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

Abstract

A lantern-type diruthenium(II,III) complex [Ru₂(HNOCPh)₄(BF₄)(H₂O)] was prepared from [Ru₂(HNOCPh)₄Cl]_n by removal of the axial chlorido-bridge using AgBF₄ in THF. The room temperature magnetic moment (per Ru₂⁵⁺ unit) of [Ru₂(HNOCPh)₄(BF₄)(H₂O)] is 3.84 μ_B, which is similar to that (4.15 μ_B) of [Ru₂(HNOCPh)₄Cl]_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 [Ru₂(HNOCPh)₄Cl]_n, but such a large interaction (zJ = −0.08 cm⁻¹) does not exist for [Ru₂(HNOCPh)₄(BF₄)(H₂O)], 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 [Ru₂(HNOCPh)₄(BF₄)(H₂O)]·2(acetone) showed that the axial positions of the complex were occupied by a fluorine atom of the BF₄⁻ 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 [Ru₂(HNOCPh)₄Cl]_n. The quartet ground states (S = 3/2) were reasonably interpreted for [Ru₂(HNOCPh)₄(BF₄)(H₂O)] and [Ru₂(HNOCPh)₄Cl]_n, as well as the theoretically modeled complex cation [Ru₂(HNOCPh)₄]⁺, by DFT calculation results. A Ru₂⁶⁺/Ru₂⁵⁺ redox couple was observed at 1.12 V (vs. SCE) for [Ru₂(HNOCPh)₄(BF₄)(H₂O)] in dichloromethane containing Bu₄NPF₆ as electrolyte.

1. Introduction

There has been much interest directed towards lantern-type dinuclear complexes, due to the unique properties resulting from the meta-metal interactions within the dinuclear molecules [1,2]. In the cases of tetracarboxylatodiruthenium(II,III) complexes [Ru₂(O₂CR)₄X], it is well known that the electronic configuration is σ²π⁴δ²(δ*π*)³ [1,2,3,4,5]. The spin state of S = 3/2 has also been thought to be common for the diruthenium(II,III) complex with diarylformamidinate (DArF⁻) bridges having an N,N-donor set, the chemical structure of which is shown in Scheme 1a [1,6,7,8], although a spin cross-over behavior was reported for [Ru₂(DArF)₄Cl] (Ar = p-methoxyphenyl group) [9]. Recently, [Ru₂(DArF)₄]BF₄ (Ar = p-methoxyphenyl or m-methoxyphenyl group) obtained by the removal of the axial chloride ion from [Ru₂(DArF)₄Cl] was reported to show a singlet ground state (S = 1/2) [10]. Such spin state change from S = 3/2 to S = 1/2 has not been reported on the removal of the axial halogenide ligand from [Ru₂(O₂CR)₄X]. Amidate ions with an N,O-donor set have also been known to work as a dinucleating bridging ligand to give a lantern-type structure [11,12,13,14,15,16,17,18,19,20,21]. One of the amidates is benzamidate (PhCONH⁻), the chemical structure of which is shown in Scheme 1b.

In 1985, the zigzag chain structure of [Ru₂(HNOCPh)₄Cl]_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 Ru₂⁵⁺ dinuclear cores [15]. In order to investigate the spin state of the Ru₂⁵⁺ core and the magnetic interaction through the chlorido-bridge, we newly synthesized a tetrafluoroborate complex Ru₂(HNOCPh)₄BF₄·H₂O by removing the axial chlorido-bridge of [Ru₂(HNOCPh)₄Cl]_n in the presence of AgBF₄ 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 [Ru₂(PhCONH)₄Cl]_n (zJ = −2.8 cm⁻¹), but not for Ru₂(HNOCPh)₄BF₄·H₂O (zJ = −0.08 cm⁻¹), in addition to the fact that both of the complexes have an Ru₂⁵⁺ core with a spin sate of S = 3/2, showing a large zero-field splitting (D = 61 cm⁻¹) like the other lantern-type Ru₂⁵⁺ complexes with spin state of S = 3/2 [1,2,3,4,5]. This report describes the electrochemical properties of Ru₂(HNOCPh)₄BF₄·H₂O in dichloromethane containing Bu₄NPF₆ as electrolyte, as well as the crystal structure determined for the single crystals obtained by the recrystallization of Ru₂(HNOCPh)₄BF₄·H₂O from acetone.

