Hyperfine structure of ESR spectra as a probe for heisenberg exchange couplings in nitroxide triradicals serving as building blocks for molecule-based ferrimagnets

Shiomi, Daisuke; Kaneda, C.; Kanaya, T.; Sato, Kazunobu; Takui, Takeji

doi:10.1007/bf03166637

Cited by 8 publications

(12 citation statements)

References 35 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…It is feasible to determine the magnitude of exchange interaction | J intra | in this range of energy from the hyperfine splitting pattern. Thus, the hyperfine splitting patterns have been a spectroscopic “probe” for intramolecular exchange interactions in metal-containing proteins, spin-labeled biomolecules, − and stable nitroxide oligoradicals as building blocks for crystalline magnetic materials. , …”

Section: Introductionmentioning

confidence: 99%

“…Thus, the hyperfine splitting patterns have been a spectroscopic "probe" for intramolecular exchange interactions in metal-containing proteins, spinlabeled biomolecules, 11À13 and stable nitroxide oligoradicals as building blocks for crystalline magnetic materials. 14,15 ESR spectra from some biradicals in solution show hyperfine splitting patterns of their corresponding monoradicals which are characteristic of the weak exchange limit of |J intra | , |A|, although their exchange interaction |J intra | seems strong enough (|J intra | . |A|).…”

mentioning

confidence: 99%

See 1 more Smart Citation

Biradical Paradox Revisited Quantitatively: A Theoretical Model for Self-Associated Biradical Molecules as Antiferromagnetically Exchange Coupled Spin Chains in Solution

et al. 2012

View full text Add to dashboard Cite

An ESR hyperfine splitting pattern of a biradical in solution depends on the magnitude of the intramolecular exchange interaction J(intra) compared with the hyperfine coupling constant A. Some biradicals exhibit their hyperfine splitting patterns characteristic of a monoradical, even though their exchange interaction is strong enough, |J(intra)| ≫ |A|. The contradiction in ESR spectroscopy is known as "biradical paradox", puzzling scientists for a long time. In this study, it is shown from ESR spectral simulations underlain by a theoretical model of a series of spin Hamiltonians that noncovalent aggregation of biradical molecules in solution leads to the appearance of paradoxical ESR spectra. Most of the spins in an aggregate of one dimension lose their contribution to the ESR spectra owing to intermolecular antiferromagnetic interactions J(inter), leaving two outermost spins ESR-active in the aggregate of one dimension. Paradoxical ESR spectra appear only when J(intra) and J(inter) fall within a particular range of the magnitudes which depends on the number of molecules in the aggregate.

show abstract

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

Biradical Paradox Revisited Quantitatively: A Theoretical Model for Self-Associated Biradical Molecules as Antiferromagnetically Exchange Coupled Spin Chains in Solution

et al. 2012

View full text Add to dashboard Cite

show abstract

“…20,25 This spectral pattern indicates that hyperfine coupling constants A N of six nitrogen nuclei in 4 are almost equivalent and that all the intramolecular exchange interactions J(π), J(σ), and J′(σ) are larger than |A N |. In our previous studies, 9,11,12 the 14 N hyperfine splitting patterns of nitronyl nitroxide triradicals have been analyzed by use of a spin Hamiltonian of eq 1 plus the electronic Zeeman and the 14 N hyperfine terms where g, µ B , and B stand for the g-factor, Bohr magneton, and the static magnetic field, respectively. The parameter A N denotes …”

Section: Dft Molecular Orbitals and Phenomenological Spin Hamiltonianmentioning

confidence: 90%

“…9,11,12 It has been known that the simulated hyperfine splitting patterns are insensitive to the difference of |J(π)|, |J(σ)|, and |J′(σ)| in the strong exchange limit. 9,11,12 Although the amplitude of J(π) is expected to be much larger than those of J(σ) and J′(σ) from the chemical structure of 4, the deviation of molecular symmetry of exchange interactions from equilateral as well as isosceles triangles is not detectable in hyperfine ESR spectroscopy of fluid solutions for the strong exchange limit. The hyperfine coupling constants for 5 are in agreement with those for nitronyl nitroxide monoradicals with similar structures.…”

