Direct Synthesis of Spin‐Crossover Complexes: An Unexpectedly Revealed New Iron‐Triazolic Structure

Abstract

Spin‐crossover complexes form one of the biggest families of switchable compounds. Here we show a new way to obtain spin‐crossover materials by direct synthesis from metallic iron. Four complexes of FeII with 4‐R‐1,2,4‐triazoles have been synthesized by a direct metal oxidation: [Fe(NH2trz)3]SO4, [Fe(NH2trz)3](BF4)2 and two polymorphs of [Fe(Htrz)2(trz)]BF4. Surprisingly high quality of PXRD pattern of [Fe(NH2trz)3]SO4 allowed to perform Rietveld refinement and obtain reliable crystal structure of the latter. All compounds have been studied by magnetic susceptibility measurements, optical reflectivity, differential scanning calorimetry and Raman spectroscopy. Importantly, spin‐crossover characteristics of the complexes obtained by this unusual method are preserved, thus revealing a new effective approach of “direct synthesis” towards switchable coordination compounds.

Thermal hysteresis of stress and strain in spin-crossover@polymer composites: towards a rational design of actuator devices

“…18. We shall note that among the numerous Fe( ii ) triazole complexes, 41 we opted for compounds 1 and 4 because of their robust and well reproducible spin crossover properties and, importantly, because their crystal structure is known, 36,42 which is not frequent in this family of compounds. On the other hand, compounds 2 and 3 , which can be considered as derivatives of 1 , were added to the study with the aim to more firmly confirm the main findings.…”

Rational direct synthesis of [Fe(Htrz)2(trz)](BF4) polymorphs: temperature and concentration effects

“…However, this is a surfactantfree synthesis that can be of importance in the integration into composites 3,19,20 and hybrid nanomaterials [21][22][23] , deserving then an in-depth investigation. Very recently, new approaches have been proposed for the direct synthesis of such triazole-based compounds, starting from metallic iron 24 or using mechanochemistry 25 as well as surfactant-free synthesis like spraydrying 26 or flow chemistry coupled to supercritical fluids treatment 27,28 . The aim of this paper is to investigate the direct synthesis conditions to obtain NPs of the [Fe(Htrz)2(trz)](BF4) in the appropriate phase.…”

Cooperative Spin Crossover above Room Temperature in the Iron(II) Cyanoborohydride–Pyrazine Complex

“…The obtained critical temperatures ( T 1/2 ↑ = 338 K and T 1/2 ↓ = 322 K) are similar to those obtained in other experiments. Average values of the enthalpy change (Δ H ) and the entropy change (Δ S ) associated with spin transition, Δ H = 19.4 kJ mol –1 and Δ S = 58.7 J mol –1 K –1 , are consistent with the values typically observed for other cooperative spin transitions. , …”