Bis(2,2′-bipyridine){ethyl 4′-[N-(4-carbamoylphenyl)carbamoyl]-2,2′-bipyridine-4-carboxylate}ruthenium(II) bis[hexafluoridophosphate(V)]

In the title compound, [Ru(C10H8N2)2(C21H18N4O4)](PF6)2, the RuII complex cation reveals a slightly distorted octahedral coordination. The coordination bonds of the 4,4′-substituted bipyridyl donors [Ru—N = 2.038 (3) and 2.051 (3) Å] are shorter than those of the 2,2′-bipyridyl donors [Ru—N1 = 2.065 (3)–2.077 (3) Å], due to the electron-withdrawing effects of the substituents at the 4,4′-positions. The angles between the pyridyl planes of the three bipyridyl ligands are 1.5 (2), 6.3 (3) and 8.7 (2)°, respectively. The cations are connected by anions via N—H⋯F interactions.


Bis(2,2'-bipyridine){ethyl 4'-[N-(4-carbamoylphenyl)carbamoyl]-2,2'-bipyridine-4-carboxylate}ruthenium(II) bis[hexafluoridophosphate(V)]
M. Hirahara, S. Masaoka and K. Sakai Comment Continuous efforts have been made to elucidate the molecular catalysis of platinum(II) complexes in photochemical hydrogen production from water (Sakai et al., 1993;Sakai & Ozawa, 2007;Ozawa et al., 2007;Ozawa & Sakai, 2007). The results obtained so far suggest that destabilization of the HOMO, which generally corresponds to the filled Pt II d z 2 orbital, gives rise to the higher H 2 -evolving activity of the complexes (Sakai & Ozawa, 2007). It has also been ascertained that the amidatebridged dinuclear platinum(II) complexes having a strong metal-metal interaction exhibit considerably higher H 2 -evolving activity in comparison with the mononuclear complexes, which has been attributed to their highly destabilized HOMOs arising from the anti-bonding couple of the filled Pt II d z 2 orbitals (Sakai & Ozawa, 2007). Moreover, the first effective model of a `photo-hydrogen-evolving' molecular device possessing both a light-harvesting capability and an H 2 -evolving activity was developed in our group (Ozawa & Sakai, 2006). Since this molecular device is made up of a photosensitizing tris(2,2'bipyridine)ruthenium(II) derivative and a mononuclear (4-carbamoyl-4'-carboxy-2,2'-bipyridine)dichloroplatinum(II) fragment, it is important to develop an amidate-bridged diplatinum(II) complex tethered to tris(2,2'-bipyridine)ruthenium(II) photosensitizers. In order to develop such systems, tris(2,2'-bipyridine)ruthenium(II) derivatives having an uncoordinated amide group must be prepared as a synthetic precursor. The title compound has been prepared as one of such precursor compounds. The actual application of this complex ligand will be separately reported elsewhere.
On the other hand, the plane defined by atoms C31, O1, and O2 from the ethoxycarbonyl unit is slightly tilted with respect to the connecting pyridyl plane (N5→C25) at an angle of 4.5 (4)°. The carbamoyl plane defined with atoms C34, O3, and N7 is even more tilted with respect to the connecting pyridyl plane (N6→C30) at an angle of 15.1 (5)°. The aromatic plane consisting of atoms C35-C40 is tilted with respect to the above-mentioned carbamoyl unit (C34/O3/N7) at an angle of 26.6 (3)°, where the six-atom r.m.s. deviation given in the best-plane calculation for the C35-C40 plane was 0.0056. The C35-C40 plane is also tilted with regard to the terminal carbamoyl unit (C41/O4/N8) at an angle of 7.9 (2)°.

supplementary materials sup-2
The crystal packing is stabilized with van der Waals interactions with contributions of the hydrogen bonds formed between the F atoms of PF 6 and the N-H units of carbamoyl groups ( negatively-charged atoms and alpha C atoms from heterocyclic rings (Schottel et al., 2008).

Experimental
As described below, the ligand L was synthesized in three steps and was finally reacted with cis-RuCl 2 (bpy) 2 .2H 2 O to give the final product (I).
Next, 4-carboxy-4'-ethoxycarbonyl-2,2'-bipyridine monohydrate was prepared from the partial hydrolysis of 4,4'-diethoxycarbonyl-2,2'-bipyridine as follows. To a solution of 4,4'-diethoxycarbonyl-2,2'-bipyridine (1.50 g, 5.0 mmol) in absolute dichloromethane (200 ml) was dropwisely added a solution of potassium hydroxide (0.23 g, 5.00 mmol) in ethanol (50 ml) at 273 K over 1 h. This procedure was carried out under Ar atmosphere. The reaction mixture was further stirred for 1 d, during which the temperature of the solution was gradually raised to room temperature. The colourless solid precipitated was collected by filtration and washed with ethyl acetate. The ethyl acetate washing was evaporated to dryness to collect the unreacted 4,4'-diethoxycarbonyl-2,2'-bipyridine (0.525 g, 35%). The colourless precipitate was re-dissolved in water and acidified by 1 N hydrochloric acid to give the product as a colourless solid, which was collected by filtration and dried in vacuo (yield 0.812 g, 60%). Anal. Calcd for C 14 N 2 H 14 O 5 : C,57.92;H,4.86;N,9.65. Found: C,57.27;H,4.68;N,9.67 former solution at 273 K over 20 min. The reaction mixture was further stirred for 1 d in Ar, during which the temperature of the mixture was gradually raised to room temperature. The reaction mixture was then evaporated to a total volume of 5 ml followed by addition of water (200 ml). The white solid precipitated was collected by filtration and washed with water (20 ml), with an aqueous 5% NaHCO 3 solution (20 ml), with an aqueous 5% citric acid solution (20 ml), and finally with water (20 ml). The white solid was dried in vacuo (yield 208 mg, 36.5%). The washing from the aqueous 5% NaHCO 3 solution was acidified by HCl to give the unreacted starting bpy derivative (

Refinement
All H atoms were placed in idealized positions (methyl C-H = 0.96 Å, methylene C-H = 0.97 Å, aromatic C-H = 0.95 Å, and amide N-H = 0.86 Å), and included in the refinement in a riding-model approximation, with U iso (H) = 1.5Ueq(methyl C) and U iso (H) = 1.2Ueq(methylene C, aromatic C, and amide N). In the final difference Fourier map, the highest peak was located 0.88 Å from atom Ru1. The deepest hole was located 0.47 Å from atom P1.
Figures Fig. 1. The molecular structure of (I) with the complex cation and anions showing the atomlabeling scheme. Displacement ellipsoids are drawn at the 50% probability level. Crystal data [Ru(C 10

Special details
Experimental. The first 50 frames were rescanned at the end of data collection to evaluate any possible decay phenomenon. Since it was judged to be negligible, no decay correction was applied to the data. 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 > σ(F 2 ) is used only for calculating Rfactors(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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq