Studies of Transition Metal Complexes Containing Pentaamine Ligands
This thesis presents the study of two pentadentate pentaamine ligands N¹,N¹'-(pyridine-2,6-diylbis(methylene))bis(ethan-1,3-diamine)(mpyden) and N²,N²-bis(2-aminoethyl)propane-1,2,3-triamine (bapt) and the associated transition metal complexes of the these two ligands. Two new complexes Co(mpyden)(O₂)(mpyden)Co₄ and (mpyden)Co(O₂)Co(mpyden)₅, which contain a peroxido, and superoxido bridging ligand, respectively, have been prepared and characterised. An attempt to synthesise the bapt ligand for the first time was unsuccessful.
The cobalt complexes of which a crystal structures was obtained are shown to be dinuclear with each exhibiting a distorted octahedral geometry in which all five nitrogen atoms of the mpyden ligand are coordinated to the cobalt (III) ion, and are bridged by a peroxido ligand in a μ₂-η¹,η¹ fashion. The charge is balanced by four perchlorate ions, in one of which exhibits moderate disorder, and the other by five perchlorate ions, all of which are extremely disordered. The mpyden ligand adopts an fmf configuration about each metal ion. The Co-N bond lengths around each Co(III) ion of Co(mpyden)(O₂)(mpyden)Co₄ complex lie in the range 1.874(4) Å – 1.982(5) Å. The Co-N bonds to the aromatic N donor atoms are both significantly shorter than those to the aliphatic N atoms. The (mpyden)Co(μ-O₂)Co(mpyden)₅ complex has two separate confirmation but only one is shown, disorder is also present in its superoxido bridge.
The attempted complexation of mpyden with Ni(II), Mn(II), Cu(II), Fe(II), Zn(II), and others resulted in formation of precipitate with Fe and Mn solutions. However, ESI-MS suggested that a mononuclear complex was formed upon coordination of mpyden ligands to Cu (II), Zn (II), Ni(II) and Co(II) in aqueous solution.
The attempted synthesis of the bapt (N²,N²-bis(2-aminoethyl)propane-1,2,3-triamine) ligand is described.