Simultaneous magneto-dielectric transitions in a fluorescent Hofmann-type coordination polymer

Abstract

The design of magnetic molecular materials exhibiting multiple functions has garnered significant interest owing to their potential applications in molecular switches, sensors, and data storage devices. In this study, we synthesized a two-dimensional (2D) Fe^II-based Hofmann-type coordination polymer, namely {Fe(DPPE)₂[Ag(CN)₂]₂}·2EtOH (1), using a luminescent ligand 1,1-diphenyl-2,2-di(4-pyridylbiphenyl)ethylene (DPPE). Single-crystal structural analyses and magnetic measurements revealed a thermally induced spin crossover (SCO) with the transition temperature T_1/2 = 231 K. Variable-temperature fluorescence emission spectra indicated the coexistence of spin crossover and fluorescence properties. Moreover, a pronounced dielectric change (Δε′ = 1.2 at 0.5 kHz) was observed during the SCO process, confirming the simultaneous magnetic and dielectric switching arising from the rearrangement of 3d electrons and deformation of the Fe^II-centered coordination sphere. This work provides an approach to explore the interplay between magnetic, dielectric, and fluorescence properties, and holds significance for developing multifunctional molecular materials.