TY - JOUR
T1 - Structures and spin states of mono- and dinuclear iron(II) complexes of imidazole-4-carbaldehyde azine and its derivatives
AU - Sunatsuki, Yukinari
AU - Kawamoto, Ryohei
AU - Fujita, Kunihiro
AU - Maruyama, Hisashi
AU - Suzuki, Takayoshi
AU - Ishida, Hiroyuki
AU - Kojima, Masaaki
AU - Iijima, Seiichiro
AU - Matsumoto, Naohide
N1 - Funding Information:
This work was supported by a Grant-in-Aid for Scientific Research (Nos. 16205010, 17350028 and 20550064) from the Ministry of Education, Science, Sports, and Culture of Japan.
Copyright:
Copyright 2010 Elsevier B.V., All rights reserved.
PY - 2010/8
Y1 - 2010/8
N2 - Mononuclear [Fe(H2LR)2]X2 (R = H, 2-Me, 5-Me, 2-Et-5-Me; X = ClO4, BF4) and dinuclear [Fe2(H2LR)3]X4 complexes containing imidazole-4-carbaldehyde azine (H2LH) and its derivatives prepared by condensation of 4-formylimidazole, 2-methyl- or 5-methyl-4-formylimidazole, or 2-ethyl-4-methyl-5-formylimidazole, with hydrazine in a 2:1 mole ratio in methanol, were prepared and their magnetostructural relationships were studied. In the mononuclear complexes, H2LR acts as an unsymmetrical tridentate ligand with two imidazole nitrogen atoms and one azine nitrogen atom, while in the dinuclear complexes, H2LR acts as a dinucleating ligand employing four nitrogen atoms to form a triple helicate structure. At room temperature, [Fe2(H2LH)3](ClO4)4 and [Fe2(H2L2-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 H2L2-Me with electron-donating methyl groups being stronger than H2LH, with the order of the ligand field strengths being H2L2-Me > H2LH. However, in the mononuclear [Fe(H2LH)2](ClO4)2 and [Fe(H2L2-Me)2](ClO4)2 complexes, a different order of ligand field strengths, H2LH > H2L2-Me, was observed because [Fe(H2LH)2](ClO4)2 was in the LS state while [Fe(H2L2-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 H2L2-Me ligand and the other ligand in [Fe(H2L2-Me)2](ClO4)2 is responsible for the observed change in the spin state. The same is true for [Fe(H2L2-Et-5-Me)2](ClO4)2, while [Fe(H2L5-Me)2](ClO4)2 does not involve such a steric congestion and stays in the LS state over the temperature range 5-300 K. Two kinds of crystals (polymorphs) were isolated for [Fe2(H2LH)3](BF4)4 and [Fe2(H2L2-Et-5-Me)3](ClO4)4, and they exhibited different magnetic behaviors.
AB - Mononuclear [Fe(H2LR)2]X2 (R = H, 2-Me, 5-Me, 2-Et-5-Me; X = ClO4, BF4) and dinuclear [Fe2(H2LR)3]X4 complexes containing imidazole-4-carbaldehyde azine (H2LH) and its derivatives prepared by condensation of 4-formylimidazole, 2-methyl- or 5-methyl-4-formylimidazole, or 2-ethyl-4-methyl-5-formylimidazole, with hydrazine in a 2:1 mole ratio in methanol, were prepared and their magnetostructural relationships were studied. In the mononuclear complexes, H2LR acts as an unsymmetrical tridentate ligand with two imidazole nitrogen atoms and one azine nitrogen atom, while in the dinuclear complexes, H2LR acts as a dinucleating ligand employing four nitrogen atoms to form a triple helicate structure. At room temperature, [Fe2(H2LH)3](ClO4)4 and [Fe2(H2L2-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 H2L2-Me with electron-donating methyl groups being stronger than H2LH, with the order of the ligand field strengths being H2L2-Me > H2LH. However, in the mononuclear [Fe(H2LH)2](ClO4)2 and [Fe(H2L2-Me)2](ClO4)2 complexes, a different order of ligand field strengths, H2LH > H2L2-Me, was observed because [Fe(H2LH)2](ClO4)2 was in the LS state while [Fe(H2L2-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 H2L2-Me ligand and the other ligand in [Fe(H2L2-Me)2](ClO4)2 is responsible for the observed change in the spin state. The same is true for [Fe(H2L2-Et-5-Me)2](ClO4)2, while [Fe(H2L5-Me)2](ClO4)2 does not involve such a steric congestion and stays in the LS state over the temperature range 5-300 K. Two kinds of crystals (polymorphs) were isolated for [Fe2(H2LH)3](BF4)4 and [Fe2(H2L2-Et-5-Me)3](ClO4)4, and they exhibited different magnetic behaviors.
KW - Dinuclear complexes
KW - Helicates
KW - Iron(II) complexes
KW - Spin states
KW - Spin-crossover
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U2 - 10.1016/j.ccr.2009.11.016
DO - 10.1016/j.ccr.2009.11.016
M3 - Review article
AN - SCOPUS:77953127739
SN - 0010-8545
VL - 254
SP - 1871
EP - 1881
JO - Coordination Chemistry Reviews
JF - Coordination Chemistry Reviews
IS - 15-16
ER -