Modulating multi-channel bistability in cyanide-bridged {Fe2Fe} spin-crossover coordination polymers

Abstract

Multi-channel bistable materials have emerged as compelling candidates for applications in information encryption and smart devices. However, achieving systems that simultaneously exhibit tunable transitions and pronounced thermal hysteresis remains a formidable challenge. In this work, we introduce a ligand-modulation strategy wherein subtle substituent modifications precisely regulate intermolecular interactions, thereby enabling a controllable transformation from a one-step spin-crossover (SCO) transition in {[(Tp)Fe^III(CN)₃][Fe^II_0.5(L1)]} (1) to a two-step transition in {[(Tp)Fe^III(CN)₃][Fe^II_0.5(L2)]} (2) (L1 = 5-pyridin-4-ylthiophene-2-carboxaldehyde, L2 = 1-(5-pyridin-4-ylthiophen-2-yl)ethanone), accompanied by thermal hysteresis. Remarkably, the stepwise transitions and their associated hysteresis were concurrently manifested in optical absorption and dielectric responses, demonstrating cooperative multistate modulation across photonic, magnetic, and electronic channels. This study, therefore, establishes a viable molecular-level approach for realizing tunable stepwise transitions with thermally hysteretic behavior in multiple-channel functionalities, paving the way for the development of next-generation multifunctional switchable materials and devices.