Meixiang Wan

Experimental spin density in the first purely organic ferromagnet : the β para-nitrophenyl nitronyl nitroxide

Abstract A purely organic ferromagnet, the β form of the para-nitrophenyl nitronyl nitroxide (p-NPNN), was investigated by conventional and polarized neutron diffraction. Several approaches were used to reconstruct the spin density distribution in the radical. Quantitative results in the form of atomic spin populations were obtained, and are discussed in comparison with those previously obtained experimentally for a related phenyl-substituted nitronyl nitroxide. The spin delocalization and/or spin polarization effects are responsible for the transfer of the spin density to the nitrophenyl group. In the framework of the McConnell mechanism these effects play a key role in the intermolecular ferromagnetic interaction, which passes through both the nitro and the phenyl fragments. Hartree-Fock-based ab initio theoretical spin densities found in the literature are inconsistent with the experimental results.

Doped polyaniline with C60

Abstract The electronic structure and the electrical properties of polyaniline (PANI) doped with C 60 were measured as a function of the concentration of C 60 molecules and preparation conditions. For lower C 60 concentration (less than 1.0 mol. %), a series of experimental results suggests that the enhanced conductivity of PANI-C 60 composites may be due to acid doping PANI in air. For higher C 60 concentrations (10–20 mol. %), however, the charge transfer between PANI and C 60 molecules in PANI-C 60 composites was observed from UV-Visible absorption and the FTIR spectrum. Poor conductivity of PANI-C 60 composites at room temperature may be attributed to a low degree of doping and the large size of C 60 molecules as dopants, which results in a decrease in the conductivity along and between the PANI polymer chains.

Neutron diffraction observation of a ferromagnetic phase transition in a purely organic crystal

Abstract The ferromagnetic phase transition was observed by zero field neutron diffraction for the first time in a purely organic material, the β form of the para- nitrophenyl nitronyl nitroxide p-NPNN. The direction of spontaneous magnetization along the 19A crystallographic axis proposed by previous zero field muon spin rotation experiments is consistent with our results. The observed increase of Bragg intensity below TC is in agreement with the value expected from previous polarized neutron diffraction studies.

Reinvestigation of the magnetic properties of the Schiff-base polymer with iron (II) sulfate

Abstract The magnetic properties of the Schiff-base polymer with iron (II) sulfate have been reinvestigated. Nanocrystalline impurities of magnetite, corresponding to about 3% of the total weight, have been witnessed by mean of X-ray diffraction and Mossbauer spectroscopy and are responsible for the unusual magnetic properties observed in this metal-organic polymer. The average size of these particles is found to be in the 15–20 nm range.

Protonic doping in free-standing film of polyaniline

Abstract An influence of the protonation state on the conductivity at room temperature, activation energies, WPS, ESR and UV-Visible absorption spectra for free standing film of polyaniline (PANI) was measured. All results obtained are in agreement with the model of conducting island, which metallic islands is due to polaron formed by protonation processes and seperated by insulating medium.

Magnetic properties of doped polyaniline with tetrachloferrate counter-ions

Abstract The structure of doped polyaniline (PANI) with FeCl 4 − counter-ions was characterized by elemental analysis, FTIR, XPS and X-ray diffraction, and its magnetic properties were investigated by ESR, Mossbauer and magnetization measurements. The temperature dependence of the magnetic susceptibility (χ) of doped PANI-FeCl 4 − exhibits a Cuire-Weiss law with a negative Weiss constant ( θ = −2.61 K). This suggests that an antiferromagnetic interaction in doped PANI-FeCl 4 − is taking place. It may be due to an interaction between the d -electrons of the ions and π-electrons of the PANI polymer chain.

The Experimental Spin Density of Two Nitrophenyl Nitroxides: A Nitronyl Nitroxide and an Imino Nitroxide

Abstract We have determined, by polarized neutron diffraction, the spin density of two nitrophenyl nitroxides: the para-nitrophenyl nitronyl nitroxide (p-NPNN), which is a ferromagnet at low temperature, and the meta-nitrophenyl imino nitroxide (m-NPIN), which exhibits antiferromagnetic coupling. Several methods were used to reconstruct the spin density distribution, including the maximum entropy method. Our data provide the basis for a better knowledge of the electronic configuration. The nodes of the SOMO are directly observed and the spin polarization effects which give rise to a negative spin density on several atomic sites is discussed.

Neutron diffraction studies of the first purely organic ferromagnetic crystal

Abstract The first purely organic ferromagnetic material, the β form of the para-nitrophenyl nitronyl nitroxide p-NPNN, was studied by single crystal neutron diffraction. A zero field unpolarized neutron experiment performed in the temperature range 50–800 mK provides the first direct evidence of spontaneous ferromagnetic bulk ordering below T C = 0.67 K. The data obtained in the polarized neutron experiment was used to reconstruct the spin density distribution and explain the mechanisms of magnetic interaction.

Crystal structures of NTDIOO derivatives

Abstract Crystal and molecule structures of two NTDIOO derivatives have been determined by means of X-ray diffraction. Crystal 3: C15H18N3O4, Mw = 304, monoclinic, space group P2 1 a , with following unit cell parameters: a = 27.457(10) A , b = 7.419(4) A , c = 7.664(4) A , β = 97.82°, V = 1547.1(1.8) A , Z = 4. The final R is 0.085 for 1032 independent reflections with |F0| > 4σ(F0). Crystal 5: C17H20N3O4, Mw = 330, monoclinic, space group P2 1 n , with following unit cell parameters: a = 22.920(6) A , b = 6.133(4) A , c = 12.005(4) A , β = 98.59°, V = 1669.8(2.1) A 3 , Z = 4. The final R is 0.085 for 1010 independent reflections with |F0| > 3σ(F0). The probable relationship between the magnetic properties of these nitronyl nitroxides and crystal structures has been discussed.

Synthesis, characterization and magnetic properties of NTDIOO derivatives☆

Three kinds of NTDIOO derivatives contained carbon-carbon double bonds were synthesized and their molecular structures were characterized by means of elemental analysis, IR, ESR, and UV-vis absorption spectra. All magnetic measurements for NTDIOO derivatives show that antiferromagnetic interactions existed in these derivatives. Results obtained in this paper suggest that both spin polarization and conjugated effects for NTDIOO system might not be a main factor to contribute the ferromagnetic interaction. However, the distance between spin and the displacement of radicals in the crystal is a main factor for ferromagnetic coupling in NTDIOO system.