Crystal Structure of (μ-Phenoxo)bis(μ-pentafluorobenzoate)dicobalt(II, III) Complex with a Dinucleating Ligand

The end-off type dinucleating ligands, having a phenolic and alcoholic oxygen as an endogenous bridge, have been used for modeling carboxylate-bridged bimetallic active sites of metalloproteins,1–4 such as hemerythrin (Hr)5 and methane monooxygenase (MMO).6 The bimetallic active centers of metalloproteins have been known to exhibit various oxidation states: dimetal(II, II), dimetal(II, III), dimetal(III, III), dimetal (III, IV), and dimetal(IV, IV).1–6 Synthetic model complexes with various oxidation states are of particular importance for obtaining fundamental insights into structural and spectroscopic properties of the active centers in metalloproteins.1–4 Previously, we reported on the synthesis and characterization of mixed-valence complexes, [FeFe(bpmp)(RCO2)2] and [MnMn(bpmp)(RCO2)2] (R = CH3 and C6H5), having an end-off type dinucleating ligand with pyridyl groups (bpmp).7,8 In this paper, we report on the crystal structure of the dicobalt(II, III) mixed-valence complex [CoCo(bpmp)(C6F5CO2)2](ClO4)2·C2H5OC2H5 (1) (Fig. 1). A mixture of Co(ClO4)2·6H2O (0.183 g, 0.5 mmol) and Hbpmp (0.133 g, 0.25 mmol) in methanol (20 mL) was added a methanol solution (5 mL) containing C6F5CO2H (0.106 g, 0.5 mmol) and triethylamine (69 μL, 0.5 mmol) to give a darkbrown solution under air. Diethyl ether (30 mL) was added to the resulting dark-brown solution to give a black powder, which was recrystallized from acetonitrile/diethyl ether to give single crystals of [CoCo(bpmp)(C6F5CO2)2](ClO4)2·C2H5OC2H5 (1) suitable for X-ray crystallography. Yield: 0.09 g, 27% (Anal. Found: C, 44.49; H, 3.37; N, 7.68%. Calcd for [CoIICoIII(bpmp)(C6F5CO2)2](ClO4)2·1.5CH3CN·1.5H2O, C50H40.5Cl2Co2F10N7.5O14.5: C, 44.25; H, 3.01; N, 7.74%.). 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 Bruker D8 VENTURE diffractometer (Cu Kα radiation) at 90 K. The structure was solved by a direct method (SHELXT)9 and expanded using a Fourier technique. The structure was refined by a full-matrix least-squares method by using SHELXL 201410 (Yadokari-XG).11 All non-hydrogen atoms were refined with anisotropic displacement parameters. The hydrogen atoms were included using a riding model. The crystal data are summarized in Table 1. The X-ray crystallography of 1 reveals that the asymmetric unit contains a complex cation [CoCo(bpmp)(C6F5CO2)2], two ClO4, and a diethyl ether molecule, where one of ClO4 is disordered over two orientations. An ORTEP drawing of the complex cation, [CoCo(bpmp)(C6F5CO2)2] of 1, is shown in Fig. 2. Selected bond distances (Å) and angles (°) are given in Table 2. The complex cation of 1 has distinct cobalt centers that are triply bridged by phenoxide oxygen of bpmp, and two pentafluorobenzoate groups as found for closely related dimetal(II, III) mixed valence complexes, [FeIIFeIII(bpmp)(C2H5CO2)2] (2)12 and [MnMn(bpmp)(C6H5CO2)2] (3).8 2020 © The Japan Society for Analytical Chemistry