Possible Superhigh-Spin Cluster in the Crystals of a Novel Nitronyl Nitroxide Radical as Studied by FT Pulsed ESR

Shiomi, Daisuke; Sato, Kazunobu; Takui, Takeji; Itoh, Koichi; Tamura, Masafumi; Nishio, Y.; Kajita, Kôji; Nakagawa, Mitsutoshi; Ishida, Takayuki; Nogami, Takashi

doi:10.1080/10587259908028880

Cited by 8 publications

(4 citation statements)

References 3 publications

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“…The hfcc of the two equivalent nitrogen atoms in nitronyl nitroxide monoradicals with different substitutions at α-carbon atoms is in the range of 7.00−7.81 G . The hfcc does not strongly depend on the nature of the substitution at the α-position, but solvents play a significant role.…”

Section: Resultsmentioning

confidence: 96%

Polyacene Spacers in Intramolecular Magnetic Coupling

Ali

Datta

2006

J. Phys. Chem. A

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We predict the intramolecular magnetic exchange coupling constant (J) for eleven nitronyl nitroxide diradicals (NN) with different linear and angular polyacene couplers from broken-symmetry density functional treatment. For the linear acene couplers, J initially decreases with increase in the number of fused rings. But from anthracene coupler onward, the J value increases with the number of benzenoid rings due to an increasing diradical character of the coupler moiety. The J value for the diradical with a fused bent coupler is always found to be smaller than that for a diradical with a linear coupler of the same size. The nuclear independent chemical shift (NICS) is calculated, and it is observed that the average of the NICS values per benzenoid ring in the diradical is less than that in the normal polyacene molecule. An empirical formula for the magnetic exchange coupling constant of a NN diradical with an aromatic spacer is obtained by combining the Wiberg bond order (BO), the angle of twist (phi) of the monoradical (NN) plane from the plane of the coupler, and the NICS values. A comparison of the formula with the computed values reveals that, from tetracene onward, the diradical nature of the linear acene couplers becomes prominent thereby leading to an increase in the ferromagnetic coupling constant. Isotropic hyperfine coupling constants are calculated by using a polarized continuum model for the diradicals in different solvents and in vacuum.

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Section: Resultsmentioning

confidence: 96%

Polyacene Spacers in Intramolecular Magnetic Coupling

Ali

Datta

2006

J. Phys. Chem. A

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“…Isotropic Hyperfine Coupling Constant. From the experimental work it is observed that the hfcc of the two equivalent nitrogen atoms in nitronyl nitroxide monoradicals with different substitutions at α-carbon atoms is in the range of 7.00−7.81 G . The hfcc does not strongly depend on the nature of the substitution at the α-position, but solvents play a dominant role.…”

Section: Resultsmentioning

confidence: 97%

Broken-Symmetry Density Functional Theory Investigation on Bis-Nitronyl Nitroxide Diradicals: Influence of Length and Aromaticity of Couplers

2006

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A series of nitronyl nitroxide (NN) diradicals with linear conjugated couplers and another series with aromatic couplers have been investigated by the broken-symmetry (BS) DFT approach. The overlap integral between the magnetically active orbitals in the BS state has been explicitly computed and used for the evaluation of the magnetic exchange coupling constant (J). The calculated J values are in very good agreement with the observed values in the literature. The magnitude of J depends on the length of the coupler as well as the conformation of the radical units. The aromaticity of the spacer decreases the strength of the exchange coupling constant. The SOMO-SOMO energy splitting analysis, where SOMO stands for the singly occupied molecular orbital, and the calculation of electron paramagnetic resonance (EPR) parameters have also been carried out. The computed hyperfine coupling constants support the intramolecular magnetic interactions. The nature of magnetic exchange coupling constant can also be predicted from the shape of the SOMOs as well as the spin alternation rule in the unrestricted Hartree-Fock (UHF) treatment. It is found that pi-conjugation along with the spin-polarization plays the major role in controlling the magnitude and sign of the coupling constant.

