Related Experiment Video
Updated: Mar 8, 2026
Preparation of 6-aminocyclohepta-2,4-dien-1-one Derivatives via Tricarbonyltroponeiron
Published on: August 12, 2019
Prototypical iron(ii) complex with 4-amino-1,2,4-triazole reinvestigated: an unexpected impact of water on spin
Mark B Bushuev1, Denis P Pishchur2, Ilya V Korolkov1
1Nikolaev Institute of Inorganic Chemistry, Siberian Branch of Russian Academy of Sciences, 3, Acad. Lavrentiev Ave., Novosibirsk, 630090, Russia. bushuev@niic.nsc.ru mark.bushuev@gmail.com and Novosibirsk State University, 2, Pirogova str., Novosibirsk, 630090, Russia.
Abstract:
The magnetic and thermodynamic properties of the prototypical 1D polymeric complex Fe(ATrz)3(NO3)2·H2O (ATrz = 4-amino-1,2,4-triazole) were reinvestigated to gain an insight into the impact of water molecules on the spin transition. Variations in the outerspheric water molecule content in the complex induce drastic and unpredictable changes in its spin crossover regimes. Under vacuum the complex loses water molecules and shows a wide (ca. 30 K) and reproducible hysteresis loop, Tc↑ = 337-345 K and Tc↓ = 316-313 K. In sealed ampoules the complex Fe(ATrz)3(NO3)2·H2O shows a narrow hysteresis (ca. 1-4 K), Tc↑ = 326-329 K and Tc↓ = 326-324 K. After adsorption of water the complex Fe(ATrz)3(NO3)2·nH2O (n = 1.25-1.6) demonstrates a narrow two-step spin transition. In all these cases the kinetics of the LS → HS and HS → LS transitions has decelerating non-cooperative character. For the system Fe(ATrz)3(NO3)2·nH2O (n = 3.6-16.6) wide hysteresis (ca. 5-20 K) re-appears near room temperature (Tc↑ = 319-321 K and Tc↓ = 300-315 K). Surprisingly, the kinetics of the HS → LS spin transition for the systems with high water content switches from decelerating to sigmoidal (cooperative). The activation energy of the LS → HS transition was estimated for the first time for iron(ii) spin crossover complexes with 1,2,4-triazoles (ca. 1000-2000 kJ mol-1). The systems Fe(ATrz)3(NO3)2 and Fe(ATrz)3(NO3)2·nH2O show compensation effects (ΔH - ΔS, ln A - Ea). A correlation between the Tonset↑, the ΔH values and the water content in the complex is observed: the highest ΔH values (27-29 kJ mol-1) and the lowest Tonset↑ values (317-320 K) correspond to the samples with high water content, whereas the lowest ΔH values (19-23 kJ mol-1) and the highest Tonset↑ values (337-345 K) correspond to water-free samples, Fe(ATrz)3(NO3)2. Our results provide the first experimental evidence that the presence of water (and even air humidity) produces dramatic changes in the spin crossover behavior of the prototypical 1D polymeric complex Fe(ATrz)3(NO3)2·H2O (ATrz = 4-amino-1,2,4-triazole).
Related Concept Videos
02:42Valence Bond Theory
01:26EDTA: Auxiliary Complexing Reagents
01:11Aryldiazonium Salts to Azo Dyes: Diazo Coupling
03:02Colors and Magnetism
When atoms or molecules absorb light at the proper frequency, their electrons are excited to higher-energy orbitals. For many main group atoms and molecules, the absorbed photons are in the ultraviolet range of the electromagnetic spectrum, which cannot be detected by the human eye. For coordination compounds, the energy difference between the d orbitals often allows photons in the visible range to be absorbed and emitted, which is seen as colors by the human...
01:22EDTA: Chemistry and Properties
02:34Structural Isomerism
Isomers are different chemical species that have the same chemical formula. Structural isomerism of coordination compounds can be divided into two subcategories, the linkage isomers and coordination-sphere isomers.
Linkage isomers occur when the coordination compound contains a ligand that can bind to the transition metal center through two different atoms. For example, the CN− ligand can bind through the carbon atom or through the nitrogen atom. Similarly, SCN− can...