Magnetic Ordering Controlled by Ionic Proximity in Self-Assembled Ionic Liquid Nanostructures

Abstract

Magnetic ionic liquids (MILs) commonly exhibit paramagnetic behavior because the spatially isolated and disordered arrangement of magnetic centers limits cooperative magnetic interactions. Herein, the terphenyl-based MIL 3ph-imi[FeCl4] was processed under different conditions to obtain three samples with distinct structural organizations. Liquid-nitrogen quenching produced an amorphous solid. Aging a 1.0 mg mL–1 aqueous solution at 25 °C yielded 50–90 nm spindle-shaped assemblies (Assembly-1) containing locally ordered domains, whereas aging at 5 °C generated ca. 40 μm platelets (Assembly-2) with lamellar periodicity and extended in-plane crystalline order. Magnetic measurements showed predominantly paramagnetic behavior for 3ph-imi[FeCl4]. Assembly-1 exhibited weak magnetic hysteresis at 5 K and zero-field-cooled/field-cooled (ZFC–FC) bifurcation below ca. 42 K. In contrast, Assembly-2 showed ZFC–FC bifurcation below ca. 258 K and retained a distinct hysteresis loop at 300 K. The compact molecular packing of the assembled samples may strengthen interactions among neighboring [FeCl4]− units, while the higher structural order and greater spatial continuity of Assembly-2 may support magnetic correlations across larger regions and over a wider temperature range. These findings demonstrate that temperature-regulated aqueous self-assembly provides an effective strategy for tuning the solid-state magnetic properties of small-molecule MILs.