Metallosupramolecular studies of the ambivergent ligand N-(2-pyridyl)-4-amino-4-oxobutanoic acid.
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
Eight mononuclear complexes were prepared from the N-(2-pyridyl)-4-amino-4-oxobutanoic acid (H2L1) ligand. H2L1 chelated to cobalt(II), nickel(II) and copper(II) through the pyridine and amido nitrogen atoms while the carboxylic acids did not coordinate. 1D and 3D hydrogen bonding networks were formed through interactions between non coordinated solvent molecules and anions within the crystal lattices along with carboxylic acid interaction to the metal centres. One 1D and two 2D coordination polymers were formed with cobalt(II) and nickel(II) under solvothermal conditions. The H2L1 ligand again chelated to the metal ions through the same mode seen in the mononuclear complexes. The two 2D coordination polymers were isostructural to each other and were formed with cobalt(II) and nickel(II). The carboxylate functional groups formed from the deprotonation of the carboxylic acids on the H2L1 ligand bridged two symmetry equivalent metal ions forming a [4,4] 2D coordination polymer. Multinuclear discrete complexes were formed with H2L1 and cobalt(II), copper(II) and iron(II/III) metal ions. An octanuclear cobalt metal cluster formed through slow evaporation of copper perchlorate, H2L1 in a methanol solution and the addition of triethylamine to deprotonate the carboxylic acid groups. A pentanuclear iron metal cluster with two Fe(II) centres and three Fe(II) centres was also prepared. Within this metal cluster an iron carboxylate triangle motif formed between the three Fe(II) centres with a bridging μ3-O at the centre. The H2L1 ligand coordinated to the metal ions through the pyridine nitrogen and amido oxygen atoms along with the carboxylate oxygen atoms. Magnetic characterisation of both metal clusters showed dominant antiferromagnetic interactions. A hexanuclear Cu(II) metal cluster was prepared using the H2L1 ligand and copper acetate. An in situ oxidation of the α methylene carbon adjacent to the amide functional group in the H2L1 ligand formed H2L1A. The hexanuclear complex has four square pyramidal Cu(II) ions and two square planar Cu(II) ions. Chelation to the Cu(II) centres occurred through the pyridine and amido nitrogen atoms which was not seen in any other complexes prepared in the study. The carboxylate groups bridged two Cu(II) ions. Magnetic characterisation of the metal cluster showed dominant ferromagnetic interactions between the Cu(II) metal centres.