The Hydrogen Bonding Strategy. A New Approach Towards Purely Organic/Molecular Ferromagnets

Cirujeda, Joan; Hernandez-Gasio, Esteve; Panthou, Fabrice Lanfranc de; Laugier, J; Mas, M.; Molins, Elı́es; Rovira, Concepció; Novoa, Juan J.; Rey, P.; Veciana, Jaume

doi:10.1080/10587259508034033

Cited by 27 publications

(9 citation statements)

References 28 publications

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“…This CH···ON interaction has been already pointed out in several cases. ,,, Veciana et al. discovered that o -hydroxyphenyl nitronyl nitroxide ( o -HPNN) exhibits a ferromagnetic phase transition at 0.4 K 14a…”

Section: Discussionmentioning

confidence: 78%

“…This new nitronyl nitroxide derivative, 2-(2‘,5‘-dihydroxyphenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1 H -imidazolyl-1-oxyl 3-oxide (HQNN), carries a hydroquinone moiety as hydrogen-bonding site and affords two phases of hydrogen-bonded crystals (α- and β-HQNN). The α-HQNN, in particular, was found to exhibit a ferromagnetic phase transition at 0.5 K. Meanwhile, Veciana et al prepared several derivatives of phenyl nitronyl nitroxide derivatives substituted with hydroxy group(s). , In 1995, he reported the ferromagnetic phase transition of o -hydroxyphenyl nitronyl nitroxide ( T C = 0.45 K) 14a…”

Section: Introductionmentioning

confidence: 99%

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Hydrogen-Bonded Organic Ferromagnet

et al. 1997

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Nitronyl nitroxide derivatives carrying a hydroquinone or a resorcinol moiety 2-(2‘,5‘-dihydroxyphenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxyl-3-oxide (HQNN) and 2-(3‘,5‘-dihydroxyphenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxyl 3-oxide (RSNN)) have been designed and prepared. These compounds were found to afford hydrogen-bonded crystals. In the case of HQNN, two phases of crystals (α- and β-HQNN) were obtained. Of these, the crystal structure of α-HQNN is characterized by the intramolecular hydrogen bond between the o-hydroxy group and the nitronyl nitroxide and by the intermolecular one-dimensional hydrogen-bonded chain between the o- and p-hydroxy groups of the neighboring molecules, respectively. Two of the hydrogen-bonded chains run in parallel, and they are connected by the bifurcated hydrogen bonds formed between the o-hydroxy groups of the facing molecules in the individual chain. The χT value of this crystal increased monotonously with lowering temperature (ST model, J = +0.93 K, θ = +0.46 K) and turned out to exhibit a ferromagnetic phase transition at 0.5 K. On the basis of the heat capacity data, α-HQNN was found to be a three-dimensional ferromagnet. On the other hand, the crystal of β-HQNN was characterized by the intermolecular hydrogen-bonded chain formed between the hydroxy group at the meta position and the nitronyl nitroxide and by the interchain π−π stacking. The magnetic interaction of β-HQNN was interpreted by the ferromagnetic ST model, and this ferromagnetic interaction (J = +5.0 K) was accompanied by a weak antiferromagnetic interaction (θ = −0.32 K) at lower temperatures. Although the structural feature of the crystal of RSNN resembles that of the β-HQNN, it exhibited the antiferromagnetic interaction predominantly (ST model, J = +10.0 K, θ = −4.0 K). These magnetic behaviors are consistent with McConnell's theory, when the spin densities at the interacting sites connected by hydrogen bonds are taken into account. Thus, it may be concluded that the hydrogen bond plays a role not only in constructing hydrogen-bonded crystals but also in transmitting spin polarization along the hydrogen bond.

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Section: Discussionmentioning

confidence: 78%

Section: Introductionmentioning

confidence: 99%

Hydrogen-Bonded Organic Ferromagnet

et al. 1997

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“…Up to now electron resonance methods are most popular for the determination of spin densities. For instance, ESR spectroscopy has shown that in nitronylnitroxides much spin density is located at the two nitrogen atoms. , High-resolution ESR yields additional information on most of the hydrogen atoms, and this has been particularly useful for the hydroxyphenyl derivatives of the present study . However, the sign of the spin density could not be determined experimentally by ESR.…”

Section: Introductionmentioning

confidence: 87%

“…Nitronylnitroxides 2 − 6 were prepared following the general procedure described by Ullman et al ,13c,14c Selective exchange of phenolic hydrogens for deuterium to obtain 2 - d 1 , 3 - d 1 , and 4 - d 1 was effected by repeated recrystallization from EtOD. The products were freed from EtOD under vacuum, and traces were removed by recrystallization from methylenechloride.…”

