Magnetic Sponge Behavior via Electronic State Modulations

A reversible magnetic change in response to external stimuli is a desired function of molecular magnetic materials. The magnetic change induced by a change in the intrinsic spin is significant because the magnetic change is inevitable and could become drastic. In this study, we demonstrate a reversible magnetic change closely associated with electronic state modulations, as well as structural modifications realized by solvation/desolvation cycles of a magnetic sponge. The compound was a D₂A-type layered magnet, [{Ru₂(O₂CPh-2,3,5-Cl₃)₄}₂(TCNQMe₂)]·4DCM (1; 2,3,5-Cl₃PhCO₂^- = 2,3,5-trichlorobenzoate; TCNQMe₂ = 2,5-dimethyl-7,7,8,8-tetracyanoquinodimethane; DCM = dichloromethane), where [Ru₂(O₂CPh-2,3,5-Cl₃)₄] ([Ru₂^II,II]) is an electron donor (D) and TCNQMe₂ is an electron acceptor (A). Compound 1 had a one-electron-transferred, charge-ordered state with a [{Ru₂^II,II}-TCNQMe₂^•--{Ru₂^II,III}⁺] (1e-I) formula. Strong intralayer antiferromagnetic couplings between [Ru₂^II,II] with S = 1 or [Ru₂^II,III]⁺ with S = 3/2 and TCNQMe₂^•- with S = 1/2, as well as ferromagnetic interlayer interactions, induced long-range ferrimagnetic ordering at T_c = 101 K. Interstitial DCM molecules were located between layers, and these were gradually eliminated under vacuum at 80 °C to form a solvent-free compound (1-dry) without loss of crystallinity. The electronic state of 1-dry thermally fluctuated and eventually provided a charge-disproportionate disordered state, with a [{Ru₂}^0.5+-TCNQMe₂^1.5--{Ru₂^II,III}⁺] (1.5e-I) formula as the ground state. The T_c in 1-dry was 34 K because of the presence of diamagnetic TCNQMe₂^2- in some parts of the framework. A large T_c variation with ΔT_c ≈ 70 K was switchable; switching was achieved by charge-state modulations accompanied by subtle structural modifications in solvation/desolvation treatments.