2. Results and Discussion

2.1. 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]⁺ (683.9904 m/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 Ru₂⁵⁺ 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 [Ru₂(HNOCPh)₄(BF₄)(H₂O)]. In the diffuse reflectance spectra (Figure 2), the NIR band assigned as δ (Ru₂⁵⁺) → δ* (Ru₂⁵⁺) was observed at 988 and 978 nm for [Ru₂(HNOCPh)₄Cl]_n and [Ru₂(HNOCPh)₄(BF₄)(H₂O)], respectively, in addition to the bands assigned as π(Ru-O/N,Ru₂⁵⁺) → δ* (Ru₂⁵⁺) at 484 nm (for [Ru₂(HNOCPh)₄Cl]_n) and 440 nm (for [Ru₂(HNOCPh)₄(BF₄)(H₂O)]). The band observed at 352 nm for both complexes could be attributed to the axial ligand (Cl⁻ or BF₄⁻) → σ* (Ru₂⁵⁺) charge transfer [1,3,11,13,14,17]. The absorption spectrum was measured for [Ru₂(HNOCPh)₄(BF₄)(H₂O)] in dichloromethane, although [Ru₂(HNOCR)₄Cl]_n was completely insoluble in less-donating solvents such as dichloromethane; hence, strongly donating solvents such as DMSO were used for the physicochemical measurements in the solution [11,12,14]. The absorption spectrum (Figure 3) of [Ru₂(HNOCPh)₄(BF₄)(H₂O)] in dichloromethane showed bands at 360, 470 and 965 nm similar to those in solid (352, 440 and 978 nm in the diffuse reflectance spectrum). This suggests that the dinuclear structure [Ru₂(HNOCPh)₄(BF₄)(H₂O)] is maintained in the dichloromethane solution.

2.2. Cyclic Voltammogram (CV) of [Ru₂(HNOCPh)₄(BF₄)(H₂O)]

The electrochemical redox behavior of [Ru₂(HNOCPh)₄(BF₄)(H₂O)] was investigated by the CV technique in dried dichloromethane containing 0.1 M Bu₄NPF₆ as electrolyte. The result is shown in Figure 4. The redox wave at E_1/2 ((E_pa + E_pc)/2) = 1.12 V (vs. SCE) in the oxidation side was attributed to a Ru₂⁶⁺/Ru₂⁵⁺ couple on referring to the CV results obtained for the Ru₂⁵⁺ complexes with amidato bridges [11,12,13,18], while irreversible waves were subsequently shown at ca. −0.5 and ca. −1.0 V (vs. SCE), the former being possibly attributable to the Ru₂⁵⁺/Ru₂⁴⁺ process. It has been previously reported that [Ru₂(HNOCPh)₄Cl]_n exhibits a Ru₂⁶⁺/Ru₂⁵⁺ wave at 0.66 V (vs. SCE) and an irreversible Ru₂⁵⁺/Ru₂⁴⁺ wave at ca. −0.50 V (vs. SCE) in DMSO containing 0.1 M Bu₄NClO₄ and excess of Cl⁻, while the Ru₂⁶⁺/Ru₂⁵⁺ wave was not observed in DMSO containing 0.1 M Bu₄NClO₄ without addition of Cl⁻, and redox couples associated with Ru₂⁵⁺/Ru₂⁴⁺ process were subsequently observed at −0.70 and −1.13 V (vs. SCE) [13]. The complex redox behaviors reported for [Ru₂(HNOCPh)₄Cl]_n in the DMSO solution may be due to the strong donating nature of DMSO, participating in the axial coordination instead of Cl⁻. Because the dinuclear structure of [Ru₂(HNOCPh)₄(BF₄)(H₂O)] is maintained in the less-donating dichloromethane solution, the redox behavior is considered to be rather simple and similar to that reported for [Ru₂(HNOCPh)₄Cl]_n in DMSO solution containing an excess of Cl⁻ [13]. The lantern-type dinuclear complex [Ru₂(bam)₄Cl₂] (bam⁻ = benzamidinate ion (Scheme 2a)) favors the oxidation state of Ru₂(III,III), mainly due to the strong donating nature of a benzamidinato bridging ligand having an N,N-donor set compared with the amidato bridging ligand with the N,O-donor set in [Ru₂([Ru₂(HNOCPh)₄(BF₄)(H₂O)], although the difference in the axial ligands should be taken into account. In the case of [Ru₂(bam)₄Cl₂], the Ru₂⁶⁺/Ru₂⁵⁺ couple was observed at E_1/2 = −0.231 V (vs. SCE) in chloroform containing 0.1 M Bu₄NPF₆ [23]; the redox potential is negatively shifted in potential compared with that of [Ru₂(HNOCPh)₄(BF₄)(H₂O)]. The large irreversible wave at ca. −1.0 V vs. SCE observed for [Ru₂(HNOCPh)₄(BF₄)(H₂O)] could be related to its decomposition.

