Reversible magnetic control by electrical means, which is highly desired from the viewpoint of fundamentals and technological applications such as data storage devices, has been a challenging topic. In this study, the authors demonstrate in situ magnetic phase switching between the ferrimagnetic and paramagnetic states of an electron‐donor/‐acceptor metal‐organic framework (D/A‐MOF) using band‐filling control mediated by the Li+‐ion migration that accompanies redox reactions, i.e., “magneto‐ionic control”. By taking advantage of the rechargeability of lithium‐ion battery systems, in which Li+‐ions and electrons are simultaneously inserted into/extracted from a cathode material, the reversible control of nonvolatile magnetic phases in a D/A‐MOF has been achieved. This result demonstrates that the combination of a redox‐active MOF with porous flexibility and ion‐migration capability enables the creation of new pathways toward magneto‐electric coupling devices in the field of ionics.

Construction of a molecular system in which the magnetic lattice exhibits long-range order is one of the fundamental goals in materials science. In this study, we demonstrate the artificial construction of a ferrimagnetic lattice by doping electrons into acceptor sites of a neutral donor/acceptor metal-organic framework (D/A-MOF). This doping was achieved by the insertion of Li-ions into the D/A-MOF, which was used as the cathode of a Li-ion battery cell. The neutral D/A-MOF is a layered system composed of a carboxylate-bridged paddlewheel-type diruthenium(II,II) complex as the donor and a TCNQ derivative as the acceptor. The ground state of the neutral form was a magnetically disordered paramagnetic state. Upon discharge of the cell, spontaneous magnetization was induced; the transition temperature was variable. The stability of the magnetically ordered lattice depended on the equilibrium electric potential of the D/A-MOF cathode, which reflected the electron-filling level.

Phase transitions caused by the charge instability between the neutral and ionic phases of compounds, i.e., N–I phase transitions, provide avenues for switching the intrinsic properties of compounds related to electron/spin correlation and dipole generation as well as charge distribution. However, it is extremely difficult to control the transition temperature (T c) for the N–I phase transition, and only chemical modification based on the original material have been investigated. Here, a design overview of the tuning of N–I phase transition by interstitial guest molecules is presented. This study reports a new chain coordination‐polymer [Ru2(3,4‐Cl2PhCO2)4TCNQ(EtO)2]∙DCE (1‐DCE; 3,4‐Cl2PhCO2 − = 3,4‐dichlorobenzoate; TCNQ(EtO)2 2,5‐diethoxy‐7,7,8,8‐tetracyanoquinodimethane; and DCE = 1,2‐dichloroethane) that exhibits a one‐step N–I transition at 230 K (= T c) with the N‐ and I‐states possessing a simple paramagnetic state and a ferrimagnetically correlated state for the high‐ and low‐temperature phases, respectively. The T c continuously decreases depending on the content of DCE, which eventually disappears with the complete evacuation of DCE, affording solvent‐free compound 1 with the N‐state in the entire temperature range (this behavior is reversible). This is an example of tuning the in situ T c for the N–I phase transition via the control of the interstitial guest molecules.

Electrical magnetism control is realized in a Li-ion battery system through a redox reaction involving ion migrations; “magneto-ionic control”. A quasi-layered metal–organic framework compound with a cross-linked π-conjugated/unconjugated one-dimensional chain motifs composed of electron-donor/acceptor units is developed as the cathode material. A change in magnetic phase from paramagnetic to ferrimagnetic is demonstrated by means of electron-filling control for the acceptor units via insertion of Li+-ions into pores in the material. The transition temperature is as high as that expected for highly π-conjugated layered systems, indicating an extension of π-conjugated exchange paths by rearranging coordination bonds in the first discharge process.

Construction of am olecular system in which the magnetic lattice exhibits long-range order is one of the fundamental goals in materials science.I nt his study,w e demonstrate the artificial construction of aferrimagnetic lattice by doping electrons into acceptor sites of an eutral donor/ acceptor metal-organic framework (D/A-MOF). This doping was achieved by the insertion of Li-ions into the D/A-MOF, which was used as the cathode of aL i-ion battery cell. The neutral D/A-MOF is al ayered system composed of ac arboxylate-bridged paddlewheel-type diruthenium(II,II) complex as the donor and aTCNQ derivative as the acceptor.The ground state of the neutral form was am agnetically disordered paramagnetic state.U pon dischargeo ft he cell, spontaneous magnetization was induced;t he transition temperature was variable.T he stability of the magnetically ordered lattice depended on the equilibrium electric potential of the D/A-MOF cathode,which reflected the electron-filling level.Over the past few decades,t he design of molecule-based magnets with long-range magnetic order has attracted much interest in the field of molecular functional materials.[1] One route to achieve such long-range magnetic order is to construct lattices using only paramagnetic metal ions and/or molecules with the help of superexchange coupling between paramagnetic centers via ab ridging ligand. Charge-transfer (CT) framework systems comprising electron donor (D) and electron acceptor (A) + located between layers.[4]Focusing on the generation of the radical AC À in the D 0 2 A 0 system, electron-filling control of the system should be an effective approach for the construction of an artificial magnetically ordered lattice without intra-lattice ET.T aking into account that the present "MOFs" are also characterized as atype of porous frameworks,the electrochemical insertion of ionic guests such as Li + and Na + into host frameworks is potentially applicable for electron-filling control of D/AMOFs.[5] In the process of electrochemical cation insertion, acation and electron pair is introduced into the host material and the valence of the redox-active species (that is,t he acceptor A 0 )i nt he material is directly modulated from A À -filled forms are expected to be paramagnetic, ferrimagnetic, and paramagnetic, respectively.