Magnetic Sponge with Neutral-Ionic Phase Transitions.

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 (Tc) 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 (= Tc) 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 Tc 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 Tc for the N-I phase transition via the control of the interstitial guest molecules.

Construction of an Artificial Ferrimagnetic Lattice by Lithium Ion Insertion into a Neutral Donor/Acceptor Metal-Organic Framework.

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.