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

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Massey University
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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.
Figures 1.2, 1.11 & 1.14 re-used with publishers' permission.
Ligands, Synthesis, Pyrazines, Schiff bases, Complex compounds