A complete picture of the spin density distribution in the organic radical $p{\text{-O}}_2{\text{NC}}_6{\text{F}}_4\text{CNSSN}$ has been obtained by a combination of polarized neutron diffraction, electron paramagnetic resonance (EPR), and electron-nuclear double resonance (ENDOR) spectroscopies, and ab initio density-functional theory (DFT) calculations. Polarized neutron diffraction revealed that the spin distribution is predominantly localized on the N and S atoms ($+0.25{\mu }_B$ and $+0.28{\mu }_B$, respectively) of the heterocyclic ring with a small negative spin density on the heterocyclic C atom $\left(-0.06{\mu }_B\right)$. These spin populations are in excellent agreement with both ab initio DFT calculations (spin populations on the C, N, and S sites of $-0.07$, 0.22 and 0.31, respectively) and cw-EPR studies which estimated the spin population on the N site as 0.24. The DFT calculated spin density revealed less than 1% spin delocalization onto the perfluoroaryl ring, several orders of magnitude lower than the density on the heterocyclic ring. cw-ENDOR studies at both $X$-band (9 GHz) and $Q$-band (34 GHz) frequencies probed the spin populations on the two chemically distinct F atoms. These spin populations on the F atoms ortho and meta to the dithiadiazolyl ring are of magnitude ${10}^{-3}$ and ${10}^{-4}$, respectively.

• Received 13 December 2009

DOI:https://doi.org/10.1103/PhysRevB.81.144429