Encapsulation of tetrahedral anions in nickel mesocate cages : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Chemistry at Massey University, Manawatu, New Zealand
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2022
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Massey University
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Finding ways to isolate anions and metals is a modern problem as concerns over pollution of anions have become popular in the scientific community. The applications of supramolecular structures are endless, ranging from drug delivery to refining metals at an industrial scale. In this thesis, three variations of a di-salicylaldimine linked ligands were designed to form anion encapsulating mesocates. Each ligand differs by the spacer linking the salicylaldimine units. L1 has a six-carbon spacer, L2 has a p-xylylic spacer and L3 has a m-xylylic spacer. After the synthesis and characterisation of these ligands, complexation was achieved with various nickel salts resulting in the formation of dinuclear triple-stranded mesocate complexes; [BF₄⊂Ni₂(L1)₃](BF₄)₃ (C1), [ClO₄⊂Ni₂(L1)₃](ClO₄)₃ (C2) and two dinuclear di-stranded mesocate complexes; [SO₄⊂Ni₂(L3)₂][Ni(SO₄)₂ (EtOH)₄] (C3), [ClO₄⊂Ni₂(L3)₂](ClO₄)₂ (C4). The crystals have been characterised with IR spectroscopy, UV-Vis spectroscopy, mass spectrometry, atomic absorption spectroscopy, conductivity measurements and single crystal X-ray diffraction. An uncommon mesocate structure was observed from the X-ray diffraction data collected whereby the anion in the centre of the cage forms covalent bonds with the two Ni²⁺ metal ions. In addition, metal salt extraction experiments were attempted in a two-phase solvent system with L3, nickel sulfate to assess how much nickel and sulfate could be extracted from the aqueous mixture to the organic solution. Although a reliable measurement of sulfate could not be obtained, the highest percentage of the nickel extracted measured in hexane was 89%. However, there is potential to gather a higher value using the optimal conditions found in these experiments.