Cooperative 1D Triazole-Based Spin Crossover Fe^II Material With Exceptional Mechanical Resilience

Abstract

We report here the first single crystal investigations, in both high spin (HS) and low spin (LS) states, correlated to magnetic and heat capacity measurements, of a new cooperative and robust spin transition triazole-based Fe II 1-D coordination polymer [Fe(bntrz)3][Pt(CN)4].H2O (1) (bntrz = 4-(Benzyl)-1,2,4-triazole). The compound exhibits a sharp transition at 240 K, accompanied with an anisotropic deformation of the unit cell and a significant gliding of the chains from each other. These two features are identified as the key parameters of the non-conventional mechanical resilience of this system.

One-Dimensional Thiocyanato-Bridged Fe(II) Spin Crossover Cooperative Polymer With Unusual FeN5S Coordination Sphere

“…The design of new cooperative spin crossover (SCO) materials is one of the most relevant challenges in the field of molecular materials. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] The SCO transition, which occurs generally for the transition metal complexes of d 4 -d 7 electronic configurations, can be induced by various external perturbations, such as temperature, pressure, light, and magnetic field, yielding significant structural, magnetic and optical changes. The presence the intermolecular interactions (-stacking, hydrogen bonding and van der Waals contacts) in the crystal lattice can significantly affect the cooperativity which is at the origin of the presence of wide hysteresis that required for potential applications such as displays and memory, pressure and optical sensors, and spintronic devices.…”

“…[10][11][12][13][14][15][16][17][18][19][20][21] By far, the most studied switchable molecular materials are those based on Fe(II) transition metal ion for which the magnetic switch occurs between the paramagnetic high spin (HS) state (S = 2) and the diamagnetic low spin (LS) state (S = 0). [1][2][3][4][5][6][7][8] Until now, the majority of Fe(II) SCO materials involves the FeN 6 coordination environment because of the appropriate ligand-field energy brought by the nitrogen-based ligands. [1][2][3][4][5][6][7][8][9] However, in the last few years and for a relatively short time, the number of reports on Fe(II) SCO systems with FeN 4 O 2 coordination sphere, arising from N 4 O 2 hexadentate, 22 N 2 O 2 tetradentate [23][24][25][26][27][28][29] or N 2 O tridentate [30][31][32] Schiff-base ligands, increased in a very considerable way, and some of them exhibit remarkable SCO behaviors such as bistability around room temperature and wide hysteresis loops.…”

A rare octacoordinated mononuclear iron(III) spin-crossover compound: synthesis, crystal structure and magnetic properties

“…SCO is most common in transition-metal complexes containing metal centres with a d 4 -d 7 electronic configuration, which enables them to fulfill the HS!LS transition between the T 2g and E g electronic orbitals (Harding et al, 2016;Tsukiashi et al, 2018;Znovjyak et al, 2019;Ishida et al, 2016). Among all the external stimulus induced SCO systems, the most famous is the hexacoordinated iron(II) family with diverse structure types ranging from discrete mononuclear complexes to one-dimensional (1D) chains to two/threedimensional (2D/3D) networks, in which the Fe II ions are always embedded in an octahedral coordination sphere with the usual N 6 or N 4 O 2 coordination unit (Olguín, 2020;Pittala et al, 2017;Bao et al, 2010;Petzold et al, 2018;Drahoš & Trá vníček, 2018). However, compared to the universal hexacoordinated iron(II) complexes, coordination numbers for either the Fe II ion or the Fe III ion higher than six are rarely observed in discrete molecules because high coordination numbers are usually confined to the larger metal ions of the heavier f-elements rather than the comparatively lighter 3d ones.…”

Spin Cross-Over (SCO) Complex Based on Unsymmetrical Functionalized Triazacyclononane Ligand: Structural Characterization and Magnetic Properties

“…Such complexes exhibit a reversible switch from the High Spin (HS) to the Low Spin (LS) state, as a response to an external perturbation as temperature, pressure, magnetic field, or light irradiation, when the complex involves metal ions having d 4 -d 7 electronic configuration [1][2][3][4][5][6][7][8][9][10][11][12]. To date, among the large number of SCO materials, the Fe(II) systems (d 6 configuration), for which the transition occurs between the paramagnetic high-spin (HS, S = 2, 5 T 2g ) and the diamagnetic low-spin (LS, S = 0, 1 A 1g ) states, are, by far, the most studied examples [13][14][15][16][17][18][19][20][21]. From the design point of view, a recent strategy consists in preparing SCO systems with the use of systems with the use of polydentate ligands with a large potential denticity, such as cyclam and cyclen, which are known to form very stable complexes with transition metal ions [22].…”