I Complexation of iron(II), cobalt(II), nickel(II) and copper(II) by hexadentate tripodal aminopyridyl chelators II Binding preferences for zinc(II) relative to nickel(II) and copper(II) in novel tetradentate aminopyridyl chelators
Date of Award
Program or Major
Master of Science
Roy P Planalp
Chapter I. Effects of pyridyl-ring alkylation on complexation of Fe(II), Co(II), Ni(II) and Cu(II) by chelators based on cis,cis -1,3,5-triaminocyclohexane (tach) have been studied. The chelators studied are derivatives of tachpyr, where the ring substituents are 3-Me, 4-Me, 5-Me, 6-Me or 6-MeO (tach-x-Rpyr). Divalent complexes were synthesized for most combinations of the 4 metals and 5 chelators. Their bonding and structure were analyzed by UV/Vis/NIR spectroscopy, magnetic moment determination and single crystal X-ray crystallography. Steric repulsions between the 6-substituents result in substantially weakened metal-ligand interaction. Effects of these repulsions include bond angle and length distortions, decrease of coordination number to five, shifts of d-d electronic transitions to lower energies and spin-free complexes of the bound metal ion.
Chapter II. Effects of iron-mediated oxidative dehydrogenation on tachpyr and derivatives were studied. Relative rates of iron-mediated oxidation were established for tachpyr and its 3-substituted derivatives as [Fe(tach-3-Mepyr)] 2+ > [Fe(tachpyr)]2+ > [Fe(tach-3-McOpyr)]2+ while no oxidation was seen for [Fe(tach6-Mepyr)]2+. The affinity of partially oxidized tachpyr derivatives over unoxidized derivatives towards Fe(II) was demonstrated. The lability of oxidized tachpyr derivatives was studied in an aerobic environment. Fully oxidized (trisimine) complexes were shown to be labile while partially oxidized (bisimine) complexes were determined to be inert.
Chapter III. A series of tetradentate aminopyridyl ligands was synthesized in an attempt at developing a chelator that would bind in a four-coordinate (tetrahedral) fashion and possess zinc selectivity. The resulting 1,3-diaminopropane (pn) based chelators were complexed with divalent Ni, Cu and Zn and their complexes were analyzed by UV/Vis/NIR, IR and NMR spectroscopy as well as single-crystal X-ray crystallography. It was determined that methylation of the pyridine rings at the 6-position had a greater effect on ligand affinity towards Ni(II) than homologation of the aminopyridyl arms. The crystal structures of all the Zn(II) complexes showed the metal center to be six-coordinate with a nitrate anion bound in a bidentate fashion. However, in solution the zinc complexes showed signs of lower coordination numbers of either 4 or 5.
Childers, Matthew Lloyd, "I Complexation of iron(II), cobalt(II), nickel(II) and copper(II) by hexadentate tripodal aminopyridyl chelators II Binding preferences for zinc(II) relative to nickel(II) and copper(II) in novel tetradentate aminopyridyl chelators" (2007). Master's Theses and Capstones. 263.