Date of Award
1993
Degree Type
Dissertation
Degree Name
Doctor of Philosophy
Abstract
Absorption and magnetic circular dichroism (MCD) spectra of neutral and oxidized magnesium and iron phthalocyanine (MgPc and FePc) are reported. Chemical, electrochemical and photochemical methods are employed in the generation of the stable {dollar}\pi{dollar}-cation radical of magnesium phthalocyanine. The broad absorption band at 500 nm is a "marker" band that verifies oxidation of the phthalocyanine ring. Variable temperature absorption and EPR spectra indicate that oxidized MgPc({dollar}-{dollar}1) exists in solution as a mixture of monomer ( (MgPc({dollar}-{dollar}1)) {dollar}\cdot\sp+{dollar})and dimer ( (MgPc({dollar}-{dollar}1)) {dollar}\sbsp{lcub}2{rcub}{lcub}++{rcub}{dollar}). Least squares and Simplex calculations were performed on the absorption and MCD spectra of MgPc({dollar}-{dollar}2) and MgPc({dollar}-{dollar}1) to determine the band centre energies for {dollar}\pi\to\pi{dollar}* (Q, B1, B2, N and L) and {dollar}\pi\to\pi{dollar} (in the radical cation) transitions. Deconvolution yielded band centres of 670 (Q), 361 (B1), 338 (B2), 282 (N), and 246 nm (L) for (im){dollar}\sb2{dollar}MgPc({dollar}-{dollar}2); 828 (Q), 507 ({dollar}\pi\to\pi{dollar}), 411 ({dollar}\pi\to\pi{dollar}), 387 (B1), 330 (B2), 277 (N), and 247 nm (L) for ((im){dollar}\sb{lcub}\rm n{rcub}{dollar}MgPc({dollar}-{dollar}1)) {dollar}\cdot\sp+{dollar}; and 712 (Q), 505 ({dollar}\pi\to\pi{dollar}), 420 ({dollar}\pi\to\pi{dollar}), 368 (B1), 320 (B2), 278 (N), and 249 nm (L) for ((H{dollar}\sb2{dollar}O)MgPc({dollar}-{dollar}1)) {dollar}\sbsp{lcub}2{rcub}{lcub}++{rcub}{dollar}.;Absorption and MCD spectra for L{dollar}\sb2{dollar}Fe(II)Pc({dollar}-{dollar}2) (L = im, meim, py, mepy, pip, CN, CO, NH{dollar}\sb3{dollar}), L(X)Fe(III)Pc({dollar}-{dollar}2) (L = im, CN; X = Br, CN), (X)Fe(III)Pc({dollar}-{dollar}2) (X = Cl, Fo), and Cl{dollar}\sb2{dollar}Fe(III)Pc({dollar}-{dollar}1) complexes are reported. Low temperature MCD and electron paramagnetic resonance (EPR) spectra were used to assign the above complexes ground states as {dollar}\sp1{dollar}A{dollar}\sb{lcub}\rm 1g{rcub}{dollar}, {dollar}\sp2{dollar}E{dollar}\sb{lcub}\rm g{rcub}{dollar}, {dollar}\sp4{dollar}A{dollar}\sb{lcub}\rm 2g{rcub}{dollar}, and {dollar}\sp3{dollar}E{dollar}\sb{lcub}\rm u{rcub}{dollar}, respectively. The low and intermediate spin states in iron(III) phthalocyanine are directly related to the coordination number of the ferric ion, where octahedral L(X)Fe(III)Pc({dollar}-{dollar}2) is low spin (S = 1/2) and square pyramidal (X)Fe(III)Pc({dollar}-{dollar}2) is intermediate spin (S = 3/2). The triplet (S = 1) nature of the EPR spectrum of Cl{dollar}\sb2{dollar}Fe(III)Pc({dollar}-{dollar}1) demonstrates that this ring oxidized {dollar}\pi{dollar}-cation radical exists in solution as a pure monomer. The orbital degeneracy in L(X)Fe(III)Pc({dollar}-{dollar}2) and Cl{dollar}\sb2{dollar}Fe(III)Pc({dollar}-{dollar}1) and the spin degeneracy in (X)Fe(III)Pc({dollar}-{dollar}2) results in their MCD spectra being dominated by temperature dependent C terms. The above series of neutral and oxidized iron phthalocyanine complexes were subjected to spectral deconvolution in order to isolate xy polarized {dollar}\pi\to\pi{dollar}* (q, B1, B2, N and L), {dollar}\pi\to\pi{dollar} (into the half filled 1a{dollar}\sb{lcub}\rm 1u{rcub}(\pi{dollar}) MO of the {dollar}\pi{dollar}-cation radical), MLCT (e{dollar}\sb{lcub}\rm g{rcub}{dollar}(d{dollar}\pi{dollar}) {dollar}\to{dollar} 1b{dollar}\sb{lcub}\rm 1u{rcub}(\pi{dollar}*), 1b{dollar}\sb{lcub}\rm 2u{rcub}(\pi\sp*{dollar}); present in the ferrous and ferric spectra), and LMCT (into the 3/4 filled e{dollar}\sb{lcub}\rm g{rcub}{dollar}(d{dollar}\pi{dollar}) MO of the ferric complexes) transitions. From the series of spectral fits for L{dollar}\sb2{dollar}Fe(II)Pc({dollar}-{dollar}2), the e{dollar}\sb{lcub}\rm g{rcub}{dollar}(d{dollar}\pi{dollar}) orbitals act as electron conduits between the axial and equatorial {dollar}\pi{dollar}-systems. The energy of the B1 band decreases with good {dollar}\pi{dollar} donor ligands (cyanide) and increases with good {dollar}\pi{dollar} acceptor ligands (carbon monoxide). The variation in the B1 band energy demonstrates that the ferrous to ferric oxidation increases the {dollar}\pi{dollar}-acceptor strength of the central metal.
Recommended Citation
Ough, Edward A., "Metal And Ring Oxidation In Metallophthalocyanines" (1993). Digitized Theses. 2234.
https://ir.lib.uwo.ca/digitizedtheses/2234