4.4.5.5- Tetramethylimidazoline-l-oxyl

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]. 

We report herein a single crystal polarized neutron investigation of the spin density of two purely organic nitronyl nitroxide free radicals which present ferromagnetic interactions the 2-(6-ethynyl-2-pyridyl)-4,4,5,5-tetramethylimidazoline-l-oxyl-... 

HPA = (4-pyridylthio)aceticacid 2-fur = 2-furoate a-fur = a-furoate = ([Pg.116]

Another important ESR method of NO detection is based on the interaction of NO with the stable radical phenyl-4,4,5,5-tetramethylimidazoline-l-oxyl (PTIO) and its derivatives carboxy-PTIO or trimethylammonio-PTIO [100]. It is interesting that in this assay NO reduces stable free radical PTIO to another stable free radical PTI and the N02 radical, and the reaction can be monitored by both a decrease in the ESR PTIO spectrum and an increase in the ESR PTI spectrum [101]. 

More recently, D. Gatteschi et al. have reported on a dysprosium-nitronyl nitroxide ID compound with interesting dynamic properties [76]. Their work illustrates nicely how presently coordination chemistry can modulate a known system [Dy(hfac)3NITEt] [77-80] (with hfac hexa-fluoroacetylacetonate and NITEt 4 -ethyl-4,4,5,5-tetramethylimidazoline-l-oxyl-3-oxide) to achieve fine control of the physical properties. [Dy(hfac)3 NITEt] is composed of alternating chains of Dy(hfac)3 units and NITEt radicals. This compound displays a transition to a three-dimensional mag-... 

Fig. 13. Structure of a layer in (rad)2Mn2lCu(opba)l3(DMSO)2 2H2O, with rad = 2- l-methylpyridinium-4-yl)-4,4,5,5-tetramethylimidazoline-l-oxyl-3-oxide. Reprinted from Stumpf et al. 38). Copyright 1993 American Association for the Advancement of Science.

The synthesis and characterization of the nitronyl and imino nitroxide ligands discussed in the following, namely 2-(2-pyridyl)-4,4,5,5-tetramethylim-idazoline-l-oxyl-3-oxide (abbreviated as NITPy), 2-(2-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxide (abbreviated as IMPy), 2-(2-benzimida-zolyl)-4,4,5,5-tetramethylimidazoline-l-oxyl-3-oxide (abbreviated as NITBz-ImH), 2-(2-benzimidazolyl)-4,4,5,5-tetramethylimidazoline-l-oxide (abbre-... 

Fig. 6 NO-dependent vascular permeability of solid tumors (S-180) as quantified by uptake of Evans blue albumin complex in tumor of various sizes in mice. Mice were administered with NO scavenger 2-phenyl-4,4,5,5-tetramethylimidazoline-l-oxyl 3-oxide (PTIO) orally (dose PTIO, 125 mg/kg 1 4 in 8 h). Note that EPR effect is greatly suppressed by PTIO, which is a fraction of NO contributing to EPR effect. Further note that when the tumor size is larger than 0.25 g, the contribution of NO in EPR effect is less pronounced. This implicates the importance of NO at the early stages of tumor growth (see text) (from [42] after modification)...

Gatteschi et al. [44] prepared linear chain polymers that were composed of M(hfac)2(NIT)R, where M is Cu(II), Ni(II), or Mn(II) (NIT)R is 2-alkyl-4,4,5,5-tetramethylimidazoline-l-oxyl-3-oxide and hfac is hexafluoroace-tylacetonate. Ferromagnetic ordering was observed for those polymers composed of Mn(hfac)2(NIT)Et (36) and Ni(hfac)2(NIT) Pr, respectively. The critical temperature for each polymer was 8.6 and 5.3 K, respectively. 

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