was generated for one ligand system (L3), which revealed both imine – π stacking interactions, as well as alkane hydrogen – pyridine interactions. Several complexations were attempted with the three ligand systems synthesised. Manganese and cobalt complexes were successfully synthesised with L3, the single crystal structures generated showed cyclohelicate triangles, which were unique at the time. The electrochemical analysis of these complexes in MeCN showed similar redox processes as was seen in the electrochemical analysis of L3. Signs of possible metal-metal communication within the cyclohelicate triangles was also noticed, with oxidation (and reduction) processes present. Further analysis is necessary to verify these interpretations, including magnetic analysis. Complexations with identical metal salts and L2 could not be characterised by SCXRD Other techniques such as mass spectrometry and conductivity measurements indicated the likely formation of a polymorphic – potentially cyclohelical structure with this ligand. Complexations with L1 incorporated the inclusion of a larger collection of metal salts. Unfortunately, due to time constraints, only three complexes were suitably characterised. From the various characterisation methods used, it was deduced that all three complexes were likely simple M2L1 systems, where the coordination of the 6-coordinate 3d metal centres were accompanied by the coordination of either water, solvent, counterion or a combination of these.
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    The computational investigation of a dinuclear manganese complex with Jahn-Teller compression and elongation : MSc thesis, Chemistry, Institute of Fundamental Sciences, Massey University
    (Massey University, 2017) Buchanan, Jenna K
    Complexes that possess both Jahn-Teller compression and elongation effects at metal centres within the same molecule are extremely rare with only 11 examples known in the literature. Only two of these examples exist as discrete compounds. Jahn-Teller distortions influence metal-ligand bond lengths as well as the energy levels of the eg and t2g orbitals on the metal centre. The orientation of the Jahn-Teller axes have also been found to be an influential parameter in determining the exchange interactions in MnIII dimers. X-ray crystallographic analysis of a di-manganese coordination compound serendipitously synthesised by Willoughby suggested that the complex possessed both Jahn-Teller compression and elongation. Willoughby’s complex was synthesised in a very low yield and analysis of the crystals obtained by X-ray diffraction gave a structural determination of only moderate quality. In this research project, the complex was computationally modelled in order to investigate the Jahn-Teller distortions and the coupling between the manganese centres. The bond lengths, molecular orbitals and spin density plot were explored in order to investigate these properties. The computational results gave strong evidence that Jahn-Teller compression and elongation were present in the di-manganese complex. The modelled ferromagnetic complex was found to be lower in energy than the modelled antiferromagnetic complex. Attempts were also made to re-synthesise the di-manganese complex in suitable quantity for complete structural and magnetic characterisation. Several different routes were trialled but after exhaustive attempts it was not possible to repeat the synthesis of the dinuclear complex.