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] ([Ru2II,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 [{Ru2II,II}–TCNQMe2•––{Ru2II,III}+] (1e-I) formula.
Strong intralayer antiferromagnetic couplings between [Ru2II,II] with S = 1 or [Ru2II,III]+ with S = 3/2 and TCNQMe2•– with S = 1/2,
as well as ferromagnetic interlayer interactions, induced long-range
ferrimagnetic ordering at Tc = 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+–TCNQMe21.5––{Ru2II,III}+] (1.5e-I) formula as the ground
state. The Tc in 1-dry was
34 K because of the presence of diamagnetic TCNQMe22– in some parts of the framework. A large Tc variation with ΔTc ≈ 70 K was switchable; switching was achieved by charge-state
modulations accompanied by subtle structural modifications in solvation/desolvation
treatments.