2-DIMENSIONAL FERROMAGNETIC INTERMOLECULAR INTERACTIONS IN CRYSTALS OF THE P-CYANOPHENYL NITRONYL NITROXIDE RADICAL

The crystal structure of the p-cyanophenyl nitronyl nitroxide [2-(4-cyanophenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-1-oxyl 3-N-oxide, abbreviated as p-CNPNN] radical has been solved. It belongs to the orthorhombic system, space group lc2a, with a=10.482(2)Angstrom, b=26.615(5)Angstrom, c=9.903(2)Angstrom and Z=8. The asymmetric unit contains two independent radical molecules. The intermolecular contacts between the cyano phenyl groups and the nitroxide groups form a quasi-square lattice. The magnetic susceptibility has been measured in the temperature range 1.8-300 K. The temperature dependence of the paramagnetic susceptibility above 4 K can be explained by the ferromagnetic square-lattice Heisenberg model with J/k(B)=0.75 K. Two-dimensionality of the crystal is also confirmed by single-crystal electron paramagnetic resonance (EPR) spectra.