2.3. Crystal Structure of [Ru₂(HNOCPh)₄(BF₄)(H₂O)]·2(acetone)

Single crystals suitable for X-ray crystal structure analysis were obtained as those of [Ru₂(HNOCPh)₄(BF₄)(H₂O)]·2(acetone) by the recrystallization of [Ru₂(HNOCPh)₄(BF₄)(H₂O)] from acetone. The molecular structure and its selected bond distances and angles are given in Figure 5 and Table S1, respectively. Four amidato ligands bridge two ruthenium ions with a cis-(2:2) arrangement of the ligands around Ru₂^II,III core, giving a lantern-like structure. The Ru1-Ru2 distance is 2.2793(4) Å, which is shorter than the corresponding distances (2.295(2) and 2.290(2) Å) of [Ru₂(HNOCPh)₄Cl]_n, in which chloride ions axially coordinate to ruthenium ions with Ru-Cl_ax distances of 2.572(3) and 2.612(3) Å to link the Ru₂⁵⁺ units, resulting in a zigzag chain structure with a Ru-Cl_ax-Ru bond angle of 116.2(1)˚ [15]. In [Ru₂(HNOCPh)₄(BF₄)(H₂O)]·2(acetone), both axial positions of the Ru₂⁵⁺ unit are occupied with fluorine (BF₄⁻) and oxygen (H₂O) atoms with Ru1-F1 and Ru2-O5 distances of 2.3265(19) and 2.280(2) Å, respectively. To our knowledge, only two complexes [Ru₂^III,III(DMBA)₄(BF₄)₂] (DMBA⁻ = N,N′-dimethylbenzamidinate ion (Scheme 2b)) and [Ru₂^II,III(ap)(BF₄)]·2THF (ap⁻ = 2-anilinopyridinate ion (Scheme 2c)) have been confirmed by the X-ray crystal structure analysis for the axial coordination of BF₄⁻ to the lantern-type diruthenium complex [24,25]. The Ru-F_ax bond distances are 2.366(3) and 2.389(3) Å for [Ru₂^III,III(DMBA)₄(BF₄)₂] [24] and 2.296(2) Å for [Ru₂^II,III(ap)(BF₄)]·2THF [25]; the bond lengths are similar to that (2.3265(19) Å) of [Ru₂^II,III(HNOCPh)₄(BF₄)(H₂O)]·2(acetone). Acetone molecules exist as the crystal solvent in the crystal. One of the acetone molecules participates in the hydrogen-bonding network within the crystal, as shown in Figure S1. Similar hydrogen-bonding networks have been reported for [Ru₂(HNOCMe)₄(H₂O)₂]ClO₄, [Ru₂(HNOCMe)₄(H₂O)₂]NO₃ and [Ru₂(HNOCMe)₄(H₂O)₂](BPh₄)·H₂O [26,27,28]. The acetone molecules in the crystal of [Ru₂(HNOCPh)₄(BF₄)(H₂O)]·2(acetone) could be easily removed over P₂O₅ in a desiccator at ambient temperature and pressure (See Section 3.2).

