Di-μ-acetato-κ4 O:O′-μ-oxido-κ2 O:O′-bis[cis-(2,2′-bipyridine-κ2 N,N′)-trans-(pyridine-κN)ruthenium(III)] bis(hexafluoridophosphate)

The hemerythrin-type dinuclear title complex, [Ru2(CH3COO)2O(C10H8N2)2(C5H5N)2](PF6)2, consists of two RuIII ions with a six-coordinate octahedral geometry, bridged by an oxide and two acetate ligands, with a bidentate 2,2′-bipyridine ligand and a pyridine ligand bonding at terminal positions. The Ru—Ru distance and Ru—O—Ru angle are 3.2838 (3) Å and 121.79 (7)°, respectively, and the average Ru—N(pyridine) bond length is 2.164 (8) Å. Several C—H⋯F, C—H⋯O and C—H⋯N interactions generate a three-dimensional network in the crystal structure. π–π stacking interactions [centroid–centroid distance = 3.6389 (3) Å] between inversion-related 2,2′-bipyridine rings are also observed.

supplementary materials Acta Cryst. (2013 (Sasaki et al. 1991). Although the substitution, redox and spectroscopic properties of the title complex have been reported, the structure in the solid state remains unexplored. We report here the determination of the structure of I. The molecule has a hemerythrin type diruthenium(III) core {Ru III 2 (CH 3 CO 2 ) 2 O} 2+ which consists of two Ru III ions in a six-coordinated octahedral geometry and terminal ligands (2,2′-bipyridine and pyridine). The Ru-Ru distance and the Ru-O-Ru angle are 3.2838 (3) Å and 121.79 (7)°, respectively. The average of Ru-N bond lengths at the trans-and at the cis-sites to the bridging oxido are 2.1635 and 2.0292 Å, respectively. The former is longer than the latter, and this could be interpreted as in order to the trans influence of the µ-oxido, which is a stronger electron donating ligand than acetato oxygen atoms. The average Ru-N trans length is shorter than that of III (2.185 Å), and longer than that of the complex with 1-methylimidazole instead of pyridine at the trans-to-oxido position, [Ru III 2 (CH 3 CO 2 ) 2 O(C 10 H 8 N 2 ) 2 (C 4 H 6 N 2 ) 2 ](PF 6 ) 2 (IV) (2.125 Å) (Sudha & Chakravarty, 1996). The former may be due to the steric effect of the ligands at the cis-to-oxido position: the molecular plane of the flat 2,2′-bipyridine in I is coplanar with the plane consisting of four cis-to-oxido positions ("cis plane"), and does not hinder the bonding of pyridine at the trans position, while two pyridine molecules at the cis-to-oxido position in II are almost perpendicular to the cis plane, and some steric interactions may be possible. The electronic effect is probable for the latter case: pyridine is weaker Lewis base (protonation constant exponent pK a = 5.17; Dean, 1985) than 1-methylimidazole is (pK a = 7.06; Dean, 1985), and Ru-N trans (pyridine) in I bond is weaker than Ru-N trans (1-methylimidazole) in IV. In addition, steric interactions of vicinal protons of N trans with 2,2′-bipyridine on the cis plane are stronger with 2-and 6-protons on the six-membered ring of pyridine in I than with the 2-and 5-protons on the five-membered ring of 1-methylimidazole in IV, with the result that they gives more negative effect on bonding in I. On the other hand, though the average length of Ru-N cis (2,2′-bipyridine) in I (2.0292 Å) is similar to that in IV (2.030 Å), these lengths are shorter than that of Ru-N trans (pyridine) in III (2.087 Å). This fact shows that Ru-N cis distance is influenced by the steric hindrance of ligands at the cis position rather than the electronic effect of ligands at the trans (pyridine and 1-methylimidazole) or cis (pyridine and 2,2′-bipyridine(pK a = 4.35; Dean, 1985)) sites. In the crystal structure the cations and anions are linked by C-H···F, C-H···O and C-H···N hydrogen bond interactions. In addition, π-π stacking interactions between neighbouring 2,2′-bipyridine ligands are also observed with a shortest centroid-centroid distance of 3.6389

Experimental
The complex was synthesized previously (Sasaki et al. 1991), but we have prepared single crystals by another method.
The complex with nitrile-κNs at the both trans-to-oxido sites, [Ru III 2 (CH 3 CO 2 ) 2 O(C 10 H 8 N 2 ) 2 (C 2 H 3 N) 2 ](PF 6 ) 2 (II) (10 mg, 1.0 × 10 -5 mol; Ido et al., 2013), was dissolved in CH 3 CN. Pyridine (82 mg, 1.0 × 10 -3 mol) was dissolved in this solution and kept for 12 h at 333 K. The solution was dried under vacuum to obtain precipitates, which were then recrystallized from the solution in CH 3 CN by adding Et 2 O, and washed with Et 2 O. A blue crystalline product was obtained in 73% yield. By evaporating a concentrated solution in CD 3 CN, single crystals of I were obtained. 1 H NMR (in

Refinement
The H atoms were placed in calculated positions, with C-H = 0.95 Å , and refined using a riding model, with U iso (H) = 1.2U eq for aromatic H atoms or 1.5U eq for methyl ones. Solvent accessible voids of 37Å -3 are present in the lattice.

Figure 1
The molecular structure of the complex cation of (I). Displacement ellipsoids are drawn at the 50% probability level.  The complex cations are linked by π-π interactions between neighbouring 2,2′-bipyridine ligands with centroid-centroid distance of 3.6389 (3) Å.

bis(hexafluoridophosphate)
Crystal data [Ru 2 (C 2 H 3 O 2 ) 2 O(C 10 H 8 N 2 ) 2 (C 5 H 5 N) 2 ](PF 6 ) 2 M r = 1096.74 Monoclinic, P2 1 /n Hall symbol: -P 2yn a = 12.3330 (9) Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.