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
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Date
2015
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Massey University
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Abstract
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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Keywords
Metal clusters, Magnetic properties, Ligands, Iron, Copper