Anisotropic ESR spectra of orbitally degenerate radicals. The pentachlorocyclopentadienyl radical
1975; Elsevier BV; Volume: 9; Issue: 1-2 Linguagem: Inglês
10.1016/0301-0104(75)80117-0
ISSN1873-4421
AutoresPeter Bachmann, F. Gräf, Hs. H. Günthard,
Tópico(s)Molecular spectroscopy and chirality
ResumoESR spectra of the pentachlorocyclopentadienyl radical substituted in cyclododecane single crystals are reported. Analysis of the spectra give an anisotropic g tensor with gvb = 2.0009 ± 0.0001, g⊥ = 2.0075 ± 0.0001 and an anisotropic chlorine 35 hyperfine coupling tensor with Avb = 6.58 ± 0.06 gauss, A⊥ = 1.2 ± 0.2 gauss. For accurate analysis of the spectra, the effects of the most abundant isotopic modifications and the quadrupole coupling were considered. The ESR spectra show a pronounced temperature dependence, which is shown to result from a reorientation process of the radical around its 5-fold symmetry axis. The direction of the latter axis has directly been determined by combination of ESR and X-ray data. By CNDO and INDO calculations a limited study of Jahn-Teller type distortions of the radical from its Dsh structure were investigated, which indicate local minima with C2v symmetry. Furthermore, a synthesis of the chlorine coupling tensor based on the CNDO/INDO calculations leads to good agreement with experimental data. The latter require for a satisfactory interpretation both a dynamic Jahn-Teller effect and a stochastic reorientation process.
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