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)-1,2,3,5-二噻二唑基（4-(2′-benzimidazolyl)-1,2,3,5-dithiadiazolyl，缩写HbimDTDA）在约270 K处表现出一级相变，该相变无对称性破缺，且在340 K至100 K的温度区间内始终维持其正交晶系Pbca空间群结构。伴随该可逆单晶-单晶相变，体系观测到磁化率的热滞现象。低温（LT）相因π自由基间的煎饼键合作用呈现抗磁性；在顺磁性高温（HT）相中，煎饼键合被破坏，同时出现了新的静电接触作用。得益于包含氢键在内的致密三维超分子接触网络，HbimDTDA体系成为首个DTDA自由基类磁双稳态体系的实例。