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“…Wautelet et al observed hfcc's of 4.22 and 9.10 G for monoradical 1 in CH 2 Cl 2 /xylene. The experimental hfcc for a large number of derivatives of NN in different nonaqueous solvents was found to vary in the range 7.00−7.81 G . D'Anna et al27a found that the hfcc for the two equivalent nitrogen atoms in methyl, o -tolyl, and phenyl derivatives of NN are 7.66, 7.57, and 7.62 G, respectively, in ethanol solution, and 7.44, 7.31, and 7.47 G, respectively, in benzene.…”

Section: Resultsmentioning

confidence: 99%

“…The experimental hfcc for a large number of derivatives of NN in different nonaqueous solvents was found to vary in the range 7.00−7.81 G . D'Anna et al27a found that the hfcc for the two equivalent nitrogen atoms in methyl, o -tolyl, and phenyl derivatives of NN are 7.66, 7.57, and 7.62 G, respectively, in ethanol solution, and 7.44, 7.31, and 7.47 G, respectively, in benzene. From these observations it is clear that the subtituents on the α-carbon of IN and NN do not play a significant role in determining the hfcc for the monoradical derivatives, whereas the nature of the solvent considerably affects the hfcc.…”

Section: Resultsmentioning

confidence: 99%

Ab Initio Quantum Chemical Investigation of Intramolecular Magnetic Interaction in Some Diradical Derivatives of Imino Nitroxide and Nitronyl Nitroxide

2005

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The magnetic properties of the monoradicals 2-(4-phenyl acetylene)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidozolyl-oxyl (1) and 2-(4-phenyl acetylene)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-1-oxyl-3-oxide (2) and the diradicals 2,2'-(1,2-ethynediyldi-4,1-phenylene)bis[4,4,5,5-tetramethyl-4,5-dihydro-1H-imidozolyl-oxyl] (3), 2,2'-(1,2-ethynediyldi-4,1 3,1-phenylene)bis[4,4,5,5-tetramethyl-4,5-dihydro-1H-imidozolyl-oxyl] (4), and 2,2'-(1,2-ethynediyldi-4,1 3,1-phenylene)bis[4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-1-oxyl-3-oxide] (5) are investigated by ab initio quantum chemical methods. The rule of spin alternation in the unrestricted Hartree-Fock (UHF) method clearly shows that the radical sites are antiferromagnetically coupled in 3 and ferromagnetically coupled in 4 and 5, which is consistent with a previous experiment. The molecular geometries are optimized at Hartree-Fock levels. This is followed by single-point calculations using the density functional (UB3LYP) treatment and the multiconfigurational complete active space self-consistent field (CASSCF) methodology. Magnetic exchange coupling constants are determined from the broken-symmetry approach. The calculated J values, -3.60 cm(-1) for 3, 0.16 cm(-1) for 4, and 0.67 cm(-1) for 5, are in excellent agreement with the observed values. Because of the very large size of the diradicals 3-5, the CASSCF (10,10) calculations cannot yield realistic J values. Nevertheless, the CASSCF calculations support the antiferromagnetic nature of the magnetic coupling in 3 and the ferromagnetic nature of the coupling in 4 and 5. The existence of an intramolecular magnetic coupling in 3-5 is also confirmed through computations of the isotropic hyperfine coupling constants for monoradicals 1 and 2 as well as diradicals 3-5.

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Possible Superhigh-Spin Cluster in the Crystals of a Novel Nitronyl Nitroxide Radical as Studied by FT Pulsed ESR

Cited by 8 publications

References 3 publications

Polyacene Spacers in Intramolecular Magnetic Coupling

Polyacene Spacers in Intramolecular Magnetic Coupling

Broken-Symmetry Density Functional Theory Investigation on Bis-Nitronyl Nitroxide Diradicals: Influence of Length and Aromaticity of Couplers

Ab Initio Quantum Chemical Investigation of Intramolecular Magnetic Interaction in Some Diradical Derivatives of Imino Nitroxide and Nitronyl Nitroxide

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