Single‐crystal electron‐spin resonance study of the 4‐phenyl‐1,2,3,5‐dithiadiazolyl radical

Single crystals of 4‐phenyl‐1,2,3,5‐dithiadiazolium trithiatriazinide, prepared by the reduction of S 5 N 5 + AlCl 4 − in SO 2 with, contain a trace paramagnetic impurity which is shown by EPR spectroscopy to be the dithiadiazolyl free radical. The g and 14 N hyperfine tensors of the radical were deduced from measurements made throughout three mutually orthogonal planes of crystallographically aligned specimens: g = (2.0011, 2.0075, 2.0197); 14 N(2) = (37.1, 11.3, 3.4 MHz.). Within experimental error, the two nitrogen hyperfine interaction tensors are collinear and have their maximum principal value aligned parallel to g min and perpendicular to the plane of the host cation. The results are interpreted in terms of a planar π‐radical which substitutes for the planar host cation, and which has considerable unpaired spin density in N(2p x ) atomic orbitals directed perpendicular to the heterocyclic ring.