Structural-Electronic Correlation in the First-Order Phase Transition of [FeH2L2-Me](ClO4)2 (H2L2-Me = Bis[((2-methylimidazol-4-yl)met
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- 作者：Nicolas Bré ; fuel ; Shinya Imatomi ; Haruna Torigoe ; Hiroaki Hagiwara ; Sergiu Shova ; Jean-Franç ; ois Meunier ; Sé ; bastien Bonhommeau ; Jean-Pierre Tuchagues ; Naohide Matsumoto
- 刊名：Inorganic Chemistry
- 出版年：2006
- 出版时间：October 2, 2006
- 年：2006
- 卷：45
- 期：20
- 页码：8126 - 8135
- 全文大小：373K
- 年卷期：v.45,no.20(October 2, 2006)
- ISSN：1520-510X
文摘
The synthesis and detailed study of the new mononuclear spin crossover complex [FeIIH2L2-Me](ClO4)2 (whereH2L2-Me = bis[((2-methylimidazol-4-yl)methylidene)-3-aminopropyl]ethylenediamine) are reported. Variable-temperaturemagnetic susceptibility measurements show the occurrence of a steep spin crossover centered at 171.5 K with ahysteresis loop of ca. 5 K width (
=174 K and 
= 169 K, for increasing and decreasing temperatures,respectively). The crystal structure has been resolved for the high-spin (HS) and low-spin (LS) states at 200 and123 K, respectively, revealing a crystallographic phase transition that occurs concomitantly to the spin crossover:at 200 K, the complex crystallizes in the monoclinic system, space group P21/n, while the space group is P21 at123 K. The mean Fe-N distances are shortened by 0.2 Å, but the thermal spin crossover is accompanied by significant structural changes: the rearrangement of the central atom C12 of a six-membered chelate ring of[FeIIH2L2-Me]2+ to two positions (C12A and C12B) and, consequently, the lack of an inversion center at 123 K (P21space group). Both HS and LS supramolecular structures involve all possible hydrogen bonds between imidazoleand amine NH functions, and perchlorate anions; however, the HS supramolecular structure is a one-dimensional(1D) network, and the LS phase may better be described as a two-dimensional (2D) extended structure of A andB molecules. The structural phase transition of [FeH2L2-Me](ClO4)2 seems to trigger the steep and hysteretic spincrossover. Discontinuities in the temperature dependence of the Mössbauer parameters (isomer shift and quadrupolesplitting) at the spin crossover temperature confirmed the occurrence of a structural phase transition. The experimentalenthalpy and entropy variations were determined by differential scanning calorimetry (DSC) as 7.5 ± 0.4 kJ/moland 45 ± 3 J K-1 mol-1, respectively. The regular solution theory was applied to the experimental data, yieldingan interaction parameter of 
= 3.36 kJ/mol, which is larger than 2RT1/2, which fulfills the condition for observinghysteresis.
=174 K and = 169 K, for increasing and decreasing temperatures,respectively). The crystal structure has been resolved for the high-spin (HS) and low-spin (LS) states at 200 and123 K, respectively, revealing a crystallographic phase transition that occurs concomitantly to the spin crossover:at 200 K, the complex crystallizes in the monoclinic system, space group P21/n, while the space group is P21 at123 K. The mean Fe-N distances are shortened by 0.2 Å, but the thermal spin crossover is accompanied by significant structural changes: the rearrangement of the central atom C12 of a six-membered chelate ring of[FeIIH2L2-Me]2+ to two positions (C12A and C12B) and, consequently, the lack of an inversion center at 123 K (P21space group). Both HS and LS supramolecular structures involve all possible hydrogen bonds between imidazoleand amine NH functions, and perchlorate anions; however, the HS supramolecular structure is a one-dimensional(1D) network, and the LS phase may better be described as a two-dimensional (2D) extended structure of A andB molecules. The structural phase transition of [FeH2L2-Me](ClO4)2 seems to trigger the steep and hysteretic spincrossover. Discontinuities in the temperature dependence of the Mössbauer parameters (isomer shift and quadrupolesplitting) at the spin crossover temperature confirmed the occurrence of a structural phase transition. The experimentalenthalpy and entropy variations were determined by differential scanning calorimetry (DSC) as 7.5 ± 0.4 kJ/moland 45 ± 3 J K-1 mol-1, respectively. The regular solution theory was applied to the experimental data, yieldingan interaction parameter of = 3.36 kJ/mol, which is larger than 2RT1/2, which fulfills the condition for observinghysteresis.