Magnetic properties of 2,5-difluorophenyl-α-nitronyl nitroxide and related position isomers

2,5-Difluorophenyl-α-nitronyl nitroxide (2,5-DFPNN) radical crystal 4 was found to possess an unusual crystal structure with co-existence of two rotational isomers in a single crystal showing bulk magnetic transition to quasi-one-dimensional ferromagnetic behavior with Tc at ∼0.48 K in ac susceptibility as well as heat capacity measurement. On the other hand, remarkable difference on their magnetic properties was observed in related position isomers depending upon the position of the second fluoro-substituent to the o-fluorine atom.