Files in this item
|(no description provided)|
|Title:||Part One: Epr, Thermodynamic, and Hydrogen Bonding Studies of Cobalt Dioxygen Complexes and Part Two: Structural, Spectral, and Magnetic Properties of a Copper(ii) Bimetallomer|
|Author(s):||Leslie, Kenneth Allen|
|Department / Program:||Chemistry|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Abstract:||In Part One, studies have been described which correlate the major steps involved in the process of binding dioxygen to cobalt(II) Schiff base complexes. The enthalpies of base binding to the complex Co(4,6-CH(,3)Osal-4-CF(,3)oph) were determined for the bases piperidine, 1-methylimidazole, pyridine, and tetrahydrothiophene. The enthalpies were fit to the E and C correlation, allowing E(,A) and C(,A) parameters to be calculated for Co(4,6-CH(,3)Osal-4-CF(,3)oph).
EPR spectroscopyy was used to study the 1:1 and 2:1 base adducts of Co(4,6-CH(,3)Osal-4-CF(,3)oph). The five coordinate adducts were found to reversibly bind dioxygen at low temperature. The dioxygen adducts were also studied via EPR and were found to fit the spin-pairing model for dioxygen binding. The extent of electron transfer from cobalt to the bound dioxygen was determined and found to increase as the strength of the axial base increased.
The enthalpies of dioxygen binding to Co(4,6-CH(,3)Osal-4-CF(,3)oph). Base complexes were determined for bases which fit the E and C correlation. The enthalpy of dioxygen binding was found to increase as the enthalpy of base binding increased. These observations were consistent with the electron transfer values calculated from EPR spectra. All of these studies indicate that the spin-pairing model correctly explains the process of dioxygen binding to cobalt(II) complexes.
Additional information about the nature of the bound dioxygen was obtained from the complex Co(SMDPT)(.)O(,2). The interaction of 2,2,2-trifluoroethanol with Co(SMDPT)(.)O(,2) was examined via high pressure infrared spectroscopy. The observance of an O-H frequency shift indicated that a hydrogen bond had formed between the alcohol and the terminal end of the bound dioxygen. The enthalpy of the interaction was determined by using a constant acid relationship. The results were compared to previous work which dealt with the stabilization of Co(SMDPT)(.)O(,2) by hydrogen bonders.
In Part Two, the chemistry of the bimetallomer Cu(salen)Cu(hfac)(,2) has been discussed. Variable temperature magnetic susceptibility measurements indicated the presence of an antiferromagnetic exchange interaction with a coupling constant, J, between the copper(II) centers of -20.4 cm('-1). This value differed from that expected from theory so EPR spectral studies were undertaken to explain the susceptibility results. These studies provided no definitive answers.
In order to explain these results, a single crystal X-ray diffraction study was carried out. The compound crystallizes in the triclinic space group P1 with four molecules in the unit cell. The reduced cell parameters are a = 17.03(4) (ANGSTROM), b = 19.11(4) (ANGSTROM), c = 9.89(2) (ANGSTROM), (alpha) = 96.58(11) (DEGREES), (beta) = 100.10(16) (DEGREES), (gamma) = 107.70(13) (DEGREES). The structure was refined by full-matrix least-squares methods to a weighted R factor of 0.074 for data with F(,o) (GREATERTHEQ) 3(sigma)(,F). The structural results indicate that the reduced value of J is due to the low symmetry of the bridge area which allows for only one phenolic oxygen to participate in the superexchange pathway.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1980.
|Date Available in IDEALS:||2014-12-13|