Synthesis, Structure and Magnetic and Electrochmical Properties of Tetrakis(benzamidato)diruthenium(II,III) Tetraﬂuoroborate

: A lantern-type diruthenium(II,III) complex [Ru 2 (HNOCPh) 4 (BF 4 )(H 2 O)] was prepared from [Ru 2 (HNOCPh) 4 Cl] n by removal of the axial chlorido-bridge using AgBF 4 in THF. The room temperature magnetic moment (per Ru 25+ unit) of [Ru 2 (HNOCPh) 4 (BF 4 )(H 2 O)] is 3.84 µ B , which is similar to that (4.15 µ B ) of [Ru 2 (HNOCPh) 4 Cl] n , for which magnetic measurement was newly performed in this study. These results indicate that both of the complexes have a spin state of S = 3/2, although temperature-variable (VT) magnetic moments (2–300 K) showed that considerable antiferromagnetic interaction ( zJ = − 2.8 cm − 1 ) exists through the axial chlorido-bridge for [Ru 2 (HNOCPh) 4 Cl] n , but such a large interaction ( zJ = − 0.08 cm − 1 ) does not exist for [Ru 2 (HNOCPh) 4 (BF 4 )(H 2 O)], where the large zero-ﬁeld splitting D = 61 cm − 1 is operative for both complexes, like other lantern-type diruthenium(II,III) complexes. The X-ray single-crystal structure analysis of [Ru 2 (HNOCPh) 4 (BF 4 )(H 2 O)] · 2(acetone) showed that the axial positions of the complex were occupied by a ﬂuorine atom of the BF 4 − ion and an oxygen atom of the water molecule, with distances of Ru-F ax = 2.3265(19) Å and Ru-O ax = 2.280(2) Å, respectively. The Ru-Ru bond distance was 2.2793(4) Å, which is shorter than those (2.295(2) and 2.290(2) Å) reported for [Ru 2 (HNOCPh) 4 Cl] n . The quartet ground states ( S = 3/2) were reasonably interpreted for [Ru 2 (HNOCPh) 4 (BF 4 )(H 2 O)] and [Ru 2 (HNOCPh) Cl] n , as well as the theoretically modeled complex cation [Ru 2 (HNOCPh) 4 ] + , by DFT calculation results. A Ru 26+ /Ru 25+ redox couple was observed at 1.12 V (vs. SCE) for [Ru 2 (HNOCPh) 4 (BF 4 )(H 2 O)] in dichloromethane containing Bu 4 NPF 6 as electrolyte.


Synthesis and Characterizations
The axial chloride ligand of [Ru2(HNOCPh)4Cl]n could be removed by chemical reaction with AgBF4 in THF for 24 h with stirring at room temperature, giving the tetrafluoroborate salt Ru2(HNOCPh)4BF4•H2O, the chemical formation of which was confirmed by elemental analysis in addition to the fact that ESI-TOF MS and IR spectra showed a main peak corresponding to the cationic species [Ru2(HNOCPh)4] + (683.9904m/z) and a predominant absorption appearing around 1100 cm −1 due to BF4 − ion [22].The IR spectra of [Ru2(HNOCPh)4Cl]n and Ru2(HNOCPh)4BF4•H2O are given in Figure 1; their spectral features are basically the same, other than the band due to the BF4 − ion, which indicates that Ru2(HNOCPh)4BF4•H2O has a Ru2 5+ core unit similar to that of [Ru2(HNOCPh)4Cl]n.Furthermore, the BF4 − ion and water molecule are coordinated to the dinuclear core with a unidentate mode, as shown below for the crystal structure of [Ru2(HNOCPh)4(BF4)(H2O)]•2(acetone).Hereafter, Ru2(HNOCPh)4BF4•H2O is described as In 1985, the zigzag chain structure of [Ru 2 (HNOCPh) 4 Cl] n was determined using X-ray crystal structure analysis by Chakravarty and Cotton, although the magnetic properties were not reported in spite of the interest in magnetic interaction through the axial chlorido-bridge between the spins in lantern-type Ru 2 5+ dinuclear cores [15].In order to investigate the spin state of the Ru 2 5+ core and the magnetic interaction through the chlorido-bridge, we newly synthesized a tetrafluoroborate complex Ru 2 (HNOCPh)

Magnetic Properties
In Figures 6 and 7, variable-temperature (VT) magnetic susceptibilities and moments are shown in the measured 2-300 K temperature range for [Ru2(HNOCPh)4Cl]n and [Ru2(HNOCPh)4(BF4)(H2O)], respectively.The magnetic moment (per Ru2 5+ unit) of [Ru2(HNOCPh)4Cl]n is 4.15 μB at 300 K, which indicates the existence of three unpaired electrons per the Ru2 5+ unit with an S = 3/2 state.Like the other halogenido (X)-linked Ru2 5+ polymer complexes, the magnetic moment decreases with decrease in the temperature, due to zero-field splitting (D), followed by a further steep decrease in the moment when the temperature is approaching 2 K, due to the antiferromagnetic interaction through the axial chloride ion [5,17,19,20].The magnetic moment of [Ru2(HNOCPh)4(BF4)(H2O)] is 3.84 μB at 300 K, which is also indicative of the spin state of S = 3/2 for this complex, and decreases with decrease in temperature due to zero-field splitting, without the steep decrease in the moment even when the temperature is close to 2 K.

