Crystal Structure of μ-Phenoxo-μ-benzoate-bridged Dinuclear Fe(II) Complex with a Dinucleating Ligand Having a Sterically Bulky Imidazolyl Group

Abstract

The end-off type compartmental ligands, having a phenolic and alcoholic oxygen as an endogenous bridge, have been used for modeling bimetallic active sites of metalloprotains,1–4 such as hemerythrin (Hr)5 and methane monooxygenase (MMO).6 We have demonstrated that the thermal stability of (μ-peroxo) diiron(III) complexes and the oxygenation-deoxygenation reversibility are highly dependent on the nature of the end-off type compartmental ligands.4,7–11 Previously, we reported the crystal structure of a (μ-peroxo)diiron(III) complex, [Fe2(Phbimp)(PhCO2)(O2)], with a dinucleating ligand (Ph-bimp) bearing a sterically bulky imidazolyl group,8 which was obtained in a reversible reaction of the corresponding diiron(II) precursor complex, [Fe2(Ph-bimp)(PhCO2)](BF4)2·3H2O, with dioxygen in acetonitrile at ambient temperature. In this paper, we report details of the crystal structure of the diiron(II) precursor complex [Fe2(Ph-bimp)(PhCO2)(CH3CN)](BF4)2·2CH3CN·3CH3CH2OH (1) (Fig. 1). A single crystal of [Fe2(Ph-bimp)(PhCO2)(CH3CN)](BF4)2· 2CH3CN·3CH3CH2OH (1) suitable for X-ray crystallography was obtained by recrystallization of [Fe2(Ph-bimp)(PhCO2)](BF4)2·3H2O from a mixture of acetonitrile/ethanol at ambient temperature under N2. It was picked up on a hand-made cold copper plate mounted inside a liquid N2 Dewar vessel and mounted on a glass rod at –80°C. X-ray diffraction measurements were made on a Rigaku CCD Mercury diffractometer with graphite monochromated Mo Kα radiation at 108 K. The structure was solved by a direct method (SIR 92)12 and expanded using a Fourier technique. The structure was refined by a fullmatrix least-squares method by using SHELXL 201413 (Yadokari-XG).14 All non-hydrogen atoms were refined with anisotropic displacement parameters (ADP) and all hydrogen atoms were included using a riding model. The occupancy factors were also refined for the two BF4 anions, one acetonitrile molecule, and three ethanol molecules, which were disordered over two or three orientations. Distance/ADP restraints were applied to the disordered atoms in the anions and solvents. The crystal data is summarized in Table 1. The molecular structure of complex cation [Fe2(Ph-bimp)(PhCO2)(CH3CN)] of 1 is shown in Fig. 2. Selected bond distances (Å) and angles (°) are given in Table 2. The diiron(II) center is doubly bridged by phenoxide oxygen of Ph-bimp and benzoate oxygens, as found for closely related diiron(II) complexes: [Fe2(Ph-tidp)(PhCO2)] (2) (Ph-tidp = N,N,N′,N′tetrakis(1-methyl-4,5-diphenyl-2-imidazolyl)methyl-1,3-diamino2-propanolate),9 [Fe2(L)(PhCO2)] (3) (LPh4 = N,N,N′,N′tetrakis(1-methyl-2-phenyl-4-imidazolyl)methyl-1,3-diamino2-propanolate),10 and [Fe2(N-Et-HPTB)(PhCO2)] (4) (N-EtHPTB = N,N,N′,N′-tetrakis(1-ethyl-2-benzimidazolyl)methyl1,3-diamino-2-propanolate).15 The two iron atoms in 1 have different coordination geometries. The five-coordinate iron 2019 © The Japan Society for Analytical Chemistry