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.

Structure and Heme-Independent Peroxidase Activity of a Fully-Coordinated Mononuclear Mn(II) Complex with a Schiff-Base Tripodal Ligand Containing Three Imidazole Groups

“…The CD (circular dichroism) spectrum of the methanolic solution of complex 1 did not show any significant intensity and Flack parameter for the crystal is near 0.5, suggesting that the crystal is a racemic twined crystal. Table 2 27 This is also con- 17 Considering the ionic radii of the high-spin Mn(II) and Fe(III), it is suggestive that there is a pseudo-coordination between Mn(II) and the apical tertiary amine N atom in the Mn(II) centers of complex 1. ) are connected by hydrogen bonds between imidazole and imidazolate of N imid H···· Nimid.…”

“…Structures and characteristics of several M(imtren) complexes, where M = Co(III), Fe(II), Fe(III), Mg(II), and Ru(II), have been reported. [13][14][15][16][17][18][19][20] In those, the imtren ligand hexadentately coordinates to the metal ions, forming highly symmetric octahedral geometries. For Mn(II) ion, using the methylated imtren ligand at the 4-position of the imidazole ring, Mn(II) complexes have been synthesized and structurally characterized but Mn(II)(imtren) has not been structurally characterized and its reactivity has not reported.…”

Self-Assembly of an Imidazolate-Bridged FeIII/CuII Heterometallic Cage

“…The precursor [FeH 3 L] 3+ of metalloligand FeL exists as two enantiomers in both the solid state and solution, with either a Δ (clockwise) or Λ (anticlockwise) configuration due to the screw coordination arrangement of the achiral tripodal ligand around Fe III . [14][15] That is, the deprotonated metalloligands of type FeL act as chiral building blocks incorporating secondary binding sites for further reaction with additional metal ions. 14 and perchlorate ν Cl-O (~1055 and 621 cm -1 ) 16 ( Figure S4).…”

“…[14][15] That is, the deprotonated metalloligands of type FeL act as chiral building blocks incorporating secondary binding sites for further reaction with additional metal ions. 14 and perchlorate ν Cl-O (~1055 and 621 cm -1 ) 16 ( Figure S4). The UVvis-NIR spectrum of 1 in CH 3 CN for the region 2000-200 nm ( Figure S5a and S5b), at two different concentrations, revealed two relatively low intensity absorption bands at 570 and 776 nm, and an intense band at 279 nm.…”

“…The relatively low intensity bands at 776 and 570 nm are likely to be charge-transfer transitions and a combination of d-d bands which are localised at both Fe III and Cu II centres. 14,17 Figure 1. Single-crystal structure of the heterometallic nanocage 1 and the respective coordination environments of the Fe III , Cu II -A and Cu II -B sites, which include either bound DMF or water molecules.…”