Lithium Recognition Reconfigures a Multistep Spin-Crossover Pathway in a Crown Ether-Functionalized Hofmann-Type Framework

Abstract

Chemically addressable bistable magnetic materials require molecular recognition events that do more than shift a transition temperature-they must reconfigure the underlying switching pathway. Here we report a crown ether-functionalized Hofmann-type framework, {Fe(DPy-B12C4)[Ag(CN)2]2}•2CH2Cl2 (1•2CH2Cl2), that couples Li + recognition to a pronounced reorganization of multistep spin crossover (SCO). The pristine framework exhibits guest-dependent multistep switching, whereas Li + uptake selectively suppresses the higher-temperature branch of the original transition and drives the magnetic response toward a single dominant switching event in a loading-dependent and reversible manner. Spectroscopic data support specific Li + coordination at the crown ether site, while structural and magnetic analyses indicate that ion binding reduces local conformational heterogeneity and perturbs the cooperative elastic/electronic landscape governing spin-state interconversion. This work establishes ion recognition as a chemically selective means to reconfigure cooperative SCO pathways and identifies crown ether-functionalized Hofmann-type frameworks as a platform for ion-responsive bistable magnetic materials.