Ferromagnetic Intermolecular Interactions Research Articles

Control of the structural dimensionality in hydrogen-bonded self-assemblies of open-shell molecules. Extension of intermolecular ferromagnetic interactions in α-phenyl nitronyl nitroxide radicals into three dimensions

The variation of the number and position of OH substituents at the phenyl ring of α-phenyl nitronyl nitroxide radicals yields different hydrogen-bonded molecular self-assemblies with distinct dimensionalities; the mono-ortho-substituted isomer is most remarkable since it shows a three-dimensional network of weak hydrogen bonds exhibiting a bulk ferromagnetic transition at 0.45 K.

Coexistence of intermolecular ferromagnetic interaction and [NHN]+ hydrogen bond in N-protonated m-pyridyl nitronyl nitroxide

Reaction of 2-(3-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-1-oxyl 3-N-oxide (m-PYNN) and HBr gas gives rise to the complex (m-PYNN)2HBr, in which the coexistence of an intermolecular ferromagnetic interaction and an [NHN]+ hydrogen bond is found.

Two-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-1-H-imidazol-1-oxyl 3-N-oxide, abbreviated as p-CNPNN] radical has been solved. It belongs to the orthorhombic system, space group Ic2a, with a= 10.482(2)A, b= 26.615(5)A, c=9.903(2)A 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 squarelattice Heisenberg model with J/kB= 0.75 K. Two-dimensionality of the crystal is also confirmed by single-crystal electron paramagnetic resonance (EPR) spectra.

Role of hydrogen bonds in the propagation of ferromagnetic interactions in organic molecular solids. Part 1.—The p-hydroxyphenyl α-nitronyl aminoxyl radical case

The role of hydrogen bonds in the obtention of magnetic molecular materials is investigated in a purely organic openshell molecular solid. The structural and magnetic properties of the 2-(4-hydroxyphenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-yloxyl 3-oxide radical (1) are studied in detail. The intermolecular hydrogen bonds in 1 are found to be able to control the crystal packing (i.e. the relative disposition of the radical molecules within the crystal lattice) and, at the same time, to propagate ferromagnetic intermolecular interactions along certain directions of the solid. Molecular orbital (MO) calculations, structural studies about the crystal packing, static magnetic susceptibility measurements, electron paramagnetic resonance (EPR) solution spectra and a detailed EPR study of an oriented single crystal of the title compound are presented and discussed. All these studies point strongly towards the fact that this material behaves as a quasi-two-dimensional ferromagnet, in which hydrogen bonds of O–H ⋯ O–N and C–H ⋯ O–N types are found to be responsible for the ransmission of the ferromagnetic interactions within the (a, b) crystallographic plane.

Ferromagnetic intermolecular interaction of the cation radical of m-N-methylpyridinium nitronyl nitroxide. A CASSCF study

Semi-empirical APUHF and ab initio UNO CASSCF/4-31G calculations have been carried out for the dimer of m-N-methylpyridinium nitronyl nitroxide cation ( m-MPYNN +) extracted from its experimental crystal structure in order to elucidate the origin of the large ferromagnetic effective exchange integral | J ab|. It is found that the sign of the calculated J ab is positive, and its magnitudes are 6.51 and 3.96 cm −1 by these methods, which correspond to about 80 and 50% of the experimental value, respectively. The dynamic spin polarization plays an important role in determining the sign of J ab, whereas the short intermolecular contact induced by the Coulombic attraction is reponsible for the large J ab. Implications of the calculated results are discussed in relation to the possibilities of high- T c organic ferromagnets and organic helimagnets.

Ferromagneto‐Structural Correlations in [Mn(OC6X3H2)2(bipy)]2 Compounds, X  Cl, Br

Intra- and intermolecular ferromagnetic interactions characterize the dimeric manganese complexes 1 and 2. This unexpected behavior is attributed to π-π interactions between the phenoxy ligands, to π-π interactions within the chains present in the crystal, and for 2, in addition, to π-π interactions between bromine atoms of neighboring chains. These findings should be useful for the design of molecular magnetic materials.

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

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.

