THE EXPERIMENTAL SPIN-DENSITY OF 2 NITROPHENYL, NITROXIDES - A NITRONYL NITROXIDE AND AN IMINO NITROXIDE

We have determined, by polarized neutron diffraction, the spin density of two nitrophenyl nitroxides: the para-nitrophenyl nitronyl nitroxid e (p-NPNN), which is a ferromagnet at low temperature, and the meta-ni trophenyl imino nitroxide (m-NPIN), which exhibits antiferromagnetic c oupling. Several methods were used to reconstruct the spin density dis tribution, including the maximum entropy method. Our data provide the basis for a better knowledge of the electronic configuration. The node s of the SOMO are directly observed and the spin polarization effects which give rise to a negative spin density on several atomic sites is discussed.