title: Supramolecular spin-crossover iron complexes based on imidazole-imidazolate hydrogen bonds.
abstract: The [Fe(II)(H(3)L)](BF(4))(2).3H(2)O (1) complex was synthesized, where H(3)L (tris[[2-[(imidazole-4-yl)methylidene]amino]ethyl]amine) is a tripodal ligand obtained by condensation of tris(2-aminoethyl)amine and 4-formylimidazole (fim) in a 1:3 molar ratio. Starting from 1, a series of complexes, [Fe(II)(H(1.5)L)](BF(4))(0.5) (2) (=[Fe(II)(H(3)L)][Fe(II)(L)]BF(4)), [Fe(H(1.5)L)]BF(4) (3) (=[Fe(II)(H(3)L)][Fe(III)(L)](BF(4))(2)), [Fe(III)(H(3)L)](BF(4))(3).fim.H(2)O (4), and [Fe(III)(L)].2.5H(2)O (5), has been synthesized and characterized. The single-crystal X-ray structure of each complex has been determined. The Fe(II) compound, 2, and a mixed valence Fe(II)-Fe(III) compound, 3, involve formally hemi-deprotonated ligands, H(1.5)L. The structure of 3 consists of a homochiral two-dimensional assembled sheet, arising from the intermolecular hydrogen bonds between [Fe(II)(H(3)L)](2+) and [Fe(III)(L)](0) (3). All but 5 exhibit spin crossover between low-spin (LS) and high-spin (HS) states. This is a rare case where both Fe(II) and Fe(III) complexes containing the same ligand exhibit spin-crossover behavior. Magnetic susceptibility and Mössbauer studies showed that 3 has three accessible electronic states: LS Fe(II)-LS Fe(III), HS Fe(II)-LS Fe(III), and HS Fe(II)-HS Fe(III). Compounds 1-3 show the light-induced excited spin-state trapping effect at the Fe(II) sites upon irradiation with green light. The solution magnetic properties, electronic spectra, and electrochemical properties of 1, 4, and 5 were also studied.
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
authors.forename: Hiromi
authors.initials: H
authors.lastname: Ohta
authors.forename: Masaaki
authors.initials: M
authors.lastname: Kojima
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Ikuta
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Goto
authors.forename: Naohide
authors.initials: N
authors.lastname: Matsumoto
authors.forename: Seiichiro
authors.initials: S
authors.lastname: Iijima
authors.forename: Haruo
authors.initials: H
authors.lastname: Akashi
authors.forename: Sumio
authors.initials: S
authors.lastname: Kaizaki
authors.forename: Françoise
authors.initials: F
authors.lastname: Dahan
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Tuchagues