2.4. Magnetic Properties

In Figure 6 and Figure 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 Ru₂⁵⁺ unit) of [Ru₂(HNOCPh)₄Cl]_n is 4.15 μ_B at 300 K, which indicates the existence of three unpaired electrons per the Ru₂⁵⁺ unit with an S = 3/2 state. Like the other halogenido (X)-linked Ru₂⁵⁺ 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 μ_B 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 Ru₂⁵⁺ species, the inter-dinuclear-unit interaction being taken into account by means of a mean-field approximation [3,5,29,30,31]:

χ’ = χ/{1 − (2zJ/Ng²μ_B²)χ}

(1)

where zJ is the exchange energy multiplied by the number (z) of interacting neighbors, and χ is the magnetic susceptibility.

χ = (χ_// + 2χ_⊥)/3

(2)

where χ_// and χ_⊥ are magnetic susceptibility terms defined as follows:

χ_// = (Ng²μ_B²/kT){1 + 9exp(−2D/kT)}/4{1 + exp(−2D/kT)}

(3)

χ_⊥ = (Ng²μ_B²/kT)[4 + (3kT/D){1 − exp(−2D/kT)}]/4{1 + exp(−2D/kT)}

(4)

The simulation results gave parameter values: g = 2.19, D = 61 cm⁻¹, zJ = −2.8 cm⁻¹ for [Ru₂(HNOCPh)₄Cl]_n and g = 2.01, D = 61 cm⁻¹, zJ = −0.08 cm⁻¹ for [Ru₂(HNOCPh)₄(BF₄)(H₂O)]. There is a considerable difference in zJ value between [Ru₂(HNOCPh)₄Cl]_n and [Ru₂(HNOCPh)₄(BF₄)(H₂O)]. The appreciable magnetic interaction (zJ = −2.8 cm⁻¹) is operative through the axial chlorido linker for [Ru₂(HNOCPh)₄Cl]_n, although through-space interaction (zJ = −0.08 cm⁻¹) only occurs in [Ru₂(HNOCPh)₄(BF₄)(H₂O)]. A similar discussion has been presented by Barral et al. for [Ru₂(HNOCR)₄Cl]_n (zJ = −0.3–−2.9 cm⁻¹) and [Ru₂(HNOCR)₄(THF)₂]Y (−0.1–−2.2 cm⁻¹), where R = C₆H₃-3,5-(OMe)₂, C₆H₄-p-OMe, C₆H₄-p-CMe₃, C₄H₃S, C₆H₁₁, CMe₃ and Y = BF₄⁻, SbF₆⁻ [17]. Later, using the crystal structural data, an empirical linear relationship was proposed between through-axial halogenido (X) magnetic interaction zJ and the structural parameter Ru-X/Ru-X-Ru for lantern-type Ru₂⁵⁺ complexes with amidato or carboxylato bridges [20]. According to the relationship, zJ is estimated as ca. −3.0 cm⁻¹ using the crystal data of [Ru₂(PhCONH)₄Cl]_n reported by Chakravarty and Cotton [15], which is almost consistent with the present magnetic result of zJ = −2.8 cm⁻¹ for the complex.

2.5. 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 [Ru₂(DArF)₄]BF₄. Hence, in order to clarify the favorable spin states, electronic structures and spin density distributions of [Ru₂(HNOCPh)₄(BF₄)(H₂O)] and [Ru₂(HNOCPh)₄Cl₂]⁻, as well as [Ru₂(HNOCPh)₄]⁺, which is the theoretically modeled complex with empty axial sites, unrestricted density functional theory (uDFT) calculations were performed.

