Phenyl nitronyl nitroxides

We shall consider, for purposes of illustration, the system p-(methylthio)-phenyl-nitronyl-nitroxide (MTPNN,7 in Figure 2.1) in toluene solution [38], Principal values and orientations of magnetic and diffusion tensors have been taken from QM calculations,... 

Fig. 22 The chiral conformations exhibited by phenyl nitronyl nitroxides...

Fig. 23 A spontaneously resolved chiral complex between Mn(hfac)2 and a phenyl nitronyl nitroxide which is a magnet...

A true "all-organic" ferromagnet, the orthorhombic jS-phase of p-nitro-phenyl nitronyl nitroxide, 29. was found in 1991 to have a Curie temperature TC = 0.60K [100,101]. 

Takeda, K., Konishi, K., Tamura, M. and Kinoshita, M., Magnetism of the fi-phase p-nitro-phenyl nitronyl nitroxide crystal, Mol. Cryst. Liq. Cryst., 273, 57, 1995. 

Cirujeda, J., Mas, M., MoUns, M., Lanfranc de Panthou, F., Tangier, J., Park, J. G., Paulsen, C., Rey, R, Rovira, C., and Veciana, J., Control of the structural dimensionality in hydrogen-bonded self-assemblies of open-shell molecules. Extension of intermolecular ferromagnetic interactions in (X-phenyl nitronyl nitroxide radicals into three dimensions, J. Chem. Soc. Chem. Common., 709, 1995. 

The magnetic properties and crystal structures of 2-aryl derivatives of nitronyl nitroxide have been studied extensively over the years. In particular, systematic studies on series of pyridyl and A-alkylpiridinium nitronyl nitroxides by Awaga et al. [4], hydroxyphenyl nitronyl nitroxides by Veciana et al. [5] and various derivatives of phenyl nitronyl nitroxides by our groups are very important in elucidating the correlation between the magnetic interactions and the structural... 

In the case of phenyl nitronyl nitroxides, the dihedral angle between the plane of the phenyl ring and that of the ONCNO moiety is variable. It seems that there are potential minima at several angles. In this section, some examples of magnetism of phenyl nitronyl nitroxide derivatives are presented. 

Bonnet, M., Luneau, D., Ressouche, E. et al. (1995) The experimental spin density of two nitro-phenyl nitroxides a nitronyl nitroxide and an imino nitroxide, Mol. Cryst Liqu. Cryst, 271-272, 35-53. 

Since the reported synthesis [1] of stable 2-phenyl-4,4,5,5-tetramethylimidazoline-l-oxyl-3-oxide, NitPh, considerable effort has been spent in the physical characterization of nitronyl nitroxide compounds. Their general formula is presented in Figure 1 A. These compounds carry a delocalized, S = 1/2, unpaired electron. Among them, some derivatives were found to be paramagnetic at low temperature (NitPh, [1]), others were found to exhibit an antiferromagnetic or a ferromagnetic behavior [2-7]. 

Veciana, J., Cirujeda, J., Rovira, C., Molins, E. andNovoa, J. J. (1996). Organic ferro-magnets. Hydrogen bonded supramolecular magnetic organizations derived from hydroxylated phenyl a-nitronyl nitroxide radicals. J. Phys. I Ft, 6, 1967-86. [201] Venkatesan, K. and Ramamurthy, V. (1991). Bimolecular photoreactions in crystals. In Photochemistry in organized and constrained media (ed. V. Ramamurthy), pp. 133-84. VCH Publishers, Weinheim. [236]... 

In a laser flash-photolysis study, 2-phenyladamantene was generated in benzene at room temperature from 3-noradamantyl(phenyl)diazomethane. This strained cycloalkene decays with second-order kinetics to give a dimer, and reacts much faster with O2 and Bu3SnH than with methanol, thus revealing a substantial radical character. Diphenyldiazomethanes possessing stable /er -butylaminoxyl and Ullman s nitronyl nitroxide radicals, e.g. (25), have been prepared by photolysis of the parent diazomethanes. Analysis of ESR fine structures showed that the carbene and radical centres couple ferromagnetically in these molecules, as expected. 

Y. Miura, K. Inui, F. Yamaguchi, M. Inoue, Y. Teki, T. Takui, and K. Itoh, Molecular design, synthesis, and magnetic characterization of poly(phenyl-acetylene) with pi-toporegulated pendant nitronyl nitroxide radicals as models for organic superpara- and ferromagnets, J. Polym. Sci. Polym. Chem. Ed., 30, 959 (1992). 

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