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 on e shows a paramagnetic character in the solid stale. The spin density distr ibution in these radicals is examined through continuous-wave electron para magnetic resonance and electron spin echo envelope modulation spectroscopie s. Hyperfine correlation sublevel spectroscopy provides information about t he interaction of the unpaired spin with F and N nuclei. A signal coming fr om the interaction with Br nucleus is also detected. The superhyperfine cou pling constants of the unpaired electron with the magnetic nuclei are obtai ned and values of the corresponding spin densities, f(delta) and f(sigma) - f(pi), can be estimated in the isolated radicals. Spin density distributio n 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 sp in density is observed on the fluorinated aromatic rings. They also provide a strong basis to understand the differences of the magnetic behavior of b oth molecules in terms of their respective packing in the solid state.