A CW-EPR and ESEEM spectroscopic study of the dithiadiazolyl radicals p-XC6F4CNSSN (X = CN, Br)

Abstract

Two dithiadiazolyl radicals, p-NCC6F4CNSSN and p-BrC 6 F4CNSSN, have recently been found to be paramagnetic in the solid state. While the (3-phase of the first one exhibits spontaneous magnetization below 36 K, the second one shows a paramagnetic character in the solid state. The spin density distribution in these radicals is examined through continuous-wave electron paramagnetic resonance and electron spin echo envelope modulation spectroscopies. Hyperfine correlation sublevel spectroscopy provides information about the interaction of the unpaired spin with F and N nuclei. A signal coming from the interaction with Br nucleus is also detected. The superhyperfine coupling constants of the unpaired electron with the magnetic nuclei are obtained and values of the corresponding spin densities, f and f -f, can be estimated in the isolated radicals. Spin density distribution has also been calculated in both molecules with density functional theory, being in excellent agreement with those determined from the spectra. The spin density is mainly concentrated in the dithiadiazolyl ring, but some spin density is observed on the fluorinated aromatic rings. They also provide a strong basis to understand the differences of the magnetic behavior of both molecules in terms of their respective packing in the solid state.

Direct Demonstration of the Presence of Coordinated Sulfate in the Reaction Pathway of Arabidopsis thaliana Sulfite Oxidase Using 33S Labeling and ESEEM Spectroscopy

“…The last (rightmost) expression in each line of eqs 10 is accurate to linear terms in η. Similar expressions for , although in a parametrized form, were derived previously by Alonso, et al 17 The explicit expressions obtained in that work were only given for an axial nqi tensor (η = 0).…”

Spin density studies onp-O2NC6F4CNSSN: A heavypLuzón1, Campo2, Palácio3 et al. 2010Phys. Rev. BSelf Cite18090View full textAdd to dashboardCite

“…The g value and N hyperfine interactions are simi- 32 The additional fluorine hyperfine interaction is of a similar order to that previously reported for C 6 F 5 CNSSN, p-BrC 6 F 4 CNSSN, and p-NCC 6 F 4 CNSSN. 26 Frozen solutions of 2 in deuterio-toluene at X band reveal a rhombic symmetry in the g tensor ͑g 1 g 2 g 3 ͒ with a well-resolved N hyperfine interaction to the g 3 component and with some additional evidence of a fluorine hyperfine interaction, although this was not well resolved. A plot of the angular dependencies of the hyperfine interaction and g tensor at X band has led to the observation of undershoot resonances ͑off-axis turning points͒ which might cause some spectral misassignment in the ENDOR analysis ͑vide infra͒.…”

“…Previous ab initio DFT calculations and EPR studies on related dithiadiazolyl derivatives have indicated that the spin density on the dithiadiazolyl ring substituent is negligible. 26 Therefore, in both approaches, only the atoms in the heterocyclic ring have been considered. The appropriateness of the assumption of no spin density in the atoms not in the heterocyclic ring is reflected in the good agreement factors between the fits and the data ͑ 2 = 2.33 for nine variables in the wavefunction approach and 2 = 1.28 for 25 variables in the multipolar expansion͒.…”

“…36 Recently DFT studies have been employed to model the spin density distribution in a number of perfluo-rophenyl derivatives. 26 These indicated that there was little spin density population on atoms other than those in the dithiadiazolyl ring. In the current study, our calculations have allowed us to verify these previous ab initio results.…”

“…In the current study, our calculations have allowed us to verify these previous ab initio results. 26 In addition, the complementary nature of the PND, EPR, and ENDOR techniques to determine experimentally the spin density distribution allows an excellent comparison of theoretical and experimental studies. In particular, these calculations may also probe the negative spin densities on the C site and between heteroatoms in the dithiadiazolyl ring in order to determine whether these are artifacts of the multipolarexpansion model.…”