Bushuev Mark B, Pishchur Denis P, Korolkov Ilya V, Vinogradova Katerina A
Nikolaev Institute of Inorganic Chemistry, Siberian Branch of Russian Academy of Sciences, 3, Acad. Lavrentiev Ave., Novosibirsk, 630090, Russia.
Phys Chem Chem Phys. 2017 Feb 1;19(5):4056-4068. doi: 10.1039/c6cp06854e.
The magnetic and thermodynamic properties of the prototypical 1D polymeric complex Fe(ATrz)(NO)·HO (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, T↑ = 337-345 K and T↓ = 316-313 K. In sealed ampoules the complex Fe(ATrz)(NO)·HO shows a narrow hysteresis (ca. 1-4 K), T↑ = 326-329 K and T↓ = 326-324 K. After adsorption of water the complex Fe(ATrz)(NO)·nHO (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)(NO)·nHO (n = 3.6-16.6) wide hysteresis (ca. 5-20 K) re-appears near room temperature (T↑ = 319-321 K and T↓ = 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). The systems Fe(ATrz)(NO) and Fe(ATrz)(NO)·nHO show compensation effects (ΔH - ΔS, ln A - E). A correlation between the T↑, the ΔH values and the water content in the complex is observed: the highest ΔH values (27-29 kJ mol) and the lowest T↑ values (317-320 K) correspond to the samples with high water content, whereas the lowest ΔH values (19-23 kJ mol) and the highest T↑ values (337-345 K) correspond to water-free samples, Fe(ATrz)(NO). 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)(NO)·HO (ATrz = 4-amino-1,2,4-triazole).
对典型的一维聚合物配合物Fe(ATrz)(NO)·H₂O（ATrz = 4-氨基-1,2,4-三唑）的磁性和热力学性质进行了重新研究，以深入了解水分子对自旋转变的影响。配合物中外层水分子含量的变化会在其自旋交叉区域引起剧烈且不可预测的变化。在真空中，该配合物会失去水分子，并呈现出宽约30 K且可重复的磁滞回线，T↑ = 337 - 345 K，T↓ = 316 - 313 K。在密封安瓿中，配合物Fe(ATrz)(NO)·H₂O呈现出窄磁滞（约1 - 4 K），T↑ = 326 - 329 K，T↓ = 326 - 324 K。吸附水后，配合物Fe(ATrz)(NO)·nH₂O（n = 1.25 - 1.6）表现出窄的两步自旋转变。在所有这些情况下，低自旋（LS）→高自旋（HS）和高自旋→低自旋转变的动力学具有减速的非协同特征。对于体系Fe(ATrz)(NO)·nH₂O（n = 3.6 - 16.6），在室温附近（T↑ = 319 - 321 K，T↓ = 300 - 315 K）再次出现宽磁滞（约5 - 20 K）。令人惊讶的是，对于高含水量体系，高自旋→低自旋自旋转变的动力学从减速转变为S形（协同）。首次估计了含1,2,4 - 三唑的铁（II）自旋交叉配合物的低自旋→高自旋转变的活化能（约1000 - 2000 kJ/mol）。体系Fe(ATrz)(NO)和Fe(ATrz)(NO)·nH₂O表现出补偿效应（ΔH - ΔS，ln A - E）。观察到T↑、ΔH值与配合物中含水量之间的相关性：最高的ΔH值（27 - 29 kJ/mol）和最低的T↑值（317 - 320 K）对应于高含水量样品，而最低的ΔH值（19 - 23 kJ/mol）和最高的T↑值（337 - 345 K）对应于无水样品Fe(ATrz)(NO)。我们的结果提供了首个实验证据，即水（甚至空气湿度）的存在会使典型的一维聚合物配合物Fe(ATrz)(NO)·H₂O（ATrz = 4-氨基-1,2,4-三唑）的自旋交叉行为发生显著变化。