Our zero-point energy (ZPE) calculations clearly supported the experimentally observed spin state of [Ru₂(HNOCPh)₄(BF₄)(H₂O)]; the ZPE with the S = 3/2 spin state is 7.68 Kcal/mol more stable than that with the S = 1/2 spin state. The ZPEs of [Ru₂(HNOCPh)₄Cl₂]⁻ and [Ru₂(HNOCPh)₄]⁺ with the S = 3/2 spin state were also 3.16 and 3.76 Kcal/mol more stable, respectively, than those with the S = 1/2 spin state, indicating that the axial ligation of the diruthenium(II,III) complexes with amidato-bridges do not affect the spin state of S = 3/2. In the optimized geometry for the S = 3/2 spin state, the electronic configuration of [Ru₂(HNOCPh)₄(BF₄)(H₂O)] is π⁴σ²δ²π*²δ*¹, as depicted in Figure 8. Three singly occupied molecular orbitals (SOMOs), which are observed at MO-169α~167α, are assigned as δ*(Ru₂), π*(Ru₂), and π*(Ru₂) orbitals, respectively. That is, the MO energies of anti-bonding interactions between Ru₂ ions of [Ru₂(HNOCPh)₄(BF₄)(H₂O)] are relatively unstable compared to those of bonding orbital interactions between Ru₂ ions similarly to those of typical diruthenium(II,III) tetracarboxylate complexes [1,3]. The most unstable bonding orbital interactions between Ru₂ ions are the δ(Ru₂) orbitals, which are observed at MO-166α and 166β. The σ(Ru₂) orbitals, which interact with the orbitals of atoms located at primary coordination spheres, are located at MO-157α and 153β. The degenerate π(Ru₂) orbitals are found at MO-145α, 146α, 163β and 164β, in which π(Ru₂) orbitals are considerably overlapped with the p(N) and p(O) orbitals of amidato moieties. On the other hand, the lowest unoccupied MOs (LUMOs) of α and β orbitals are σ*(Ru₂) and δ*(Ru₂) orbitals, respectively. The SOMO–LUMO and highest-occupied MO (HOMO)–LUMO gaps at α and β orbitals are estimated as 4.09 and 2.57 eV, respectively.

The DFT calculation treatments are essentially the same between the previous work on [Ru₂(DArF)₄]⁺ [10] and the present one on [Ru₂(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 [Ru₂(DArF)₄]BF₄ 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].

3. Materials and Methods

3.1. General Aspects

All reagents and solvents were used as received. The precursor complex [Ru₂(O₂CCMe)₄Cl]_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 [Ru₂(HNOCPh)₄Cl]_n and [Ru₂(HNOCPh)₄(BF₄)(H₂O)], respectively. The measured data were corrected for diamagnetic contributions [34]. Cyclic voltammograms (CVs) were measured in dichloromethane containing tetra-n-butylammonium hexafluoroborate Bu₄NPF₆ 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.

3.2. Synthesis of Complexes

3.2.1. Synthesis of [Ru₂(HNOCPh)₄Cl]_n

This complex was synthesized using a modified method described in the literature [13]. A 5.0 g (42 mmol) of PhCONH₂ was combined with 0.50 g (1.0 mmol) of Ru₂(O₂CCH₃)₄Cl 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. The yield was 0.68 g (96% based on Ru₂(O₂CCH₃)₄Cl). Anal. Calcd for Ru₂(HNOCPh)₄Cl: C, 46.83, H, 3.37, N, 7.80. Found: C, 46.65, H, 3.37, N, 7.87%. IR data (KBr disk, cm⁻¹) 3346 m, 3312 m, 3065 w, 1518 s, 1489 s, 1452 vs, 1432 s, 1217 s, 1118 s, 1029 m, 841 m, 794 m, 687 vs, 657 s, 527 s.

