title: Scan Rate Dependent Spin Crossover Iron(II) Complex with Two Different Relaxations and Thermal Hysteresis fac-[Fe(II)(HL(n-Pr))3]Cl·PF6 (HL(n-Pr) = 2-Methylimidazol-4-yl-methylideneamino-n-propyl).
abstract: Solvent-free spin crossover Fe(II) complex fac-[Fe(II)(HL(n-Pr))3]Cl·PF6 was prepared, where HL(n-Pr) denotes 2-methylimidazol-4-yl-methylideneamino-n-propyl. The magnetic susceptibility measurements at scan rate of 0.5 K min(-1) showed two successive spin transition processes consisting of the first spin transition T1 centered at 122 K (T1↑ = 127.1 K, T1↓ = 115.8 K) and the second spin transition T2 centered at ca. 105 K (T2↑ = 115.8 K, T2↓ = 97.2 K). The magnetic susceptibility measurements at the scan rate of 2.0, 1.0, 0.5, 0.25, and 0.1 K min(-1) showed two scan speed dependent spin transitions, while the Mössbauer spectra detected only the first spin transition T1. The crystal structures were determined at 160, 143, 120, 110, 95 K in the cooling mode, and 110, 120, and 130 K in the warming mode so as to follow the spin transition process of high-spin HS → HS(T1) → HS(T2) → low-spin LS → LS(T2) → LS(T1) → HS. The crystal structures at all temperatures have a triclinic space group P1̅ with Z = 2. The complex-cation has an octahedral N6 coordination geometry with three bidentate ligands and assume a facial-isomer with Δ- and Λ-enantimorphs. Three imidazole groups of fac-[Fe(II)(HL(n-Pr))3](2+) are hydrogen-bonded to three Cl(-) ions. The 3:3 NH(imidazole)···Cl(-) hydrogen-bonds form a stepwise ladder assembly structure, which is maintained during the spin transition process. The spin transition process is related to the structural changes of the FeN6 coordination environment, the order-disorder of PF6(-) anion, and the conformation change of n-propyl groups. The Fe-N bond distance in the HS state is longer by 0.2 Å than that in the LS state. Disorder of PF6(-) anion is not observed in the LS state but in the HS state. The conformational changes of n-propyl groups are found in the spin transition processes except for HS → HS(T1) → HS(T2).
authors.affiliation: †Department of Chemistry, Faculty of Science, Kumamoto University, Kurokami 2-39-1, Kumamoto 860-8555, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Fujinami
authors.affiliation: †Department of Chemistry, Faculty of Science, Kumamoto University, Kurokami 2-39-1, Kumamoto 860-8555, Japan.
authors.forename: Koshiro
authors.initials: K
authors.lastname: Nishi
authors.affiliation: †Department of Chemistry, Faculty of Science, Kumamoto University, Kurokami 2-39-1, Kumamoto 860-8555, Japan.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Hamada
authors.affiliation: †Department of Chemistry, Faculty of Science, Kumamoto University, Kurokami 2-39-1, Kumamoto 860-8555, Japan.
authors.forename: Keishiro
authors.initials: K
authors.lastname: Murakami
authors.affiliation: †Department of Chemistry, Faculty of Science, Kumamoto University, Kurokami 2-39-1, Kumamoto 860-8555, Japan.
authors.forename: Naohide
authors.initials: N
authors.lastname: Matsumoto
authors.affiliation: ‡National Institute of Advanced Industrial Science and Technology, Tsukuba 305-8566, Japan.
authors.forename: Seiichiro
authors.initials: S
authors.lastname: Iijima
authors.affiliation: §Department of Chemistry, Faculty of Science, Okayama University, Tsushima-naka 3-1-1, Okayama 700-8530, Japan.
authors.forename: Masaaki
authors.initials: M
authors.lastname: Kojima
authors.affiliation: §Department of Chemistry, Faculty of Science, Okayama University, Tsushima-naka 3-1-1, Okayama 700-8530, Japan.
authors.forename: Yukinari
authors.initials: Y
authors.lastname: Sunatsuki