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 Tc↓ = 128(2) K and Tc↑ = 188(2) K. The magnetic signature
arises from a radical/dimer interconversion involving one of the two
independent π-radicals in the P1̅ unit
cell. Variable temperature X-ray crystallography has established that
while all the radicals in HT-NDTA serve as paramagnetic (S = 1/2) centers, half of the radicals in LT-NDTA form closed-shell
N–N σ-bonded dimers (S = 0) and half
retain their S = 1/2 spin state. The wide window
of bistability (60 K) may be attributed to the large structural changes
that accompany the phase transition.