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RESEARCH INTERESTS
Chemists have developed the ability to
tune the structural and electronic properties of many molecular
species, which is useful in that it allows the design of new
materials for a range of different applications including
catalysis and optoelectronic effects. These applications require
that molecules be aligned in the solid state so that the
electronic and magnetic structures combine in the appropriate
fashion. Control over solid state structures of molecular
compounds is not straightforward, but a number of strategies have
proved successful in promoting the adoption of predictable
structures by molecular species. Thus, adding hydrogen-bonding
groups to a molecule may lead to the formation of a predictable
hydrogen-bonding network. Coordination polymerisation has also
proved useful in aligning inorganic species . The encapsulation
of a molecule into a crystalline host compound to form an
inclusion compound may also produce ordered materials.
The concept of crystal engineering has
provided a useful framework to develop rational approaches to
solid-state structural design based on the self-assembly of
molecular components. This field uses the concepts first
developed in supramolecular chemistry; in particular recognizing
the importance of hydrogen bonding,
p¼p interactions and
other “weak” interactions in generating and stabilizing larger
networks. Of particular interest for their diverse functional
properties are the “metal organic frameworks” or MOFs
(porous polymeric materials, consisting of metal ions linked by
organic bridging ligands)
and
layered hybrid perovskites (in which layers of metal
centres are separated by organic layers with no covalent bonds
linking the layers).
These materials are of interest
because of their structural, magnetic, optical and electrical
properties, particularly since these can be easily modified by
replacement of the metal, halide or amine. The tendency of the
hybrids to self-assemble from the solid or liquid phase arises
from the range of interactions seen in these compounds, from van
der Waals forces between organic components, hydrogen bonding
within the organic layer or between organic and inorganic
components to ionic and covalent bonds within the metal halide
sheets.
We have a fruitful
collaboration with Prof Klaus Koch (University of Stellenbosch) on the
self-assembly of metallomacrocyclic complexes. Using thiourea
derived ligands to form metallomacrocyclic complexes of platinum(II) or
nickel(II), whose sizes (2:2 or 3:3 metal:ligand) depend only on the
relative substitution (para vs meta) of the carbylthiourea moieties linked
through a phenylene ring, we have explored the crystal engineering and
inclusion properties of such metallomacrocycles. The Ni(II) example
is interesting as it is readily converted to octahedral geometry through
the coordination of two axial ligands perpendicular to the macrocycle
plane.
REPRESENTATIVE
PUBLICATIONS
pH control of guest
selectivity by inclusion. S. A. Bourne, K. C. Corin, L. R.
Nassimbeni, E. Weber. CrystEngComm. 2004, 6,
54-55.
Doubly-linked 1D coordination polymers derived from 2:2
metallamacrocyclic Ni(II) complexes with bipodal acylthiourea and
exo-bidentate N-donor bridging ligands: toward potentially
selective chemical sensors? O. Hallale, S. A. Bourne, K. R.
Koch. New J. Chem. 2005, 29, 1416-1423.
Anion dependent structural diversity in cobalt(II) complexes of
4,4’-bipyridine-N,N’-dioxide. S. A. Bourne, L. J. Moitsheki.
CrystEngComm. 2005, 7, 674-681
Competitive bulk liquid membrane transport and solvent extraction
of some transition and post-transition metal ions using
acylthiourea ligands as ionophores.
M. M. Habtu, S. A. Bourne, K. R. Koch, R. C. Luckay.
New J. Chem.,
2006, 30, 1155-1162
Competitive bulk liquid membrane transport and solvent extraction
of some transition and post-transition metal ions using
acylthiourea ligands as ionophores.
M. M. Habtu, S. A. Bourne, K. R. Koch, R. C. Luckay.
New J. Chem.,
2006, 30, 1155-1162.
UCT
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