Septet Spin State in the Lithium Phthalocyanine π-Radical Compound. Role of Dioxygen

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Abstract
The lithium phthalocyanine π-radical compound is a molecular semiconductor which exhibits exceptional magnetic properties. These latter are interpreted as resulting from two distinct spin species. One species is delocalized and its behaviour may be interpreted in the frame of itinerant magnetism. It is responsible of an extremely narrow ESR line. The other species is due to localization of the PcLi spins interacting with molecular oxygen. At low temperature this magnetic coupling is shown to stabilize a septet spin state which involves indirect ferromagnetic coupling between neighbouring π-spins. The experimental results obtained up to now on this unexpected spin state are presented and discussed.