Structures and Spin States of Bis(tridentate)-Type Mononuclear and Triple Helicate Dinuclear Iron(II) Complexes of Imidazole-4-carbaldehyde azine

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• 作者：Yukinari Sunatsuki ; Ryohei Kawamoto ; Kunihiro Fujita ; Hisashi Maruyama ; Takayoshi Suzuki ; Hiroyuki Ishida ; Masaaki Kojima ; Seiichiro Iijima ; Naohide Matsumoto
• 刊名：Inorganic Chemistry
• 出版年：2009
• 出版时间：September 21, 2009
• 年：2009
• 卷：48
• 期：18
• 页码：8784-8795
• 全文大小：1079K
• 年卷期：v.48,no.18(September 21, 2009)
• ISSN：1520-510X

文摘

Mononuclear [Fe(H₂L^R)₂]²⁺ and dinuclear [Fe₂(H₂L^R)₃]⁴⁺ (R = H, 2-Me, 5-Me) complexes containing the new imidazole-4-carbaldehyde azine ligand (H₂L^H) and its derivatives (H₂L^2-Me and H₂L^5-Me) prepared from the condensation reaction of 4-formylimidazole or 2-methyl- or 5-methyl-4-formylimidazole with hydrazine (2:1) were prepared, and their magnetostructural relationships were studied. In the mononuclear complexes, H₂L^R acts as an unsymmetrical tridentate ligand with two imidazole nitrogen atoms and one azine nitrogen atom, while in the dinuclear complexes, H₂L^R acts as a dinucleating ligand employing four nitrogen atoms to form a triple helicate. At room temperature, [Fe₂(H₂L^H)₃](ClO₄)₄ and [Fe₂(H₂L^2-Me)₃](ClO₄)₄ were in the high-spin (HS) and low-spin (LS) states, respectively. The results are in accordance with the ligand field strength of H₂L^2-Me with electron-donating methyl groups being stronger than H₂L^H, with the order of the ligand field strengths being H₂L^2-Me > H₂L^H. However, in the mononuclear [Fe(H₂L^H)₂](ClO₄)₂ and [Fe(H₂L^2-Me)₂](ClO₄)₂ complexes, a different order of ligand field strengths, H₂L^H > H₂L^2-Me, was observed because [Fe(H₂L^H)₂](ClO₄)₂ was in the LS state while [Fe(H₂L^2-Me)₂](ClO₄)₂ was in the HS state at room temperature. X-ray structural studies revealed that the interligand steric repulsion between a methyl group of an H₂L^2-Me ligand and the other ligand in [Fe(H₂L^2-Me)₂](ClO₄)₂ is responsible for the observed change in the spin state. Two kinds of crystals, needles and blocks, were isolated for [Fe₂(H₂L^H)₃](BF₄)₄, and both exhibited a sharp spin transition, [LS−HS] ↔ [HS−HS]. The spin transition of the block crystals is more abrupt with a hysteresis, T_c↑ = 190 K and T_c↓ = 183 K with ΔT = 7 K.