Persistent 1,3,5-benzenetriyltris(N-tert-butyl nitroxide) and its analogs with quartet ground states. Intramolecular triangular exchange coupling among three nitroxide radical centers

1,3,5-Benzenetriyltris(N-tert-butyl nitroxide (3), its 2-methoxy derivative (4), and 1,3,5-tris{p-(N-oxy-N-tert-butylamino)phenyl}benzene (5) were prepared and studied by EPR and magnetic susceptibility/magnetization measurements. Trinitroxides 3 and 4 showed EPR fine structures characteristic of quartet states: 3: g=2,0062, |D/hc|=0.009 32 cm -1 and |E/hc|=0.000 15 cm -1 ; 4: g=2.0063, |D/hc|=0.009 66 cm -1 and |E/hc|=0.000 32 cm -1 . The changes in the signal intensity vs reciprocal temperature obeyed Curie's law in the range 10-100 K, suggesting that the quartets are their ground states. Magnetization data for 3 and 4 at 1.8, 3.0, and 4.0 K in the field range 0-7 T obeyed the Brillouin function in which S=3/2