Magnetic Bistability in Crystalline Organic Radicals: The Interplay of H‑bonding, Pancake Bonding, and Electrostatics in 4‑(2′-Benzimidazolyl)-1,2,3,5-dithiadiazolyl

The neutral radical 4-(2′-benzimidazolyl)-1,2,3,5-dithiadiazolyl
(HbimDTDA) exhibits a first order phase transition around 270 K without
symmetry breaking, preserving its orthorhombic Pbca space group between 340 and 100 K. Associated with this reversible
single-crystal-to-single-crystal phase transition, thermal hysteresis
of the magnetic susceptibility is observed. The low temperature (LT)
phase is diamagnetic owing to pancake bonding between the π-radicals.
In the paramagnetic high temperature (HT) phase, the pancake bonds
are broken, and new electrostatic contacts are apparent. As a result
of the dense 3D network of supramolecular contacts, which includes
H-bonds, the HbimDTDA system provides the first example of magnetic
bistability for a DTDA radical.

中性自由基4-(2′-苯并咪唑基)-1,2,3,5-二噻二唑（HbimDTDA）在约270 K下发生一级相变，且未伴随对称性破缺；该物质在340 K至100 K的温度区间内始终维持正交晶系Pbca空间群。伴随这一可逆的单晶-单晶相变，可观测到磁化率存在热滞现象。低温（LT）相因π自由基间的煎饼键（pancake bonding）作用呈现抗磁性。在顺磁性高温（HT）相中，煎饼键发生断裂，同时出现新的静电接触。得益于包含氢键在内的致密三维超分子接触网络，HbimDTDA体系成为二噻二唑（DTDA）自由基类化合物中首个展现磁双稳态的实例。