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

Two dithiadiazolyl radicals, p-NCC6F4CNSSN and p-BrC6F4CNSSN, have recently been found to be paramagnetic in the solid state. While the beta -phase of the first one exhibits spontaneous magnetization below 36 K, the second one shows a paramagnetic character in the solid stale. 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(delta) and f(sigma) - f(pi), 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.