Magnetic Properties
In Figures 6 and 7

Magnetic Properties
In Figures 6 and 7, variable-temperature (VT) magnetic susceptibilities and moments are shown in the measured 2-300 K temperature range for [Ru2(HNOCPh)4Cl]n and [Ru2(HNOCPh)4(BF4)(H2O)], respectively.The magnetic moment (per Ru2 5+ unit) of [Ru2(HNOCPh)4Cl]n is 4.15 μB at 300 K, which indicates the existence of three unpaired electrons per the Ru2 5+ unit with an S = 3/2 state.Like the other halogenido (X)-linked Ru2 5+ polymer complexes, the magnetic moment decreases with decrease in the temperature, due to zero-field splitting (D), followed by a further steep decrease in the moment when the temperature is approaching 2 K, due to the antiferromagnetic interaction through the axial chloride ion [5,17,19,20].The magnetic moment of [Ru2(HNOCPh)4(BF4)(H2O)] is 3.84 μB at 300 K, which is also indicative of the spin state of S = 3/2 for this complex, and decreases with decrease in temperature due to zero-field splitting, without the steep decrease in the moment even when the temperature is close to 2 K.   VT magnetic behaviors are conventionally simulated using the Equations ( 1)-( 4), described below, for the S = 3/2 system with a zero-field splitting of Ru2 5+ species, the inter-dinuclear-unit interaction being taken into account by means of a mean-field approximation [3,5,[29][30][31]: where zJ is the exchange energy multiplied by the number (z) of interacting neighbors, and χ is the magnetic susceptibility.

DFT Calculations
The present complex [Ru2(HNOCPh)4(BF4)(H2O)] obtained from [Ru2(HNOCPh)4Cl]n by the removal of axial chlorido linker does not have empty axial positions, as in the case of VT magnetic behaviors are conventionally simulated using the Equations ( 1)-( 4), described below, for the S = 3/2 system with a zero-field splitting of Ru 2 5+ species, the inter-dinuclear-unit interaction being taken into account by means of a mean-field approximation [3,5,[29][30][31]: where zJ is the exchange energy multiplied by the number (z) of interacting neighbors, and χ is the magnetic susceptibility.

DFT Calculations
The present complex [Ru 2 (HNOCPh) 4 (BF 4 )(H 2 O)] obtained from [Ru 2 (HNOCPh) 4 Cl] n by the removal of axial chlorido linker does not have empty axial positions, as in the case of [Ru 2 (DArF) 4 ]BF 4 .The DFT calculation treatments are essentially the same between the previous work on [Ru 2 (DArF) 4 ] + [10] and the present one on [Ru 2 (HNOCPh) 4 ] + .When taking into consideration the fact that theoretical calculation results on diruthenium(II,III) tetracarboxylate complexes have been in accordance with the S = 3/2 ground state [1][2][3]32], we can also say that [Ru 2 (DArF) 4 ]BF 4 is a unique complex with an S = 1/2 ground state due to the π* 3 electronic configuration, where the δ* orbital is energetically higher than the π* orbitals in the case of no anti-bonding π-type interactions with axial ligands having a π character, such as Cl − ions [10].

General Aspects
All reagents and solvents were used as received.The precursor complex [Ru 2 (O 2 CCMe) 4 Cl] n was prepared according to a published procedure [33].
Elemental analyses for carbon, hydrogen, and nitrogen were performed using a Yanako CHN Corder MT-6.Infrared spectra (KBr pellets) were measured with a JASCO FT/IR-4600.Absorption spectra and diffuse spectra were obtained using JASCO V-670 and Shimadzu UV-3100 spectrometers, respectively.ESI-TOF mass spectra were taken on a Bruker microTOF.The variable temperature magnetic susceptibilities were measured over the temperature range of 2-300 K at the constant field of 0.5 T with a Quantum Design MPMS3 and MPMS XL-5 for [Ru 2 (HNOCPh) 4 Cl] n and [Ru 2 (HNOCPh) 4 (BF 4 )(H 2 O)], respectively.The measured data were corrected for diamagnetic contributions [34].Cyclic voltammograms (CVs) were measured in dichloromethane containing tetra-n-butylammonium hexafluoroborate Bu 4 NPF 6 on a BAS ALS-DY2325 electrochemical analyzer.A glassy carbon disk (1.5 mm radius), platinum wire, and saturated calomel electrodes were used as working, counter, and reference electrodes, respectively.

