SOLID-STATE H-1-MAS-NMR AND SPIN-DENSITIES ON PROTONS OF THE ORGANIC FERROMAGNETIC TEMPO DERIVATIVES

Electron spin densities on hydrogen atoms of thyleneamino)-2,2,6,6-tet ramethylpiperidin-1-oxyls (abbreviated as Ar-CH=N-TEMPO), which show f erromagnetic behavior at low temperatures, were determined in their cr ystal phases from the temperature dependence of the Fermi contact shif t measured by high speed magic angle spinning proton nuclear magnetic resonance. This method revealed a large negative hyperfine coupling co nstant for the methyl and methylene protons, A = -1.00 MHz for Ar = p- Cl-ph and A = -1.32 MHz for Ar = ph, and very small one for the aryl g roup protons, /A/ < 0.01 MHz for p-Cl-ph and A = +0.04 MHz for ph. The observed negative hyperfine coupling constant (negative spin density) of methyl and methylene protons matches with spin alternation for the intermolecular spin polarization mechanism through the contact of met hyl and/or methylene protons to adjacent N-O radical group. This conta ct potentially contributes to the intermolecular ferromagnetic interac tion.