Section: Dft Molecular Orbitals and Phenomenological Spin Hamiltonianmentioning

confidence: 99%

Exchange Interaction in Covalently Bonded Biradical−Monoradical Composite Molecules

et al. 2005

View full text Add to dashboard Cite

As a novel molecular designing for genuinely organic molecule-based ferrimagnets, we have proposed a strategy of "single-component ferrimagnetics". When a pi-biradical with an S = 1 ground state and a pi-monoradical with S = (1)/(2) are united by sigma-bonds, the pi-conjugation between the biradical and the monoradical moieties should be truncated in the resultant triradical. This gives magnetic degrees of freedom for both S = 1 and (1)/(2) in the single molecule, serving as a building block for organic molecule-based ferrimagnets under favorable conditions (single-component ferrimagnetics). We have designed and synthesized a triradical, 3-(1'-oxyl-3'-oxido-4',4',5',5'-tetramethylimidazolin-2-yl)benzoic acid 2,4-bis(1' '-oxyl-3' '-oxido-4' ',4' ',5' ',5' '-tetramethylimidazolin-2-yl)phenyl ester (4), as a model compound for the novel approach to genuinely organic ferrimagnets. In the triradical 4, a m-phenylene-bis(nitronyl nitroxide) biradical with a triplet (S = 1) ground state is united with a phenyl nitronyl nitroxide monoradical (S = (1)/(2)) by an ester coupler. Solution-phase ESR spectra from 4 exhibited a complex hyperfine splitting due to (14)N and (1)H nuclei. The analysis of the hyperfine structure based on perturbation calculations has revealed that the exchange interaction within the biradical moiety is much larger than those between the biradical and the monoradical moieties and the magnetic degrees of freedom for both S = 1 and (1)/(2) are retained in 4. An X-ray crystal structure analysis showed that the triradical molecules are arranged in a one-dimensional molecular chain in the crystal. The magnetic susceptibility in a crystalline solid state is consistent with the crystal structure.

show abstract

“…In cases where la'] is of the same order of magnitude as the isotropic hypenŸ coupling constant A~s o, the magnitude of J may be determined from liquid-solution EPR spectra by analyzing the hyperfine pattern [18,33]. The EPR spectra of the trovacene de- coupling in both complexes.…”

Section: Epr Spectroscopymentioning

confidence: 99%

Trovacenyl-based organometallic triradicals: Spin frustration, competing interactions and redox splitting

et al. 2004

View full text Add to dashboard Cite

Two new triradicals based on trovacene [(q7-tropylium)vanadium(qS-cyclopentadienyl)], 1,3,5-tri ([5]trovacenyl)benzene 4 and 1,3,5-tri([5]trovacenyl)-6-methoxybenzene 5 were prepared and their magnetic properties were studied by continuous-wave X-band electron paramagnetic resonance (EPR) spectroscopy and by temperature-dependent magnetic susceptometry. The EPR spectra of 4 and 5 in liquid toluene solution demonstrate that the three unpaired electrons localized on the vanadium atoms interact with each other in both complexes. The data from magnetic susceptometry revealed that the electron spins in both triradicals ate antiferromagnetically coupled despite the meta-phenylene bridge. The exchange coupling constants ate equal in the C3-symmetrical triradical 4 (J = J' = -0.68 cm-~), which leads to a twofold degenerate spin ground state (spin frustration). The symmetry lowering by methoxy substitution of the benzene spacer in 5 results in the effect of competing interactions ( 3 " = -1 . 8 3 cm -~ and J ' = -2 . 3 8 cm-~). In addition to magnetocommunication, the effect of ring substitution on electrocommunication is also discernable. It manifests itself in disparate redox splittings 8E1/2 (0/-, -/ 2 -) and 5EI/2 ( -/ 2 -, 2 -/ 3 -) for 5, while these parameters are equal for the C3-symmetrical trinuclear complex 4.

show abstract

Hyperfine structure of ESR spectra as a probe for heisenberg exchange couplings in nitroxide triradicals serving as building blocks for molecule-based ferrimagnets

Cited by 8 publications

References 35 publications

Biradical Paradox Revisited Quantitatively: A Theoretical Model for Self-Associated Biradical Molecules as Antiferromagnetically Exchange Coupled Spin Chains in Solution

Biradical Paradox Revisited Quantitatively: A Theoretical Model for Self-Associated Biradical Molecules as Antiferromagnetically Exchange Coupled Spin Chains in Solution

Exchange Interaction in Covalently Bonded Biradical−Monoradical Composite Molecules

Trovacenyl-based organometallic triradicals: Spin frustration, competing interactions and redox splitting

Contact Info

Product

Resources

About