Spin Transition Kinetics in the Salt [H2N(CH3)2]6[Fe3(L)6(H2O)6] (L = 4-(1,2,4-triazol-4-yl)ethanedisulfonate)

Abstract

The dimethylammonium salt of the Fe II polyanionic trimer [Fe 3 (µ-L) 6 (H 2 O) 6 ] 6(L = 4-(1,2,4-triazol-4-yl)ethanedisulfonate) exhibits a thermally induced spin transition above room temperature with one of the widest hysteresis cycles observed in a spin crossover compound (>85 K). Furthermore, the metastable high-spin (HS) state can be thermally trapped via relatively slow cooling, remaining metastable near room temperature, with a characteristic T TIESST = 250 K (TIESST = temperature-induced excited spin-state trapping). The origin for this unique behavior is still uncertain. In this manuscript, we report detailed studies on the relaxation kinetics of this system in order to disclose the mechanism and cooperativity controlling this process.

Cooperative 1D Triazole-Based Spin Crossover FeII Material With Exceptional Mechanical Resilience

“…The intrachain Fe···Fe distances in 1 are almost similar to those found in [Fe­(Htrz) 2 (trz)]­(BF 4 ), in both spin states, whereas the interchain Fe···Fe ones are significantly longer than those observed in other parent 1D triazole-based derivatives that have been structurally characterized (see Table S3). Moreover, the Fe···Fe intrachain distances in 1 appear also longer in both HS and LS states than the corresponding distances observed in discrete trinuclear complexes based on triazole ligands, − although this latter observation refers only to the few compounds that display “full” HS or LS states, i.e., involving all the iron centers. Because of the triclinic symmetry of the crystal lattice, the interchain distances do not exactly match the Fe···Fe intermolecular distances, but are shorter because the chains are slightly shifted from each other in the a direction (Figure S4).…”

Antagonist elastic interactions tuning spin crossover and LIESST behaviours in FeII trinuclear-based one-dimensional chains

“…23 In contrast, in the major part of trinuclear systems, only the central Fe II ion undergoes a SCO transition from the HS-HS-HS to HS-LS-HS states, while the two external metal ions remain in the HS state due to their FeN 3 O 3 coordination environments involving water molecules or other oxygenated species acting as terminal ligands. [28][29][30][31][32][33][34][35][36][37][38][39][40][41] It is of interest to note, however, that all the trinuclear complexes based on neutral triazole triple bridges show poorly cooperative and incomplete transitions, [28][29][30][31][32][33][34][35][36][37][38] while one of the few anionic complexes based on sulfonated triazole ligands [39][40][41] show a thermal HS-HS-HS to HS-LS-HS transition above room temperature with an unexpectedly large hysteresis loop (>85 K) and the highest temperature at which the memory effect remains in a thermally quenched SCO system (T TIESST = 250 K). 39 Thus, to achieve true SCO trinuclear complexes with three active metal centres in which the central one displays a similar environment to those involved in 1D chain polymers and to favour the occurrence of cooperative effects along the linear trinuclear system, we have extended the above synthetic approach to the use of uncommon and sophisticated cyanocarbanions which can act as terminal or bridging coligands through their various N-donor nitrile groups.…”

“…19,20 Besides these 1-D systems, di- and trinuclear discrete complexes based on similar triple triazole bridges have also been reported, and most of them have been structurally characterised. 21–41 These polynuclear systems could help modeling and tuning the SCO characteristics of 1D coordination polymers, especially trinuclear complexes in which the central metal ion shows a similar environment to the one involved in 1D coordination polymers. Dinuclear systems show various SCO behaviours including abrupt or incomplete gradual thermal transitions and photo-induced LIESST effects, 21–27 and some of them stand out due to their multifunctional characteristics such as the presence of synergic SCO/fluorescence 21 or the on/off photo-control of magnetic interactions.…”

Tuning the spin crossover behavior of the polyanion [(H2O)6Fe3(μ-L)6]6–: the case of the cesium salt

“…Both solutions were mixed for 10 minutes under stir-One example is the polyanion [Fe 3 (µ-L 6 )(H 2 O) 6 ] 6-(1, L = 4-(1,2,4-triazol-4-yl)ethanedisulfonate). 88,89 Its molecular structure consists of a linear array of three octahedral Fe(II) centers, which are bridged by two triple 1,2,4-triazole bridges. The two terminal Fe(II) centers complete their octahedral coordination with three water molecules.…”