The Coordination Chemistry of Modified Pyrimidine-Hydrazone Strands and their Incorporation into Polymer Gels

Abstract

A series of pyrimidine-hydrazone (pym-hyz) molecular strands have been modified with terminal hydroxymethyl and acryloyl functional groups in order to allow their incorporation into co-polymer gels. This thesis describes the synthesis of these strands, their Pb(II), Zn(II), Cu(II) and Ag(I) complexes, and their incorporation into co-polymer gel actuators.

Chapter one introduces the aspects of supramolecular chemistry which are important to this work, such as supramolecular and molecular self-assembly. The focus then shifts to foldamers, and the evolution of the pym-hyz helicity codon, which undergoes a reversible, dynamic structural change due to the coordination of certain metal ions. An introduction is then given to polymer gels as actuators, and how the incorporation of modified pym-hyz strands into a polymer gel would result in an actuator driven by the dynamic shape change of the pym-hyz helicity codon. Chapter two describes the design, synthesis and characterisation of three different lengths of pym-hyz strand, containing either terminal hydroxymethyl (L1-3) or acryloyl function groups (L4-6). The helical structure of these strands and the transoid conformation of the pym-hyz linkages within them are described by NMR spectroscopy and X-ray crystallography. Chapter three presents a review of the supramolecular architectures commonly constructed from pym-hyz based ligands and salts of Pb(II) and Zn(II) ions, followed by a description of the complexes formed by reacting L1-6 with these metal ions in a variety of metal to ligand ratios. NMR spectroscopy showed that the hydroxymethyl and acryloyl groups of L1-6 inhibited the formation of [2x2] grid complexes at a 1:1 metal to ligand ratio, but that linear complexes could be formed with an excess amount of either Pb(II) or Zn(II) ions. The X-ray crystal structures of fourteen of these complexes are reported and compared, the majority of which consist of a pym-hyz strand, saturated with metal ions, with a linear shape and cisoid pym-hyz linkages. The exceptions are the distorted [2x2] grid complexes [PbL1(ClO4)]4(ClO4)4 (4) and [PbL1(ClO4)]4(ClO4)4•4CH3NO2 (5) and the horse-shoe shaped complex [Pb2L2(ClO4)2(CH3CN)(H2O)](ClO4)2•2CH3CN•C4H10O•H2O (10). Chapter four opens with a review of the brief use of Cu(II) ions in the coordination chemistry of pym-hyz ligands, followed by a description of the Cu(II) complexes of L1-6. The complexes are analysed with UV-Vis and IR spectroscopy, the results of which showed that reacting L1-6 with an excess of Cu(II) ions resulted in linear complexes. Eight X-ray crystal structures of the Cu(II) complexes of L1 and L4 are presented and compared, the majority of which are linear in shape with two Cu(II) ions coordinated to each ligand molecule. Again, the addition of hydroxymethyl and acryloyl arms to these ligands prevented the formation of [2x2] grid structures at low metal to ligand ratios. Instead, the addition of Cu(II) ions to L1 in a 1:1 metal to ligand ratio resulted in the bent mono-Cu(II) complexes [Cu(L1H)(ClO4)2]ClO4 (17), [Cu(L1H)(CH3CN)](ClO4)3∙½H2O (18) and [CuL1(SO3CF3)]2(SO3CF3)2•CH3CN (19). Chapter five covers the Ag(I) chemistry of pym-hyz strands, followed by the description of the Ag(I) complexes of ligands L1, L2, L4 and L5 including eight X-ray crystal structures. The complexes were characterised in solution by NMR spectroscopy. The behaviour of these ligands to Ag(I) ions was highly dependent on the choice of counterion and solvent. Linear complexes of L1 and L4 were synthesised using an excess of AgSO3CF3 in CH3CN, while double helicates were formed from L1, L2 and L5 by employing a 1:1 metal to ligand ratio with either AgSO3CF3 or AgBF4. Chapter six concludes the thesis by explaining how ligands L4-6 were incorporated into co-polymer gels. The design and synthesis of these gels is described, as are the volume changes that they exhibited in CH3CN upon the addition of Pb(II), Zn(II) and Cu(II) ions. The swelling of the L5 and L6 gels with Pb(II) and Zn(II) was reversed by the addition of a competing ligand, then controlled by changes in pH. The swelling of these gels with Cu(II) was reversed by reducing the Cu(II) ions to Cu(I). All of the gels were characterised by microanalysis, which showed the extent to which the L4-6 ligands were saturated with metal ions. The addition of Pb(II) and Zn(II) ions to the L4-6 gels was also characterised by 1H NMR spectroscopy.