Crystal Structure of a Dinuclear Co Complex with Doubly Bridged Fluorides: Di-μ-fluoride Bis{(2-pyridylmethyl)bis(2-quinolylmethyl)amine} Dicobalt(II) Bis(tetrafluoroborate), [Co2(μ-F)2(pbqa)2](BF4)2

Dioxo-, dihydroxoand difluoro-bridged dinuclear metal complexes are well known. Their research concerning the complexes plays an important role in understanding the properties of metal–metal interaction such as energy, electron transfer, valence intermolecular charge-transfer, magnetic coupling. Also, these complexes have been interesting regarding organic synthesis catalysis and photosynthesis catalysis.1 The study of a fluorine crosslinked dinuclear cobalt complex has been reported by Cho et al.2 The fluorine source has an origin from hydrolysis of the tetrafluoroborate ions. The difluoride bridged dinuclear cobalt complex described in this manuscript has tetrafluoroborate ions too. However, the cobalt–cobalt distance is closed due to strong π–π interactions between two quinoline rings of ancillary ligands. In 2014, we reported on the crystal structure of [Co2(μ-F)2(Me3tpa)2](BF4)2 (Me3tpa = tris(6methyl-2-pyridylmethyl)amine), which involves μ-fluoro bridged between two cobalt(II) ions; the distance of Co···Co was 3.158 Å.3 We expected a greater steric hindrance and electronic effect of the ancillary ligand than Mentpa (n = 1, 2, 3), and chose pbqa (pbqa = (2-pyridylmethyl)bis(2-quinolylmethyl) amine)4,5 containing quinoline groups. In this paper we describe the synthesis and crystal structure of a μ-fluoro di-cobalt(II) complex using a simpler ancillary ligand, and have also compared it with [Co2(μ-F)2(Me3tpa)2](BF4)2. (Fig. 1). Crystals suitable for the single-crystal X-ray structure analysis were obtained as follows. A solution of Co(BF4)2·6H2O in dry methanol was added to a methanol solution of (2-pyridylmethyl)bis(2-quinolylmethyl)amine (pbqa). The resulting solution was stirred for 30 min. The methanol solution was transferred to some glass tubes, and diethyl ether was added to the solution slowly. After this sealed glass tube was left standing at ambient temperature, over a period of 9 days, brown microcrystals of [Co2(μ-F)2(pbqa)2](BF4)2 separated from the solution. Characterization was on the basis of ESI-MS, a satisfactory elemental analysis and single crystal crystallographic data. X-ray diffraction data for one of these crystals were collected at 100 K on a Rigaku XtaLAB P200 using multi-layer mirror monochromated Mo-Kα radiation. Crystal data and details concerning the data collection are given in Table 1. The structure was solved by direct methods, and refined by fullmatrix least-squares methods. Hydrogen atoms were refined using the riding model with C–H = 0.95 or 0.98 Å and with Uiso(H) = 1.2Ueq(C). The final crystals of a full matrix leastsquares refinement on F2 was based on 7897 observed reflections and 447 variable parameters, and converged (largest parameters shift was 0.00 times its esd) with unweighted and weighted agreement factors of R1 = 0.0403 (I > 2σ(I)) and wR2 = 0.1018 (all data). The standard deviation of an observation of unit weights was used. The maximum and minimum peaks on the final difference Fourier map corresponded to 0.931 and –0.311 eÅ–3, respectively. Crystallographic data have been deposited with Cambridge Crystallographic Data Centre: Deposit number CCDC-1882663. Copies of the data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/ retrieving.html), or from the Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge, CB2 1EZ, UK; Fax: +44 1223 336033; email: deposit@ccdc.cam.ac.uk). The chemical structure and an ORTEP view of the complex are shown in Figs. 1 and 2. The two CoII ions are bridged by 2019 © The Japan Society for Analytical Chemistry