3.2.2. Synthesis of [Ru₂(HNOCPh)₄(BF₄)(H₂O)]

A 50.3 mg (0.070 mmol) of Ru₂(HNOCPh)₄Cl was reacted with 15.0 mg (0.077 mmol) of AgBF₄ 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 AgBF₄. 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 P₂O₅ in desiccator for 20 h to give a yellowish-brown powder. The yield was 31.5 mg (57.1% based on Ru₂(O₂CMe)₄Cl). Anal. Calcd for [Ru₂(HNOCPh)₄(BF₄)(H₂O)]: C, 42.71, H, 3.33, N, 7.11. Found: C, 42.73, H, 3.45, N, 7.44%. IR data (KBr disk, cm⁻¹) 3354 m, 3050 w, 1690 m, 1616 m, 1600 m, 1514 s, 1464 s, 1450 vs, 1427 s, 1221 s, 1118 s, 1080 m, 1025 s, 838 s, 790 m, 691 vs, 646 s, 522 s, 457 w. HR-ES(ESI-TOF): Found 683.9904 m/z. (calcd for [M]⁺ 683.9895).

3.3. Crystal Structure Determination

The single crystals of [Ru₂(HNOCPh)₄(BF₄)(H₂O)]·2(acetone) suitable for X-ray crystal structure analysis were obtained by the recrystallization of [Ru₂(HNOCPh)₄(BF₄)(H₂O)] from acetone. X-ray crystallographic data (

Table 1. Crystallographic data and structure refinement of [Ru₂(HNOCPh)₄(BF₄)(H₂O)]·2(acetone).

	Parameter Values a
Empirical formula	C34H38BF4N4O7Ru2
Formula mass	903.63
Temperature	123(2) K
Crystal system	Monoclinic
Space group	P21/n
a	14.412(2) Å
b	15.669(3) Å
c	16.388(3) Å
α	90°
β	93.743(2)°
γ	90°
Unit-cell volume, V	3692.7(10) Å3
Formula per unit cell, Z	4
Density, Dcalcd	1.625 g cm−3
Crystal size	0.200 × 0.170 × 0.050 mm
Absorption coefficient, μ	0.890 mm−1
θ range for data collection	2.833–27.499˚
Reflections collected/unique	8333/7421
R indices [I > 2σ(I)] b	R1 = 0.0361, wR2 = 0.0866
Goodness-of-fit on F2	1.045

^a Standard deviations in parentheses; ^b R₁ = Σ||F_o| − |F_c||/Σ|F_o|; wR₂ = [Σw(F_o² − F_c²)²/Σ(F_o²)²]^1/2.

) 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 (F²) 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.

CCDC-1835304 contains the supplementary crystallographic data for [Ru₂(HNOCPh)₄(BF₄)(H₂O)]·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.

3.4. Computational Details

All density functional theory (DFT) calculations applied in this study were performed with broken symmetry (BS) uB3LYP functional with LANL08f for Ru atom and 6-31G** for other atoms. The molecular geometries of [Ru₂(HNOCPh)₄(BF₄)(H₂O)], [Ru₂(PhCONH)₄Cl₂]⁻, and [Ru₂(HNOCPh)₄]⁺ were fully optimized in the gas phase, and then the obtained optimized geometries were checked by frequency analysis. The relative energies of their diruthenium complexes with S = 3/2 and 1/2 states were compared with zero-point energies (ZPEs). The molecular orbitals of [Ru₂(HNOCPh)₄(BF₄)(H₂O)] were drawn by a GaussView program.

4. Conclusions

A lantern-type diruthenium(II,III) complex [Ru₂(HNOCPh)₄(BF₄)(H₂O)] was prepared from [Ru₂(HNOCPh)₄Cl]_n by removal of the axial chlorido-bridge using AgBF₄ in THF. The dinuclear structure axially coordinated by BF₄⁻ and H₂O was determined for the former complex by X-ray crystal structure analysis. The temperature dependent magnetic susceptibility and moment data showed that both of the complexes [Ru₂(HNOCPh)₄(BF₄)(H₂O)] and [Ru₂(HNOCPh)₄Cl]_n have a quartet ground state, the electronic structure of which, π⁴σ²δ²π*²δ*¹, was demonstrated by DFT calculations. The Ru₂⁶⁺/Ru₂⁵⁺ redox couple was observed at 1.12 V (vs. SCE) for [Ru₂(HNOCPh)₄(BF₄)(H₂O)] in dichloromethane containing Bu₄NPF₆ as electrolyte.