FERROMAGNETIC PROPERTIES AND CRYSTAL-STRUCTURES OF PYRIDYL AND PYRIDINIUM ALPHA-NITRONYL NITROXIDES

Magnetic properties and crystal structures of pyridyl and pyridinium a lpha-nitronyl notroxides have been studied. The intermolecular magneti c coupling is ferromagnetic in the crystal of p-pyridyl alpha-nitronyl nitroxide (PYNN), while it is antiferromagnetic in m- or o-PYNN. The ferromagnetic properties of p-PYNN can be understood in terms of an on e-dimensional (1D) ferromagnetic chain which is consistent with the mo lecular arrangement in the crystal. The temperature dependence of the magnetic susceptibilities of the m- and p-N-methylpyridinium alpha-nit ronyl nitroxide (MPYNN) iodide salts are well fitted by the singlet-tr iplet model, although their intradimer magnetic couplings are opposite s: it is ferromagnetic in m-MPYNN and it is antiferromagnetic in p-MPY NN. X-ray crystal analysis has been carried out using a stable crystal , m-MPYNN.(BF4)x.I1-x (x=0.72), showing that the molecules exist as a dimer, and the dimer units form a 2D triangular lattice