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Electronic Structure of a Stable Phenalenyl Radical as Studied by ESR/ENDOR, Paramagnetic NMR Spectroscopy and SQUID Measurements

1999; Volume: 334; Issue: 1 Linguagem: Inglês

10.1080/10587259908023302

1058-725X

Kozo Fukui, Kazunobu Sato, Daisuke Shiomi, Takeji Takui, Koichi Itoh, Takashi Kubo, K. Gotoh, Kagetoshi Yamamoto, Kazuhiro Nakasuji, Akira Naito,

Electron Spin Resonance Studies

Abstract We have studied magnetic properties and electronic structures of a novel persistent neutral radical, 2,5,8-tri-tert-butylphenalenyl(2), which is the first example of alternant hydrocarbon π-radical isolated in the crystalline state. The observed magnetic susceptibilities of polycrystalline sample 2 were reproduced by assuming the thermal equilibrium between singlet ground state and excited triplet state of the dimer (2J/k B = −2×103 K) with traces of paramagnetic impurity molecules (0.3mol%). The π-spin density distribution of radical 2 was determined by liquid-phase cw-ESR, 1H-ENDOR/TRIPLE, and paramagnetic 1H-NMR measurements. The origin of the large inter-molecular antiferromagnetic interaction in the crystal 2 was explained by an occurrence of effective SOMO-SOMO overlap between the two radicals on the six equivalent α-positions with large positive spin densities of the carbon sites.