An Electron‐Transfer Ferromagnet with T_c=107 K Based on a Three‐Dimensional [Ru₂]₂/TCNQ System

Abstract

The design of dp-pp molecular systems with efficient electronic communication is a long-standing goal in the field of inorganic chemistry. Guiding principles for this research are provided by the seminal studies on the Creutz-Taube ion, [(H 3 N) 5 Ru(m-pyz)Ru(NH 3 ) 5 ] 5+ (pyz = pyrazine), discovered in 1969, [1] as well as subsequent related compounds [2] that undergo charge-transfer interactions between mixed-valent metal ions through an organic bridging ligand. Various experimental investigations to evaluate the electron-transfer dynamics were undertaken and theoretical interpretations from kinetic and, thermodynamic approaches were developed by Hush, [3] Marcus and Sutin, [4] and others.[5]In the context of the current work, we also note the important contributions of Crutchley and co-workers, who explored electron-transfer processes in dinuclear ruthenium-(III) complexes bridged by the 1,4-dicyanamidobenzene dianion (Dicyd 2À ) or one of its substituted derivatives. [6] Interestingly, this class of compounds demonstrated strong intramolecular magnetic coupling between Ru III S = 1/2 spins via the pp orbital of the Dicyd bridge with J exceeding 400 cm À1 closely associated with a highly conjugated p-d network, classified as Class II or III behavior on the RobinDay scale.[7] A crucial design ingredient for such systems is a 1:2 ratio of the one-electron donor (D, i.e., Dicyd) to the oneelectron acceptor (A, i.e., a Ru III ion) that can lead to an electron-transfer resonance of type [ ]. Our research is directed at the synthesis of coordination framework solids with dp/pp conjugation with the goal of achieving hybrid magnetic and conducting properties. In short, our research in this area can be expressed conceptually as "expanding the Creutz-Taube molecule to higher dimensions". The strategy is to design networks with a D:A ratio of 2:1 or 1:2 which involve a one-electron transfer that "turns on" electron-transfer resonance. In this vein, we chose to study the family of paddlewheel-type diruthenium(II,II) complexes with S = 1 as an electron donor to undergo the reversible redox reaction [Ru 2 II,II ]$[Ru 2 II,III ] without a significant change of structure.[8] The molecule concomitantly acts as a linear building block, [9] with 7,7,8,8-tetracyanoquinodimethane (TCNQ) acting as an electron acceptor and tetrakis-monodentate donor ligand. In earlier work, the 2:1 assemblies [{Ru 2 (O 2 CCF 3 )} 2 TCNQ]·3 S (S = toluene, 1 a;[10] pxylene, 1 b) [11] and [{Ru 2 (O 2 CCF 3 )} 2 TCNQF 4 ]·3 p-xylene (TCNQF 4 = 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane; 2), [11] with two-dimensional (2D) fishing-net-like (hexagonal) layered structures ( Figure 1) were synthesized.While 1 a and 1 b showed poor if any [Ru 2 ]!TCNQ electron transfer, 2 exhibited significant electron-transfer resonance which led to unusual magnetic properties, that is, the compound is a metamagnet with T N = 95 K (a field-induced ferromagnet), albeit not the high-T c ferromagnet that we were seeking.Herein we report a new structural type...

Unexpected structural and electronic effects of internal rotation in diruthenium paddlewheel complexes containing bulky carboxylate ligands

“…Diruthenium complexes have a unique electronic structure and interesting physical properties that are responsible for the current popularity and continued expansion of this field. Potential applications for these complexes have been found in a wide variety of areas such as catalysts [2][3][4] and antitumour metallopharmaceuticals [5][6][7], as well their incorporation into supramolecular arrays [8][9][10][11][12] that can have interesting magnetic [13][14][15] and optoelectronic properties [16][17][18]. Recent studies have also highlighted the potential use of diruthenium compounds as molecular wires [19,20], and there is often a strong relationship between the structure of these complexes and their reactivity or electronic structure [21].…”

Doping Effect in Three-dimensional Donor–Acceptor Magnet: Percolated Magnetic Pathways Dominated by Local Electron Transfers

“…•¹ as A ¹ ) is a radical with S = 1/2, providing a ferrimagnet with a magnetic-phase-transition temperature, T c = 107 K. 12 Meanwhile, a similar D 2 A-type three-dimensional compound using m- …”

“…All compounds showed a similar behavior, in which » gradually increases from 300 K on cooling, followed by an abrupt increase around 100 K, indicative of magnetic phase transition, as was found in 1 (T c (1) = 107 K). 12 Based on ac magnetic susceptibility data ( Figure 3b and Figure S2), 16 T c of 10%, 12.5%, and 15%, determined by reading the temperature at which the »¤¤ signal leaves the baseline on cooling, are 99, 91, and 84 K, respectively (inset of Figure 3a). Thus, the increase in the doping ratio causes decreases T c .…”

Synthesis, structure and physical properties of the one-dimensional chain complex of tetrathiafulvalene carboxylate

“…Bi-functional materials combining magnetic and conducting properties in the same crystal lattice have attracted much attention in recent years [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] . Many complexes possessing both the conducting π-electrons and magnetic d-electrons (π-d system) have been synthesized and characterized.…”

“…However, the π-d interactions, if there are any, are very weak because the magnetic and conducting parts are absolutely separated from each other and the π-d interactions could occur only through space. Direct coordination of paramagnetic metal ions to organic radicals is another strategy to construct π-d system [10][11][12][13][14][15][16] . This kind of complexes, which has been designated as "fused π-d system" by Yamashita et al, [10] facilitates the π-d interactions due to covalent linker between the magnetic and conducting parts.…”