ChemInform Abstract: Molecular and Crystal Engineering in the Design of Organic Solids with Ferromagnetic Intermolecular Interactions

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Pyrimidines as Ferromagnetic Exchange Couplers in Dinuclear Oxovanadium(IV) Complexes

Abstract The intramolecular magnetic interactions between 1/2 spins of two oxovanadium(IV) ions were studied in the complexes L[VO(hfac)2]2 (hfac = hexafluoroacetylacetonate, L = 4-methyl-, 4,6-dimethyl-, 4-amino- and unsubstitute-pyrimidines, and quinazoline). The magnetic measurements revealed that the vanadium spins were ferromagnetically coupled through the pyrimidine bridges with J/kB = 1.1–2.7 K. The intermolecular ferromagnetic interaction was found in the case of L = pyrimidine.

Magnetic properties and crystal structure of the p-fluorophenyl nitronyl nitroxide radical crystal: ferromagnetic intermolecular interactions leading to a three-dimensional network of ground triplet dimeric molecules

The crystal of p-fluorophenyl nitronyl nitroxide [2-(4-fluorophenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-1-oxyl 3-oxide, abbreviated as p-FPNN] radical has been found to possess a dimeric structure. Each dimer is related to adjacent ones by four-fold screw symmetry to form a three-dimensional network. The temperature dependence of the paramegnetic susceptibility is explained by the formation of a triplet state within the dimer and additional interdimer ferromagnetic interactions. The intra- and inter-dimer exchange interactions are estimated to be J/kB= 5.0 K and J′/kB= 0.02 K, respectively. The molecular arrangement in the dimer suggests that the intermolecular interactions between the NO group and the phenyl ring are favourable to ferromagnetic coupling. Slight structural changes below ca. 100 K have been studied by use of electron paramagnetic resonance and powder X-ray diffraction measurements.

Magnetic properties of 1,5-dimethylverdazyl radicals. I. Evidence for the ferromagnetic exchange interaction in 3-(4-chlorophenyl)-1,5-dimethyl-6-thioxoverdazyl radical solid

Magnetic susceptibilities of 3-(4-chlorophenyl)-1,5-dimethyl-6-thioxoverdazyl ( p-CDTV) and 3-(4-bromophenyl)-6-thioxoverdazyl ( p-BDTV) radicals have been measured in the temperature range between 4.0 and 300 K. The susceptibility of p-CDTV follows the Curie—Weiss law with a Curie constant of 0.381 K emu/mol and a positive Weiss constant of θ = + 3.2 K, suggesting intermolecular ferromagnetic exchange interaction between neighboring radicals. On the other hand, the magnetic susceptibility of p-BDTV exhibits a broad maximum at 26.5 K. This susceptibility can be explained by the one-dimensional Heisenberg model with negative exchange interaction of 2 J/ k= −41.3 K.

Crystal structures and magnetic properties of a nitronyl nitroxide and of its imino analog. Crystal packing and spin distribution dependence of ferromagnetic intermolecular interactions

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTCrystal structures and magnetic properties of a nitronyl nitroxide and of its imino analog. Crystal packing and spin distribution dependence of ferromagnetic intermolecular interactionsFabrice Lanfranc de Panthou, Dominique Luneau, Jean Laugier, and Paul ReyCite this: J. Am. Chem. Soc. 1993, 115, 20, 9095–9100Publication Date (Print):October 1, 1993Publication History Published online1 May 2002Published inissue 1 October 1993https://doi.org/10.1021/ja00073a027RIGHTS & PERMISSIONSArticle Views283Altmetric-Citations78LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (665 KB) Get e-AlertsSupporting Info (2)»Supporting Information Supporting Information Get e-Alerts

Spin Correlations in Organic Radical Magnets

Abstract The Electron Paramagnetic Resonance (EPR) technique is described as a valuable tool in order to probe the spin correlations in π-radical magnets. The peculiar features of the EPR response of low dimensional exchange coupled spin systems are recalled. The extreme sensitivity of the resonance field to both magnetic and dipolar interactions is emphasized. The example materials include phthalocyanine radical derivatives and nitronyl nitroxide radical derivatives. Both exhibit either anti ferromagnetic or ferromagnetic intermolecular interactions.

