Synthesis and spin-crossover characteristics of polynuclear 4-(2′-hydroxy-ethyl)-1,2,4-triazole Fe(II) molecular materials

doi:10.1016/S1387-1609(98)80006-6

Comptes Rendus de l'Académie des Sciences - Series IIC - Chemistry

Volume 1, Issue 8, August 1998, Pages 523-532

Comptes Rendus de l'...

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Abstract

A new series of Fe(II) spin-crossover materials of formula [Fe(hyetrz)₃](Anion)₂•xH₂O, where hyetrz = 4-(2′-hydroxy-ethyl)-1,2,4-triazole and Anion = Cl⁻, NO₃⁻, Br⁻, I⁻, BF₄⁻, ClO₄⁻, PF₆⁻, have been prepared and the spin transition characteristics studied. The structure of these compounds consists of linear chains in which the Fe(II) ions are linked by triple N1,N2-1,2,4-triazole bridges. Most of the hydrated compounds show non-classical spin-crossover behaviour associated with the removal of lattice water molecules, which initially stabilize the low-spin state. However for two of them, the perchlorate and the iodide compounds, the transition temperature is shifted to higher temperatures by dehydration. For the corresponding dehydrated compounds, the transition temperature T_1/2 increases with decreasing anion radii. [Fe(hyetrz)₃]I₂ represents one of the few Fe(II) spin-crossover materials showing a spin transition in the close vicinity of room temperature (291 K) accompanied by a thermal hysteresis (12 K).

Résumé

Une nouvelle série de composés du Fe(II) à transition de spin, de formule [Fe(hyetrz)₃](Anion)2•xH₂O, où hyetrz =4-(2′-hydroxy-éthyl)-1,2,4-triazole et Anion = Cl⁻, NO₃⁻, Br⁻, I⁻, BF₄⁻, ClO₄⁻, PF₆⁻, a été préparée et étudiée. Ces composés sont constitués de chaînes linéaires dans lesquelles les ions Fe²⁺ sont reliés par trois ponts formés par les azotes N1 et N2 des ligands 1,2,4-triazole. La plupart des composés hydratés présentent une transition de spin non classique, gouvernée par la perte des molécules d'eau qui, initialement, stabilisaient l'état bas spin. Deux d'entre eux (ClO₄⁻ et I⁻), cependant, présentent une température de transition légèrement augmentée par déshydratation. Lorsque ces composés ont été déshydratés par chauffage, leur température de transition T_1/2 augmente quasi linéairement avec le rayon de l'anion. Lorsque l'anion utilisé est l'iodure, le composé correspondant présente une transition de spin proche de la température ambiante (T_1/2 ↑ = 297 K et T_1/2 ↓ = 285 K) accompagnée d'une hystérésis thermique (12 K), ce qui a rarement été observé avec les composés du Fe(II) à transition de spin.

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Memoire court/Short communicationSynthesis and spin-crossover characteristics of polynuclear 4-(2′-hydroxy-ethyl)-1,2,4-triazole Fe(II) molecular materialsSynthèse et caractérisation de nouveaux matériaux moléculaires à transition de spin à base de 4-(2′-hydroxy-éthyl)-1,2,4-triazole

Abstract

Résumé

Aust. J. Chem.

Struct. Bonding (Berlin)

New J. Chem.

Angew. Chem. Int. Ed. Engl.

Mol. Cryst. Liq. Cryst.

Phil. Trans. R. Soc. London A

Low spin to high spin transition

1,2,4-triazoles as ligands for iron(II) high spin to low spin crossovers

Science

Adv. Mater.

Mol. Cryst. Liq. Cryst.

J. Mater. Chem.

Chem. Mater.

Memoire court/Short communication
Synthesis and spin-crossover characteristics of polynuclear 4-(2′-hydroxy-ethyl)-1,2,4-triazole Fe(II) molecular materialsSynthèse et caractérisation de nouveaux matériaux moléculaires à transition de spin à base de 4-(2′-hydroxy-éthyl)-1,2,4-triazole