title: Prototypical iron(ii) complex with 4-amino-1,2,4-triazole reinvestigated: an unexpected impact of water on spin transition.
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)2and 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).
authors.affiliation: Nikolaev 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.
authors.forename: Mark B
authors.identifier: http://orcid.org/0000-0003-3830-8353
authors.initials: MB
authors.lastname: Bushuev
authors.affiliation: Nikolaev 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.
authors.forename: Denis P
authors.initials: DP
authors.lastname: Pishchur
authors.affiliation: Nikolaev 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.
authors.forename: Ilya V
authors.initials: IV
authors.lastname: Korolkov
authors.affiliation: Nikolaev 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.
authors.forename: Katerina A
authors.initials: KA
authors.lastname: Vinogradova