Molecular and Crystal Engineering in the Design of Organic Solids with Ferromagnetic Intermolecular Interactions

Abstract A brief account on organic solids showing ferromagnetic (FM) intermolecular interactions is given, paying special attention to the crystal design involved. In addition, new crystal engineering approaches are proposed in order to obtain FM couplings between organic free radicals.

α-Nitronyl Nitroxide Cation Radicals: Crystal Engineering for the Molecular Based Organic Ferromagnetism

Abstract Magnetic properties and crystal structures of N-alkylpyridinium α-nitronyl nitroxide cation radicals, has been studied. Some of them have been found to have ferromagnetic intermolecular interaction which are much stronger than those in the α-nitronyl nitroxide free radicals. Further, a m-N-methyl-pridinium α-nitronyl nitroxide salt crystallizes into a trigonal space group with a triangular lattice, which includes both of the ferromagnetic and antiferromagnetic interactions.

Ferro- and Anteferromagnettc Interactions and Crystal Structures of Some Organic Radicals Based on Nitronyl Nitroxide

Abstract Our recent results of magnetization, susceptibility and electron paramagnetic resonance (EPR) measurements and crystal structure determinations for the organic radiclals based on a-nitronyl nitroxide are described. The 3-quinolyl derivative with ferromagnetic intermolecular interaction shows a considerable shift of resonance field in EPR at low temperature probably due to short-range magnetic-order formation. The p-diethylaminophenyl derivative is characterized as a typical one-dimensional Heisenberg antiferromagnet.

Intermolecular Ferromagnetic Interaction of 4-Benzylideneamino-2,2,6,6-tetramethylpiperidin-1-oxyl

Abstract The magnetic properties of a polycrystalline sample of the title compound were studied on a SQUID magnetometer. The intermolecular ferromagnetic interaction was indicated by the upward deviation of the magnetization curves from a Brillouin function with S = 1/2 below 16 K and by the increasing effective moment with decreasing temperature. The Weiss constant was + 0.7 K. The radicals possessing a 9-anthryl or 3-perylenyl group in place of the phenyl group showed anitiferromagnetic interaction.

Hydrogen Bonds as a Crystal Design Element for Organic Molecular Solids with Intermolecular Ferromagnetic Interactions

Hydrogen Bonds as a Crystal Design Element for Organic Molecular Solids with Intermolecular Ferromagnetic Interactions

Intermolecular Ferromagnetic Interaction of 4-(2-Naphthylmethyleneamino)-2,2,6,6-tetramethylpiperidin-1-oxyl

Abstract The magnetic susceptibility and magnetization of a polycrystalline sample of the title compound were measured on a Faraday balance and a SQUID susceptometer. The intermolecular ferromagnetic interaction was indicated by the facts that the χmolT value increased with decreasing temperature and that the magnetization measured at 1.7 and 4.2 K saturated more rapidly than that of a Brillouin function with S = 1/2.

Ferro- and antiferromagnetic intermolecular interactions in the aromatic heterocyclic derivatives of α-nitronyl nitroxide

Magnetization isotherms up to 5.5 T and temperature dependence of magnetic susceptibility down to 1.8 K of the organic neutral radicals, 3- and 4-quinolyl nitronyl nitroxide and 2,6-pyridinediyl bis(nitronyl nitroxide), are described. 3-quinolyl nitronyl nitroxide exhibit ferromagnetic intermolecular interaction with the Weiss constant Θ = 0.27 K, whereas 4-quinolyl nitronyl nitroxide shows antiferromagnetic intermolecular interaction with the exchange coupling constant J/k = −7.8 K. This significant difference between the magnetic properties of two compounds are discussed in terms of their crystal structures. The temperature dependence of product of paramagnetic susceptibility and temperature, χ pT, of a biradical 2,6-pyridinediyl bis(nitronyl nitroxide) shows a plateau at low temperatures in addition to the usual plateau observed in the high-temperature region. This peculiar behavior is interpreted in terms of the multi-spin system associated with a combined effect of ferro- and antiferro-magnetic couplings.