Intermolecular Magnetic Interactions Research Articles

Novel magnetic interactions in the open-shell NO–HF complex

The J ′=3/2 (f)− J ″=1/2 (f) rotational transition of the open-shell van der Waals complex NO–HF has been observed using a Fourier transform microwave spectrometer. The transition shows a rich hyperfine structure due to coupling of the NO electronic spin and orbital angular momenta with the N nucleus and also with both the H and F nuclei in a novel intermolecular magnetic hyperfine interaction. The N hyperfine coupling reveals the splitting of the Π state degeneracy into A ′ and A ″ states, with the A ′ state lower in energy.

Orbital Interaction Analysis of McConnell's Model for Through-Space Magnetic Coupling

McConnell's model for through-space magnetic interaction can be interpreted from the vantage point of molecular orbital interactions. Intermolecular magnetic interactions are analyzed in several stacking modes of diphenylmethyl radical. The nodal properties which lead to the overlap (or lack of it) of the singly occupied molecular orbitals in this system play an essential role in the ferromagnetic coupling of molecules in extended systems. These nodal characteristics, and the overlaps governing orbital interaction are as important as the spin-polarization effects.

Synthesis and Magnetic Characterization of Metallocene-Substituted α-Nitronyl Nitroxide Radicals

The synthesis and magnetic characterization of a series of α-metallocenyl nitronyl nitroxide monoradicals (M = Fe, Ru, Os) are reported. Intra- and intermolecular magnetic interactions in this series of compounds have been studied in detail by ESR spectroscopy and magnetic measurements. ESR spectra of monoradicals in dilute solutions under isotropic conditions show a small spin density on the metal centers. In the solid state, the radicals derived from ferrocene and ruthenocene show a paramagnetic behavior with very weak antiferromagnetic intermolecular interactions, as ascertained from magnetic susceptibility measurements. This behavior is rationalized, for the ferrocene derivative, by means of its crystal structure.

Role of Jahn-Teller Distortion in Magnetic and Optical Properties of TDAE-C 60

A model for ferromagnetism of TDAE-C 60 is proposed. It is based on charge-transfer induced intramolecular Jahn-Teller (CTJT) distortion and intermolecular cooperative Jahn-Teller (CJT) distortion, and ferromagnetism is caused by orbital ordering. The relation between intermolecular magnetic interaction and orientations of distorted C 60 molecules is discussed. Possible JT-distorted crystal structures which are likely to exhibit three-dimensional ferromagnetic ordering are proposed, and suggestions are made as to X-ray, Raman and neutron diffraction measurements which may confirm the proposed structures.

Organic Ferromagnets. Hydrogen Bonded Supramolecular Magnetic Organizations Derived from Hydroxylated Phenyl ?-Nitronyl Nitroxide Radicals

The capacity of hydrogen bonds as crystalline design elements for the prepara- tion of solid state supramolecular organizations with relevant magnetic properties is reviewed. It will be shown here that hydrogen bonds fuIfiII two distinct purposes. One function is a struc- tural one through which is possible to central up to certain level the relative arrangements of radical molecules. The other rote of hydrogen bonds is a magnetic one smce these bonds intro- duce proper pathways for the transmission of intermolecular magnetic interactions. Using this methodological approach several molecular magnetic solids have been prepared with hydroxy- Iated phenyl a-nitronyl nitroxide radicals. These molecular sohds are formed by supramolecular motifs (dimers, chains, and planes) bonded by strong hydrogen bonds which are hnked to each other by other weak forces that form the rest of the crystals. Consequently, the solids show different structural dimensionalities that in some cases do trot agree with trie magnetic ones. Accordingly with such distinct structural and magnetic dimensionalities, the resulting molecu- Iar solids show a wide variety of magnetic behaviors. Remarkable are the purely organic 2-D and 3-D ferromagnets reported here. Finally, the most relevant mechanisms explaining inter- moIecuIar magnetic interactions as weII as the most promismg applications expected for purely orgamc magnets are aise mcluded.

Nuclear spin conversion in molecules: Experiments on 13CH3F support a mixing-of-states model.

