Oxygen chemisorption on γ-Al2O3·phthalocyaninato·-cobalt(II): Coordination of O2 by complexed cobalt centers; Tumbling of molecular oxygen on surface cobalt centers

The system phthalocyaninatocobalt(II)·Al2O3, ([Co(pc)]·γ-Al2O3), if contacted with air at high temperatures (70 - 150 °C), has been found to be active to oxygen chemisorption. ESR measurements revealed that the chemisorption is a reversible process, leading to the formation of [Co(pc)O2]·γ-Al2O3 as a paramagnetic intermediate. ESR spectroscopy has also been used to investigate the rate of angular reorientation of O2 absorbed on the [Co(pc)]·γ-Al2O3 surface at a variety of temperatures. Computer simulations of the ESR spectra were compared with spectra obtained experimentally, and correlation times for reorientation and anisotropic g values were calculated. The fitting of the anisotropic g values to a model based on second-order perturbation theory suggests that the ground state of [Co(pc)O2]·γ-Al2O3 is (x2 - y2)2(z2)2(xz or yz)2(yz or xz), with the unpaired electron localized mainly on cobalt. According to this finding, oxygen interacts with cobalt mainly through a π overlap. © 1982.