Section: Methodsmentioning

confidence: 99%

Determination of the Spin Distribution in Nitronylnitroxides by Solid-State ¹H, ²H, and ¹³C NMR Spectroscopy

et al. 1999

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Nitronylnitroxide radicals substituted by 2‘-hydroxy-, 3‘-hydroxy-, 4‘-hydroxy-, and 4‘-methoxyphenyl groups and by a methyl group (2, 3, 4, 5, and 6, respectively) have been investigated in the solid state with 1H, 2H, and 13C NMR spectroscopy under magic angle spinning (MAS) and in solution with 1H and 2H NMR spectroscopy. Well-resolved 13C MAS NMR spectra have been recorded which show signals in ranges up to almost 1900 ppm. The 1H NMR signal spread does not exceed 60 ppm (except for a unique methyl signal of 6 near −230 ppm), and the resolution is worse than that of 13C NMR spectra. Narrower signals have been obtained with 2H NMR spectroscopy. The signals have been assigned with the help of various criteria including the results of ab initio calculations. From the NMR data it has been concluded that the nitronylnitroxide five-ring is puckered, thus rendering all substituents inequivalent. Signal coalescence at elevated temperatures has shown that these inequivalencies are partly averaged out while the puckering is maintained. Dynamics of this sort have not been observed when OH···ON bridges render the lattice more rigid. The spin densities at the carbon and hydrogen atoms have been obtained from the NMR data. They are in accord with theoretical results in the limit of approximation. The spin maps so obtained confirm that the polarization mechanism determines the spin distribution in 2−6. The distribution is modulated by hyperconjugation and competing polarization paths. It is concluded that solid-state NMR spectroscopy may be an alternative to polarized neutron diffraction in evaluating the spin distribution in radicals. The weak and strong points of the method are discussed.

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“…For the purely organic species, the effect of the hydrogen bonds on the relative orientation of the spin carriers and their participation in the magnetic exchange interactions provides useful information. [1][2][3][4][5][6][7][8][9][10][11] Specifically, the hydrogen bonds can modulate properties by avoiding proximity of NO groups, for example, by involving them in intra-or inter-molecular interactions, [12][13][14][15][16] e.g. in crystals of nitronyl nitroxides derived from triazole 17 and imidazole.…”

Section: Introductionmentioning

confidence: 99%

Polymorphs of a pyrazole nitronyl nitroxide and its complexes with metal(ii) hexafluoroacetylacetonates

et al. 2006

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The synthesis of pyrazol-4-yl nitronyl nitroxide is reported, along with the crystal structures of its polymorphs and coordination compounds with nickel(II) and cobalt(II) hexafluoroacetylacetonate. The polymorphic forms of the pure radical show very different magnetic properties: the alpha form shows only antiferromagnetic interactions while those of the beta form reveal competing ferro-and anti-ferromagnetic interactions. This phenomenon can be traced to the relative orientations of the spin carriers in the crystal. These, in turn, are determined in large measure by the hydrogen bonding networks, where a competition between [N-H … O] and [N-H … N] hydrogen bonds is observed. This delicate balance is also seen in the coordination chemistry of the radical acting as a ligand for the hexafluoroacetylacetonate complexes of nickel(II) and cobalt(II). In the former, a 2 : 1 radical : metal complex is formed because of coordination of the pyrazolyl nitrogen atom only. In the latter, a cyclic dimer is formed which involves both the nitrogen and oxygen as coordinating atoms. In both cases, the NH groups of the pyrazolyl moiety lead to the formation of hydrogen bonded networks in the crystals. The magnetic properties of the complexes reveal antiferromagnetic interactions. However, the pyrazolyl nitronyl nitroxide has been proven an interesting component for the formation of coordination compounds with hydrogen bonds in between the magnetic components.

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The Hydrogen Bonding Strategy. A New Approach Towards Purely Organic/Molecular Ferromagnets

Cited by 27 publications

References 28 publications

Hydrogen-Bonded Organic Ferromagnet

Hydrogen-Bonded Organic Ferromagnet

Determination of the Spin Distribution in Nitronylnitroxides by Solid-State ¹H, ²H, and ¹³C NMR Spectroscopy

Polymorphs of a pyrazole nitronyl nitroxide and its complexes with metal(ii) hexafluoroacetylacetonates

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The Hydrogen Bonding Strategy. A New Approach Towards Purely Organic/Molecular Ferromagnets

Cited by 27 publications

References 28 publications

Hydrogen-Bonded Organic Ferromagnet

Hydrogen-Bonded Organic Ferromagnet

Determination of the Spin Distribution in Nitronylnitroxides by Solid-State 1H, 2H, and 13C NMR Spectroscopy

Polymorphs of a pyrazole nitronyl nitroxide and its complexes with metal(ii) hexafluoroacetylacetonates

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Determination of the Spin Distribution in Nitronylnitroxides by Solid-State ¹H, ²H, and ¹³C NMR Spectroscopy