Antiferromagnetic Exchange Interaction among the Three Spins Placed in an Isosceles Triangular Configuration in 2,4-Dimethoxy-1,3,5-benzenetriyltris(N-tert-butyl nitroxide)
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- 作者：Junpei Fujita ; Masakazu Tanaka ; Hiroshi Suemune ; Noboru Koga ; Kenji Matsuda ; and Hiizu Iwamura
- 刊名：Journal of the American Chemical Society
- 出版年：1996
- 出版时间：October 2, 1996
- 年：1996
- 卷：118
- 期：39
- 页码：9347 - 9351
- 全文大小：202K
- 年卷期：v.118,no.39(October 2, 1996)
- ISSN：1520-5126
文摘
2,4-Dimethoxy-1,3,5-benzenetriyltris(N-tert-butylnitroxide) (3) was prepared by lithiation of2,4-dimethoxy-1,3,5-tribromobenzene followed by the reaction with2-methyl-2-nitrosopropane and subsequent oxidation withAg2O.The triradical crystallizes in the orthorhombic space groupPnma (no. 62) with four molecules in the unit cellofdimensions a = 18.200(3) Å, b =19.018(3) Å, and c = 6.659(5) Å. X-rayanalysis for an orange plate singlecrystal of 3 revealed that the three nitroxide radicals in amolecule have large dihedral angles (90
and 79)betweenN-O bonds and the benzene ring plane in the all-syn conformation andthe distances between them are 5.44 and5.28 Å. An EPR spectrum of triradical 3 in frozentoluene solution showed quartet signals (g = 2.0062,
D/hc =0.010, and E/hc = 0.0004cm-1) in addition to the signals atg = 4.019 and 6.035 due to 
ms= 2 and 3 transitions,respectively. Temperature dependence of molar susceptibility for amicrocrystalline sample obtained by SQUIDmeasurements suggested that the antiferromagnetic interaction producesa doublet ground state in triradical 3.Experimental data were fitted in terms of the equation derivedfrom an isosceles triangular three spin system (H=-2J(SA1SB+ SBSA2 +
SA1SA2)) with negativeJ's to afford two sets of the best fitting parameters:J/kB = -41.5K, = 0.31 and J/kB = -22.3K, = 2.29. The former J/kBvalue is more consistent with J/kB= -39.7 K for thereference biradical,1-bromo-2,4-dimethoxy-3,5-benzenediylbis(N-tert-butylnitroxide) (4). In triradical 3,therefore,the ground spin state would be a doublet with the strongerantiferromagnetic interaction between the spins at 1 and3 positions and 3 and 5 positions polarizing the ferromagneticalignment of the 1 and 5 spins, providing the firstdemonstration of an organic triradical showing competinginteractions.
and 79)betweenN-O bonds and the benzene ring plane in the all-syn conformation andthe distances between them are 5.44 and5.28 Å. An EPR spectrum of triradical 3 in frozentoluene solution showed quartet signals (g = 2.0062,D/hc =0.010, and E/hc = 0.0004cm-1) in addition to the signals atg = 4.019 and 6.035 due to ms= 2 and 3 transitions,respectively. Temperature dependence of molar susceptibility for amicrocrystalline sample obtained by SQUIDmeasurements suggested that the antiferromagnetic interaction producesa doublet ground state in triradical 3.Experimental data were fitted in terms of the equation derivedfrom an isosceles triangular three spin system (H=-2J(SA1SB+ SBSA2 +SA1SA2)) with negativeJ's to afford two sets of the best fitting parameters:J/kB = -41.5K, = 0.31 and J/kB = -22.3K, = 2.29. The former J/kBvalue is more consistent with J/kB= -39.7 K for thereference biradical,1-bromo-2,4-dimethoxy-3,5-benzenediylbis(N-tert-butylnitroxide) (4). In triradical 3,therefore,the ground spin state would be a doublet with the strongerantiferromagnetic interaction between the spins at 1 and3 positions and 3 and 5 positions polarizing the ferromagneticalignment of the 1 and 5 spins, providing the firstdemonstration of an organic triradical showing competinginteractions.