Irreversible Structural Phase Transition in [(9‐triptycylammonium) ([18]crown‐6)][Ni(dmit)2]: Origin and Effects on Electrical and Magnetic Properties

Materials exhibiting irreversible phase transitions, leading to changes in their properties, have a potential for novel application in electronic components such as a non‐rewritable high‐security memory. Here, we focused on the two salts, [(9‐triptycylammonium)([18]crown‐6)][Ni(dmit)2] (1) and [(9‐triptycylammonium)([15]crown‐5)][Ni(dmit)2] (2), which featured 2D sheet structures with alternately stacked cation and anion layers. Both salts exhibit similar cation arrangements, however, their anion arrangements differ significantly. The temperature‐dependent magnetic susceptibilities of 1 and 2 were well reproduced by the alternating chain model (JAC1/kB = −306(8), JAC2/kB = −239(3) K) and the Curie‐Weiss model (θ = −3.9(1) K), respectively. 1 experience a reversible phase transition around 40‐60 K, causing anomalies in magnetic behavior. Moreover, an irreversible single‐crystal‐to‐single‐crystal phase transition to 1’ undergo at ~381 K, inducing a rearrangement of [Ni(dmit)2]− anions and a resistivity decrease from 6.5 × 106 to 6.5 × 102 Ω cm. The susceptibility curve of 1’ was reproduced by a combination of the Curie‐Weiss and dimer models (Jdimer/kB = −407(5), θ = −26.7(5) K). The irreversible transition of 1 is the first example for such supramolecule and [Ni(dmit)2]− system to our knowledge, in opening potential new‐type materials.