Using light-induced drift as a tool to separate nuclear spin isomers, we have studied the ortho-para conversion process for gaseous $^{13}\mathrm{CH}_{3}$F interacting with ${\mathrm{O}}_{2}$, ${\mathrm{N}}_{2}$, ${\mathrm{CH}}_{3}$Cl, and ${\mathrm{CH}}_{3}$F itself. It is found that the conversion rate is significantly smaller for collisions with ${\mathrm{O}}_{2}$ or ${\mathrm{N}}_{2}$ than with ${\mathrm{CH}}_{3}$Cl or ${\mathrm{CH}}_{3}$F. The data show that intermolecular magnetic interactions do not play a leading role in the conversion. In order to test an alternative model based on mixing of states due to intramolecular interactions, pressure broadening has been measured for these systems. The observed correlation between conversion rates and broadening coefficients supports this mixing-of-states model. \textcopyright{} 1996 The American Physical Society.

Pressure effects on intermolecular interactions of the organic ferromagnetic crystalline beta -phase p-nitrophenyl nitronyl nitroxide.

The pressure effects on intermolecular magnetic interactions in a prototype and genuine organic ferromagnet, \ensuremath{\beta}-phase crystal of p-nitrophenyl nitronyl nitroxide, have been studied by the simultaneous measurements of magnetic susceptibility and heat capacity under the hydrostatic pressure of the range 0--7.7 kbar. A reduction of the Curie temperature from 0.61 K at an ambient pressure to 0.35 K at 7.2 kbar has been observed. This makes a significant contrast to the pressure-induced enhancement of the N\'eel temperature of organic antiferromagnets. The reduction of exchange interactions in the present compound is verified by the estimation of the ground-state energy under the pressures. Another remarkable feature of the results is a lowering of magnetic lattice dimensionality under pressure; the heat capacity curve under the pressure P=7.2 kbar shows the short-range-ordering behavior expected of a low-dimensional Heisenberg ferromagnetic above the Curie temperature. This suggests that the interactions between the adjacent ac planes are relatively weakened to other interactions in the compressed crystal. These observed results are interpreted in terms of the virtual charge transfer mechanism rather than pressure effects on the dipolar interactions. \textcopyright{} 1996 The American Physical Society.

Intermolecular versus intramolecular interactions in nuclear spin conversion: Experiments on 13CH3F–O2

Ortho–para conversion for gaseous 13CH3F is measured in mixtures with O2. As collision partner, O2 is found to be 4 times less efficient for conversion that CH3F itself. This demonstrates that intramolecular rather than intermolecular magnetic interactions provide the main pathway leading to nuclear spin conversion for such molecules.

The role of orbital interactions in determining ferromagnetic coupling in organic molecular assemblies

McConnell's model for through-space magnetic interaction can be interpreted from the vantage point of molecular orbital interactions. Intermolecular magnetic interactions are analyzed in several stacking modes of allyl, diphenylmethyl, and nitroxide radical systems. The nodal properties which lead to the overlap (or lack of it) of the singly occupied molecular orbitals in these systems play an essential role in the ferromagnetic coupling of molecules in extended systems. These nodal characteristics and the overlaps governing orbital interaction are as important, we argue, as the spin-polarization effects from electron correlation.

The importance of hydrogen bonds in the crystal packing of polyhydroxylated α-phenyl nitronyl nitroxides

We report the main geometric characteristics of strong hydrogen bonds found between the OH and the NO groups in a series of single crystals of mono and dihydroxylated α-phenyl nitronyl nitroxides. The strong directionality observed for such hydrogen bonds in this family of radicals permits the formation of well defined supramolecular structures and consequently this strategy can be a useful tool for the obtainment of designed intermolecular magnetic interactions.

