Magnetic Sponge with Neutral–Ionic Phase Transitions

Abstract

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.

Host–Guest Hydrogen Bonding Varies the Charge‐State Behavior of Magnetic Sponges

“…Hence, the modulation of the intrinsic spin state in a correlated lattice would be an efficient strategy for a drastic and huge change of magnetism, which could be designed by controlling the intra‐lattice electron transfer (ET) . To obtain such charge‐flexible magnets, we have focused on a class of magnetic metal‐organic frameworks comprising electron‐donor (D) and ‐acceptor (A) compositions (D/A‐MOFs), where the ET or charge transfer (CT) was regulated not only by the choice of the D/A units, but also by the bonding nature of the frameworks and/or the packing mode . In our molecular design, carboxylate‐bridged paddlewheel‐type diruthenium(II,II) complexes ([Ru 2 II,II ]) and 7,7,8,8‐tetracyano‐ p ‐quinodimethane derivatives (TCNQR x ) have been employed as the D and A, respectively, to control the degree of D→A CT by chemically modifying D/A units in several types of frameworks .…”

Host–Guest Hydrogen Bonding Varies the Charge‐State Behavior of Magnetic Sponges

“…[8,9] Hence,t he modulation of the intrinsic spin state in ac orrelated lattice would be an efficient strategy for adrastic and huge change of magnetism, which could be designed by controlling the intralattice electron transfer (ET). [12,15] In our molecular design, carboxylate-bridged paddlewheel-type diruthenium-(II,II) complexes ([Ru 2 II,II ]) and 7,7,8,8-tetracyano-p-quinodimethane derivatives (TCNQR x )h ave been employed as the Da nd A, respectively,tocontrol the degree of D!ACTby chemically modifying D/A units in several types of frameworks. [12,15] In our molecular design, carboxylate-bridged paddlewheel-type diruthenium-(II,II) complexes ([Ru 2 II,II ]) and 7,7,8,8-tetracyano-p-quinodimethane derivatives (TCNQR x )h ave been employed as the Da nd A, respectively,tocontrol the degree of D!ACTby chemically modifying D/A units in several types of frameworks.…”

“…[12,15] In our molecular design, carboxylate-bridged paddlewheel-type diruthenium-(II,II) complexes ([Ru 2 II,II ]) and 7,7,8,8-tetracyano-p-quinodimethane derivatives (TCNQR x )h ave been employed as the Da nd A, respectively,tocontrol the degree of D!ACTby chemically modifying D/A units in several types of frameworks. [12,15,23] Herein, we report au nique D 2 A-layered compound, [{Ru 2 (m-FPhCO 2 ) 4 } 2 TCNQ(OMe) 2 ]·nDCE (1-nDCE; m-FPhCO 2 À = m-fluorobenzoate;T CNQ(OMe) 2 = 2,5-dimethoxyl-7,7,8,8-tetracyanoquinodimethane;D CE = 1,2dichloroethane), which adopts three types of charge-ordered states depending on the degree of solvation of DCE, that is, nDCE:2e-I for the fully solvated compound (pristine form; 1-4DCE), 1.5e-I d for the solvent-free compound (1), and 1e-I for apartially solvated intermediate state (1-DCE with n 1) ( Figure 1a). Inspired by the superior flexibility of the charge state in our D/A-MOFs,the chemi-or physisorption of guest molecules into ap orous D/A-MOF (that is,p seudopolymorphs) could bring about amodulation of charge states in the host framework, consequently resulting in ad rastic magnetic change.…”

“…[10][11][12] To obtain such chargeflexible magnets,w eh ave focused on ac lass of magnetic metal-organic frameworks comprising electron-donor (D) and -acceptor (A) compositions (D/A-MOFs), [13,14] where the ET or charge transfer (CT) was regulated not only by the choice of the D/A units,but also by the bonding nature of the frameworks and/or the packing mode. [12,15] In our molecular design, carboxylate-bridged paddlewheel-type diruthenium-(II,II) complexes ([Ru 2 II,II ]) and 7,7,8,8-tetracyano-p-quinodimethane derivatives (TCNQR x )h ave been employed as the Da nd A, respectively,tocontrol the degree of D!ACTby chemically modifying D/A units in several types of frameworks. [16][17][18] In the family of D 2 A-type layers,f ive distinct types of charge-ordered states have been characterized so far; the neutral state (N;D 0 2 A 0 ), [19] the one-electron-transferred state (1e-I;D 0.5+ 2 A À ), [20] the two-electron-transferred state (2e-I;D + 2 A 2À ), [21] and two types of partial-electron-transferred state (1.5e-I;D 0.75+ 2 A 1.5À )w ith ac harge-disproportionated ordered form (1.5e-I o ) [22] and ad isordered form (1.5e-I d ) [12] (Scheme 1).…”

“…Inspired by the superior flexibility of the charge state in our D/A-MOFs,the chemi-or physisorption of guest molecules into ap orous D/A-MOF (that is,p seudopolymorphs) could bring about amodulation of charge states in the host framework, consequently resulting in ad rastic magnetic change. [12,15,23] Herein, we report au nique D 2 A-layered compound, [{Ru 2 (m-FPhCO 2 ) 4 } 2 TCNQ(OMe) 2 ]·nDCE (1-nDCE; m-FPhCO 2 À = m-fluorobenzoate;T CNQ(OMe) 2 = 2,5-dimethoxyl-7,7,8,8-tetracyanoquinodimethane;D CE = 1,2dichloroethane), which adopts three types of charge-ordered states depending on the degree of solvation of DCE, that is, nDCE:2e-I for the fully solvated compound (pristine form; 1-4DCE), 1.5e-I d for the solvent-free compound (1), and 1e-I for apartially solvated intermediate state (1-DCE with n 1) ( Figure 1a). These three types of states clearly modify the magnetic phases and the corresponding critical temperatures (T c ); paramagnetic (2e-I), ferrimagnetic with T c = 30 K(1.5e-I d ), and ferrimagnetic with T c = 88 K( 1e-I).…”