RESUMO
The title radical Râ , synthesized by reduction of the corresponding cation R+, is thermally stable up to ~380â K in the crystalline state under anaerobic conditions. With SQUID magnetometry, single-crystal and powder XRD, solid-state EPR and TG-DSC, reversible spin-Peierls transition between diamagnetic and paramagnetic states featuring ~10â K hysteretic loop is observed for Râ in the temperature range ~310-325â K; ΔH=~2.03â kJ mol-1 and ΔS=~6.23â J mol-1 K-1. The transition is accompanied by mechanical movement of the crystals, i. e., by thermosalient behavior. The low-temperature diamagnetic P-1 polymorph of Râ consists of Râ 2 π-dimers arranged in ( Râ 2 )n π-stacks; whereas the high-temperature paramagnetic P21/c polymorph, of uniform ( Râ )n π-stacks. With the XRD geometries, CASSCF and broken-symmetry DFT jointly suggest strong antiferromagnetic (AF) interactions within Râ 2 and weak between Râ 2 for the ( Râ 2 )n stacks; and moderate AF interactions between Râ for the ( Râ )n stacks. The fully hydrocarbon archetype of Râ does not reveal the aforementioned properties. Thus, the fluorinated 1,3,2-benzodithiazolyls pave a new pathway in the design and synthesis of metal-less magnetically-bistable materials.