Observation of reversible three-step solid-to-solid phase transitions in a nickel-bis-1,2-dithiolene magnetic molecule solid

Abstract

An ion-pair compound 1,6-bis(1-methylimidazolium)hexane bis(maleonitrio-dithiolato)nickelate was synthesized and structurally characterized. This compound crystallizes in the triclinic space group P -1, and the anions form the alternating stacks in the crystal. Reversible three-step solid-to-solid phase transitions occur at ~ 210, ~ 320 and ~ 432 K upon cooling. The entropy change of phase transition was estimated to be 25.4 J⋅K − 1 ⋅ mol − 1 and 9.97 J ⋅ K − 1 ⋅ mol − 1 for the transitions at ~ 320 and ~ 432 K, respectively. The hysteresis effect was observed in the χ m –T plot for the transitions at ~ 210 and ~ 320 K. The mechanisms of transitions are discussed based on the crystal structure and thermal analyses. Three-step reversible solid-to-solid phase transitions, including two hysteretic magnetic and one crystal-to-plastic crystal transitions, occur in a 1-D S = 1/2 molecular magnetic solid. ► Nickel-bis-1, 2-dithiolene anion combined with the ionic liquid component to yield a one-dimensional spin chain compound. ► Three-step reversible solid-to-solid phase transition. ► Hysteretic magnetic transition. ► Crystal-to-plastic crystal transition.