Crystal engineering with 2,2':6',2"- terpyridine derivatives and their metal complexes : from simple building blocks to coordination polymers and networks

This thesis concerns the design of ligands for use in the construction of larger
supramolecular systems, with emphasis on the application of 4'-substitured 2,2',6',2''-
terpyridine ligands and their iron(II) and ruthenium(II) complexes in crystal engineering.
The first section considers 4'-hydrazone functionalized 2,2',6',2''-terpyridines and their
dynamic behaviour in solution and structural characteristics in the solid state, with respect
to protonation. Neutral, mono- and di-protonated ligands are considered. The iron(II) and
ruthenium(II) complexes of these ligands are reported and their properties studied by
variable temperature NMR, UV-visible spectroscopy and single crystal X-ray
crystallography. Subtle changes in substituents were found to have dramatic effects on
crystal packing and some common packing arrangements were identified. A range of
potential ‘expanded ligands’ (complexes which can themselves act as ligands for additional
metal centres), are introduced in the next section. These can be potentially used to bridge
metal centres to form both discrete and infinite structures, in particular in the solid state. In
a systematic study of single crystal X-ray crystal structures of these complexes many were
found to be more flexible than they first appear, and that the crystal packing arrangements
were often sensitive to solvent. The next section describes the first crystallographically
characterized coordination polymers and networks which include metal bis(terpyridine)
units. Self-complementary hydrogen bonding was also found to be a stabilizing motif, with
a number of such structures prepared. The final chapter blends the ideas of previous
sections: 4'-(x-pyridyl) functionalized 2,2',6',2''-terpyridine ligands are used to form
‘expanded ligands’ with iron(II) and ruthenium(II) centres. These were characterized in
solution, with protonation of the distant pendant pyridyl ring found to significantly
influence the MLCT absorption of the complexes. These complexes were incorporated into
two larger structures and characterised by single crystal X-ray crystallography. A selfcomplementary
hydrogen bonded polymer which possesses nanopores through the crystal
lattice is reported. Iron bis(thiocyanate) was also used to form a bridged coordination
polymer.