Molecular flexibility demonstrated by paramagnetic enhancements of nuclear relaxation. Application to alamethicin: a voltage-gated peptide channel

A nitroxide spin label attached to the C-terminus of the channel forming peptide alamethicin produces an enhancement of the nuclear spin-lattice relaxation rates of peptide protons as a result of both intermolecular and intramolecular magnetic dipole-dipole interactions. The intermolecular contribution provides evidence that alamethicin monomers collide preferentially in a C-terminal-to-N-terminal configuration in methanol. From the intramolecular paramagnetic enhancement of nuclear spin-lattice relaxation times, effective distances between the unpaired electron on the nitroxide at the C-terminus of alamethicin and protons along the peptide backbone were calculated. These distances are much shorter than distances based on the reported crystal structure of alamethicin, and cannot be accounted for by motion in the bonds that attach the nitroxide to the peptide. In addition, the differences between distances deduced from the nuclear spin relaxation and the distances seen in the crystal structure increase toward the N-terminal end of the peptide. The simplest explanation for these data is that the alamethicin backbone suffers large structural fluctuations that yield shorter effective distances between the C-terminus and positions along the backbone. This finding can be interpreted in terms of a molecular mechanism for the voltage-gating of the alamethicin channel. When the distances between a paramagnetic center and a nucleus fluctuate, paramagnetic enhancements are expected to yield distances that are weighted by r-6, and distances calculated using the Solomon-Bloembergen equations may more nearly represent a distance of closest approach than a time average distance. Therefore, the use of paramagnetic centers such as spin labels or metal ions with long electron T1 values provides a distance measurement that reflects a dynamically averaged structure where the averaging process heavily weights short distances. The results of such measurements, when combined with other structural information, may provide particularly clear evidence for the magnitude of structural fluctuations involving distances greater than 10 A.

Bimetallic Derivatives of [M(en)3]3+ Ions (M = Cr, Co): An Approach to Intermolecular Magnetic Interactions in Molecular Magnets

The research in Zaragoza and Barcelona has been supported respectively by Grants 3380183, 409184, MAT88/0174, and MAT911681 from the Comision Asesora de Investigacion Cientifica y Tecnica of the Ministerio de Educacion y Ciencia. The research in Chicago has been supported by Grant DMR-8515224 and DMR-8815798 from the Solid State Chemistry Program, Division of Materials Research of the National Science Foundation. The cooperative work has been supported by Grant CCB-8504/001 from the American-Spain Joint Committee for Technical and Scientific Cooperation.

Optical And Magnetic Properties Of Rigid Rod Conjugated Molecules

ABSTRACTA series of new stable fiinctionalised aryl ethynyl compounds bearing nitronyl-nitroxy and galvinoxyl radicals were synthesised as potential organic magnets with optical properties. Our goal is to construct biradicals in linear or broken rod molecules with the aim of probing i) the efficiency of the conjugation for the intramolecular spin exchange, and / or ii) the inter-Molecular Magnetic interaction between the neighboring radicals in the solid state Materials.We focused our attention on the preparation of phenoxy, and galvinoxyl biradicals of the conjugated phenyl and thienyl diethynyl Moieties. The synthesis of these new components will be presented. Their optical and magnetic properties will be discussed both in solution and in the solid state.

Iron(II) complexes of ortho-functionalized naphthoquinones. 2. Crystal and molecular structure of bis(aquo)bis(lawsonato)iron(II) and intermolecular magnetic exchange interactions in bis(3-aminolawsonato)iron(II)

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTIron(II) complexes of ortho-functionalized naphthoquinones. 2. Crystal and molecular structure of bis(aquo)bis(lawsonato)iron(II) and intermolecular magnetic exchange interactions in bis(3-aminolawsonato)iron(II)Prafulla Garge, Rajeev Chikate, Subhash Padhye, Jean Michel Savariault, Philippe De Loth, and Jean Pierre TuchaguesCite this: Inorg. Chem. 1990, 29, 18, 3315–3320Publication Date (Print):September 1, 1990Publication History Published online1 May 2002Published inissue 1 September 1990https://doi.org/10.1021/ic00343a012RIGHTS & PERMISSIONSArticle Views276Altmetric-Citations68LEARN 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 (798 KB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

Magnetic Phenomena in Molecular Solids: A Tutorial Approach

Abstract Some basic concepts in magnetism are discussed in the context of molecular solids. A brief outline about the experimental techniques useful to investigate these new magnetic materials is given, with special emphasis in the a.c. susceptibility technique. The basic idea that bulk magnetism can only be achieved by means of inter-molecular magnetic interactions is outlined after explaining the thermodynamic fundamentals of magnetic ordering. Some extension is devoted to account for the phenomena associated with superparamagnetism, since very high spin molecules may exhibit these magnetic properties in the absence of inter-molecular interactions. Finally, some fundamental properties of ferromagnetic materials are commented on discussing how they might affect to molecular ferromagnets.

