Magnetic Bistability in Naphtho-1,3,2-dithiazolyl: Solid State Interconversion of a Thiazyl π‑Radical and Its N–N σ‑Bonded Dimer

Crystals of the heterocyclic radical naphtho-1,3,2-dithiazolyl NDTA display magnetic bistability with a well-defined hysteretic phase transition at <i>T</i>_c↓ = 128(2) K and <i>T</i>_c↑ = 188(2) K. The magnetic signature arises from a radical/dimer interconversion involving one of the two independent π-radicals in the <i>P</i>1̅ unit cell. Variable temperature X-ray crystallography has established that while all the radicals in HT-NDTA serve as paramagnetic (<i>S</i> = 1/2) centers, half of the radicals in LT-NDTA form closed-shell N–N σ-bonded dimers (<i>S</i> = 0) and half retain their <i>S</i> = 1/2 spin state. The wide window of bistability (60 K) may be attributed to the large structural changes that accompany the phase transition