SPIN-DENSITIES IN FREE-RADICALS

Polarized neutrons are well adapted for determining the spin distribution in compounds containing free radicals. However, due to the complexity of the crystal structure, it is usually not possible to measure a complete set of magnetic structure factors in order to make a classical Fourier synthesis of the spin density: for those reflections for which the nuclear structure is weak, the magnetic structure factors cannot be determined by the polarized neutron technique. Because of this, it is more useful to analyse the data in terms of a multipole expansion around the atomic centers, which provides an analytical description of the spin density, and hence to determine population parameters. This method is applied to the di- (2, 2, 6, 6-tetramethyl-4-piperidinyl-1-oxyl)-suberate, where the location of the unpaired spin on the nitroxide radical is controversial. It is found that it is located on the NO group and almost equally shared between the oxygen and the nitrogen atoms. © 1979.