Intermolecular Magnetic Interaction in the Crystal of Bis(p-decyloxy-phenyl) Nitroxide

Intermolecular Magnetic Interaction in the Crystal of Bis(p-decyloxy-phenyl) Nitroxide

Direct synthesis, spectral and magnetic properties of trans-aniono(1,4,10,13-tetraoxa-7,16-diazacyclooctadecane-7-acetato) copper(II) complexes

7-Carboxymethyl-7,16-diaza-18-crown-6 acid hydrates (LH·H 2O) and their copper(II) complexes [CuLX], (X = Cl, Br, NO 3, ClO 4 and CH 3CO 2) were obtained. The earlier X-ray investigation of the [CuLCl] complex, as well as the IR and UV-vis spectral evidence for the complexes revealed the inner chelate structure with the six-coordinated copper(II) ion embedded inside the macrocyclic ligand (deformed octahedral, 4+2, N,N, CO 2 −,X −,O,O-coordination sphere) and the trans arrangement of the CO 2 and X ligands. The spectral data, the conductivity measurements and the chemical properties show the existence of the macrocyclic inclusion cation [CuL] + and the formulation of the complexes as the [(CuL) +X −] inner salts. The magnetic moments of the complexes amount to 1.76–1.83 BM at room temperature and 1.3–0.92 BM at 4.2 K. These results revealed the monomeric form of the complexes with the occurrence of the intermolecular (through space) magnetic super-exchange interactions of copper(II) paramagnetic centres.

Frequency dependence of the effects of eccentricity on nuclear magnetic relaxation in liquids. 13C relaxation of neopentane due to free radicals

Measurements of the relaxation time T 1 of the central and of the four equivalent off center 13C nuclei in neopentane, C(CH 3) 4, were performed in solutions containing di- tert-butyl nitroxide free radicals. In such systems, the intermolecular dipole magnetic interaction with the electronic spins of the free radicals is the only efficient relaxation mechanism for the resonating 13C nuclei. The difference between the relaxation times of the central and of the off-center carbons was measured at three different resonance frequencies (15, 25, and 63 MHz) at T = 303 K. It is shown that spin exchange has a negligible effect and the results are interpreted using the spectral densities resulting from the molecular translational and rotational motions as we established previously. It is shown that the effects of eccentricity cannot be explained with a uniform equilibrium distribution of the interacting molecules. It is essential to take into account pair correlation effects and the translational diffusive motion of the molecules must be described by a Smoluchowski equation. Good agreement with experiment is then obtained for the relaxation times and the effects of eccentricity.

Magnetic interactions between nitroxide free radicals and lanthanides or Cu2+ in liquids

Heisenberg exchange has been found in all previous work to be the dominant intermolecular magnetic interaction between paramagnetic species in solutions of low viscosity, and this conclusion is confirmed here in analysis of interactions between Cu2+ and a nitroxide free radical. Exchange between a fast relaxing metal ion and a slow relaxing radical contributes equally to the transverse and longitudinal relaxation probabilities, T−12 and T−11, of the radical. A new result that could be of significance in investigations of molecular dynamics in liquids is that dipole–dipole interactions between ions of the lanthanide series and free radicals are dominant in all conditions over Heisenberg exchange. In the liquid phase, Gd3+ is particularly effective in inducing free radical longitudinal relaxation.

Proton-spin-lattice relaxation and self-diffusion in methanes: II. Experimental results for proton-spin-lattice relaxation times

The proton-spin-lattice relaxation time T 1 has been measured in CH 4 and deuteroderivates and in mixtures of CH 4 and CD 4, using a spin-echo spectrometer. Both temperature and density were varied over a wide range (77–300 K, density up to 550 amagat), covering the gaseous, liquid and solid phases. From T 1 in CH 4-CD 4 mixtures the contribution of intermolecular magnetic dipole-dipole interactions to the relaxation rate in liquid and solid CH 4 is calculated.