Synthesis of [Ru 2 (HNOCPh) 4 Cl] n
This complex was synthesized using a modified method described in the literature [13].A 5.0 g (42 mmol) of PhCONH 2 was combined with 0.50 g (1.0 mmol) of Ru 2 (O 2 CCH 3 ) 4 Cl under nitrogen.The mixture was heated to 150 • C and stirred for 72 h.Excess of the ligand was then removed by sublimation under the reduced pressure, followed by washing thoroughly with acetone and being dried by heating for 3 h under vacuum to give a brown powder.A 50.3 mg (0.070 mmol) of Ru 2 (HNOCPh) 4 Cl was reacted with 5.0 mg (0.077 mmol) of AgBF 4 in THF (50 mL) with stirring at room temperature for 24 h in the dark.The white precipitate of AgCl was removed by filtration over celite.The filtrate was employed for evaporation to remove the solvent.The resultant brown powder was dissolved in chloroform and employed for filtration over celite to further remove AgCl and unreacted AgBF 4 .The filtrate was again employed for evaporation to remove the solvent.The formed powder was dissolved in acetone and filtered.The precipitate formed by concentration of the filtrated solution was collected by suction filtration, washed with diethylether and dried over P 2 O 5 in desiccator for 20 h to give a yellowish-brown powder.The yield was 31.

Crystal Structure Determination
The single crystals of [Ru 2 (HNOCPh) 4 (BF 4 )(H 2 O)]•2(acetone) suitable for X-ray crystal structure analysis were obtained by the recrystallization of [Ru 2 (HNOCPh) 4 (BF 4 )(H 2 O)] from acetone.X-ray crystallographic data (Table 1) was collected for a single crystal at 123(2) K on a RIGAKU Saturn 70 CCD system equipped with Mo rotating-anode X-ray generator with monochromated Mo Kα radiation (λ = 0.71075 Å).Diffraction data were processed using CrystalClear-SM (RIGAKU).The structure was solved by direct methods (SIR-2011) and refined using the full-matrix least-squares technique (F 2 ) with SHELXL-2014 as part of the CrystalStructure 4.2.5 software.Non-hydrogen atoms were refined with anisotropic displacement parameters, and all hydrogen atoms were located at calculated positions and refined with a riding model.)]•2(acetone).These data can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

H 2 O
by removing the axial chlorido-bridge of [Ru 2 (HNOCPh) 4 Cl] n in the presence of AgBF 4 in THF solution.The variable-temperature (VT) magnetic susceptibility measurements were performed in the 2-300 K temperature range for both complexes.The comparison of the VT magnetic behaviors indicated that a considerably large antiferromagnetic interaction through the axial chlorido-bridge exists for [Ru 2 (PhCONH) 4 Cl] n (zJ = −2.8cm −1 ), but not for Ru 2 (HNOCPh) 4 BF 4 •H 2 O (zJ = −0.08 cm −1 ), in addition to the fact that both of the complexes have an Ru 2 5+ core with a spin sate of S = 3/2, showing a large zero-field splitting (D = 61 cm −1 ) like the other lantern-type Ru 2 5+ complexes with spin state of S = 3/2 [1-5].This report describes the electrochemical properties of Ru 2 (HNOCPh) 4 BF 4 •H 2 O in dichloromethane containing Bu 4 NPF 6 as electrolyte, as well as the crystal structure determined for the single crystals obtained by the recrystallization of Ru 2 (HNOCPh) 4 BF 4 •H 2 O from acetone.

Figure 6 .
Figure 6.Variable temperature of magnetic susceptibility χM (red circles) and moment μeff (blue circles) for [Ru2(HNOCPh)4Cl]n.The solid black lines were calculated and drawn with the parameter values described in the text.

Figure 6 .
Figure 6.Variable temperature of magnetic susceptibility χM (red circles) and moment μeff (blue circles) for [Ru2(HNOCPh)4Cl]n.The solid black lines were calculated and drawn with the parameter values described in the text.

Figure 6 .
Figure 6.Variable temperature of magnetic susceptibility χ M (red circles) and moment µ eff (blue circles) for [Ru 2 (HNOCPh) 4 Cl] n .The solid black lines were calculated and drawn with the parameter values described in the text.

Figure 7 .
Figure 7. Variable temperature of magnetic susceptibility χ M (red circles) and moment µ eff (blue circles) for [Ru 2 (HNOCPh) 4 (BF 4 )(H 2 O)].The solid black lines were calculated and drawn with the parameter values described in the text.